U.S. patent application number 16/586707 was filed with the patent office on 2020-04-09 for short/open protecting circuit and a method thereof.
The applicant listed for this patent is Chengdu Monolithic Power Systems Co., Ltd.. Invention is credited to Shufa Jiang, Taofeng Li, Junxin Tan, Li Yang, Bo Yu.
Application Number | 20200113023 16/586707 |
Document ID | / |
Family ID | 65348787 |
Filed Date | 2020-04-09 |
United States Patent
Application |
20200113023 |
Kind Code |
A1 |
Yu; Bo ; et al. |
April 9, 2020 |
SHORT/OPEN PROTECTING CIRCUIT AND A METHOD THEREOF
Abstract
A short protecting circuit for a LED (Light-emitting Diode)
driver for powering a plurality of LED strings, having: a short
comparing circuit, configured to provide a plurality of short fault
indicating signals; a first logic circuit, configured to provide a
short fault signal based on the plurality of short fault indicating
signals to indicate a short fault condition; a timing circuit,
configured to provide a short protecting enable signal; and a
second logic circuit, configured to provide a plurality of short
isolating signals; wherein the short isolating signals are blocked
when an open fault signal is valid.
Inventors: |
Yu; Bo; (Hangzhou, CN)
; Tan; Junxin; (Hangzhou, CN) ; Li; Taofeng;
(Hangzhou, CN) ; Jiang; Shufa; (Hangzhou, CN)
; Yang; Li; (Hangzhou, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Chengdu Monolithic Power Systems Co., Ltd. |
Chengdu |
|
CN |
|
|
Family ID: |
65348787 |
Appl. No.: |
16/586707 |
Filed: |
September 27, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H05B 45/54 20200101;
H05B 45/52 20200101; H05B 45/50 20200101; H05B 45/46 20200101; H05B
47/24 20200101 |
International
Class: |
H05B 33/08 20060101
H05B033/08 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 9, 2018 |
CN |
201811172807.8 |
Claims
1. A short protecting circuit for a LED (Light-emitting Diode)
driver powering a plurality of LED strings, comprising: a short
comparing circuit, configured to receive a short threshold and a
plurality of feedback voltages, and to provide a plurality of short
fault indicating signals, wherein each feedback voltage indicates a
voltage across an associated LED string of the plurality of LED
strings, and wherein each short fault indicating signal is
generated based on comparing the associated feedback voltage with
the short threshold; a first logic circuit, configured to receive
the plurality of short fault indicating signals, and to provide a
short fault signal based on the plurality of short fault indicating
signals to indicate a short fault condition, wherein the short
fault signal is valid when at least one short fault indicating
signal of the plurality of short fault indicating signals is valid;
a timing circuit, configured to receive the short fault signal, and
to provide a short protecting enable signal, wherein the short
protecting enable signal is valid when the short fault signal
indicates the short fault condition for a preset time period; and a
second logic circuit, configured to receive the plurality of short
fault indicating signals and the short protecting enable signal,
and to provide a plurality of short isolating signals, wherein each
short isolating signal is generated based on performing a logic
operation to the short protecting enable signal and the associated
short fault indicating signal of the plurality of short fault
indicating signals; wherein the plurality of short isolating
signals is blocked when an open fault signal is valid.
2. The short protecting circuit of claim 1, wherein the short
comparing circuit further receives the open fault signal, and
wherein the short comparing circuit is disabled when the open fault
signal indicates an open fault condition.
3. The short protecting circuit of claim 1, wherein the timing
circuit further receives the open fault signal, and wherein the
timing circuit is disabled when the open fault signal indicates an
open fault condition.
4. The short protecting circuit of claim 1, wherein the first logic
circuit further receives the open fault signal, and wherein the
short fault indicating signals are blocked and the short fault
signal is invalid when the open fault signal indicates an open
fault condition.
5. The short protecting circuit of claim 1, wherein the second
logic circuit further receives the open fault signal, and wherein
the short isolating signals are blocked when the open fault signal
indicates an open fault condition.
6. The short protecting circuit of claim 1, further comprising: an
open comparing circuit, configured to receive the plurality of
feedback voltages and an open threshold, and to provide a plurality
of open fault indicating signals, wherein each open fault
indicating signal is generated based on comparing the associated
feedback voltage with the open threshold; a third logic circuit,
configured to receive the plurality of open fault indicating
signals and an OVP signal, and to provide a plurality of current
isolating switch control signals and the open fault signal, wherein
each current isolating switch control signal is generated based on
performing a logic operation to the associated open fault
indicating signal and the OVP signal, and the open fault signal is
generated based on performing a logic operation to the plurality of
current isolating switch control signals, and wherein the OVP
signal indicates if a power supply voltage provided to the LED
strings is higher than an OVP threshold or not.
7. An open and short to ground protecting circuit for a LED
(Light-emitting Diode) driver for powering a plurality of LED
string, comprising: an open comparing circuit, configured to
receive an open threshold and a plurality of feedback voltages, and
to provide a plurality of open fault indicating signals, wherein
each feedback voltage indicates a voltage across an associated LED
string of the plurality of LED strings, and wherein each open fault
indicating signal is generated based on comparing the associated
feedback voltage with the open threshold; a third logic circuit,
configured to receive the plurality of open fault indicating
signals and an OVP signal, and to provide a plurality of current
isolating switch control signals and an open fault signal, wherein
each current isolating switch control signal is generated based on
performing a logic operation to the associated open fault
indicating signal and the OVP signal, and the open fault signal is
generated based on performing a logic operation to the plurality of
open fault indicating signals, and wherein the OVP signal indicates
if a power supply voltage provided to the plurality of LED strings
is higher than an OVP threshold or not; a short to ground
protecting circuit, configured to receive the plurality of feedback
voltages, a short to ground threshold and the open fault signal,
wherein when the open fault signal is valid, the short to ground
circuit provides a short to ground indicating signal based on
performing a logic operation to comparison results of each feedback
voltage of the plurality of feedback voltages with the short to
ground threshold; and a fourth logic circuit, configured to receive
the short to ground indicating signal and the plurality of current
isolating switch control signals, and to provide a plurality of
feedback isolating switch control signals, wherein each feedback
isolating switch control signal is generated based on performing a
logic operation to the associated current isolating switch control
signal and the short to ground indicating signal.
8. The open and short to ground protecting circuit of claim 7,
further comprising: an over voltage protecting circuit, configured
to receive the OVP threshold and the power supply voltage for
powering the plurality of LED strings, and to provide the OVP
signal based on a comparison result of the power supply voltage
with the OVP threshold.
9. A LED driver, comprising: a voltage regulating circuit,
configured to provide a power supply voltage to a plurality of LED
strings; a current regulating circuit, configured to receive a
current regulating signal, wherein the current regulating circuit
is coupled to the plurality of LED strings to regulate a current
flowing through the LED string of plurality of LED strings based on
the current regulating signal; a feedback selecting circuit, having
a plurality of feedback isolating switches, wherein each feedback
isolating switch is coupled to a connection node between the
associated LED string of the plurality of LED strings and the
current regulating circuit, and wherein the feedback selecting
circuit receives a plurality of feedback voltages at the plurality
of connection nodes, and to provide a minimum feedback voltage to
the voltage regulating circuit, to regulate the power supply
voltage; a short protecting circuit, configured to provide a
plurality of short isolating signals, wherein each short isolating
signal controls a connection between the associated LED string and
the current regulating circuit, and wherein the short protecting
circuit comprises: a short comparing circuit, configured to receive
a short threshold and the plurality of feedback voltages, and to
provide a plurality of short fault indicating signals, wherein each
feedback voltage represents a voltage across an associated LED
string of the plurality of LED strings, and wherein each short
fault indicating signal is generated based on comparing the
associated feedback voltage with the short threshold; a first logic
circuit, configured to receive the plurality of short fault
indicating signals, and to provide a short fault signal based on
the plurality of short fault indicating signals to indicate a short
fault condition, wherein the short fault signal is valid when at
least one short fault indicating signal of the plurality of short
fault indicating signals is valid; a timing circuit, configured to
receive the short fault signal and an open fault signal, and to
provide a short protecting enable signal, wherein the short
protecting enable signal is valid when the short fault signal
indicates the short fault condition for a preset time period; and a
second logic circuit, configured to receive the plurality of short
fault indicating signals and the short protecting enable signal,
and to provide the plurality of short isolating signals, wherein
each short isolating signal is generated based on performing a
logic operation to the associated short fault indicating signal and
the short protecting enable signal; wherein the plurality of short
isolating signals is blocked when an open fault signal is
valid.
10. The LED driver of claim 9, wherein the short comparing circuit
further receives the open fault signal, and wherein the short
comparing circuit is disabled when the open fault signal indicates
an open fault condition.
11. The LED driver of claim 9, wherein the timing circuit further
receives the open fault signal, and wherein the timing circuit is
disabled when the open fault signal indicates an open fault
condition.
12. The LED driver of claim 9, wherein the first logic circuit
further receives the open fault signal, and wherein the plurality
of short fault indicating signals are blocked and the short fault
signal is invalid when the open fault signal indicates an open
fault condition.
13. The LED driver of claim 9, wherein the second logic circuit
further receives the open fault signal, and wherein the short
isolating signals are blocked when the open fault signal indicates
open fault.
14. The LED driver of claim 9, wherein the current regulating
circuit comprises a plurality of control units, and wherein each
control unit is coupled to the associated LED string, and wherein
each control unit comprises: a current control switch, coupled in
series with the associated LED string; a resistor, coupled between
the current control switch and a ground reference; an amplifying
circuit, having a first input terminal configured to receive the
current regulating signal, a second input terminal coupled to a
connection node of the current control switch and the resistor, and
an output terminal coupled to a control terminal of the current
control switch; and a current isolating switch, coupled between the
output terminal of the amplifying circuit and the ground
reference.
15. The LED driver of claim 14, further comprising: an open
comparing circuit, configured to receive the plurality of feedback
voltages and an open threshold, and to provide a plurality of open
fault indicating signals, wherein each open fault indicating signal
is generated based on comparing the associated feedback voltage
with the open threshold; a third logic circuit, configured to
receive the plurality of open fault indicating signals and an OVP
signal, and to provide a plurality of current isolating switch
control signals and the open fault signal, wherein each current
isolating switch control signal is generated based on performing a
logic operation to the associated open fault indicating signal and
the OVP signal, and the open fault signal is generated based on
performing a logic operation to the plurality of the open fault
indicating signals, and wherein the OVP signal indicates if the
power supply voltage is higher than an OVP threshold or not.
16. The LED driver of claim 15, further comprising: an isolating
logic circuit, configured to receive the plurality of short
isolating signals, and the plurality of current isolating switch
control signals, and to provide a plurality of control signals to
the plurality of current control switches respectively, wherein
each control signal is generated based on performing a logic
operation to the associated short isolating signal and the
associated current isolating switch control signal.
17. The LED driver of claim 14, further comprising an open and
short to ground protecting circuit, wherein the open and short to
ground protecting circuit comprises: an open comparing circuit,
configured to receive the plurality of feedback voltages and an
open threshold, and to provide a plurality of open fault indicating
signals, wherein each open fault indicating signal is generated
based on comparing the associated feedback voltage with the open
threshold; a third logic circuit, configured to receive the
plurality of open fault indicating signals and an OVP signal, and
to provide a plurality of current isolating switch control signals
and the open fault signal, wherein each current isolating switch
control signal is generated based on performing a logic operation
to the associated open fault indicating signal and the OVP signal,
and the open fault signal is generated based on performing a logic
operation to the plurality of open fault indicating signals, and
wherein the OVP signal indicates if a power supply voltage provided
to the plurality of LED strings is higher than an OVP threshold or
not; a short to ground protecting circuit, configured to receive
the plurality of feedback voltages, a short to ground threshold and
the open fault signal, wherein when the open fault signal is valid,
the short to ground circuit provides a short to ground indicating
signal based on performing a logic operation to comparison results
of each feedback voltage of the plurality of feedback voltages with
the short to ground threshold; and a fourth logic circuit,
configured to receive the short to ground indicating signal and the
plurality of current isolating switch control signals, and to
provide a plurality of feedback isolating switch control signals,
wherein each feedback isolating switch control signal is generated
based on performing a logic operation to the associated current
isolating switch control signal and the short to ground indicating
signal.
18. The LED string control circuit of claim 17, wherein the open
and short to ground protecting circuit further comprises: an over
voltage protecting circuit, configured to receive the OVP threshold
and the power supply voltage, and to provide the OVP signal based
on a comparison result of the power supply voltage and the OVP
threshold.
19. The LED string control circuit of claim 17, further comprising:
an isolating logic circuit, configured to receive the plurality of
short isolating signals, and the plurality of feedback isolating
switch control signals, and to provide a plurality of control
signals to the plurality of feedback isolating switches
respectively, wherein each control signal is generated based on
performing a logic operation to the associated short isolating
signal and the associated feedback isolating switch control signal.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to and the benefit of
Chinese Patent Application No. 201811172807.8, filed on Oct. 9,
2018, which is incorporated herein by reference in its
entirety.
FIELD
[0002] The present invention relates generally to electronic
circuits, and more particularly but not exclusively to short/open
protecting circuits in LED (light-emitting diode) applications.
BACKGROUND
[0003] Today, LED backlighting is more and more widely adopted by
monitors. For example, in LCD TV field, LED is tending to replace
the traditional CCFL as the backlighting source. In backlighting
applications, LEDs are arranged in multiple strings that are
powered by a LED driver as shown in FIG. 1. In FIG. 1, the LED
driver comprises: a voltage regulating circuit 101 configured to
provide a power supply voltage Vout to the LED strings; and a
current regulating circuit 102 configured to regulate each current
flowing through an associated LED string of the plurality of LED
strings. To provide a high enough voltage to the plurality of LED
strings, the voltage regulating circuit 101 receives a plurality of
feedback voltages FB1.about.FBn of the LED strings, and selects a
minimum feedback voltage to control the power supply voltage
Vout.
[0004] In a LED system, when short/open fault happens in any one of
the LED strings, a protection mechanism is needed to process the
faulted LED string to ensure the proper function of the rest of the
LED strings.
[0005] When an open fault happens, the conventional way is to pull
the faulted LED string to a ground reference. In that case, the
minimum feedback voltage would be near zero. After a control loop
regulation, the power supply voltage Vout increases to high enough
to trigger the OVP (over voltage protection). As a result, the
voltage regulator stops working, and meanwhile the faulted LED
string is removed from the control loop. In this way, the LED open
fault protection is realized. When a short fault happens, the
feedback voltage of the shorted LED string increases to trigger the
short fault protection. However, the feedback voltages
FB1.about.FBn increase as the power supply voltage Vout increases
when open fault happens too. The increase of the feedback voltage
FB1.about.FBn caused by the open fault may mis-trigger the short
fault protection.
[0006] In some cases, when short to ground fault happens, i.e., a
LED string is shorted to ground reference, the power supply voltage
Vout increases too with the same theory analyzed above. In these
cases, the short to ground fault may be misjudged as the open
fault.
SUMMARY
[0007] It is an object of the present invention to provide a fault
handling mechanism used with the LED drivers.
[0008] In accomplishing the above and other objects, there has been
provided, in accordance with an embodiment of the present
invention, a short protecting circuit for a LED (Light-emitting
Diode) driver powering a plurality of LED strings, comprising: a
short comparing circuit, configured to receive a short threshold
and a plurality of feedback voltages, and to provide a plurality of
short fault indicating signals, wherein each feedback voltage
indicates a voltage across an associated LED string of the
plurality of LED strings, and wherein each short fault indicating
signal is generated based on comparing the associated feedback
voltage with the short threshold; a first logic circuit, configured
to receive the plurality of short fault indicating signals, and to
provide a short fault signal based on the plurality of short fault
indicating signals to indicate a short fault condition, wherein the
short fault signal is valid when at least one short fault
indicating signal of the plurality of short fault indicating
signals is valid; a timing circuit, configured to receive the short
fault signal, and to provide a short protecting enable signal,
wherein the short protecting enable signal is valid when the short
fault signal indicates the short fault condition for a preset time
period; and a second logic circuit, configured to receive the
plurality of short fault indicating signals and the short
protecting enable signal, and to provide a plurality of short
isolating signals, wherein each short isolating signal is generated
based on performing a logic operation to the short protecting
enable signal and the associated short fault indicating signal of
the plurality of short fault indicating signals; wherein the
plurality of short isolating signals is blocked when an open fault
signal is valid.
[0009] In accomplishing the above and other objects, there has been
provided, in accordance with an embodiment of the present
invention, an open and short to ground protecting circuit for a LED
(Light-emitting Diode) driver for powering a plurality of LED
string, comprising: an open comparing circuit, configured to
receive an open threshold and a plurality of feedback voltages, and
to provide a plurality of open fault indicating signals, wherein
each feedback voltage indicates a voltage across an associated LED
string of the plurality of LED strings, and wherein each open fault
indicating signal is generated based on comparing the associated
feedback voltage with the open threshold; a third logic circuit,
configured to receive the plurality of open fault indicating
signals and an OVP signal, and to provide a plurality of current
isolating switch control signals and an open fault signal, wherein
each current isolating switch control signal is generated based on
performing a logic operation to the associated open fault
indicating signal and the OVP signal, and the open fault signal is
generated based on performing a logic operation to the plurality of
open fault indicating signals, and wherein the OVP signal indicates
if a power supply voltage provided to the plurality of LED strings
is higher than an OVP threshold or not; a short to ground
protecting circuit, configured to receive the plurality of feedback
voltages, a short to ground threshold and the open fault signal,
wherein when the open fault signal is valid, the short to ground
circuit provides a short to ground indicating signal based on
performing a logic operation to comparison results of each feedback
voltage of the plurality of feedback voltages with the short to
ground threshold; and a fourth logic circuit, configured to receive
the short to ground indicating signal and the plurality of current
isolating switch control signals, and to provide a plurality of
feedback isolating switch control signals, wherein each feedback
isolating switch control signal is generated based on performing a
logic operation to the associated current isolating switch control
signal and the short to ground indicating signal.
[0010] In accomplishing the above and other objects, there has been
provided, in accordance with an embodiment of the present
invention, a LED driver, comprising: a voltage regulating circuit,
configured to provide a power supply voltage to a plurality of LED
strings; a current regulating circuit, configured to receive a
current regulating signal, wherein the current regulating circuit
is coupled to the plurality of LED strings to regulate a current
flowing through the LED string of plurality of LED strings based on
the current regulating signal; a feedback selecting circuit, having
a plurality of feedback isolating switches, wherein each feedback
isolating switch is coupled to a connection node between the
associated LED string of the plurality of LED strings and the
current regulating circuit, and wherein the feedback selecting
circuit receives a plurality of feedback voltages at the plurality
of connection nodes, and to provide a minimum feedback voltage to
the voltage regulating circuit, to regulate the power supply
voltage; a short protecting circuit, configured to provide a
plurality of short isolating signals, wherein each short isolating
signal controls a connection between the associated LED string and
the current regulating circuit, and wherein the short protecting
circuit comprises: a short comparing circuit, configured to receive
a short threshold and the plurality of feedback voltages, and to
provide a plurality of short fault indicating signals, wherein each
feedback voltage represents a voltage across an associated LED
string of the plurality of LED strings, and wherein each short
fault indicating signal is generated based on comparing the
associated feedback voltage with the short threshold; a first logic
circuit, configured to receive the plurality of short fault
indicating signals, and to provide a short fault signal based on
the plurality of short fault indicating signals to indicate a short
fault condition, wherein the short fault signal is valid when at
least one short fault indicating signal of the plurality of short
fault indicating signals is valid; a timing circuit, configured to
receive the short fault signal and an open fault signal, and to
provide a short protecting enable signal, wherein the short
protecting enable signal is valid when the short fault signal
indicates the short fault condition for a preset time period; and a
second logic circuit, configured to receive the plurality of short
fault indicating signals and the short protecting enable signal,
and to provide the plurality of short isolating signals, wherein
each short isolating signal is generated based on performing a
logic operation to the associated short fault indicating signal and
the short protecting enable signal; wherein the plurality of short
isolating signals is blocked when an open fault signal is
valid.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 schematically shows a prior art LED driver.
[0012] FIG. 2 schematically shows a current regulating circuit 102
in accordance with an embodiment of the present invention.
[0013] FIG. 3 schematically shows a short protecting circuit 30 in
accordance with an embodiment of the present invention.
[0014] FIG. 4 schematically shows a short protecting circuit 40 in
accordance with an embodiment of the present invention.
[0015] FIG. 5 schematically shows a short protecting circuit 50 in
accordance with an embodiment of the present invention.
[0016] FIG. 6 schematically shows a short protecting circuit 60 in
accordance with an embodiment of the present invention.
[0017] FIG. 7 schematically shows an open and short to ground
protecting circuit 70 in accordance with an embodiment of the
present invention.
[0018] FIG. 8 schematically shows a LED driver 80 in accordance
with an embodiment of the present invention.
[0019] FIG. 9 schematically shows a control method 90 of processing
LED strings faults.
[0020] FIG. 10 schematically shows a control method 100 of
processing LED strings faults.
[0021] The use of the same reference label in different drawings
indicates the same or like components.
DETAILED DESCRIPTION
[0022] In the present invention, numerous specific details are
provided, such as examples of circuits, components, and methods, to
provide a thorough understanding of embodiments of the invention.
Persons of ordinary skill in the art would recognize, however, that
the invention can be practiced without one or more of the specific
details. In other instances, well-known details are not shown or
described to avoid obscuring aspects of the invention.
[0023] FIG. 1 schematically shows a prior art LED driver 10. The
LED driver 10 comprises: the voltage regulating circuit 101,
configured to provide the power supply voltage Vout to the
plurality of LED strings; the current regulating circuit 102,
configured to receive a current regulating signal Iref, and coupled
to a plurality of feedback terminals P1.about.Pn to regulate a
plurality of currents flowing through the associated LED strings; a
feedback selecting circuit 103, configured to receive the plurality
of feedback voltages FB1.about.FBn, and to provide a minimum
feedback voltage FB_min with a minimum voltage value to the voltage
regulating circuit 101, to regulate the power supply voltage Vout;
an open protecting circuit 104, configured to receive the plurality
of feedback voltages FB1.about.FBn, an open threshold Vth_open and
an OVP signal Sovp, and to provide a plurality of open isolating
signals OP_mf1.about.OP_mfn to the plurality of LED strings
respectively; a short protecting circuit 105, configured to receive
the plurality of feedback voltages FB1.about.FBn, a short threshold
Vth_short, and to provide a plurality of short isolating signals
SRT_mf1.about.SRT_mfn; and a logic circuit 106, configured to
receive the plurality of open isolating signals OP_mf1.about.OPmfn,
and the plurality of short isolating signals SRT_mf1.about.SRT_mfn,
and to provide a plurality of string isolating signals
Markoffl-Markoffn; wherein n is the number of the LED strings. The
value of the open threshold Vth_open is near zero.
[0024] In FIG. 1, the logic circuit 106 performs a logic operation
to each one of the plurality of open isolating signals
OP_mf1.about.OP_mfn and the associated one of the plurality of
short isolating signals SRT_mf1.about.SRT_mfn. For any single LED
string LEDx, if one of the open isolating signal OP_mfx and the
short isolating signal SRT_mfx is valid, which means there is an
open fault or a short fault in the LED string, the associated
isolating signal Markoffx is valid, and indicates to isolate the
fault LED string, wherein any label suffixed by letter x represents
the label of a signal or of a component associated with the LED
string LEDx, and wherein x represents any one of the numbers
between 1 and n. By isolating, it means that the fault LED string
is disconnected from the current regulating circuit 102, and the
associated feedback signal FBx is blocked.
[0025] In the example of FIG. 1, when the OVP signal Sovp is valid,
i.e., the power supply voltage Vout is higher than an OVP threshold
Vth_OVP, the voltage regulating circuit 101 stops working until the
power supply voltage Vout decreases below a value lower than the
OVP threshold Vth_OVP.
[0026] As shown in FIG. 1, the LED driver further comprises a
feedback control circuit 107. In normal operation, the plurality of
feedback isolating switches ST1.about.STn in the feedback control
circuit 107 are all turned on, so that the plurality of feedback
voltages FB1.about.FBn all could be provided to the feedback
selecting circuit 103. When any one of the LED string needs to be
isolated, the associated isolating signal Markoffx turns off the
associated feedback isolating switch STx, to cut off the associated
feedback voltage FBx of the LED string LEDx from the control
loop.
[0027] In the prior art LED driver in FIG. 1, when any one of the
LED strings is open, a value of the associated feedback voltage FBx
of that open LED string is near the value of the ground reference.
The feedback selecting circuit 103 then selects the minimum
feedback voltage FB_min with the minimum value, i.e., the feedback
voltage FBx of the open LED string LEDx, to the voltage regulating
circuit 101. The voltage regulating circuit 101 has a voltage
regulating loop, which regulates the power supply voltage Vout
based on the minimum feedback voltage FB_min. When the minimum
feedback voltage FB_min decreases, the power supply voltage Vout is
regulated to increase, vice versa. When the minimum feedback
voltage FB_min decreases to the value of the ground reference,
e.g., zero, the power supply voltage Vout is regulated to increase
above the OVP threshold Vth_OVP, and the over voltage protection
would be triggered. As a result, the voltage regulating circuit 101
stops working until the power supply voltage Vout decreases below a
safe threshold. Meanwhile, the open LED string is isolated by the
open protecting circuit 104 when the feedback voltage FBx of the
open LED string is detected being lower than the open threshold
Vth_open. The voltage regulating circuit 101 restarts after the
power supply voltage decreases below the safe threshold.
[0028] When any one of the LED string LEDx is shorted, the feedback
voltage FBx of the associated LED string increases due to the
decreased voltage across the associated LED string. When the
feedback voltage FBx increases to a short threshold Vth_short, the
short fault protection is triggered. When the short fault condition
maintains for a preset time period Tshort, the short protecting
circuit provides the associated short isolating signal SRT_mfx to
isolate the shorted LED string. By isolating, it means the short
LED string is disconnected from the current regulating circuit 102,
and the associated feedback voltage FBx is blocked, i.e., the
associated feedback isolating switch STx in the feedback control
circuit 107 is turned off. In one embodiment, the value of the
short threshold Vth_short is 5V.
[0029] From the above illustration, it could be known that the
power supply voltage Vout increases when an open fault protection
is triggered. At this time, except for the feedback voltage FBx of
the opened LED string, the feedback voltages FB1.about.FBn of the
other LED strings increase as the power supply voltage Vout
increases. If any one of the feedback voltages FB1.about.FBn
reaches the short threshold Vth_short, the short fault protection
may be mis-triggered, and then all the LED strings are
isolated.
[0030] In some applications, a feedback terminal Px may be shorted
to the ground reference. As shown in FIG. 1, when the feedback
terminal Px is shorted to the ground reference, the minimum
feedback voltage FB_min would be the value of the ground reference.
Then the power supply voltage Vout increases, and may mis-trigger
the over voltage protection. Meanwhile, an open fault protection
may be mis-triggered too because the low feedback voltage value of
the fault LED string. Then the fault LED string is isolated by the
open protecting circuit 104. However, the voltage regulating
circuit 101 still be working normally after the short to ground LED
string is isolated. It should be noted that isolating the fault LED
string is realized by disconnecting the fault LED string from the
current regulating circuit 102 and blocking the associated feedback
voltage. When the LED string is shorted to the ground reference,
the LED string is still connected to the power supply voltage in a
shorted way when the LED string is isolated. Thus, if the voltage
regulating circuit 101 keeps working, then a current flowing
through the short to ground LED string increases rapidly, and may
shoot through the short to ground LED string, and the voltage
regulating circuit 101 would be damaged too.
[0031] Thus, there is a need to identify the different faults, and
to deal with the different faults correctly.
[0032] FIG. 2 schematically shows a current regulating circuit 20
in accordance with an embodiment of the present invention. The
current regulating circuit 20 may be used with the LED driver shown
in FIG. 1. As shown in FIG. 2, the current regulating circuit 20
comprises n control units 201.about.20n configured to control n LED
strings respectively, wherein each control unit 20x comprises a
current control switch SNx, a resistor Rx and an amplifying circuit
CPx, wherein any label suffixed by letter x represents the label of
a signal or of a component associated with the LED string LEDx, and
wherein x represents any one of the numbers between 1 and n. The
current regulating signal Iref regulates a current flowing through
a current control switch SNx, i.e, the current flowing through the
associated LED string, by adjusting an output of an associated
amplifying circuit CPx. An associated current isolating switch SGx
is coupled between the output of the amplifying circuit CPx and a
ground reference. When the LED string LEDx needs to be isolated,
the associated current isolating switch SGx is turned on by the
associated isolating signal Markoffx, and a control terminal of the
associated current control switch SNx is pulled to the ground
reference to turn off the associated current control switch SNx, to
disconnect the associated LED string LEDx from the current
regulating circuit 20.
[0033] FIG. 3 schematically shows a short protecting circuit 30 in
accordance with an embodiment of the present invention. As shown in
FIG. 3, the short protecting circuit 30 comprises: a short
comparing circuit 301, configured to receive the plurality of
feedback voltages FB1.about.FBn and the short threshold Vth_short,
and to provide the plurality of short fault indicating signals
SRT1.about.SRTn, wherein each short fault indicating signal is
generated based on comparing the associated feedback voltage with
the short threshold Vth_short; a first logic circuit 302,
configured to receive the plurality of short fault indicating
signals SRT1.about.SRTn, and to provide a short fault signal
Fault_S based on the plurality of short fault indicating signals
SRT1.about.SRTn to indicate a short fault condition, wherein when
one of the short fault indicating signals SRT1.about.SRTn is valid
(the short fault happens), the short fault signal Fault_S is valid;
a timing circuit 303, configured to receive the short fault signal
Fault_S and an open fault signal Fault_O, and to provide a short
protecting enable signal EN_S based on the short fault signal
Fault_S and the open fault signal Fault_O, wherein the short
protecting enable signal EN_S is valid when the short fault signal
Fault_S indicates the short fault condition for a preset time
period Tshort, in the premise that the open fault signal Fault_O is
invalid; and a second logic circuit 304, configured to receive the
plurality of short fault indicating signals SRT1.about.SRTn and the
short protecting enable signal EN_S, and to provide the plurality
of short isolating signals SRT_mf1.about.SRT_mfn, wherein each
short isolating signal is generated based on performing a logic
operation to the associated short fault indicating signal and the
short protecting enable signal EN_S.
[0034] In one embodiment, the short comparing circuit 301 comprises
n comparators, wherein each comparator is configured to receive the
short threshold Vth_short and one feedback voltage of the plurality
of feedback voltages FB1.about.FBn, and to provide each short fault
indicating signal based on the associated feedback voltage and the
short threshold Vth_short. When a feedback voltage FBx is higher
than the short threshold Vth_short, the associated short fault
indicating signal SRTx is valid, which indicates that the
associated LED string LEDx is shorted, wherein any label suffixed
by letter x represents the label of a signal or of a component
associated with the LED string LEDx, and wherein x represents any
one of the numbers between 1 and n.
[0035] In one embodiment, a short fault indicating signal's valid
state is represented by high level voltage, and the first logic
circuit 302 comprises an OR gate. When any one of the short fault
indicating signal SRTx turns high, the short fault signal Fault_S
provided by the first logic circuit 302 goes high, i.e., be valid,
and indicates there is a shorted LED string. It should be
understood that, when the valid state of a short fault indicating
signal is represented by other voltage levels, the structure of the
first logic circuit 302 would be changed accordingly. For example,
when the valid state of the short fault indicating signal is
represented by low level voltage, the first logic circuit 302 may
comprise an AND gate, and the valid state of the short fault signal
is the low level voltage then. When the valid state of the short
fault indicating signal is represented by the low level voltage,
the first logic circuit 302 may also comprise a NAND gate, and then
the valid state of the short fault signal Fault_S is high level
voltage. The examples here are to illustrate the variability of the
short fault indicating signals SRT1.about.SRTn and the first logic
circuit 302. Any circuit could implement the function of the first
logic circuit 302 descried here could be used with the present
invention.
[0036] In FIG. 3, the timing circuit 303 is configured to receive
the short fault signal Fault_S and the open fault signal Fault_O.
When the open fault signal Fault_O is invalid but the short fault
signal Fault_S is valid, the timing circuit 303 starts working, and
provides the short protecting enable signal EN_S, wherein the short
protecting enable signal EN_S turns valid when the valid state of
the short fault signal Fault_S maintains for the time period
Tshort. When the open fault signal Fault_O is valid, no matter the
short fault signal Fault_S is valid or not, the timing circuit 303
does not work, and the short protecting enable signal EN_S is
invalid in this situation.
[0037] In one embodiment, the second logic circuit 304 comprises a
plurality of AND gates, wherein each AND gate receives the short
protecting enable signal EN_S and the associated short fault
indicating signal SRTx, and wherein based on the short protecting
enable signal EN_S and the associated short fault indicating
signals SRTx, each AND gate provides an associated short isolating
signal SRT_mfx. It should be understood that when the valid state
of the plurality short fault indicating signals SRT1.about.SRTn,
the short protecting enable signal EN_S or the plurality of short
isolating signals SRT_mf1.about.SRT_mfn is represented by other
voltage levels, the structure of the second logic circuit 304 would
be changed accordingly.
[0038] FIG. 4 schematically shows a short protecting circuit 40 in
accordance with an embodiment of the present invention. As shown in
FIG. 4, the short protecting circuit 40 comprises: the short
comparing circuit 301, configured to receive the plurality of
feedback voltages FB1.about.FBn and the short threshold Vth_short,
and to provide the plurality of short fault indicating signals
SRT1.about.SRTn, wherein each short fault indicating signal is
generated based on comparing the associated feedback voltage with
the short threshold Vth_short; a first logic circuit 402,
configured to receive the plurality of short fault indicating
signals SRT1.about.SRTn and the open fault signal Fault_O, and to
provide the short fault signal Fault_S based on the plurality of
short fault indicating signals SRT1.about.SRTn and the open fault
signal Fault_O to indicate the short fault condition; a timing
circuit 403, configured to receive the short fault signal Fault_S,
and to provide a short protecting enable signal EN_S, wherein the
short protecting enable signal EN_S is valid when the short fault
signal Fault_S indicates the short fault condition for the preset
time period Tshort; the second logic circuit 304, configured to
receive the plurality of short fault indicating signals
SRT1.about.SRTn and the short protecting enable signal EN_S, and to
provide the plurality of short isolating signals
SRT_mf1.about.SRT_mfn, wherein each short isolating signal is
generated based on performing a logic operation to the associated
short fault indicating signal and the short protecting enable
signal EN_S.
[0039] The difference between the short protecting circuit 40 in
FIG. 4 and the short protecting circuit 30 in FIG. 3 is that: the
open fault signal Fault_O is provided to the first logic circuit
402 instead of the timing circuit 303. When the open fault signal
Fault_O is valid, i.e., at least one LED string is opened, the
plurality of short fault indicating signals SRT1.about.SRTn are
blocked by the first logic circuit 402. In the example of FIG. 4,
the high level voltage of any one of the short fault indicating
signals SRT1.about.SRTn indicates a short fault, and the low level
voltage of the open fault signal Fault_O indicates an open fault.
Based on this situation, the first logic circuit 402 comprises two
AND gates, wherein a first AND gate receives all of the plurality
of short fault indicating signals SRT1.about.SRTn, and a second AND
gate receives the open fault signal Fault_O and an output signal of
the first AND gate. In another embodiment, the high level voltage
of the short fault indicating signal indicates a short fault, and
the high level voltage of the open fault signal Fault_O indicates
an open fault. Based on this situation, the open fault signal
Fault_O is inverted before AND operation. It should be understood
that when the valid state of input signals of the first logic
circuit 402 is represented by other voltage levels, the structure
of the first logic circuit 402 would be changed accordingly.
[0040] FIG. 5 schematically shows a short protecting circuit 50 in
accordance with an embodiment of the present invention. As shown in
FIG. 5, the short protecting circuit 50 comprises: the short
comparing circuit 301, configured to receive the plurality of
feedback voltages FB1.about.FBn and the short threshold Vth_short,
and to provide the plurality of short fault indicating signals
SRT1.about.SRTn, wherein each short fault indicating signal is
generated based on comparing the associated feedback voltage with
the short threshold Vth_short; the first logic circuit 302,
configured to receive the plurality of short fault indicating
signals SRT1.about.SRTn, and to provide a short fault signal
Fault_S based on the plurality of short fault indicating signals
SRT1.about.SRTn to indicate the short fault condition, wherein when
one of the short fault indicating signals SRT1.about.SRTn is valid
(the short fault happens), the short fault signal Fault_S is valid;
the timing circuit 403, configured to receive the short fault
signal Fault_S, and to provide the short protecting enable signal
EN_S, wherein the short protecting enable signal EN_S is valid when
the short fault signal Fault_S indicates the short fault condition
for the preset time period Tshort; a second logic circuit 504,
configured to receive the plurality of short fault indicating
signals SRT1.about.SRTn, the open fault signal Fault_O and the
short protecting enable signal EN_S, and to provide the plurality
of short isolating signals SRT_mf1.about.SRT_mfn, wherein each
short isolating signal is generated based on performing a logic
operation to the associated short fault indicating signal and the
short protecting enable signal EN_S, and wherein the plurality of
short fault indicating signals are blocked when the open fault
signal Fault_O is valid. That is to say, the short isolating
signals SRT_mf1.about.SRT_mfn are invalid when the open fault
signal Fault_O is valid, regardless of the states of the short
fault indicating signal SRT1.about.SRTn.
[0041] FIG. 6 schematically shows a short protecting circuit 60 in
accordance with an embodiment of the present invention. As shown in
FIG. 6, the short protecting circuit 60 comprises: a short
comparing circuit 601, configured to receive the plurality of
feedback voltages FB1.about.FBn, the short threshold Vth_short and
the open fault signal Fault_O, and to provide the plurality of
short fault indicating signals SRT1.about.SRTn, wherein each short
fault indicating signal is generated based on comparing the
associated feedback voltage with the short threshold Vth_short, and
wherein the short comparing circuit 601 is disabled when the open
fault signal Fault_O is valid; the first logic circuit 302,
configured to receive the plurality of short fault indicating
signals SRT1.about.SRTn, and to provide a short fault signal
Fault_S based on the plurality of short fault indicating signals
SRT1.about.SRTn to indicate the short fault condition, wherein when
one of the short fault indicating signals SRT1.about.SRTn is valid
(the short fault happens), the short fault signal Fault_S is valid;
the timing circuit 403, configured to receive the short fault
signal Fault_S, and to provide the short protecting enable signal
EN_S, wherein the short protecting enable signal EN_S is valid when
the short fault signal Fault_S indicates the short fault condition
for the preset time period Tshort; the second logic circuit 304,
configured to receive the short fault indicating signals
SRT1.about.SRTn and the short protecting enable signal EN_S, and to
provide the short isolating signals SRT_mf1.about.SRT_mfn based on
the logic operation of the short fault indicating signals
SRT1.about.SRTn and the short protecting enable signal EN_S.
[0042] In FIG. 6, when the open fault signal Fault_O is valid,
i.e., an open fault condition, the short comparing circuit 601 is
disabled, otherwise, the short comparing circuit 601 is
enabled.
[0043] FIG. 7 schematically shows an open and short to ground
protecting circuit 70 in accordance with an embodiment of the
present invention. As shown in FIG. 7, the open and short to ground
protecting circuit 70 comprises: an open comparing circuit 701,
configured to receive the plurality of feedback voltages
FB1.about.FBn and the open threshold Vth_open, and to provide the
plurality of open fault indicating signals OP1.about.OPn, wherein
each open fault indicating signal is generated based on comparing
the associated feedback voltage with the open threshold Vth_open; a
third logic circuit 702, configured to receive the plurality of
open fault indicating signals OP1.about.OPn and the OVP signal
Sovp, and to provide a plurality of current isolating switch
control signals OPI1.about.OPIn and the open fault signal Fault_O,
wherein each current isolating switch control signal is generated
based on performing a logic operation to the associated open fault
indicating signal and the OVP signal Sovp, and wherein the open
fault signal Fault_O is generated based on performing a logic
operation to the plurality of open fault indicating signals
OP1.about.OPn; a short to ground protecting circuit 703, configured
to receive the plurality of feedback voltages FB1.about.FBn, a
short to ground threshold Vth_sg and the open fault signal Fault_O,
wherein in the premise that the open fault signal Fault_O is valid,
the short to ground protecting circuit 703 provide a short to
ground indicating signal Slatch based on performing a logic
operation to comparison results of each feedback voltage of the
plurality of feedback voltages with the short to ground threshold;
and a fourth logic circuit 704, configured to receive the short to
ground indicating signal Slatch and the plurality of current
isolating switch control signals OPI1.about.OPIn, and to provide a
plurality of feedback isolating switch control signals
OPV1.about.OPVn, wherein each feedback isolating switch control
signal is generated based on performing a logic operation to the
associated current isolating switch control signal with the short
to ground indicating signal Slatch.
[0044] In FIG. 7, the open comparing circuit 701 compares each one
of the plurality of feedback voltages FB1.about.FBn with the open
threshold Vth_open, and provides the plurality of open fault
indicating signals OP1.about.OPn to indicate if there is any
feedback voltage FBx being lower than the open threshold Vth_open,
wherein any label suffixed by letter x represents the label of a
signal or of a component associated with the LED string LEDx, and
wherein x represents any one of the numbers between 1 and n.
[0045] In one embodiment, the third logic circuit 702 receives the
plurality of open fault indicating signals OP1.about.OPn, and
performs a logic operation to each one of the open fault indicating
signals OP1.about.OPn with the OVP signal Sovp, e.g., AND
operation, and then provides the plurality of current isolating
switch control signals OPI1.about.OPIn based on the logic operation
results respectively. When the OVP signal Sovp indicates that the
power supply voltage Vout is higher than the OVP threshold Vth_OVP,
and meanwhile one of the open fault indicating signal OPx indicates
that the feedback voltage FBx is lower than the open threshold
Vth_open, the associated current isolating switch control signal
OPIx turns on the associated current isolating switch SGx. As a
result, the associated current control switch SNx is turned off,
and the associated string LEDx is disconnected from the current
regulating circuit 102. Also, a logic operation is performed to all
of the plurality of current isolating switch control signals
OPI1.about.OPIn, and the open fault signal Fault_O is generated
based on the logic operation result. To be specific, when one of
the plurality of current isolating switch control signal OPIx is
valid, i.e., the current isolating switch control signal OPIx is
going to turn on the associated current isolating switch SGx, the
open fault signal Fault_O is valid.
[0046] As illustrated before, a valid open fault signal Fault_O
doesn't necessary mean there is an open LED string. A short to
ground fault condition needs to be excluded. In one embodiment, the
short to ground protecting circuit 703 comprises a comparing
circuit and a logic circuit. The open fault signal Fault_O is
adopted as an enable signal of the short to ground protecting
circuit 703. The comparing circuit of the short to ground
protecting circuit 703 compares each one of the plurality of
feedback voltages FB1.about.FBn with the short to ground threshold
Vth_sg, and provides a plurality of comparing results. The logic
circuit of the short to ground protecting circuit 703 performs a
logic operation to all of the plurality of comparing results to
generate the short to ground indicating signal Slatch. When any one
of the plurality of comparing results indicates that one of the
plurality of feedback voltages is lower than the short to ground
threshold Vth_sg, the short to ground indicating signal Slatch is
valid, indicating that there is a LED string being shorted to the
ground. Then the short to ground indicating signal Slatch latches
the LED driver until restarted.
[0047] The fourth logic circuit 704 receives the short to ground
indicating signal Slatch and the plurality of current isolating
switch control signals OPI1.about.OPIn, and performs a logic
operation to each one of the plurality of current isolating switch
control signals OPI1.about.OPIn with the short to ground indicating
signal Slatch. When the short to ground indicating signal Slatch is
invalid, the plurality of current isolating switch control signals
OPI1.about.OPIn are provided as the plurality of feedback isolating
switch control signals OPV1.about.OPVn to control the plurality of
feedback isolating switches ST1.about.STn in the feedback control
circuit 107 respectively, i.e., the current isolating switch
control signal OPIx, which turns on the associated current
isolating switch SGx, turns off the associated feedback isolating
switch STx, to block the associated feedback voltage FBx. When the
short to ground indicating signal Slatch is valid, which means
there is a LED string shorted to the ground, the plurality of
feedback isolating switch control signals OPV1.about.OPVn turn off
all of the plurality of feedback isolating switches ST1.about.STn
in the feedback control circuit 107.
[0048] In one embodiment, the OVP signal Sovp is generated by an
over voltage protecting circuit which may comprise a comparator,
wherein the comparator receives the power supply voltage Vout and
the OVP threshold Vth_ovp, and provides the OVP signal Sovp based
on a comparison result of the power supply voltage Vout and the OVP
threshold Vth_ovp. The detail of the over voltage protecting
circuit is not shown in the drawings for brevity.
[0049] The present invention involves several logic circuits.
Persons of ordinary skill in the art should know that the logic
circuits may change according to the forms of the input/output
signals. The logic circuits in the present invention are
illustrated as examples. Persons of ordinary skill in the art could
adopt the proper logic circuits in accordance with the application
in the light of the present invention.
[0050] FIG. 8 schematically shows a LED driver 80 in accordance
with an embodiment of the present invention. The LED driver 80
comprises: the voltage regulating circuit 101, configured to
provide the power supply voltage Vout to the plurality of LED
strings; the current regulating circuit 102, configured to receive
the current regulating signal Iref, wherein the current regulating
circuit 102 is coupled to the plurality of LED strings to regulate
a current flowing through a LED string of the plurality of LED
strings based on the current regulating signal Iref; the feedback
selecting circuit 103, configured to receive the plurality of
feedback voltages FB1.about.FBn, and to provide the minimum
feedback voltage FB_min to the voltage regulating circuit 101 to
regulate the power supply voltage Vout; the open and short to
ground protecting circuit 70, configured to receive the plurality
of feedback voltages FB1.about.FBn, the open threshold Vth_open and
the OVP signal Sovp, and to provide the plurality of short
isolating signals SRT_mf1.about.SRT_mfn based on the plurality of
feedback voltages FB1.about.FBn, the open threshold Vth_open and
the OVP signal Sovp; the short protecting circuit 30, configured to
receive the plurality of feedback voltages FB1.about.FBn and the
short threshold Vth_short, and to provide the plurality of short
isolating signals SRT_mf1.about.SRT_mfn based on the plurality of
feedback voltages FB1.about.FBn and the short threshold Vth_short;
and an isolating logic circuit 801, configured to receive the
plurality of short isolating signals SRT_mf1.about.SRT_mfn, the
plurality of current isolating switch control signals
OPI1.about.OPIn and the plurality of feedback isolating switch
control signals OPV1.about.OPVn, and to perform a logic operation
to each one of the plurality of short isolating signals
SRT_mf1.about.SRT_mfn and the associated one of the plurality of
current isolating switch control signals OPI1.about.OPIn, wherein
based on each logic operation result of the plurality of logic
operation results, the isolating logic circuit 801 provides the
associated one of the plurality of control signal MFI1.about.MFIn
to the associated one of the plurality of current control switch
SN1.about.SNn. Furthermore, the isolating logic circuit 801
performs a logic operation to the short isolating signal of the
plurality of short isolating signals SRT_mf1.about.SRT_mfn and the
associated feedback isolating switch control signal of the
plurality of feedback isolating switch control signals
OPV1.about.OPVn, wherein based on each one of the plurality of
logic operation results, the isolating logic circuit 801 provides a
control signal of the plurality of control signals MFV1.about.MFVn
to the associated feedback isolating switch of the plurality of
feedback isolating switches ST1.about.STn.
[0051] In one embodiment, the isolating logic circuit 801 comprises
a plurality of logic gates. For example, the isolating logic
circuit 801 may comprise a set of n AND gates, wherein each AND
gate receives the short isolating signal SRT_mfx of the short
isolating signals and the associated current isolating switch
control signal OPIx, and provides the associated control signal
MFIx to control the associated current control switch SNx based on
performing AND operation to the short isolating signal SRT_mfx and
the associated current isolating switch control signal OP Ix,
wherein any label suffixed by letter x represents the label of a
signal or of a component associated with the LED string LEDx, and
wherein x represents any one of the numbers between 1 and n.
Meanwhile, the isolating logic circuit 801 further comprises
another set of n AND gates, wherein each AND gate receives the
short isolating signal of the plurality of short isolating signals
SRT_mfx and the associated feedback isolating switch control signal
OPVx, and provides the control signal MFVx to control the
associated feedback isolating switch STx based on performing the
AND operation to the short isolating signal SRT_mfx and the
associated feedback isolating switch control signal OPVx. Persons
of ordinary skill in the art should know that the structure of the
isolating logic circuit 801 may change according to the signal
forms of the switch control signals.
[0052] It should be understood that the short protecting circuit 30
in FIG. 8 could be replaced by the short protecting circuit 40 in
FIG. 4, the short protecting circuit 50 in FIG. 5 or the short
protecting circuit 60 in FIG. 6.
[0053] FIG. 9 schematically shows a control method 90 of processing
faults of the plurality of LED strings. The plurality of LED
strings are powered by the voltage regulating circuit 101 as shown
in FIG. 1, and the currents flowing through each one of the
plurality of LED strings are regulated by the current regulating
circuit 102 as shown in FIG. 1. The control method 90 comprises:
step 901, generating a plurality of short fault indicating signals
to indicates a short fault condition of the plurality of LED
strings respectively, wherein each short fault indicating signal is
generated by comparing the feedback voltage of the associated LED
string with a short threshold; step 902, generating a short fault
signal by performing a logic operation to all of the plurality of
short fault indicating signals, wherein when any one of the short
fault indicating signal indicates a short fault condition, the
short fault signal is valid, otherwise, the short fault signal is
invalid; step 903, generating a short protecting enable signal
after the short fault signal maintains valid state for a preset
time period in the premise of an open fault signal being invalid;
and step 904, providing a plurality of short fault indicating
signals to control the isolation of the plurality of LED strings
respectively when the short protecting enable signal is valid.
[0054] In one embodiment, step 904 comprises: adopting the
plurality of short fault indicating signals to control the
transmission of the plurality of feedback voltages of the LED
strings respectively; and adopting the plurality of short fault
indicating signals to control the connections between the plurality
of LED strings and the current regulating circuit respectively.
[0055] FIG. 10 schematically shows a control method 100 of
processing faults of the plurality of LED strings. The plurality of
LED strings are powered by the voltage regulating circuit 101 as
shown in FIG. 1, and the currents flowing through each one of the
plurality of LED strings are regulated by the current regulating
circuit 102 as shown in FIG. 1. The control method 100 comprises:
step 1001, generating a plurality of open fault indicating signals
to indicates an open fault condition of the plurality of LED
strings respectively, wherein each open fault indicating signal is
generated by comparing the feedback voltage of the associated LED
string with an open threshold; step 1002, providing the plurality
of open fault indicating signals to control the connections between
the plurality of LED strings and the current regulating circuit
respectively in the premise of that an OVP signal indicates an over
voltage fault condition of the power supply voltage supplied to the
plurality of LED strings; step 1003, generating an open fault
signal by performing a logic operation to the plurality of open
fault indicating signals, wherein when any one of the plurality of
open fault indicating signals indicates an open fault, the open
fault signal is valid to indicate the open fault condition; step
1004, generating a short to ground indicating signal based on
comparing results of each one of the plurality of feedback voltages
with a short to ground threshold in the premise of the open fault
signal being valid; step 1005, latching the voltage regulating
circuit to stop powering the plurality of LED strings when the
short to ground indicating signal is valid; and step 1006, adopting
the plurality of open fault indicating signals to control the fed
back of the feedback voltages of the plurality of LED strings
respectively when the short to ground indicating signal is
invalid.
[0056] In one embodiment, when the OVP signal is valid, i.e., the
power supply voltage Vout is higher than the OVP threshold Vth_OVP,
the voltage regulating circuit 101 stops working until the power
supply voltage drops below the safe threshold.
[0057] Obviously many modifications and variations of the present
invention are possible in light of the above teachings. It is
therefore to be understood that within the scope of the appended
claims the invention may be practiced otherwise than as
specifically described. It should be understood, of course, the
foregoing disclosure relates only to a preferred embodiment (or
embodiments) of the invention and that numerous modifications may
be made therein without departing from the spirit and the scope of
the invention as set forth in the appended claims. Various
modifications are contemplated and they obviously would be resorted
to by those skilled in the art without departing from the spirit
and the scope of the invention as hereinafter defined by the
appended claims as only a preferred embodiment(s) thereof has been
disclosed.
* * * * *