GB2319414A - Thermal protection of electronic switches - Google Patents
Thermal protection of electronic switches Download PDFInfo
- Publication number
- GB2319414A GB2319414A GB9623855A GB9623855A GB2319414A GB 2319414 A GB2319414 A GB 2319414A GB 9623855 A GB9623855 A GB 9623855A GB 9623855 A GB9623855 A GB 9623855A GB 2319414 A GB2319414 A GB 2319414A
- Authority
- GB
- United Kingdom
- Prior art keywords
- electrical circuit
- switch
- voltage
- circuit according
- control means
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
- 230000001419 dependent effect Effects 0.000 claims description 3
- 238000012544 monitoring process Methods 0.000 claims description 3
- 230000004044 response Effects 0.000 claims description 2
- 230000005669 field effect Effects 0.000 claims 1
- 230000007423 decrease Effects 0.000 description 2
- 238000013021 overheating Methods 0.000 description 2
- 238000010586 diagram Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000006870 function Effects 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
- H03K17/51—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used
- H03K17/56—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices
- H03K17/60—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices the devices being bipolar transistors
- H03K17/615—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices the devices being bipolar transistors in a Darlington configuration
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H5/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal non-electric working conditions with or without subsequent reconnection
- H02H5/04—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal non-electric working conditions with or without subsequent reconnection responsive to abnormal temperature
- H02H5/044—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal non-electric working conditions with or without subsequent reconnection responsive to abnormal temperature using a semiconductor device to sense the temperature
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
- H03K17/08—Modifications for protecting switching circuit against overcurrent or overvoltage
- H03K17/082—Modifications for protecting switching circuit against overcurrent or overvoltage by feedback from the output to the control circuit
- H03K17/0826—Modifications for protecting switching circuit against overcurrent or overvoltage by feedback from the output to the control circuit in bipolar transistor switches
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
- H02H3/40—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to ratio of voltage and current
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
- H02H3/44—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to the rate of change of electrical quantities
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
- H03K17/08—Modifications for protecting switching circuit against overcurrent or overvoltage
- H03K2017/0806—Modifications for protecting switching circuit against overcurrent or overvoltage against excessive temperature
Landscapes
- Emergency Protection Circuit Devices (AREA)
- Protection Of Static Devices (AREA)
Abstract
A drive circuit comprises main and sensing switching devices 18,16 thermally coupled on a common die 36. The output 28 of the sensing switching device 16, which supplies a fixed load 12, is monitored by a control unit 10, and if the voltage there falls below a certain value (figure 2), indicating a rise in temperature of the main device 18 due to overload, the main switch 18 is turned off. Alternatively, rate of change of temperature may be monitored. The cutoff criterion may be stored in an electrically reprogrammmable memory in the control unit 10. The circuit may comprise Darlington switches or FETs, and may be used in a vehicle.
Description
THERMAL PROTECTION OF ELECTRONIC DEVICES
The present invention relates to the protection from overload of an electronic circuit component such as a power device using the thermal characteristics of the component.
In particular it concerns the protection of a switching component which is controlled by a control means to drive a load. The present invention is, for example, suitable for application in the electrical systems of vehicles.
Such a circuit is disclosed in GB 2 272 407, which describes a circuit in which a pair of switching devices is mounted on a common die, and the input of one of them is monitored and used to detect overheating of the other.
It has been found that there are disadvantages with the circuit described in GB 2 272 407. In particular, the voltage at the inputs of the switching devices can vary depending on the details of the switching device used, and the values of various resistors forming part of it or associated with it, such as input resistors.
The present invention provides an electrical circuit comprising a control means, and first and second switch means which are thermally coupled to one another and have first and second outputs respectively for driving first and second loads respectively, the first switch means having a switch output connected to an input of the control means and the second switch means having a switch input connected to an output of the control means, wherein the voltage of the switch output is dependent upon the temperature of the first switch means, and the control means is arranged to monitor the voltage at said switch output and turn off the second switch means to turn off power to the second load in response to a pre-determined change in said voltage.
The switch means may be mounted on the same die.
Said pre-determined change may comprise passing through a threshold voltage, to either a higher or a lower voltage, or exceeding a pre-determined rate of change.
Preferably the control means includes a memory, such as
E2ROM, onto which the character of said pre-determined change can be written. This enables the temperature monitoring to be matched accurately to the switch means.
Preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which:
Figure 1 is a circuit diagram of an embodiment of the invention; and
Figure 2 is a graph of the output voltage to a switch means of the embodiment of Figure 1 as a function of temperature.
A control chip 10 forming part of a control unit 8 is arranged to control first and second loads 12, 14 via a switch means 15. The switch means 15 comprises two switch devices 16, 18, each being made up of a pair of bi-polar transistors in a Darlington configuration. Each of the switch devices 16, 18 has an input 20, 22 connected via a resistor 21, 23 to a respective output 24, 26 of the control chip 10, a collector output 28, 30 connected to a respective one of the loads 12, 14 and an emitter 32, 34 connected to earth. The switch devices 16, 18 are therefore controlled independently of each other by the control chip 10 to drive the loads 12, 14. The first load 12 is in this case a fixed load internal to the control unit 8, and the second load is an external load, in this case a relay coil.
The switching devices 16, 18 are mounted on a common die 36 close to one another. Because the die 36 on which the switching devices 16, 18 are mounted is thermally conductive the switching devices are thermally coupled to one another so that if one of them heats up for any reason, the other one heats up also.
The switching devices 16, 18 have characteristics which are thermally dependent, and therefore the voltages on their outputs vary if the devices are subjected to temperature changes. In particular the voltage Vx at the output 28 of the first switch device 16 decreases as the temperature of that device increases, as shown in Figure 2.
Vx is about 1V at 25"C, and decreases at a rate of about 10 mV / C The output 28 to the first switch device 16 is connected to an A/D input 37 of the control chip 10 via a resistor 38 so that the control chip 10 can monitor the voltage Vx. The input 37 of the control chip 10 is also connected to ground via a Zener diode 40. This limits to about 4.5V the voltage fed to the input 37 from the output 28, thereby protecting the control unit 10 from an overvoltage. This is necessary because, when the switching devices 16, 18 are turned off, the voltage at the output 28 is approximately equal to the battery voltage of 12V, whereas the control chip 10 can only take a voltage of about SV at its input 37.
Under normal use, because the second load 14 is external, it will vary slightly and so the current through the second switch device 18 will vary slightly. This will affect the temperature of the two switch devices 16, 18 and therefore the voltage Vx. Because the first load 12 is internal it is fixed and therefore has little or no effect on the temperature of the switch devices or the voltage Vx.
The control chip 10 monitors the temperature of the switch means 15 by repeatedly checking the voltage Vx against a value Vm stored in E2ROM memory in the control chip to check that Vx does not fall below Vm.
In the event of overheating of the control means 15, either because of a short on the external load 14 or because of heat reaching the switching means from some other source, the control chip detects that the voltage Vx has dropped below Vm and turns off the power to the external load 14.
It would obviously be possible in other circumstances for the control chip to turn off the power to any number of loads which it controlled depending on what was required for the greatest safety.
Claims (9)
1. An electrical circuit comprising a control means, and
first and second switch means which are thermally
coupled to one another and have first and second
outputs respectively for driving first and second loads
respectively, the first switch means having a switch
output connected to an input of the control means and
the second switch means having a switch input connected
to an output of the control means, wherein the voltage
of said switch output is dependent upon the temperature
of the first switch means, and the control means is
arranged to monitor the voltage at said switch output
and turn off the second switch means to turn off power
to the second load in response to a pre-determined
change in said voltage.
2. An electrical circuit according to claim 1 wherein said
switch output is connected to a monitoring input of the
control means and the circuit further comprising
voltage limiting means for limiting the voltage to said
monitoring input.
3. An electrical circuit according to claim 1 or claim 2
wherein the switch means are mounted on a common die.
4. An electrical circuit according to any foregoing claim
wherein said pre-determined change comprises passing
through a threshold voltage.
5. An electrical circuit according to any foregoing claim
wherein said pre-determined change comprises exceeding
a pre-determined rate of change.
6. An electrical circuit according to any foregoing claim
wherein the control means includes a memory onto which
the character of said pre-determined change can be
written.
7. An electrical circuit according to claim 6 wherein said
memory comprises E2ROM.
8. An electrical circuit according to any foregoing claim
wherein at least one of the switch means comprises at
least one transistor.
9. An electrical circuit according to claim 8 wherein at
least one of the switch means comprises at least one
pair of transistors in a Darlington configuration.
l0.An electrical circuit according to claim 8 or claim 9
wherein at least one of the transistors is a field
effect transistor.
ll.An electrical circuit substantially as hereinbefore
described with reference to the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9623855A GB2319414A (en) | 1996-11-16 | 1996-11-16 | Thermal protection of electronic switches |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9623855A GB2319414A (en) | 1996-11-16 | 1996-11-16 | Thermal protection of electronic switches |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB9623855D0 GB9623855D0 (en) | 1997-01-08 |
| GB2319414A true GB2319414A (en) | 1998-05-20 |
Family
ID=10803045
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9623855A Withdrawn GB2319414A (en) | 1996-11-16 | 1996-11-16 | Thermal protection of electronic switches |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2319414A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE10121881A1 (en) * | 2001-05-05 | 2002-11-14 | Infineon Technologies Ag | Method for controlling semiconductor element and circuit arrangement monitors rate of change of semiconductor temperature |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2210501A (en) * | 1987-09-28 | 1989-06-07 | Mitsubishi Electric Corp | Temperature protection of semiconductor power devices |
| GB2273213A (en) * | 1992-12-05 | 1994-06-08 | Rover Group | Thermal protection of electronic devices |
-
1996
- 1996-11-16 GB GB9623855A patent/GB2319414A/en not_active Withdrawn
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2210501A (en) * | 1987-09-28 | 1989-06-07 | Mitsubishi Electric Corp | Temperature protection of semiconductor power devices |
| GB2273213A (en) * | 1992-12-05 | 1994-06-08 | Rover Group | Thermal protection of electronic devices |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE10121881A1 (en) * | 2001-05-05 | 2002-11-14 | Infineon Technologies Ag | Method for controlling semiconductor element and circuit arrangement monitors rate of change of semiconductor temperature |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9623855D0 (en) | 1997-01-08 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| 732E | Amendments to the register in respect of changes of name or changes affecting rights (sect. 32/1977) | ||
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |