U.S. patent application number 12/338907 was filed with the patent office on 2009-10-15 for current-level decision device for a power supply device and related power supply device.
Invention is credited to Chia-Chieh Hung, Chi-Hao Wu.
Application Number | 20090256533 12/338907 |
Document ID | / |
Family ID | 41163426 |
Filed Date | 2009-10-15 |
United States Patent
Application |
20090256533 |
Kind Code |
A1 |
Wu; Chi-Hao ; et
al. |
October 15, 2009 |
Current-level Decision Device for a Power Supply Device and Related
Power Supply Device
Abstract
An current-level decision device for a power supply device
includes a reception end for receiving a current sense signal, a
reference voltage generator for generating a first reference
voltage, a reference voltage correction unit coupled to the
reference voltage generator and the reception end for adjusting the
reference voltage according to variation of the current sense
signal, so as to generate a second reference voltage, a comparator
coupled to the reception end and the reference voltage correction
unit for comparing the current sense signal and the second
reference voltage to generate a comparison result, and a control
unit coupled to the comparator for controlling a switch transistor
of the power supply according to the comparison result.
Inventors: |
Wu; Chi-Hao; (Taipei City,
TW) ; Hung; Chia-Chieh; (Taoyuan County, TW) |
Correspondence
Address: |
NORTH AMERICA INTELLECTUAL PROPERTY CORPORATION
P.O. BOX 506
MERRIFIELD
VA
22116
US
|
Family ID: |
41163426 |
Appl. No.: |
12/338907 |
Filed: |
December 18, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61044908 |
Apr 15, 2008 |
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Current U.S.
Class: |
323/224 |
Current CPC
Class: |
H02M 3/33507
20130101 |
Class at
Publication: |
323/224 |
International
Class: |
G05F 1/613 20060101
G05F001/613 |
Claims
1. A current-level decision device for a power supply comprising: a
reception end for receiving a current sense signal; a reference
voltage generator for generating a reference voltage; a reference
voltage correction unit, coupled to the reference voltage generator
and the reception end, for adjusting the first reference voltage
according to variation of the current sense signal, so as to
generate a second reference voltage; a first comparator, coupled to
the reception end and the reference voltage correction unit, for
comparing the current sense signal and the second reference
voltage, to generate a first comparison result; and a control unit,
coupled to the first comparator, for controlling a power switch of
the power supply according to the first comparison result.
2. The current-level decision device of claim 1, wherein the
reference voltage correction unit comprises: a switch unit,
comprising a first end, a second end and a third end, for
conducting a signal connection between the first end and the third
end according to signals received by the second end; a first
current source, coupled to the first end of the switch unit, for
generating a first current; a second comparator, coupled to the
reference voltage generator, the reception end and the second end
of the switch unit, for comparing the first reference voltage and
the current sense signal, to generate a second comparison result to
the second end of the switch unit; a filtering unit, coupled to the
third end of the switch unit, for performing filtering on signals
of the third end of the switch unit; a division unit, coupled to
the filtering unit, for generating a current signal according to a
filtering result of the filtering unit; and a current to voltage
conversion unit, coupled to the division unit and the first
comparator, for generating the second reference voltage to the
first comparator according to the current signal generated by the
separation unit.
3. The current-level decision device of claim 2, wherein the switch
unit is a p-type metal oxide semiconductor field effect transistor,
the first end is a source, the second end is a gate, and the third
end is a drain.
4. The current-level decision device of claim 2, wherein the
filtering unit comprises: a first capacitor, having one end coupled
to the third end of the switch unit, and the other end coupled to a
ground; a resistor, coupled to the third end of the switch unit;
and a second capacitor, having one end coupled to the resistor, and
the other end coupled to a ground.
5. The current-level decision device of claim 2, wherein the
division unit comprises: a current output end, coupled to the
current to voltage conversion unit, for outputting the current
signal; a second current source, coupled to the current output end,
for generating a second current to the current output end; and a
third current source, coupled to the current output end, the
filtering unit and a ground, for generating a third current from
the current output end to the ground, and adjusting the third
current according to the filtering result of the filtering
unit.
6. The current-level decision device of claim 2, wherein the
current to voltage conversion unit is a resistor.
7. The current-level decision device of claim 2 further comprising
a reset unit, having a first end coupled to the third end of the
switch unit, a second end coupled to a reset signal generator, and
a third end coupled to a ground, for conducting a signal connection
between the first end and the third end according to signals
received by the second end.
8. The current-level decision device of claim 7, wherein the reset
unit is an n-type metal oxide semiconductor field effect
transistor, the first end is a drain, the second end is a gate, and
the third end is a source.
9. A power supply capable of preventing an over-current damage
comprising: a transformer, comprising a primary winding circuit and
a secondary winding circuit; a switch transistor, coupled to the
primary winding circuit; a current sensing unit, coupled to the
switch transistor, for generating a current sense signal according
to current flowing through the switch transistor in the primary
winding circuit; and a current-level decision device, coupled to
the current sensing unit and the switch transistor, comprising: a
reception end for receiving a current sense signal; a reference
voltage generator for generating a first reference voltage; a
reference voltage correction unit, coupled to the reference voltage
generator and the reception end, for adjusting the first reference
voltage according to variation of the current sense signal, so as
to generate a second reference voltage; a first comparator, coupled
to the reception end and the reference voltage correction unit, for
comparing the current sense signal and the second reference
voltage, to generate a first comparison result; and a control unit,
coupled to the first comparator, for controlling a power switch of
the power supply according to the first comparison result.
10. The power supply of claim 9, wherein the reference voltage
correction unit comprises: a switch unit, comprising a first end, a
second end and a third end, for conducting a signal connection
between the first end and the third according to signals received
by the second end; a first current source, coupled to the first end
of the switch unit, for generating a first current; a second
comparator, coupled to the reference voltage generator, the
reception end and the second end of the switch unit, for comparing
the first reference voltage and the current sense signal, to
generate a second comparison result to the second end of the switch
unit; a filtering unit, coupled to the third end of the switch
unit, for performing filtering on signals of the third end of the
switch unit; a division unit, coupled to the filtering unit, for
generating a current signal according to a filtering result of the
filtering unit; and a current to voltage conversion unit, coupled
to the division unit and the first comparator, for generating the
second reference voltage to the first comparator according to the
current signal generated by the separation unit.
11. The power supply of claim 10, wherein the switch unit is a
p-type metal oxide semiconductor field effect transistor, the first
end is a source, the second end is a gate, and the third end is a
drain.
12. The power supply of claim 10, wherein the filtering unit
comprises: a first capacitor, having one end coupled to the third
end of the switch unit, and the other end coupled to a ground; a
resistor, coupled to the third end of the switch unit; and a second
capacitor, having one end coupled to the resistor, and the other
end coupled to a ground.
13. The power supply of claim 10, wherein the division unit
comprises: a current output end, coupled to the current to voltage
conversion unit, for outputting the current signal; a second
current source, coupled to the current output end, for generating a
second current to the current output end; and a third current
source, coupled to the current output end, the filtering unit and a
ground, for generating a third current from the current output end
to the ground, and adjusting the third current according to the
filtering result of the filtering unit.
14. The power supply of claim 10, wherein the current to voltage
conversion unit is a resistor.
15. The power supply of claim 10 further comprising a reset unit,
having a first end coupled to the third end of the switch unit, a
second end coupled to a reset signal generator, and a third end
coupled to a ground, for conducting a signal connection between the
first end and the third end according to signals received by the
second end.
16. The power supply of claim 15, wherein the reset unit is an
n-type metal oxide semiconductor field effect transistor, the first
end is a drain, the second end is a gate, and the third end is a
source.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 61/044,908, filed on Apr. 15, 2008 and entitled
"Over Current Protection Circuit with Adaptive Reference in a Power
Supply Device", the contents of which are incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention is related to a current-level decision
device for a power supply and related power supply, and more
particularly, to a current-level decision device and related power
supply capable of regulating a reference voltage based upon
variation of a current sense signal, to make an actual voltage for
activating over-current protection equal to an expected voltage for
activating the over-current protection, to greatly improve the
problem of time delay and voltage draft of the protection
point.
[0004] 2. Description of the Prior Art
[0005] Power supply is used to provide an electrical power for
operating an electronic device. According to the circuit
architecture, power supplies can be classified into two types,
Linear and Switching. A switching power supply has benefits of
small volume, light weight and high power efficiency, so it can be
widely used in various kinds of electronic devices, such as mobile
phone, PDA, computer and peripherals, server and network
appliances.
[0006] For sustaining the normal operation of the power supply, the
protection mechanism of a control circuit for protecting the power
supply is a very critical part (for example, protection functions
of over-voltage, over-current, and over-power), and once the
overload or the short condition happens, a power supply with
complete protection functions can prevent the internal components
or related appliances from being damaged.
[0007] Please refer to FIG. 1, which illustrates a schematic
diagram of a switching power supply 10 of the prior art. The
switching power supply 10 comprises the over-current protection
function, and is used to convert an input voltage signal VIN to an
output voltage signal VOUT with a proper voltage level. The
switching power supply 10 comprises a transformer 100, a control
unit 102, a comparator 104, a switch transistor Q1 and a current
sensing resistor Rs. The operations of the circuit are stated as
follows. First, the current sensing resistor Rs generates the
current sense signal VCS based upon the primary winding current Id
of the transformer 100. Second, the comparator 104 compares the
current sense signal VCS and a reference voltage VREF, and outputs
an indication signal SOC to the control unit 102, such that the
control unit 102 can determine whether it has fallen into the range
of current protection. For example, when the current sense signal
VCS is higher than the reference voltage VREF, the comparator 104
can indicate an over-current condition happens via the indication
signal SOC, the control unit 102 can turn off the switch transistor
Q1 to reduce current in the primary winding.
[0008] Simply speaking, the protection mechanism mentioned above is
to compare the current sense signal VCS and the reference voltage
VREF, such that the primary winding current can be controlled
within a proper range for the purpose of protection. However, when
the current sense signal VCS is higher than the reference voltage
VREF, the switch transistor Q1 cannot be turned off immediately
owing to some non-ideal factors, and it will take an interval of
time for the control unit 102 to turn off the switch transistor Q1.
That is to say, there exists a time delay T_D, starting from the
moment for the over-current condition being detected to the time
for the switch transistor Q1 being turned off, and the current
level right before being turned off will surpass the pre-defined
level by a specific amount. In other words, the voltage level right
before the over-current protection starts (abbreviated as
"protection point voltage" hereafter) will be larger than the
voltage level when the over-current condition is taking place. For
different voltage level of the input voltage VIN, the voltage level
of the protection point voltage varies accordingly.
[0009] For more details, please refer to FIG. 2, which illustrates
the voltage difference of the protection point voltage for
different input voltages within the same time delay. The input
voltage VIN of the switching power supply 10 is proportional to the
slope of the current sense signal VCS. Therefore, with the same
reference voltage VREF, a higher input voltage VH will generate a
current sense signal VCS of bigger slope, and a lower input voltage
VL will generate a current sense signal VCS of smaller slope. Note
that, a power supply always has the same time delay T_D since the
time delay T_D is independent of the level of the input voltage
VIN. As illustrated in FIG. 2, when the current sense signal VCS
rises to the power limiting level corresponding to the reference
voltage VREF, or the current sense signal VCS is greater than or
equal to the reference voltage VREF, the comparator 104 transmits
the indication signal SOC to the control unit 102, such that the
switch transistor Q1 can be turned off. Since the circuit coming
with the non-ideal factor, therefore, after the transmission delay
T_D, the switch transistor Q1 starts being turned off, and the
primary winding current Id can then be cut off. From the moment of
the over-current condition being detected to the switch transistor
Q1 being turned off, the input voltage VIN will continue to
transfer power, such that the protection point voltage becomes
VOPPH for the high input voltage VH, or the protection point
voltage becomes VOPPL for the low input voltage VL. In other words,
the protection point voltage will be higher than the reference
voltage VREF, and as the input voltage VIN gets higher, the
situation becomes even more obvious. Under this situation, when the
input voltage VIN varies in a wide range, the protection point
voltage will drift seriously, such that the output power levels
corresponding to the high and the low input voltages differs a
lot.
SUMMARY OF THE INVENTION
[0010] It is therefore a primary objective of the claimed invention
to provide a current-level decision device for a power supply and
the related power supply.
[0011] The present invention discloses a current-level decision
device for a power supply, which comprises a reception end for
receiving a current sense signal, a reference voltage generator for
generating a first reference voltage, a reference voltage
correction unit, coupled to the reference voltage generator and the
reception end, for adjusting the first reference voltage according
to variation of the current sense signal, so as to generate a
second reference voltage, a first comparator, coupled to the
reception end and the reference voltage correction unit, for
comparing the current sense signal and the second reference
voltage, to generate a first comparison result, and a control unit,
coupled to the first comparator, for controlling a power switch of
the power supply according to the first comparison result.
[0012] The present invention also discloses a power supply capable
of preventing an over-current damage, which comprises a
transformer, comprising a primary winding circuit and a secondary
winding circuit, a switch transistor, coupled to the secondary
winding circuit, a current sensing unit, coupled to the switch
transistor, for generating a current sense signal according to
current flowing through the switch transistor in the primary
winding circuit, and a current-level decision device, coupled to
the current sensing unit and the switch transistor, which further
comprises a reception end for receiving a current sense signal, a
reference voltage generator for generating a first reference
voltage, an reference voltage correction unit, coupled to the
reference voltage generator and the reception end, for adjusting
the first reference voltage according to variation of the current
sense signal, so as to generate a second reference voltage, a first
comparator, coupled to the reception end and the reference voltage
correction unit, for comparing the current sense signal and the
second reference voltage, to generate a first comparison result,
and a control unit coupled to the first comparator for controlling
a power switch of the power supply according to the first
comparison result.
[0013] These and other objectives of the present invention will no
doubt become obvious to those of ordinary skill in the art after
reading the following detailed description of the preferred
embodiment that is illustrated in the various figures and
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 illustrates a schematic diagram of a switching power
supply of the prior art.
[0015] FIG. 2 illustrates the voltage difference of the protection
point voltages for different input voltages within the same time
delay.
[0016] FIG. 3 is a schematic diagram of a power supply in
accordance with an embodiment of the present invention.
[0017] FIG. 4 is a schematic diagram of a current-level decision
device as shown in FIG. 3.
[0018] FIG. 5 illustrates a schematic diagram of the reference
voltage correction unit shown in FIG. 4 according to a preferred
embodiment of the present invention.
[0019] FIG. 6 illustrates a schematic diagram of generating a
second comparison result in FIG. 5.
DETAILED DESCRIPTION
[0020] Please refer to FIG. 3, which is a schematic diagram of a
power supply 30 in accordance with an embodiment of the present
invention. Preferably, the power supply 30 is a switching power
supply, and capable of preventing over-current damage. The power
supply 30 comprises a transformer 300, a switch transistor Q1, a
current sensing resistor Rs and a current-level decision device
302. The transformer 300, composed of a primary winding circuit and
a secondary winding circuit, is used for transforming the input
voltage signal VIN to an output voltage signal VOUT. The switch
transistor Q1, coupled to the primary winding of the transformer
300, is used for the switching the operations of the transformer
300. The current sensing resistor Rs, coupled to the switch
transistor Q1, generates a current sense signal VCS based upon the
primary winding current Id flowing through the switch transistor
Q1. The current-level decision device 302, coupled to the switch
transistor Q1 and the current sensing resistor Rs, is used for
monitoring the primary winding current Id to be operated within a
protected range. Once the current Id operates outside the protected
range, the switch transistor Q1 will be turned off to reach the
goal of over-current protection.
[0021] Please refer to FIG. 4, which is a schematic diagram of the
current-level decision device 302 as shown in FIG. 3. The
current-level decision device 302 comprises a reception end 400, a
reference voltage generator 402, a reference voltage correction
unit 404, a first comparator 406 and a control unit 408. The
reception end 400, coupled to the current sensing resistor Rs, is
used for receiving the current sense signal VCS, such that the
current sense signal VCS is transferred to the reference voltage
correction unit 404 and the first comparator 406. The reference
voltage generator 402, coupled to the reference voltage correction
unit 404, is used for generating a first reference voltage VREF1.
The reference voltage correction unit 404 can receive the current
sense signal VCS and the first reference voltage VREF1, and adjusts
the first reference voltage VREF1 according to variation of the
current sense signal VCS, so as to generate a second reference
voltage VREF2. Furthermore, the first comparator 406 compares the
current sense signal VCS and the second reference voltage VREF2 to
generate a first comparison result CMP1 and output to the control
unit 408, such that the control unit 408 controls the conduction
status of the switch transistor Q1 according to the first
comparison result CMP1. Simply speaking, the current-level decision
device 302 can adjust the first reference voltage VREF1 according
to variation of the current sense signal VCS, such that the second
reference voltage VREF2 can meet the demands of different system
requirements.
[0022] Please refer to FIG. 5, which illustrates a schematic
diagram of the reference voltage correction unit 404 shown in FIG.
4 according to a preferred embodiment of the present invention. The
reference voltage correction unit 404 comprises a switch transistor
Q2, a reset transistor Q3, a first current source 500, a second
comparator 502, a filtering unit 504, a division unit 506 and a
resistor 508. The second comparator 502 is used for comparing the
first reference voltage VREF1 and the current sense signal VCS, to
generate a second comparison result CMP2 to a gate of the switch
transistor Q2, so as to control the conduction status of the switch
transistor Q2. In this embodiment, the switch transistor Q2 is an
n-type metal oxide semiconductor field effect transistor (MOSFET).
Therefore, as shown in FIG. 6, when the current sense signal VCS is
smaller than the first reference voltage VREF1, the second
comparison result CMP2 is in low level, and the switch transistor
Q2 is turned off. When the current sense signal VCS is greater than
the first reference voltage VREF1, the second comparison result
CMP2 is in high level, and the switch transistor Q2 is turned on,
such that current generated by the first current source 500 flows
through the filtering unit 504. The filtering unit 504 comprises
capacitors C1, C2 and a resistor R1, and is utilized for filtering
signals of the drain of the switch transistor Q2. The division unit
506 comprises a second current source 510 and a third current
source 512, and the third current source 512 is controlled by a
filtering result of the filtering unit 504, so as to adjust the
current amount flowing through the resistor 508. The resistor 508
is acted as a current to voltage converter. In other words, when
the current sense signal VCS is greater than the first reference
voltage VREF1, the reference voltage correction unit 404 can
increase current generated by the third current source 512, to
reduce current flowing through the resistor 508. As a result, the
second reference voltage VREF2 becomes smaller than the first
reference voltage VREF1, to meet requirements of different systems.
Furthermore, in FIG. 5, the reset transistor Q3 is an n-type
MOSFET, and utilized for resetting the reference voltage correction
unit 404 according to a reset signal RST, so as to recover the
second reference voltage VREF2 to an initial value (i.e. the first
reference voltage VREF1).
[0023] Therefore, the power supply 30 can adjust the first
reference voltage VREF1 via the reference voltage correction unit
404, to solve the problem of time delay, and prevent the voltage
drifting problem associated with the protection points. Note that,
FIG. 3 to FIG. 5 exhibit embodiments of the present invention, and
those skilled in the art can make numerous modifications and
alterations accordingly.
[0024] To sum up, the present invention regulates the reference
voltage based upon variation of the current sense signal, such that
the actual voltage for activating the over-current protection is
identical to the expected voltage for activating the over-current
protection, meanwhile, the problems of time delay and the drift of
the protection point voltage can be greatly improved.
[0025] Those skilled in the art will readily observe that numerous
modifications and alterations of the device and method may be made
while retaining the teachings of the invention. Accordingly, the
above disclosure should be construed as limited only by the metes
and bounds of the appended claims.
* * * * *