JPS6125324Y2 - - Google Patents

Description

[Detailed description of the invention] This invention supplies current to the load through a power transistor, and controls the driving transistor to conduct or disconduct, thereby making the power transistor conductive or nonconductive. The present invention relates to a power transistor drive circuit configured to control the supply of current, and is particularly intended to prevent damage to the power transistor when a load is short-circuited.

In a conventional power transistor drive circuit, when a PNP type power transistor is used as the power transistor, the emitter of the power transistor 12 is connected to the positive power supply terminal 11 as shown in FIG. 1, and the collector is connected to the load 13. grounded through. On the other hand, the control signal from the input terminal 14 is supplied to the base of the driving transistor 16 through the resistor 15.

The output of the driving NPN type transistor 16 is further amplified by the transistor 17, and the emitter of the transistor 16 is connected to the base of the transistor 17, and the transistors 16, 1
The collectors of transistors 7 and 7 are connected together and further connected to the base of power transistor 12 through resistor 18, and the emitter of transistor 17 is grounded.

When the control signal at the input terminal 14 goes high, the transistors 16 and 17 become conductive, which causes the power transistor 12 to conduct and supply current to the load 13. In such a drive circuit, the load 13
When the power transistor 12 is short-circuited, excessive power flows to the power transistor 12 and the transistor 12 is destroyed.

When an NPN type is used as the power transistor 12, the collector of the power transistor 12 is connected to the power supply terminal 11 through the load 13, as shown in FIG.
The emitter of the driving transistor 13, which is connected to the power transistor 12 and whose emitter is grounded, is connected to the power transistor 12.
The collector is connected to the power supply terminal 11 through a resistor 18. The rest is the same as in the case of FIG.

In this case as well, when the control signal applied to the terminal 14 becomes high level, the transistors 16 and 17 become conductive and a current is supplied to the base of the power transistor 12, and this transistor 12 becomes conductive and the load 13
Current is supplied to

In this case as well, if the load 13 was short-circuited, an overcurrent would flow through the transistor 12 and there was a risk that the transistor 12 would be destroyed.

The purpose of this invention is to provide a protection circuit in a transistor drive circuit that supplies current to a load through a power transistor to prevent the power transistor from being destroyed when the load is short-circuited.

According to this invention, the base of a protection transistor is connected to the connection point between the power transistor and the load, and when the load is short-circuited, the protection transistor detects the potential change and the protection transistor becomes conductive. The base of the drive transistor is controlled to be non-conductive. Furthermore, since the protection transistor is in a conductive state when driving, a control signal can be applied to the base of the drive transistor through a capacitor to control the drive transistor regardless of whether the protection transistor is conductive. Ru.

FIG. 3 shows a case where a PNP type is used as a power transistor, and parts corresponding to those in FIG. , 22 are connected through a series circuit. In this case, the diodes 21 and 22 have opposite polarities, and the diode 22 on the transistor 16 side is arranged in the forward direction between the base and emitter of the transistor 16. Also, diodes 21, 22
A resistor 23 is connected in series therebetween, and a diode 24 is connected in series with the diode 22 in the forward direction on the transistor 16 side.

A connection point between the diode 21 and the resistor 23 is connected to a driving power supply terminal 26 through a resistor 25.

A starting capacitor 27 is connected in parallel with the series circuit of diodes 21 and 22. That is, one end of the starting capacitor 27 is connected to the input terminal 14, and the other end is connected to the base of the transistor 16. Furthermore, a protection transistor 28 is provided, and in this figure, the protection transistor 28 is of the PNP type, and its emitter is connected to the connection point of the diode 21 and the resistor 23, its collector is grounded, and its base receives power through the diode 29. It is connected to the connection point between the load transistor 12 and the load 13 . diode 29
has a polarity that is in the forward direction with respect to the base emitter of the protection transistor 28.

In this configuration, when no current is being supplied to the load 13, the base of the protection transistor 28 is at ground potential through the load 13, so the protection transistor 28 is in a conductive state. Therefore, the current from the power supply 26 through the resistor 25 flows to the transistor 28 side, and no current is supplied to the base of the transistor 16, and the transistors 16 and 17
is in a non-conducting state.

In this state, when a control signal is applied to the input terminal 14 and becomes high level, a charging current flows to the capacitor 27, and a base current is supplied to the transistor 16. Therefore, transistors 16 and 17 become conductive, and the base potential of power transistor 12 drops, and transistor 12 becomes conductive, supplying current to load 13. As a result, the collector potential of the transistor 12 rises, the base potential of the protection transistor 28 rises, and the transistor 28 becomes non-conductive.

Therefore, the resistors 25, 2 are connected to the driving power supply terminal 26.
3. The base current is supplied to the transistor 16 through the diodes 22 and 24, and the transistor 1
6 and 17 are maintained in a conductive state.

When the input terminal 14 becomes a low level, a current flows from the driving power supply terminal 26 through the resistor 25, the diode 21, and the input terminal 14, the potential at the connection point of the diode 21 and the resistor 23 decreases, and the current flows to the transistor 16 side. is switched to the diode 21 side, transistors 16 and 17 become non-conductive, and power transistor 12 also becomes non-conductive.

When the load 13 is short-circuited while current is being supplied to the load 13, the base potential of the protection transistor 28 decreases and the protection transistor 28 becomes conductive, and this current flows through the resistor 25, and the resistor 23 and The potential at the connection point of the diode 21 decreases, that is, the base potential of the transistor 16 decreases, and base current is no longer supplied to the transistors 16 and 17.
7 becomes non-conductive. Therefore, power transistor 1
2 also becomes non-conductive, preventing excessive current from continuing to flow through the transistor 12.

When the input terminal 14 becomes high level while the load 13 is short-circuited, the charging current for the capacitor 27 flows into the bases of the transistors 16 and 17, and these transistors 16 and 17 become conductive momentarily, so that the power transistor 12 Although a current momentarily flows through, the protection transistor 28 is not prevented from conducting because the load 13 is short-circuited.
Therefore, transistor 28 remains conductive and transistors 16 and 17 immediately become non-conductive.

An example in which an NPN type is used as a power transistor is shown in FIG. 4, in which parts corresponding to those in FIGS. 2 and 3 are given the same reference numerals. In this case, an NPN type is used as the protection transistor 28, its collector is connected to the connection point of the diode 21 and the resistor 23, and its emitter is grounded.

Further, a diode 31 and a resistor 32 are connected in series with the diode 29 so that the transistor 28 does not conduct when current is being supplied to the load 13. The diode 24 on the base side of the driving transistor 16 is omitted.

When the power transistor 12 is not supplying current to the load 13, a high potential is applied to the base of the transistor 23 from the power supply terminal 11 through the load 13. Protection transistor 28 is therefore conductive. In this state, when the input terminal 14 becomes high level, the charging current for the capacitor 27 flows to the bases of the transistors 16 and 17, and these transistors 16 and 17 become conductive. Therefore, a base current is supplied to the power transistor 12, and the transistor 12 becomes conductive.
Current is supplied to the load 13. Therefore, the base potential of the protection transistor 28 decreases, making the transistor 28 non-conductive, and current is supplied from the drive power supply terminal 26 to the transistors 16 and 17 through the resistors 23 and 25 and further through the diode 22, so that the power transistor 12 The conductive state is maintained.

In this state, when the input terminal 14 becomes low level, the resistor 25 and diode 2 are connected to the power supply terminal 26.
1 flows to the input terminal 14 side, and the supply of base current to the transistors 16 and 17 is switched to the terminal 14 side, and these transistors 1
6 and 17 become non-conductive. Therefore, the supply of base current to the power transistor 12 is also stopped, and the current to the load 13 is cut off.

When the load 13 is short-circuited while current is being supplied to the load 13, the base potential of the protection transistor 28 rises and the transistor 28 becomes conductive, and current flows to the transistor 28 side through the resistor 25, and the transistors 16 and 17 The base current for is cut off. Therefore, the power transistor 12 also becomes non-conductive, preventing excessive current from continuing to flow therein.

When a high level is applied to the input terminal 14 while the load 13 is short-circuited, the charging current of the capacitor 27 momentarily flows through the transistors 16 and 17, causing current to flow through the power transistor 12, but since the load 13 is short-circuited, it is not protected. The base potential of the transistor 28 is held at a high level, and the transistors 16 and 17 are immediately cut off without being kept conductive. At this time, the resistor 32 is connected to the power supply terminal 11.
This prevents an overvoltage from being applied to the base of the protection transistor 28.

As mentioned above, according to the power transistor drive circuit of this invention, when the load is short-circuited, the power transistor is shut off and overcurrent continues to flow through the power transistor, preventing it from being destroyed. be done. Moreover, the protection transistor maintains a conductive state and turns the power transistor into a non-conductive state when no current is being supplied to the load, but supplies charging current for the capacitor 27 to the drive transistors 16 and 17 at startup. and instantaneously conducts it to protect transistor 2.
It is possible to start with 8 non-conducting.

[Brief explanation of the drawing]

Figures 1 and 2 are connection diagrams showing conventional power transistor drive circuits, Figures 3 and 4 respectively.
Each figure is a connection diagram showing an example of a power transistor drive circuit according to this invention. 12: Power transistor, 13: Load, 1
6: Drive transistor, 28: Protection transistor, 14: Input terminal.

Claims (1)

[Scope of utility model registration request] A power transistor is connected in series with the load,
The power transistor is controlled to be conductive or non-conductive by applying a control signal to the base of a driving transistor connected between the base of the transistor and one end of the power supply to control the driving transistor to be conductive or non-conductive. In the power transistor drive circuit configured as above, a diode series circuit with opposite polarities connected in series between an input terminal driven by the control signal and the base of the drive transistor, and a connection of the diodes are provided. A resistor is connected between the resistor and the power source, the collector emitter is connected between the connection point of the resistor and the diode, and the ground, and the base is connected to the connection point of the power transistor and the load. A power transistor drive circuit comprising: a protection transistor that conducts when the power transistor is non-conducting and becomes non-conductive when the load is short-circuited; and a starting capacitor connected in parallel with the series circuit. .