CN103532364A - Overheating protection circuit for power transistor - Google Patents
Overheating protection circuit for power transistor Download PDFInfo
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- CN103532364A CN103532364A CN201310509560.5A CN201310509560A CN103532364A CN 103532364 A CN103532364 A CN 103532364A CN 201310509560 A CN201310509560 A CN 201310509560A CN 103532364 A CN103532364 A CN 103532364A
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- transistor
- power transistor
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- protection circuit
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Abstract
An overheating protection circuit for a power transistor comprises a sensing emitting electrode. One differential amplifier is driven from a base and the sensing emitting electrode of the transistor and is provided with an output end which is coupled to the power transistor. When the potential of the sensing emitting electrode exceeds that of the base electrode, the output of the amplifier can lower the voltage of the base electrode to limit a current of the power transistor. For a silicon transistor, a circuit can restrain the sensing emitting electrode to work at the maximum temperature of about 250 DEG C; and when a hot point doesn't exist, and the sensing emitting electrode is heated uniformly, the temperature of the transistor is limited to about 200 DEG C.
Description
Technical field
Be applicable to use a plurality of independent small-sized emitters parallel join effectively, by ballast resistance independently, create a power transistor, also with a discrete sensing emitter relevant to power device emitter, react the focus on power transistor.
Background technology
By comparing sensing emitter and the current potential between remote emitter, carry out thermal gradient detection, method comprises when gradient is over certain predetermined threshold value, closes power transistor.By connecting a differential amplifier, it has a fixing offset potentials between sensing emitter and the distance transmission utmost point.The base stage of power transistor is coupled in the output of differential amplifier.Therefore,, when potential difference surpasses skew, power transistor base stage can be dragged down, and it is turned off.Yet this method needs one and do not heated by power emitter, or is at least the long-range emitter that degree of heat is lighter, produce a gradient response.
Summary of the invention
An object of the present invention is to provide the electromotive force on the sensing emitter of a kind of circuit in can responding power transistor arrangement, and when the emitter-base potential of power transistor represents excess Temperature, reduce the On current of power transistor.
It is of the present invention that to enter an object be to use a differential amplifier, it has the input between the sensing emitter of the base stage of being coupling in and power transistor, also has the individual output on base stage circuit that is coupling in, when the electromotive force of sensing emitter-base stage surpasses temperature, the On current of power transistor can reduce like this.
Technical solution of the present invention is:
The emitter base voltage of junction transistor is the accurate indication of junction temperature.These transistors are commonly used in power supply IC and provide thermal overload protection as transducer.Yet, single transducer, this is just usually located near a larger power transistor it, the temperature peak of its not direct responding power transistor inside.Method described herein has adopted distributed sensor bending to be arranged in whole power array, and this is response temperature peak value not.
In reality, with distributed sensing emitter of current offset, cause, when emitter-base potential is zero, being heated to equably 200 ℃.Higher temperature can cause the reverse of emitter-base potential, but can prevent that heating-up temperature from surpassing 200 ℃, when sensing electromotive force reverses, by control circuit, reduces the dissipation in power transistor, because it will reverse at higher temperature.If only having the sensing emitter of half is under peak temperature, 20 ℃ of extra zero sense potential that rise at the 220th ℃ will be had.Transducer when 1/10th is in temperature peak, and near 250 ℃, sensing current potential is zero.Therefore peak temperature remains on a rational value, even there is serious focus in power array.This and conventional method contrast, and destructive temperature can occur under the poorest situation.
It can rather than be positioned at distributed sensor under the delay of several milliseconds of needs of the transducer outside array tens microseconds and respond an excess temperature situation.Therefore, there is no need limit dissipation power electricity.Electrical power limit must also have component tolerances factor based on the poorest situation of expection.Eliminating this Power Limitation has not only increased peak power, but also increases continuous rating power, can guarantee.At one time, provide and control better temperature peak.In a word, restriction is to be determined by the temperature of physical device, rather than an area of safety operaton according to supposition condition of work limits.
In circuit of the present invention, the right base stage of difference transistor intercouples, to protect the sensing emitter of power transistor.A relatively little electric current is pulled out from sensing emitter, and setting up one is its sensing emitter electromotive force of the hottest partial function.Differential pair work becomes a current mirror load, and a single-ended drive is provided, and high-gain amplifier level is provided, and it is included in a frequency compensation electric capacity of conventional operation amplifier mode.High gain amplifier drives the controlled stage being coupling between power transistor emitter and basic driver input conversely.As long as the device biasing below the critical temperature of the sensed emitter operation of differential pair, high-gain amplifier will be lower than its conduction threshold, and its output will be high level, with closing control level.In this case, power transistor will normally move.When the temperature of sensing emitter surpasses critical temperature, differential pair, by the high-gain amplifier level of driver, enters conducting state, opens controlled stage.This will reduce power transistor biasing, so do not have further temperature to rise, will be possible.Because whole amplifier and control circuit are linear in its operation, and have suitable gain, critical temperature threshold value can effectively be moved, overheated to prevent the focus that power transistor is the warmmest.Therefore, restriction is to be determined by the temperature of physical device, rather than an area of safety operaton according to supposition condition of work limits.
Contrast patent documentation: the temperature protection circuit 201220402544.7 of CN202798441U inverter.
Accompanying drawing explanation:
Fig. 1 is the rough schematic view of circuit of the present invention.
Fig. 2 is the schematic diagram of circuit of the present invention.
Embodiment:
The simplified schematic of power transistor, also has its sensing emitter and thermal control circuit as shown in Figure 1.Sensing emitter 10 shares a base stage 11 with power transistor 12.A current source bias sensing emitter is at an electric current
i 1, making in the limiting temperature place of needs emitter-base potential is zero.Operational amplifier 14 is as controller.When the electromotive force of sensing emitter 10 electromotive force lower than base stage 11, amplifier is output as high level, and prevents from being coupled to base circuit by a diode 15.If sensing emitter electromotive force rises to base potential, the output potential of amplifier will reduce, and absorbs the driving of base stage by this diode.At limiting temperature place, allow the sensing electromotive force be zero to be thing very easily.A nonzero value can produce a reference voltage at the input circuit place of amplifier.If protection power transistor is unique Consideration, the design of control amplifier will be relatively simple.But in many application, the thermal limit of power transistor enters steady dead-beat, may cause electrical Interference or other undesirable impact.Under transducer outside array, this target waits to realize.Because the heat lag of transducer in the loop compensation of the IC actual exceeds time constant.Use integrator sensor, stable circulation is in the cards, because can greatly reduce delay.Yet the little electric capacity that reaches required time constant needs the internal bias electric current of a microampere left and right.Microampere order circuit, must normal working temperature be approximately 175 ℃, needs new method for designing.A feature of the present invention is to use inverted NPN transistor, controls like that as will be described below low current node.When transistorized emitter is as collector electrode, caused current gain lower, but can make up this point with circuit engineering.The most important thing is, inverted transistor does not have the parasitic leakage current of normal node.At 175 ℃, this spurious leakage itself can be in microampere scope.
Although the circuit forward bias sensing emitter in Fig. 1 and detect it with respect to the electromotive force of transistor base, should be understood that, sensing emitter may be reverse bias, and its leakage of sensing.This is feasible, because the reverse leakage current of PN junction is relevant to temperature.Under this mode of operation, although likely, do not have preferred version as described herein good.
Output transistor shown in Fig. 2 schematic diagram and its breaking circuit, can be regarded as a composite crystal tubular construction.The collector electrode of power output transistor 12 is provided to terminal 16.Its main emitter 17 is actually and is comprised of a plurality of single emitter, and each comprises a series of steady resistance.Resistor 18 is effective values of emitter resistance in parallel.Therefore, terminal 19 represents the emitter of output transistor.Terminal 20 represents the base stage of compound transistor.
Transistor 21 is to connect into Darlington driver, and at terminal 20 places, its base stage forms the base stage of Darlington.The emitter of resistance 22 Returning driver transistors 21 is to terminal 19.
Transistor 23 and 24 forms a differential pair, and it has the tail current being arranged by current source 35
i 2.The base stage of transistor 23 is coupled to the base stage 11 of output transistor 12, and the base stage of transistor 24 is coupled to sensing emitter 10.Therefore, differential pair can respond the differential voltage between base stage 11 and the sensing emitter of transistor 12.
Transistor 26 and 27 is coupled and forms a current mirror configuration.Will be noted that, these two transistor operations are at their opposite state, and this will discuss in more detail below.This means, shown collector electrode will be as emitter, and emitter will be as collector electrode.Transistor 28 returns to transistor 27 collector electrodes (inverted emitter) to its base stage, usings and forces it as a diode.Transistor 28 is isolated the base current of current mirrors, prevents the collector electrode of transistor 27.Current source 29 and 30, provides the electric current of relatively little coupling
i 3with
i 4to current mirror, provide bias current.
i 3with
i 4match, and be less than
i 2.
Resistor 31 and 32 is as coupling element, and this is common current mirror and the transistor 23 and 24 of differential connection.In normal operation, when sensing emitter 10 is low levels, nearly all electric current in current source 25
i 2inflow transistor 24.This is by the current potential of 27 the emitter (inverted collector electrode) of pulling up transistor.This operation can cause transistor 26 On currents, and is significantly greater than transistor 27.The collector electrode of transistor 26 (inverted emitter) is therefore low level.It is low level that the conducting meeting of transistor 26 makes the base potential of transistor 33, to it and transistor 34 are ended.Electric current from current source 35
i 5therefore the base potential of transistor 36 can be drawn high, thereby be closed.Electric current from current source 35
i 5the transistor 37 connecting by diode and resistance 38.After these two elements with
i 5, be selected to produce the base potential of required transistor 36.The emitter current return current groove that anti-transistor 39 is transistor 33.Electric current groove guarantees that transistor 34 is closed tightly when transistor 33 is closed.In above-mentioned situation, power transistor 12 will work, as long as be less than the electromotive force on resistor 38 by the electromotive force on ballast resistor 18.Peak anode current is limited in a value, by the pressure drop at resistance 18 two ends, and can fusion chip metal or bonding wire.
The focus producing at power transistor 10, or its working temperature generally rises, and the electromotive force on sensing emitter 10 can rise along with base potential.Be on duty while being zero, transistor 20 will the same conducting with 21.Therefore, the electromotive force that the emitter of transistor 26 (inverted collector electrode) is located rises, and the electromotive force that the emitter of transistor 27 (inverted collector electrode) is located declines.If transistor 26 and 27 matches, current source 29 and 30 matches, and resistor 31 and 32 matches, the electromotive force that the collector electrode of transistor 26 (inverted emitter) is located, by deficiency so that transistor 33 and 34 conductings.Yet the further increase of temperature surpasses the electromotive force that causes sensing emitter 10 electromotive force of the base stage 11 of transistor 12.In this region, approaching under off state, differential amplifier is by its highest gain-state.Along with temperature increases, the electric current in transistor 26 will be lowered therewith, and the electric current of transistor 27 will increase.When the electric current of transistor 26 conductings fully reduces, signal source 29 will pull up transistor 33 base potential, and provides electric current in this.This will open transistor 33, transistor 34, and electric current will flow through transistor 34 from current source 35 like this.When the electric current of transistor 34 conductings approaches current source 35, the base stage of transistor 36 is dragged down, thereby opens it.When this happens, the base stage of driving transistors 21 is dragged down, thereby controls the electric current in transistor 12.
Electric capacity 41 is connected between transistor 33 and the input and output of 34 Darlington pairs, to provide, turn-offs amplifier frequency compensation.This contributes to circuit to keep stable.
41 required capacitances depend on the mutual conductance of transistor 26 and 27, and lower operating current has lower mutual conductance, and need less electric capacity.Transistor 26 and 27 operating current can not be reduced to so low, at the parasitic leakage current of active collector electrode (inverted emitter), affect bias current when temperature approaches 175 ℃.Opposite direction connection is placed on leakage current on the collector electrode of transistor 23 and 24, and they are operated under high electric current, and the leakage current of microampere order is negligible like this.Complete this part thing, the parasitic leakage current on transistor 26 and 27 active collector electrode can reduce to submicron level by meticulous design.
The circuit of example: Fig. 2 forms with IC form, uses the single piece of silicon element of traditional PN junction isolation.PNP transistor is vertical double diffusion structure, and NPN transistor is traditional transversary.Use following component value:
| Element | | Unit |
| Resistance | ||
| 18 | 0.15 | Ohm |
| Resistance 22 | 200 | Ohm |
| Electric |
100 | Microampere |
| Current source 25 | 200 | Microampere |
| Current source 29,30 | 1 | Microampere |
| Resistance 31,32 | 800 | Ohm |
| Current source 35 | 750 | Microampere |
| Resistance 38 | 2.3k | Ohm |
| Electric capacity 41 | 20 | Pico farad |
This circuit is used for limiting the electric current of output transistor, when sensing emitter (at any point along its length) is over approximately 225 ℃, because life period between near the sensing emitter hot generation and its arrival lags behind, by sensing emitter being placed near power emitter, can significantly improve the ability of the response burst pulse of equipment.Yet, the transistor that 300 ° of K, rated power are 90 watts, the pulse of 10 milliseconds can consume 120 watts, and the pulse of 1 millisecond is 240 watts, and 0.2 millisecond of pulse is 600 watts.
Those skilled in the art also will appreciate that, the present invention can be different from above-mentioned example, and described example only for illustrative purposes, rather than restrictive, and the present invention is only defined by the claims scope.
Claims (6)
1. a power transistor overheating protection circuit, it is characterized in that: at one, have base stage, emitter and collector to also have in an independent distribution and the power transistor closely-related sensing emitter of a plurality of independently emitter temperatures, an overheating protection circuit comprises: the current device of the sensing emitter that is used for setovering discrete, and wherein discrete sensing emitter can depend on that it works under the electromotive force of hot part at one; One is used for, when discrete sensing emitter indication surpasses temperature, reducing the device at the electric current of described power transistor.
2. a kind of power transistor overheating protection circuit according to claim 1; it is characterized in that: the device that is wherein used for detecting comprises a differential input stage; its input is coupled to sensing emitter; another input is coupled to the base stage of power transistor; also have an output, be coupled to the device reducing at the electric current of described power transistor.
3. a kind of power transistor overheating protection circuit according to claim 1, is characterized in that: wherein the output of differential input stage is coupled to one difference input, Single-end output, and is operated in the current mirror load under low current.
4. a kind of power transistor overheating protection circuit according to claim 1, is characterized in that: wherein current mirror load is comprised of inverted NPN transistor, and near their leakage current transistor closing temperature is less than their operating current.
5. a kind of power transistor overheating protection circuit according to claim 1, is characterized in that: wherein the input of an anti-phase amplifying stage of high-gain is coupled in the output of current mirror load, drives in turn the device reducing at the electric current of described power transistor.
6. a kind of power transistor overheating protection circuit according to claim 1, is characterized in that: wherein current mirror load relies on the current source work that low current is provided, and described low current maintains a level less with respect to the tail current of differential input stage.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201310509560.5A CN103532364A (en) | 2013-10-25 | 2013-10-25 | Overheating protection circuit for power transistor |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201310509560.5A CN103532364A (en) | 2013-10-25 | 2013-10-25 | Overheating protection circuit for power transistor |
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| CN103532364A true CN103532364A (en) | 2014-01-22 |
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| CN201310509560.5A Pending CN103532364A (en) | 2013-10-25 | 2013-10-25 | Overheating protection circuit for power transistor |
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Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4669026A (en) * | 1985-09-09 | 1987-05-26 | National Semiconductor Corporation | Power transistor thermal shutdown circuit |
-
2013
- 2013-10-25 CN CN201310509560.5A patent/CN103532364A/en active Pending
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4669026A (en) * | 1985-09-09 | 1987-05-26 | National Semiconductor Corporation | Power transistor thermal shutdown circuit |
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Application publication date: 20140122 |