KR940004704Y1 - Protecting circuit for power transistor - Google Patents

Abstract

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Description

Power Transistor Protection Circuit

1 is a conventional power transistor driving circuit diagram.

2 is a power transistor protection circuit of the present invention.

3 is a timing diagram of a control signal and a synchronization signal.

* Explanation of symbols for main parts of the drawings

COM1-COM4: Comparator T11-T12: Trans

7-1,7-2: Power transistor drive unit

The present invention relates to an electronic cooker protection circuit, and more particularly, to a power transistor protection circuit suitable for the safe operation of the inverter power transistor.

Referring to the accompanying drawings, the inverter power transistor driving circuit of the conventional electronic cooker is as follows.

1 is a circuit diagram of a conventional power transistor driving circuit. As shown therein, an inverter unit 3 receiving an input power voltage AC through a full-wave rectifier 1 and then a low pass filter 2 and an input power supply voltage. In the AC, the current detection unit 4 detects the current through the current transformer CT, and detects the presence or absence of overpower, and the detection signal and the input detection unit 4 detecting the inverter unit 3. A photocoupler is provided with a control path of a control unit 5 for receiving the output signal and outputting the synchronization signal as a mutually inverted synchronization signal through the comparators COM1 and COM2, and the system controller for driving the inverter unit 3. The output terminals of the control signal interface unit 6 detected by the PC and output through the transistor Q1 and the comparator COM1 outputting the synchronization signal of the synchronization unit 5 are transistors Q2 and Q4. Is a transistor connected in common with the base and the collector of transistor Q2 is connected to the base. The emitter of Q3 is commonly connected to the collector of transistor Q4, the base of transistor Q7 and the collector of transistor Q6, and the output terminal of the control signal interface 6 is connected to the transistor of Q5. The base is connected to the base of the transistor Q6, and the collector of the transistor Q7 is connected to the base of the transistor Q7, and then the collector of the transistor Q7 is connected to the power transistor of the inverter section 3. The output terminal of the first power transistor driver 7-1 which is connected to the driving transformer T11 to output the power transistor driving signal and the comparator COM2 which outputs the synchronization signal of the synchronization unit 5 is a transistor ( The output terminals of the control signal interface unit 6 are connected to the bases of the transistors Q11, respectively, and the collectors of the transistors Q8, Q11 are connected to the transistors Q9, Q10, and Q10, respectively. We connect to base of (Q12) each Then, the emitter of the transistor Q9 is commonly connected to the collectors of the transistors Q10 and Q12 and the base of the transistor Q13 to drive the collector of the transistor Q13 to drive the power transistor of the inverter unit 3. The second power transistor driver 7-2 connected to the transformer T12 was configured.

The operation and problems of the conventional power transistor driving circuit constructed as described above are as follows.

In the absence of a control signal for driving the inverter unit 3, in particular, since the transistor Q1 is turned on with the photocoupler PC off in the initial state, the output of the control signal interface unit 6 has a low potential, and In the base 5, when the high potential is output through the comparator COM1 and the low potential through the comparator COM2, the first power transistor driver 7-1 receives a synchronous signal to the base Q2. And Q4 are turned on, and the transistor Q5 to which the control signal is applied is turned off and the transistor Q3 is turned off, so the transistor Q7 is turned off and the transformer T11 does not operate.

In the second power transistor driver 7-2, the transistors Q8 and Q10 to which the synchronization signal is applied are turned on with the tongue-off state turned on, but the transistor Q11 to which the control signal is applied is turned on. Since the transistor Q12 is turned off and turned on, the transistor Q13 is also turned off so that the transformer T12 does not operate.

At this time, when the photo coupler PC is turned on by the control signal for driving the inverter unit 3, the transistor Q1 is turned off to output the high potential control signal from the control signal interface unit 6.

By the high potential control signal, the transistors Q5 and Q11 of the first power transistor driver 7-1 and the second power transistor driver 7-2 are turned on to turn on the transistors Q6 and Q12. Since the signal is turned off, the transistors Q2, Q4 or Q8, Q10 alternately turn on / off each other by the synchronization signal through the comparators COM1 and COM2.

When this transistor Q2, Q4 or transistors Q8 and Q10 are turned off, transistor Q3 or Q9 is turned on to turn transistor Q7 or transistor Q13 to turn on Since the T11 or the transformer T12 is operated, the power transistor of the inverter unit 3 is driven. Therefore, when the control signal is the high potential that is the drive signal of the inverter unit 3, the transistor Q7 and the transistor Q13 are repeatedly inverted on and off by the synchronizing signal, thereby mutually transducing the transformer T11 and the transformer T12. It is alternately turned on and off to drive the power transistor of the inverter unit (3).

However, in such a conventional power transistor driving circuit, when the on time of the transistor Q7 or the transistor Q13 is longer than the normal time, the on time of the power transistor of the inverter unit 3 becomes long, and an over output occurs instantaneously. There is a problem that the power transistor is destroyed or the power supply voltage Vcc is dropped to cause a malfunction.

In view of such a problem, the present invention senses the on time of a transistor for driving a power transistor for driving a power transistor of an inverter unit, and when it is longer than the normal time, feeds a control signal to a transistor receiving a synchronization signal, thereby transducing the transistor for driving the transistor. The power transistor protection circuit is designed to protect the power transistor by turning off, which will be described in detail with reference to the accompanying drawings.

FIG. 2 is a circuit diagram of a power transistor protection scheme of the present invention, and as shown therein, an inverter unit 3 that receives a power supply voltage AC through a full-wave rectifier 1 and a low pass filter 2, and an input power supply voltage AC. ) Detects the current through the current transformer CT and detects the presence and overpower of the input detector 4, the signal of the input detector 4, and the signal from the inverter unit 3, A synchronizing unit 5 for inverting the synchronizing signal through the comparators COM1 and COM2, and a control signal interface for detecting the control signal of the system control unit with the photocoupler PC and outputting it through the transistor Q1. The collector 6 and the collector of the transistor Q5 to which the control signal of the control signal interface unit 6 is applied to the base are connected to the base of the transistor Q6, and the synchronizing signal is transferred through the comparator COM1. Q2), applied to the base of (Q4) and the collector of the transistor (Q2) Is connected to the base of the transistors Q4 and Q6 and the base of the transistor Q7, and then the collector of the transistor Q7 is connected to the base for power transistor driving. The first power transistor driver 7-1 connected to the T11 and the synchronization signal of the synchronizer 5 are applied to the bases of the transistors Q8 and Q10 through the comparator COM2, and the control is performed. The emitter of the transistor Q9 which connected the collector of the transistor Q11 to which the control signal of the signal interface unit 6 is applied to the base to the base of the transistor Q12, and connected the collector of the transistor Q8 to the base. Is connected to the collectors of the transistors Q10 and Q12 and the base of the transistor Q13, and then the second power transistor driver which connects the collector of the transistor Q13 to the transformer T12 for driving the power transistor ( 7-2) In the water transistor driving circuit, a collector connection point (A) and a transformer (T) of the transformer (T11) and the transistor (Q7) of the first power transistor driver (7-1) and the second power transistor driver (7-2). And the collector connection point B of the transistor Q13 are commonly connected to the inverting input terminal of the resistor R21 and the comparator COM3 through the diodes D21 and D22, respectively, and the inverting input of the comparator COM3. A common voltage is connected to the terminal, and a reference voltage is applied by connecting the connection point of the resistor R23 connected to the non-inverting input terminal of the comparator COM3 and the resistor R22 connected to the power supply voltage Vcc terminal. The output terminal of (COM3) is connected to the power supply voltage (Vcc) terminal through the resistor (R24) and the grounded capacitor (C21) and the grounded resistor (R26) through the resistor (R25), and then the comparator (COM4). ) Is connected to the non-inverting input terminal of), and is connected to the power supply voltage (Vcc) terminal of the inverting input terminal of the comparator COM4. The reference voltage is applied by connecting the connection point of the resistor R28 and the grounded resistor R29, and the output terminal of the comparator COM4 is connected to the power supply voltage Vcc terminal through the resistor R31, and the grounded capacitor ( C22) and the grounded resistor R30, are connected to the non-inverting input terminal of the comparator COM4 through the diode D23, and the output terminal of the comparator COM4 is connected to the resistor R32. After the diode D24, the base connection point C and the second power transistor driver 7-2 of the first and second transistors Q1 and Q5 are supplied with the synchronization signal. The power transistor protection circuit of the inverter unit 3 was configured by common connection to the base connection points D of (Q8) and (Q10).

The operation and effects of the inventive power transistor protection circuit constructed as described above are as follows.

When the transistors Q7 and Q13 of the power transistor driver are turned off, the potentials of the connection points A and B are high potentials, and the potential of the inverting input terminal of the comparator COM3 is the reference voltage of the non-inverting input terminal. Since it is higher than the potential, the output of the comparator COM3 becomes the low potential, and the output point of the comparator COM4 becomes the low potential as the low potential output of the comparator COM3, and the connection point C for receiving the synchronization signal of the power transistor drive unit is input. ), (D) has no effect and is driven according to the synchronization signal.

However, when the power transistor driver operates, that is, when the transistor Q7 or the transistor Q13 is turned on, the connection points A, and (A) of the transistors Q7, Q13 and the transformers T11, T12 ( When the connection point A or the connection point B, in which the transistors Q7 and Q13 are turned on, is turned on, the potential of the inverting input terminal of the comparator COM3 is lower than the reference voltage potential of the non-inverting input terminal. The output of (COM3) becomes high potential. When the output of the comparator COM3 becomes high, the capacitor C21 is charged.

Then, as shown in the timing diagram of the control signal and the synchronization signal in FIG. 3, when the synchronization off time Td of the transistors Q7 and Q13 is reached, the output of the comparator COM3 becomes low potential again, The capacitor C21 discharges and is refreshed again.

However, if the turn-on time (Ton1 or Ton2 in FIG. 3) of the transistor Q7 or the transistor Q13 becomes abnormally long, the output of the comparator COM3 continues to output a high potential, thereby increasing the charge potential of the capacitor C21. When longer than the set on time (Ton, max = Ton1 + Ton2), the output of the comparator (COM4) becomes a high potential, and the output is fed back to its non-inverting input terminal through the diode (D23) and the resistance (R32) and The transistors Q3 and Q1 are turned on by applying a high potential to the contacts C and D of the power transistor driver through the diode D24 to turn on the transistors Q2, Q4 and Q8, Q10. The transistors Q7 and Q13 are turned off by turning off Q9. By turning off these transistors Q7 and Q13, the transformers T11 and T12 are turned off and the power transistor of the inverter section 3 stops driving, thereby making it safe.

Here, if the size of the capacitor C21 and the resistor R25 is adjusted so that the capacitor C21 can be sufficiently discharged during the synchronous off time Td of the transistors Q7 and Q13 in the steady state, a problem occurs in the normal operation. none.

Therefore, when the turn-on time of the drive transistors Q7 and Q13 of the transformers T11 and T12 for driving the inverter unit 3 is sensed and abnormally longer the turn-on time Ton1 and Ton2 are compared, the comparator COM3 ) And (COM4) to generate and feed back a control signal to turn off the transistors (Q7) and (Q13), thereby protecting the power transistor of the inverter unit (3).

As described above, when the system is operated unstable and the driving time of the power transistor is abnormally long, there is an effect of protecting the power transistor by preventing the risk of overpower generation.

Claims (1)

The synchronization signal is applied to the base connection point C of the transistors Q2 and Q4 and the base connection point D of the transistors Q8 and Q10, respectively, and the drive control signal is applied to the transistors Q5 and Q11. Drive the transformers T11, T12 for driving the power transistors of the inverter unit 3, and the transformers T11, T12 for connecting the collectors through connection points A and B respectively. In the power transistor drive circuit composed of the power transistor drive units 7-1 and 7-2, which drive the transistors Q7 and Q13, the transformers T11, T12, and transistor Q7. , (A) and (B) are connected to the inverting input terminal of the comparator (COM3) to which the reference voltage is applied to the non-inverting input terminal through the diodes (D21) and (D22), respectively. A comparison in which a reference voltage is applied to the inverting input terminal after connecting the output terminal of the comparator COM3 to the capacitor C21 and the resistor R26 through the resistor R25. Is connected to the non-inverting input terminal of COM4, and the output terminal of the comparator is connected to the capacitor C22 and the resistor R30, and then connected to the non-inverting input terminal of the comparator COM4 through the diode D23. In addition, the resistor R32 and the diode D24 are connected to the contacts C and D which receive the synchronization signals of the power transistor drivers 7-1 and 7-2. Power transistor protection circuit characterized in that.