U.S. patent application number 12/885355 was filed with the patent office on 2011-01-13 for circuit arrangement for overtemperature detection.
This patent application is currently assigned to INFINEON TECHNOLOGIES AG. Invention is credited to Steffen Thiele.
Application Number | 20110006801 12/885355 |
Document ID | / |
Family ID | 38749268 |
Filed Date | 2011-01-13 |
United States Patent
Application |
20110006801 |
Kind Code |
A1 |
Thiele; Steffen |
January 13, 2011 |
Circuit Arrangement for Overtemperature Detection
Abstract
A method and system is provided for retrieving information about
operational data from a plurality of building systems and service
and maintenance information for a plurality of building sites. A
customer web portal is provided with a database for storing the
operational data and the service information allowing users to more
readily generate reports and obtain service related information for
a plurality of sites without having to maintain separate database
systems at remote locations.
Inventors: |
Thiele; Steffen; (Munich,
DE) |
Correspondence
Address: |
MAGINOT, MOOR & BECK
111 MONUMENT CIRCLE, SUITE 3000, BANK ONE CENTER/TOWER
INDIANAPOLIS
IN
46204
US
|
Assignee: |
INFINEON TECHNOLOGIES AG
Neubiberg
DE
|
Family ID: |
38749268 |
Appl. No.: |
12/885355 |
Filed: |
September 17, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11731765 |
Mar 29, 2007 |
7835129 |
|
|
12885355 |
|
|
|
|
Current U.S.
Class: |
324/762.09 |
Current CPC
Class: |
H03K 17/0822 20130101;
H03K 17/6877 20130101; H03K 2017/0806 20130101; H03K 2217/0018
20130101 |
Class at
Publication: |
324/762.09 |
International
Class: |
G01R 31/26 20060101
G01R031/26 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 29, 2006 |
DE |
102006014523.2-33 |
Claims
1. A circuit arrangement for detecting the overtemperature of a
semiconductor body, the circuit arrangement comprising: at least
one field effect transistor including a load terminal; a parasitic
diode integrated in the semiconductor body, the parasitic diode
connecting the load terminal of the field effect transistor to a
bulk terminal of the semiconductor body; an evaluating unit
electrically connected to the parasitic diode via the bulk terminal
at the semiconductor body, the evaluating unit configured to feed a
current into the parasitic diode and evaluate a
temperature-dependent voltage drop across the parasitic diode, the
direction of the current fed into the diode being such that it is
operated in the forward direction; wherein the evaluating unit
comprises a short circuit device operable to temporarily short
circuit the parasitic diode.
2. The circuit arrangement as claimed in claim 1 wherein the field
effect transistor is provided as a power transistor structure.
3. The circuit arrangement as claimed in claim 1, wherein the field
effect transistor provides a power transistor structure, wherein
the short circuit device is configured to short circuit the
parasitic diode when the field effect transistor is switched on and
a voltage occurs along a drain-source path of the power transistor
structure which is above a preset comparison voltage.
4. The circuit arrangement as claimed in claim 1, wherein the short
circuit device is configured to short circuit the parasitic diode
when the field effect transistor is switched off and a voltage
occurs at a drain terminal of the power transistor structure which
is above a preset comparison voltage.
5. The circuit arrangement as claimed in claim 1, wherein the short
circuit device is configured to short circuit the parasitic diode
if an operating voltage, which is above a preset comparison
voltage, provides for an excessive voltage at a drain terminal of
the power transistor structure.
6. The circuit arrangement as claimed in claim 1, wherein the short
circuit device includes a switching element, and wherein the
evaluating unit is an external evaluating unit, the short circuit
device being arranged in the external evaluating unit.
7. The circuit arrangement as claimed in claim 1, wherein the field
effect transistor includes a load path, wherein the parasitic diode
is connected to a further parasitic diode as diodes in series
opposition, and wherein the diodes in series opposition are
connected in parallel with the load path of the field effect
transistor.
8. The circuit arrangement as claimed in claim 1, wherein the
evaluating unit is thermally decoupled and arranged separately from
the semiconductor body.
9. The circuit arrangement as claimed in claim 1, wherein the
evaluating unit is configured to compare the voltage drop across
the parasitic diode with a preset comparison voltage.
10. The circuit arrangement as claimed in claim 1, wherein the
evaluating unit is configured to compare the voltage drop across a
diode structure in the evaluating unit with a comparison voltage
dependent on the temperature of the evaluating unit.
11. The circuit arrangement as claimed in claim 9, wherein the
evaluating unit is configured to generate an overtemperature
detection signal when a predeterminable difference of the voltage
drop across the parasitic diode and the preset comparison voltage
is reached.
12. The circuit arrangement of claim 10, wherein the evaluating
unit comprises current/voltage converters configured to convert the
voltage drop across the diode structure and/or the comparison
voltage into currents.
13. The circuit arrangement as claimed in claim 12, wherein the
evaluating unit is configured to generate an overtemperature
detection signal when a predetermined difference of the currents is
reached.
14. The circuit arrangement as claimed in claim 10, wherein the
current/voltage converters comprise resistor components of the same
material.
15. The circuit arrangement as claimed in claim 1, wherein the
voltage across a load path of the field effect transistor is
monitored.
16. The circuit arrangement as claimed in claim 1, wherein the
evaluating unit is configured to be activated or deactivated by an
external signal.
17. The circuit arrangement as claimed in claim 1, wherein the
parasitic diode is a source-bulk diode inherent in the field effect
transistor.
18. The circuit arrangement as claimed in claim 7, wherein the
further parasitic diode is a drain-bulk diode inherent in the field
effect transistor.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of, and claims the
benefit of, prior application Ser. No. 11/731,765, filed on Mar.
29, 2007, which in turn claims priority from German patent
application no. 10 2006 014 523.2-33, filed Mar. 29, 2006, the
contents of which are incorporated herein by reference.
TECHNICAL FIELD
[0002] The invention relates to a circuit arrangement for
overtemperature detection in transistors, particularly power
transistors.
BACKGROUND
[0003] Power transistors are transistors which provide for large
current and voltage amplitudes and are thus suitable for directly
operating loads with relatively large powers. Power transistors are
used, for example, in output stages and switching stages for
industrial electronics and motor vehicle engineering.
[0004] In this context, the temperature of a power transistor
represents a significant factor for its functional capability. An
overtemperature of the power transistor, generated, for example, by
a higher ambient temperature or by malfunction such as a short
circuit of loads, can lead to it being damaged or destroyed and in
addition can also lead to impairment or even destruction of the
load. It is essential, therefore, to detect any overtemperature of
power transistors in time and reliably in order to be able to take
suitable measures such as, for example, switching off the
transistor or the load before critical temperature values and thus
the damage limit are/is reached.
[0005] To determine the temperature of a semiconductor component, a
temperature sensor can be attached to the package of the
semiconductor component or to its semiconductor body/chip. It can
be inappropriate that the sensor and the actual semiconductor
component are two separate components, as a result of which the
sensor only detects the temperature externally on the semiconductor
component which can deviate considerably from the temperature in
the interior of the semiconductor component and, in addition, has
an unwanted inertia in the case of rapid temperature changes in the
interior of the semiconductor component. It is precisely the
temperature in the interior of the semiconductor body, however,
which is relevant to the determination of critical operating
states.
[0006] There is a general need for a circuit arrangement with a
temperature sensor which is integrated into the same semiconductor
body like the power transistor, where the temperature sensor
reliably provides a voltage dependent on the temperature in the
interior of the semiconductor body.
SUMMARY
[0007] In one embodiment of the invention a diode structure is
additionally integrated into a semiconductor body. The diode
structure is fed with a current in its forward direction from a
current source. The voltage drop across the diode structure is
dependent on the temperature of the diode structure and thus on the
temperature of the transistor structure, and can therefore be used
for overtemperature detection by an evaluating unit, wherein the
protection of the power transistor and of the co-integrated
temperature sensor due to undesirable destruction guaranteed by the
evaluating unit.
[0008] Using a diode structure integrated into the semiconductor
body, which is fed in the forward direction (not in the reverse
direction) by a current (not by a voltage) provides for a large
signal swing, and due to the fact that a switching element located
in the evaluating unit actively produces a short circuit between
the bulk of the semiconductor body and the source of the power
transistor when this is required due to the operating state of the
power transistor or of the evaluating unit, which for the first
time enables the arrangement according to at least one embodiment
of the invention to be used for overtemperature detection in
n-channel LS switches and in p-channel HS switches.
[0009] Further advantages can also be obtained if the (for example
separate, particularly external) evaluating unit for detecting the
overtemperature and the power transistor structure are thermally
decoupled from one another, which has a positive influence on the
accuracy and reliability of the evaluating unit, and due to the
fact that the influence of the ambient temperature on the power
transistor structure and the evaluating unit can be taken into
consideration.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The invention can be better understood with reference to the
following drawings and description. The components in the figures
are not necessarily to scale, instead emphasis being placed upon
illustrating the principles of the invention. Moreover, in the
figures, like reference numerals designate corresponding parts. In
the drawings:
[0011] FIG. 1 shows the chip-on-chip technology for measuring the
temperature;
[0012] FIG. 2 shows the measurement of the leakage current of an
integrated diode in the reverse direction at the n-channel HS
switch;
[0013] FIG. 3 shows the measurement of the diode voltage of a
forward-polarized diode on the exemplary n-channel HS switch;
[0014] FIG. 4 shows an n-channel LS switch and a parasitic diode
structure;
[0015] FIG. 5 shows a p-channel HS switch and a parasitic diode
structure;
[0016] FIG. 6 is a circuit diagram of a temperature sensor
integrated in a semiconductor body, with parasitic diode structure
and a separate evaluating unit, taking into consideration the
ambient temperature, according to a first embodiment of the
invention;
[0017] FIG. 7 is a circuit diagram of a temperature sensor
integrated in a semiconductor body, with parasitic diode structure
and a separate evaluating unit with voltage/current converters
according to a second embodiment of the invention;
[0018] FIG. 8 is a circuit diagram of a temperature sensor
integrated in a semiconductor body, with parasitic diode structure
and a separate evaluating unit with monitoring of the voltage at
the drain terminal of the power transistor structure according to a
third embodiment of the invention; and
[0019] FIG. 9 is a circuit diagram of a temperature sensor
integrated in a semiconductor body, with parasitic diode structure
and a separate evaluating unit with external activation of the
measurement according to a fourth embodiment of the invention.
DETAILED DESCRIPTION
[0020] To determine the temperature of a semiconductor component
100, a temperature sensor 101 can be attached to the package of the
semiconductor component 100 or to its semiconductor body/chip (see
FIG. 1). Sometimes it can be useful that the sensor and the actual
semiconductor component are not two separate components, as a
result of which the sensor only detects the temperature externally
on the semiconductor component which can deviate considerably from
the temperature in the interior of the semiconductor component and,
in addition, has an unwanted inertia in the case of rapid
temperature changes in the interior of the semiconductor component.
It is precisely the temperature in the interior of the
semiconductor body, however, which is relevant to the determination
of critical operating states.
[0021] To determine the internal temperature of a semiconductor
component, diode structure may be provided in the same
semiconductor body in which the semiconductor component is
integrated, the diode structure being connected to a supply
voltage.
[0022] FIG. 2 shows an example of an n-channel HS switch (HS=High
Side; LS=Low Side). The arrangement according to FIG. 2 comprises a
power transistor structure 102 integrated in a semiconductor body
and an evaluating unit 103, electrically connected to the former,
for overtemperature detection of the power transistor structure
102. In addition to the power transistor structure 102, a
reverse-biased bipolar diode structure 104 is also integrated in
the semiconductor body, which is fed from a current source 107
located in the separate evaluating unit 103 via an additional body
or bulk terminal 105 on the semiconductor body by a reference
current 106 in the reverse direction of the diode structure 104.
The diode structure 104 can be formed, e.g., by the bulk drain
diode always present in a MOSFET. The usual short circuit between
source and bulk does not exist in this and the following
embodiments.
[0023] The measuring voltage 108 dropped accordingly across the
diode structure 104 and dependent on the temperature of the diode
structure 104 and thus on the temperature of the semiconductor body
and thus, in turn, on the temperature of the power transistor
structure 102 is compared with a comparison voltage 109 in the
evaluating unit 103 in order to generate from this a signal 110
identifying an overtemperature. In this arrangement, the voltage
109 of a voltage source 112, present at one input of a comparator
111, is compared with the voltage 108 at the body terminal 105 of
the diode structure 104. If the voltage at the body terminal 105 of
the diode structure 104 exceeds the permanently preset value of the
reference voltage source 112, the signal state at the output of the
comparator 111 changes and generates the signal 110 identifying an
overtemperature of the power transistor. In this way, the diode
structure 104 is used as temperature sensor for the temperature of
the power transistor structure 102, the diode structure 104 being
operated in the reverse direction with an impressed current.
[0024] This makes use of the fact that the reverse current of the
diode structure, detected by an evaluating unit, is exponentially
dependent on the temperature so that the temperature in the
semiconductor body can be inferred from the reverse current. If the
reverse current of the diode structure 104 exceeds the current 106
predetermined by the current source 107, the voltage at the body
terminal 105 changes and the voltage drop across the diode
structure 104 drops. In consequence of this process, the comparator
111 generates the overtemperature signal 110 as described. However,
this reverse current exhibits a significant, that is to say
analyzable, amount only at high temperatures due to the exponential
characteristic, so that the signal deviation of such a diode
structure temperature sensor is small.
[0025] Although it is possible to partially compensate for this
disadvantage by constructing the diode structure with the greatest
possible area, this runs counter to the general demand for the
highest possible degree of miniaturization of semiconductor
components. In addition, diode structures always have a barrier
layer capacitance in which a charge is stored. This stored charge
can cause a current which may be greater than the reverse current
used for temperature detection which unacceptably influences the
measurement result.
[0026] Furthermore, the power transistor structure can also be
arranged as p-channel LS switch in the arrangement according to
FIG. 2. The aforementioned disadvantages with regard to temperature
range, signal deviation also exist in this case.
[0027] For determining the internal temperature of a semiconductor
component, a diode structure may be provided in the same
semiconductor body in which the semiconductor component is
integrated, the diode structure being operated by an impressed
current in its forward direction. The circuit arrangement according
to FIG. 3 again comprises a power transistor structure 102
integrated in a semiconductor body and an evaluating unit 103
electrically connected to the former, for detecting overtemperature
of the power transistor structure 102 which is only used for
representing the basic principle in this case. In addition to the
power transistor structure 102, a bipolar diode structure 104 is
again also integrated in the semiconductor body, which diode
structure is fed from the current source 107 located in the
separate evaluating unit 103 via the additional body terminal 105
at the semiconductor body via the reference current 106 in the
forward direction of the diode structure 104 compared with FIG.
2.
[0028] The voltage 108 correspondingly dropped across the diode
structure 104, which is dependent on the temperature of the diode
structure 104 and thus on the temperature of the semiconductor body
and thus, in turn, on the temperature of the power transistor
structure 102 is again compared with a comparison voltage 109 in
the evaluating unit 103 in order to generate from this, analogously
to the circuit arrangement in FIG. 2, a signal 110 identifying an
overtemperature. Apart from the exemplary embodiment of the power
transistor structure 102 as n-channel HS switch, the power
transistor structure 102 in FIG. 3 can also be constructed as
p-channel LS switch.
[0029] The disadvantageous effect is here that for such an
arrangement of the diode structure 104 according to FIG. 3, in the
case of an n-channel LS switch, the corresponding supply voltage is
not constantly applied to the drain terminal of the power
transistor structure 102 but that, due to, e.g., switching
processes of the power transistor structure, the voltage 108
dropped across the diode structure 104 in dependence on the
temperature is subject to large voltage swings. An additional
disadvantageous factor is that, for the arrangement according to
FIG. 3, in the case of a p-channel HS switch, ground potential is
not constantly applied to the drain terminal of the power
transistor structure 102 but, due to, e.g., switching processes of
the power transistor structure, the voltage 108 dropped across the
diode structure 104 in dependence on temperature is also subject to
large voltage swings. It is also a disadvantageous factor that the
opening of the bulk-source short circuit produced by the diode
structure 104 also being integrated no longer guarantees the
dielectric strength of the power transistor. At a high voltage
between drain and source of the power transistor structure 102,
this can lead to a voltage breakdown which takes place at a lower
voltage than defined by the voltage class of the power transistor
structure which is specified with the bulk short circuited with the
source. In addition, the high voltage between source and drain
produces a high voltage between collector and emitter of an NPN
transistor formed from two individual diode structures.
[0030] The circuit diagram according to FIG. 4 shows a power
transistor 1, constructed as n-channel LS switch, including a
parasitic diode structure 8, which is always present when MOS
technology is used, which is located in the reverse direction
between bulk terminal 15 and drain terminal 9. The parasitic diode
structure 8 can be formed by the bulk-drain diode always present in
MOS transistors.
[0031] Compared with FIG. 3, the arrangement according to FIG. 4
thus additionally takes into consideration the parasitic diode
structure 8 which always exists in MOS transistors but which was
neglected in the preceding figures. In this arrangement, a power
transistor structure 7 is connected with its drain terminal 9 via
an external load resistor 10 to a positive supply potential 11 and
with its source terminal 12 to ground potential, as a result of
which a load current 13, flowing into the drain terminal 9 of the
power transistor structure 7, can be generated in dependence on a
voltage, not designated in greater detail here, on the gate
terminal of the power transistor structure 7. Furthermore, the
co-integrated diode structure 2 (e.g. the bulk-source diode which
must not be short circuited in the present case) is connected in
series opposition to the parasitic diode structure 8 (e.g. the
bulk-drain diode) and the diode structures 2 and 8 are connected in
parallel with the load path of the power transistor structure 7. A
bulk-source diode structure 2 is operated in the forward direction
with an impressed current 14 as a result of which a voltage 16
dropped across the diode structure 2 is generated.
[0032] This voltage 16 is not equal to the load path voltage of the
power transistor structure 7 and is used for overtemperature
detection of the power transistor. Furthermore, the voltage across
the load path at drain 9 is compared with a preset voltage value 17
of a reference voltage source 18. In the present case, this
comparison takes place via a comparator 19, to the inverting input
of which the preset comparison voltage 17 is applied and the
non-inverting input of which is connected to the drain terminal 9
of the power transistor structure 7 of the semiconductor body 1.
The comparator 19 can suitably have a switching characteristic with
hysteresis.
[0033] If the voltage present at the drain terminal 9 of the power
transistor structure 7 exceeds the value of the comparison voltage
17, the state of the signal at the output of the comparator 19
changes and short circuits the diode structure 2 via a transistor
structure 49. A short circuit of the diode structure 2 also takes
place due to the switching-through of the transistor structure 49
if then a control signal "OFF" is activated, this control signal
"OFF" and the output of the comparator 19 being linked via an OR
gate 63 preceding the gate of the transistor structure 49.
[0034] It has an advantageous effect that the bulk-source diode
(co-integrated diode structure 2) can be used as sensor element for
the temperature measurement without reducing the dielectric or
break-down strength of the power transistor. This is achieved by
the fact that the bulk-source short circuit of the power transistor
is only temporarily opened for a permissible range of the voltage,
predetermined by the reference voltage 17, at the drain of the
power transistor which is below the hazard limit for the effects
mentioned above. It also has an advantageous effect that no current
flow generated by the impressed current 14 takes place at the
source and the drain output of the power transistor if this is
switched off (active "OFF" signal). It also has an advantageous
effect that a temperature measurement is now possible with the
power transistor switched on and thus a low load path voltage
between drain and source of the power transistor (voltage at drain
9 lower than reference voltage 17). A further possible embodiment
is obtained from specifying a maximum permissible voltage at the
load path for the temperature measurement, which can also be
monitored by measuring the operating voltage, for example in bridge
circuits.
[0035] The circuit diagram of FIG. 5 shows the basic principle of
an arrangement with a power transistor constructed as p-channel HS
switch, including the parasitic diode structure 8, which is always
present when using MOS technology, which is located in the reverse
direction between drain terminal 9 and bulk terminal 15 (parasitic
drain-bulk diode), and the diode structure 2 (source-bulk diode).
The evaluating unit also shown corresponds to that of FIG. 4 and is
only slightly less adapted to the changed application.
[0036] The arrangement according to FIG. 5 again comprises the
parasitic diode structure 8. The power transistor structure 7 is
now connected with its drain terminal 9 to ground via an external
load resistor 10 and connected to a positive supply potential 11
with its source terminal 12, as a result of which a load current 13
flowing from the drain terminal 9 of the power transistor structure
7 is generated in dependence on the voltage at the gate terminal.
Furthermore, the co-integrated diode structure 2 (source-bulk
diode) is connected in series opposition to the parasitic diode
structure 8 (drain-bulk diode) and the diode structures 2 and 8 are
connected in parallel with the load path of the power transistor
structure 7.
[0037] In this arrangement, the source-bulk diode structure 2 is
operated with the impressed current 14 in the forward direction, as
a result of which the voltage 16 dropped across the diode structure
2 is generated. This voltage 16 is used for overtemperature
detection of the power transistor. Furthermore, the voltage at the
drain terminal 9 of the power transistor is compared with the
preset voltage value 17 of the reference voltage source 18. In the
present case, this comparison is made via the comparator 19, to the
positive input of which the preset comparison voltage 17 is applied
and the negative input of which is connected to the drain terminal
9 of the power transistor structure 7. The comparator 19 can
suitably have a switching characteristic with hysteresis.
[0038] If the voltage across the load path exceeds the value of the
comparison voltage 17, the state of the signal at the output of the
comparator 19 changes and short circuits the diode structure 2 via
the transistor structure 49. A short circuit of the diode structure
2 due to the switching-though of the transistor structure 49 also
occurs when the control signal "OFF" is activated, this control
signal "OFF" and the output of the comparator 19 being linked via
the NOR gate 68 preceding the gate terminal of the transistor
structure 49. This again results in the same advantageous effects
as in the arrangement from FIG. 4. The operating voltage can also
be monitored again, e.g. in bridge circuits, in order to prevent
the maximum permissible load path voltage possibly being exceeded
whilst the bulk-source short circuit is opened at the same
time.
[0039] The circuit arrangement according to FIG. 6 comprises a
power transistor structure 7 integrated in a semiconductor body 1
and an evaluating unit 3, which is electrically connected to the
former but is spatially separate and thermally decoupled from it,
for overtemperature detection of the power transistor structure 7.
In the power transistor structure 7, which, in the present case, is
an n-channel MOS field effect transistor but could equally be a
bipolar transistor, IGBT, thyristor etc., a bipolar diode structure
2 is co-integrated in the semiconductor body 1 in addition to the
power transistor structure 7, which diode structure is fed from a
current source 5 located in the separate evaluating unit 3 via an
additional body or bulk terminal 15 at the semiconductor body 1 by
a reference current 14 in the forward direction of the diode
structure 2. The voltage 16 correspondingly dropped across the
diode structure 2, dependent on the temperature of the diode
structure 2 and thus on the temperature of the power transistor
structure 7, is compared with a comparison voltage 22 in the
evaluating unit 3 in order to generate from it a signal 20
identifying an overtemperature. In this way, the diode structure 2
(the bulk-source diode in the case shown) is used as temperature
sensor for the temperature of the power transistor structure 7, the
diode structure 2 being operated in the forward direction with an
impressed current.
[0040] FIG. 6 also comprises the parasitic bulk-drain diode
structure 8 which is always present when MOS technologies are used,
and forms a bipolar transistor together with the diode structure 2.
A device of comparator 65 and reference voltage source 64 for
monitoring the load path voltage at the drain 9 is also contained
therein.
[0041] The circuit arrangement according to FIG. 6 additionally
contains a monitoring circuit with a reference voltage source 64
for generating a reference voltage 67, a comparator 65 (possibly
with hysteresis) and an MOS field effect transistor 66. In this
arrangement, the non-inverting input of the comparator 65 is
connected to the drain terminal 9 of the power transistor structure
7 and the reference voltage 67 is present at the inverting input of
the comparator 65. The output of the comparator 65 is connected to
the gate of the transistor 66. The drain terminal of the transistor
66 is connected to the body terminal 15 of the semiconductor body 1
and the current source 5 whilst the source terminal of the
transistor 66 is connected to ground.
[0042] The monitoring circuit has the purpose of monitoring the
amplitude of the voltage at the drain terminal 9 of the power
transistor structure 7 and comparing it with the preset reference
voltage 67. In this way, an excessive voltage at the drain terminal
9 of the power transistor structure 7 is detected which, with the
bulk-source short circuit being opened at the same time and the
dielectric strength of the semiconductor structure 1 thus being
reduced, can lead to its destruction. The reference voltage 67 can
be selected to be very low so that temperature detection is only
carried out when the load path, represented by the resistor 10, via
the power transistor structure 7 is connected. The reference
voltage 67 can also assume higher values as long as its value is
below the critical maximum load path voltage leading to a
destruction, which is reduced by the source-bulk short circuit
being opened.
[0043] If then the voltage to ground, present at the drain terminal
9, exceeds the value of the reference voltage 67, for example
because the load path is not connected, the gate of the transistor
66 is driven via the output of the comparator 65 and the diode
structure 2 is short circuited via the transistor 66 as a result of
which the current used for overtemperature detection (largely) does
not flow through the diode structure 2 but (largely) flows through
the source-drain path of the transistor 66. In this case, however,
the signal 20 cannot be used as a measure of an overtemperature
detection since the voltage 16 dropped across the short circuited
diode structure 2 is then always very low independently of the
actual temperature of the power transistor structure 7 and the
voltage 16 is thus always lower than the voltage 22 used for the
comparison and for detecting an overtemperature.
[0044] The effect, which can be reproduced quantitatively, that the
voltage occurring at a diode structure operated in the forward
direction with the impressed current depends on the temperature of
this diode structure is utilized in such a manner that due to the
conductance of the diode structure, which rises with temperature,
the voltage dropped across the diode structure with a constant
impressed current is reduced. The forward voltage of a diode
structure changes linearly with about -2 mV per degree Celsius
(.degree. C.).
[0045] The diode structure 2 used for temperature measurement is
co-integrated into the semiconductor body 1 in such a manner that,
in operation, it is essentially subject to the same heating as the
power transistor structure 7 itself and thus can be used as a
measure of the operating temperature of the power transistor
structure 7 and thus for overtemperature detection of the power
transistor structure 7. The additional, externally accessible body
or bulk terminal 15 is provided at the semiconductor body 1 for the
purpose of feeding the current 14 into the diode structure 2 and
for measuring the voltage 16 dropped across this diode structure 2
(in the case of an external evaluating circuit as in the present
case).
[0046] In the circuit arrangement according to FIG. 6, the diode
structure 2 is connected in the forward direction between body and
ground. A further diode structure 8 is located between body (and
thus body terminal 15) and drain terminal 9 of the power transistor
structure 7, this being the parasitic bulk-drain diode structure
always present. In this arrangement, the power transistor structure
7 is connected with its drain terminal 9 with a positive supply
potential 11 via an external load resistor 10 and with its source
terminal 12 to ground potential as a result of which a load current
13 flowing into the drain terminal 9 of the power transistor
structure 7 can be generated.
[0047] As already explained, the circuit arrangement according to
FIG. 6 comprises a current source 5 for generating the impressed
current 14 for the diode structure 2 and additionally a first
embodiment of a comparison circuit 4 for comparing the voltage 16
dropped across the diode structure 2 with a preset comparison
voltage 22. In the present case, the comparison circuit 4 consists
of a comparator 19, to the positive input of which a preset
comparison voltage 22 generated by a circuit 21 is applied and the
negative input of which is connected to the terminal 15 of the
semiconductor body 1 and to which voltage 16 dropped across the
diode structure 2 is thus applied. The comparator 19 can suitably
have a switching characteristic with hysteresis.
[0048] In this arrangement, the circuit 21 is constructed in such a
manner that the comparison voltage 22 generated by it is
temperature-dependent, in such a manner that an increase in
temperature of the evaluating unit 3, and thus an increase in
temperature of the circuit 21, leads to an increase in the
comparison voltage 22 generated from it.
[0049] An increase in temperature of the evaluating unit 3 occurs,
for example, if the ambient temperature increases at which the
evaluating unit 3 and correspondingly also the semiconductor body 1
are operated. This is the case, for instance, in applications in a
motor vehicle where semiconductor bodies and circuits used in the
engine compartment are heated to a different degree by radiation of
engine heat in dependence on the operating state and
weather-related external temperatures. In this manner, the limit
value of the overtemperature to be determined can be automatically
adapted to the prevailing ambient temperatures, for example
reduced, in order thus to take into account, for example, the
circumstance that a value of the overtemperature which is critical
or damaging for the operation is lower at high ambient temperatures
than at low ambient temperatures.
[0050] The prerequisite for taking the ambient temperature into
consideration with sufficient accuracy is that the semiconductor
body 1 and the evaluating unit 3 are thermally decoupled but are
placed so close to one another spatially that the same ambient
temperature is applied to them. However, thermally decoupling also
means, in particular, that the two are not so close that the heat
dissipation of the power transistor influences the ambient
temperature in the area of the evaluating circuit. In applications
in which this ambient temperature is generated, for example by a
heat-radiating source such as a motor vehicle engine, this ambient
temperature changes very rapidly with distance from the source and
a spatially more separate arrangement of the semiconductor body 1
and the evaluating unit 3 would not achieve the desired effect.
[0051] According to FIG. 6, the circuit 21 for generating the
comparison voltage 22 comprises an MOS field effect transistor 39,
an MOS field effect transistor 40, a bipolar transistor 41 and a
bipolar transistor 42 and a resistor 23, a resistor 43 and a
resistor 46. The transistor 39 is a p-channel MOS field effect
transistor and connected with its source terminal to a positive
supply potential 47 and to the source terminal of the transistor 40
which is also of the p-channel type. The drain terminal of the
transistor 39 is connected to the gate terminal of the transistor
39 and to the collector terminal of the transistor 41; similarly,
there is a connection between the gate terminal of the transistor
39 and the gate terminal of the transistor 40. The drain terminal
of the transistor 40 is connected to the collector terminal of the
transistor 42 which, in turn, is connected to the base terminal of
the transistor 42 and to the base terminal of the transistor 41.
Furthermore, the emitter terminal of the transistor 42 is connected
to the resistor 46 and the emitter terminal of the transistor 41 is
connected to the resistor 46 via the resistor 43. The two resistors
46 and 23 represent a voltage divider, the comparison voltage 22
dropped across the resistor 23 being applied to the positive input
of the comparator 19.
[0052] With a rising ambient temperature acting on the evaluating
unit 3 and thus on the components contained in this evaluating unit
3, linearly increasing currents through a first resistor 23, a
second resistor 43 and a third resistor 46 are generated in the
circuit 21. As a result, a voltage drop 22 rising linearly with the
temperature is generated at the first resistor 23, which, in the
present embodiment, is used as comparison voltage 22 for later
comparison by the comparator 19 with the voltage 16 dropped across
the diode structure 2, applied to the negative input of the
comparator 19.
[0053] In this way, an increase of the ambient temperature acting
on the evaluating unit 3, by increasing the comparison voltage 22,
leads to a reduction in the difference between the voltage 16 at
the diode structure 2 and the comparison voltage 22 as a result of
which the limit value for detection of an overtemperature of a
power transistor structure 7 is reached earlier. The heating of the
semiconductor body 1, and thus of the power transistor structure 7,
necessary for reaching the overtemperature is less for high ambient
temperatures. At low ambient temperatures, a greater range of
heating of the power transistor structure 7 is thus permitted
(temperature swing) than is the case at high ambient
temperatures.
[0054] Corresponding to the circuit arrangements according to FIG.
4 and FIG. 5, the voltage 16 at the diode structure 2 and a
comparison voltage 22 are again compared by the comparator 19. The
comparison voltage 22 and the impressed current 14 are selected in
such a manner that the voltage 16 dropped across the diode
structure 2 at permissible operating temperatures of the
semiconductor body 1 is greater than the comparison voltage 22
preset in the evaluating unit 3. If the voltage 16 dropped across
the diode structure 2 exceeds the value of the comparison voltage
22 with increasing temperature of the semiconductor body 1, and if
the voltage 16 is thus lower than the comparison voltage 22, the
state of the signal 22 at the output of the comparator 19 changes
and thus indicates that an overtemperature of the power transistor
structure 7 has been reached. In this case, as stated above, the
limit value of the overtemperature to be determined is not preset
but is dependent on the ambient temperature acting on the circuit
arrangement 21.
[0055] The circuit arrangement according to FIG. 7 again contains a
semiconductor body 1 and an external, thermally decoupled
evaluating unit 3. The structure of the power transistor structure
7 and of the diode structures 2 and 8 is identical with that shown
in FIG. 6. In contrast to the embodiments described above, the
voltages used for detecting an overtemperature are first converted
into corresponding currents, namely voltage 16 into current 25 and
comparison voltage 28 into current 26, for the purpose of the
evaluation.
[0056] This is achieved by a voltage/current converter 24 for
converting a voltage 16 dropped across the diode structure 2 into a
current 25 and by a voltage/current converter 27 for converting a
comparison voltage 28 into a current 26. In this arrangement, the
voltage/current converters 24 and 27 are initially reproduced as
abstract circuit blocks in FIG. 7. The current 25 generated by the
voltage/current converter 24 and the current 26 generated by the
voltage/current converter 27 are subtracted at a node 29 and, if
necessary, converted into a voltage. The resultant current or the
resultant voltage, respectively, are again evaluated by a using a
comparator 19 (for example by a comparison with zero).
[0057] If the first current 25 generated by converting the voltage
16 measured at the diode structure 2 falls below the value of the
second current 26 generated by converting the comparison voltage 28
due to a temperature increase, the state of the signal at the
output 20 of the comparator 19 changes and thus indicates that an
overtemperature of the power transistor structure 7 has been
reached. The limit value of the overtemperature to be determined
can be selected freely by suitably choosing the preset comparison
voltage 28.
[0058] FIG. 8 shows a development of the circuit arrangement shown
in FIG. 7, with voltage/current converter 24 and voltage/current
converter 27. In this arrangement, the voltage/current converter 24
contains an operational amplifier 30, an MOS field effect
transistor 31, an MOS field effect transistor 35 and a resistor 32
across which a voltage 33 proportional to the voltage 16 dropped
across a diode structure 2 is dropped. In the voltage/current
converter 24, the gate terminals of the two transistors 31 and 35
are connected to the output of the operational amplifier 30, the
source terminals of the transistors 31 and 35 also being connected
to one another and being connected to the positive supply potential
34. The drain terminal of the transistor 31 is connected to ground
via the resistor 32. The voltage 33 dropped across the resistor 32
is fed back to the non-inverting input of the operational amplifier
30, at the inverting input of which the voltage across the diode
structure 2 is present. The operational amplifier 30 corrects the
voltage 33 across the resistor 32 in such a manner that it is equal
to the voltage across the diode structure 2. The current through
the source/drain path of the transistor 31 is thus equal to the
ratio of voltage 33 to the value of the resistor 32. Accordingly,
the current through the source-drain path of the transistor 35,
forming the output current, is then proportional to the current
through the source/drain path of the transistor 31 and proportional
to the voltage across the diode structure 2, the output current
thus becoming lower with increasing temperature of the
semiconductor body 1.
[0059] The drain terminal of the second transistor 35 is connected
to a node 29 so that the current 25 from the voltage/current
converter 24 acting as current source flows into the node 29, a
current 26 flowing off again via the voltage/current converter 27
acting as current sink so that the difference between the two
currents can be evaluated by the comparator 19 (for example by
comparison with a fixed threshold or zero). The voltage/current
converter 27 is that from the circuit 21, explained in FIG. 6, for
generating an ambient-temperature-dependent reference voltage.
Accordingly, the circuit 21 again contains the transistor 39,
transistor 40, transistor 41 and transistor 42, resistor 43 and
resistor 45. In addition, an MOS field effect transistor 36, an MOS
field effect transistor 37 and an MOS field effect transistor 38
are provided in the exemplary embodiment according to FIG. 9.
[0060] A current, which is proportional to the current 48 through
the source-drain path of the transistor 39 flows through the
source-drain path of the transistor 38, the source and gate
terminals of which are in each case connected to the source and
gate terminals of transistor 40, in the manner of a current mirror,
just like it does through the source-drain path of transistor 40,
so that a current rising linearly with the ambient temperature of
the evaluating unit 3, which is defined by the ratio of the voltage
44 dropped across the resistor 43 and the resistance value of the
resistor 43, is provided.
[0061] The current provided by the transistor 38 is then mirrored
by means of a (further) current mirror consisting of transistors 36
and 37, in such a manner that the current 26 flowing off from the
node 29 is generated. Due to the current 48 being mirrored twice in
the voltage/current converter 27, the current 26 is thus produced
which also rises linearly with the ambient temperature of the
evaluating unit 3.
[0062] From the current 25, depending linearly on the voltage 16 at
the diode structure 2 and becoming lower with rising temperature of
the semiconductor body 1, the current 26 becoming greater with
ambient temperature is subtracted at the node 29. The node 29 is
connected to the comparator 19 so that the difference produced by
subtracting the currents 25 and 26 at the comparator 19 is a
measure of whether the operating temperature of the power
transistor structure 7 integrated in the semiconductor body 1 is
permissible or not, the relevant limit value being dependent on the
ambient temperature represented by the current 26.
[0063] If the current 25 drops below the current 26 (for example in
the case of the zero-point comparison: current 25-current 26<0),
the state of the signal 20 at the output of the comparator 19
changes and thus indicates that an overtemperature of the power
transistor 7 has been reached. The heating of the power transistor
structure 7 necessary for reaching the overtemperature is thus less
at higher ambient temperatures of semiconductor body 1 and
evaluating unit 3.
[0064] According to the embodiment, a greater heat range of the
power transistor structure 7 (temperature swing) is permitted at
the same time at low ambient temperatures of the semiconductor body
1 and the evaluating unit 3 than is the case at higher ambient
temperatures. A significant advantage consists in that, due to the
use of identical materials and possibly identical dimensions in the
resistors 32 and 43, the absolute accuracy tolerances of these
resistors compensate for the temperature dependences reducing the
measuring accuracy and thus allow the absolute accuracies to be
distinctly increased.
[0065] The circuit arrangement according to FIG. 8 also contains a
monitoring circuit 52 with a reference voltage source for
generating a reference voltage 50, a comparator 51 (possibly with
hysteresis) and an MOS field effect transistor 49. In this
arrangement, the non-inverting input of the comparator 51 is
connected to the drain terminal 9 of the power transistor structure
7 and a reference voltage 50 is present at the inverting input of
the comparator 51. The output of the comparator 51 is connected to
the gate of the transistor 49. The drain terminal of the transistor
49 is connected to the body terminal 15 of the semiconductor body 1
and the current source 5 while the source terminal of the
transistor 49 is connected to ground.
[0066] It is the purpose of the monitoring circuit 52 to monitor
the magnitude of the voltage at the drain terminal 9 of the power
transistor structure 7 and to compare it with a preset reference
voltage 50. In this way, an excessive voltage at the drain terminal
9 of the power transistor structure 7 is detected which, with the
bulk-source short circuit being opened at the same time and the
dielectric strength of the semiconductor structure 1 thus being
reduced, can lead to its destruction. The reference voltage 50 can
be selected to be very low in order to carry out temperature
detection only when the load path, represented by the resistor 10,
is connected via the power transistor structure 7. The reference
voltage 50 can also assume higher values as long as its value is
below the critical maximum load path voltage leading to a
destruction, which is reduced by opening the source-bulk short
circuit.
[0067] If then the voltage to ground, present at the drain terminal
9, exceeds the value of the reference voltage 50, for example
because the load path is not connected, the gate of the transistor
49 is driven via the output of the comparator 51 and the diode
structure 2 is short circuited via the transistor 49 as a result of
which the current used for overtemperature detection (largely) does
not flow through the diode structure 2 but (largely) flows through
the source-drain path of the transistor 49. With the load path
switched off, the current at the drain terminal 9 is very low in
any case. In this case, however, the signal 20 cannot be used as a
measure of overtemperature detection since then the voltage 16
dropped across the short circuited diode structure 2 is always very
low independently of the actual temperature of the power transistor
structure 7 and the current 25 is thus always lower than the
current 26 used for the comparison and for detecting an
overtemperature. For the case of restoring the source-bulk short
circuit with an excessive voltage at the drain 9, it is then no
longer possible to monitor the temperature. This state is obtained,
for example, with a very high load (short circuit) or a normal
switching-off process. Since the temperature monitoring is used in
any case for switching off the switch with an excessive temperature
and to prevent further power input, this behavior does not have a
disadvantageous effect. The dielectric strength of the power
transistor, which, in the normal case, is present due to the
bulk-source short circuit with the technology used, which is no
longer given by using the co-integrated diode structure 2 in the
present case, is restored by short circuiting the diode structure 2
via the transistor 49 with excessive voltage values at the
drain.
[0068] In the circuit arrangement according to FIG. 9, a further
embodiment of a circuit for overtemperature detection of a power
transistor structure 7 with a monitoring circuit 52, extended with
respect to FIG. 8, and a further embodiment of the voltage/current
converter 27 is provided. Semiconductor body 1 and voltage/current
converter 24 correspond to those shown in FIG. 8.
[0069] The monitoring circuit 52 contains an inverter 53, an OR
gate 54 and an MOS field effect transistor 49. A logical input
signal is fed in at a terminal 55 of the evaluating unit 3 in order
to be able to activate and deactivate the evaluating circuit 3 from
the outside. Compared with the embodiment according to FIG. 8, the
output of the comparator 51 is not connected directly to the gate
terminal of the transistor 49 but initially to a first input of the
OR gate 54. The terminal 55 is connected to the input of the
inverter 53, the output of which is connected, in turn, to a second
input of the OR gate 54, the output of the OR gate 54 being coupled
to the gate terminal of the transistor 49.
[0070] The logic level H (power transistor structure 7: "ON") at
terminal 55 of the evaluating unit 3 stands for the case in which
the temperature detection and the monitoring of the voltage at the
drain terminal 9 is to be activated, wherein this level can be
generated, for example, by a load connected via the power
transistor structure 7. The logic level H at the terminal 55 is
converted into the logic level L by the inverter 53 and applied to
the second input of the OR gate 54. If the output signal of the
comparator 51 has the logic level L, that is to say the voltage at
the drain terminal 9 of the power transistor structure 7 is below
the preset reference voltage 50, the temperature detection is
carried out as described above.
[0071] If the output signal of the comparator 51 has the logic
level H, that is to say the voltage at the drain terminal 9 of the
power transistor structure 7 is above the preset reference voltage
50 and thus in a range which could result in the destruction of the
semiconductor body 1, the diode structure 2 is again short
circuited via the transistor 49, driven by the output signal from
the OR gate 54. Such a case is, for example, that of an avalanche
in which a bipolar transistor formed from the two diode structures
2 and 8, which is already active, forms the weak point. The
temperature is therefore monitored only in the switched-through
state of the power transistor structure 7 and/or when the voltage
drops below the maximum permissible load path voltage predetermined
by the voltage 50.
[0072] If the logic level L (power transistor structure 7: "OFF")
is present at terminal 55 of the evaluating unit 3, temperature
detection is deactivated. In this event, the logic level L at
terminal 55 is first converted into the logic level H via the
inverter 53 and applied to the second input of the OR gate 54.
Independently of the value of the level present at the first input
of the OR gate 54 (from output of the comparator 51), a signal with
the logic level H is thus generated in every case at the output of
the OR gate 54 and the diode structure 2 is again short circuited
via the transistor 49. As stated above, the signal 20 cannot be
used for overtemperature detection in all cases in which the diode
structure 2 is short circuited via the transistor 49.
[0073] FIG. 9 also shows a further embodiment of the
voltage/current converter 27 from FIG. 7 which has a supply
potential 47, a resistor 56, a resistor 61, a bipolar transistor
57, a bipolar transistor 58, a bipolar transistor 59 and a bipolar
transistor 60. In this arrangement, the transistor 57 is connected
with its collector terminal to the supply potential 47 via the
resistor 56. The base terminal of the transistor 57 is connected to
the base terminal of the transistor 58 and to the collector
terminal of the transistor 57. The collector terminal of the
transistor 58 is connected to the node 29 at which the current 25
from the voltage/current converter 24 and the current 26 into the
voltage/current converter 27 are subtracted from one another for
the purpose of evaluation by the comparator 19 and thus for
generating the signal 20. Furthermore, the emitter terminal of the
transistor 57 is connected to the collector terminal of the
transistor 59, the emitter terminal of the transistor 58 is
connected to the collector terminal of the transistor 60, the
emitter terminal of the transistor 57 is connected to the base
terminal of the transistor 60 and the emitter terminal of the
transistor 58 is connected to the base terminal of the transistor
59. The emitter terminal of the transistor 59 is connected directly
to ground; the emitter terminal of the transistor 60 is connected
to ground via the resistor 61. The limit value of the
overtemperature is again dependent on the ambient temperature at
the evaluating unit 3. Similarly, by suitably using resistor
components of the same material for the resistors 32 and 61 in the
voltage/current converters 24 and 27, the absolute accuracy
tolerances of these resistors and thus different temperature
dependences reducing the measuring accuracy are again compensated
for and the absolute accuracy of the overtemperature detection is
thus distinctly increased.
[0074] The exemplary embodiments do not show start-up circuits
which could be necessary under some circumstances when switching on
the circuit arrangement but which do not have any significance for
the basic function of the circuit arrangement and have therefore
been omitted for the sake of clarity. The expert can however easily
use known start-up circuits for the respective purpose.
[0075] While the invention disclosed herein has been described in
terms of several different embodiments, there are numerous
alterations, permutations, and equivalents which fall within the
scope of this invention. It should also be noted that there are
many alternative ways of implementing the methods and compositions
of the present invention. It is therefore intended that the
following appended claims be interpreted as including all such
alterations, permutations, and equivalents as fall within the true
spirit and scope of the present invention.
* * * * *