JPH0749869Y2 - Transistor switching circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a transistor switching circuit suitable for driving a relay, a motor, a solenoid, etc., even when a large current flows when the solenoid, etc. is short-circuited or the motor is restrained. The present invention relates to a durable transistor switching circuit.

(Prior Art) A conventional transistor switching circuit is constructed as shown in FIG. That is, the current detection resistor 1 and the switching transistor 2 were connected in series to the power supply B _AT .

Therefore, when the current flowing through the load R _L increases, the voltage drop of the resistor 1 increases, and this voltage drop increases.
When V _{BE (ON)} rises, the base of transistor 2
The emitters are short-circuited by the transistor 3 so that the transistor 2 is cut off.

The transistor 4 is a control transistor that is turned on by the voltage applied to the control terminal C to turn on the transistor switching circuit.

(Problems to be solved by the invention) When the conventional transistor switching circuit as described above is used, since the switching transistor and the current detection resistor are connected between the power supply and the load, the voltage supplied to the load Has a problem that the voltage drop of the current detection resistor and V _{CE (ON)} of the switching transistor are lowered.

Particularly in battery-driven equipment, loss in the power supply path is a particular problem.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and provide a transistor switching circuit capable of reducing the voltage drop in the voltage supply path to the load.

(Means for Solving Problems) In order to solve the above problems, the present invention has the following configuration.

A switching transistor in which an emitter and a collector are connected in series between a power supply and a load, and a base of the switching transistor is connected via a first resistor, and is turned on / off by a control voltage to drive the switching transistor on / off. Connect the first control transistor and the collector to the base of the switching transistor and the emitter to the emitter of the switching transistor,
The base is connected to the collector of the switching transistor via the second resistor to detect the collector-emitter voltage of the switching transistor, and when this voltage exceeds the base-emitter on-voltage, the switching transistor is turned on and the switching transistor is turned on. And a second control transistor for turning off the first control transistor in preference to the control by the first control transistor, a collector connected to the base of the second control transistor, an emitter connected to the emitter of the second control transistor, and a power supply to the base. A third control transistor for controlling the second control transistor to be in an off state by supplying a voltage through a time constant circuit and turning on the power supply to the load for a predetermined period after the power supply to the load is started.

(Operation) In the present invention, the switching transistor is turned on / off by the first control transistor which is turned on / off by the control voltage, and the switching transistor is connected to the load while the switching transistor is on. The power supply voltage is applied. However, since only the switching transistor is connected in series between the power supply and the load, there is no voltage drop caused by the current detection resistor as in the past, and the power supply voltage is applied to the load. .

Further, the emitter-collector voltage of the switching transistor is detected by the second control transistor. When the collector-emitter voltage of the switching transistor exceeds a predetermined value, the switching transistor has priority over the control of the first control transistor. The second control transistor controls the off state.

As a result, when the load current increases, the current flowing through the switching transistor increases, and the collector-emitter voltage of the switching transistor increases, which is detected by the second control transistor and the switching transistor is controlled by the first control transistor. The transistor is protected by being turned off in priority to the control by the transistor. Furthermore, unless the first control transistor is turned off, the switching transistor cannot be controlled to be turned on.

Further, the third control transistor controls the second control transistor to be in the OFF state for a predetermined period after the power supply to the load is started, so that the power supply voltage is applied to the load and the power supply voltage is again applied to the load after being cut off. Can be done reliably.

(Embodiment of the Invention) FIG. 1 is a circuit diagram showing a configuration of an embodiment of the present invention.

The power supply B _AT is connected to the load R _L via the switching transistor 2.
Connected to. The base of the switching transistor 2 is a transistor 4 corresponding to the first control transistor through a parallel circuit of a bias resistor 11 and a capacitor 12.
It is grounded via the transistor 4 and the transistor 4 has a control terminal C
Controlled by the voltage applied to the on / off state,
When the transistor 4 is turned on / off, the switching transistor 2 is turned on / off.

A transistor 13 for detecting V _{CE of the} switching transistor 2 is connected between the collector and the emitter of the switching transistor 2 via a resistor 14. Transistor
The collector of 13 is connected to the base of the switching transistor 2, and the emitter of the transistor 13 is connected to the power supply B _AT together with the emitter of the switching transistor 2. The transistor 13 corresponds to the second control transistor.

On the other hand, the emitter of the transistor 15 is connected to the power supply B _AT ,
The collector is connected to the base of the transistor 13, and the base is connected to the collector of the transistor 4 through a differentiating circuit composed of the resistors 16 and 17, the capacitor 18 and the diode 19 to control the transistor 13 to be turned off at the time of startup.

The transistor 15, the resistors 16 and 17, the capacitor 18, and the diode 19 are a starting circuit that enables starting when the switching transistor 2 is turned off and then turned on again.

In the present invention configured as described above, when the control terminal C is set to a high potential, the transistor 4 is turned on and the resistance 1
A differentiating circuit consisting of 6, 17, capacitor 18, and diode 19 acts, and the base of transistor 15 is temporarily resistor 1
7, grounded through capacitor 18 and transistor 4. Therefore, the transistor 15 is controlled to the ON state, and the base of the transistor 13 is loaded by the resistor 14 into the load R _L.
Despite being grounded through, it is controlled to the off state and can be activated. Therefore, the base of the switching transistor 2 is grounded via the resistor 11 and the transistor 4, the switching transistor 2 is controlled to be in the ON state, and the voltage of the power supply B _AT is applied to the load R _L via the switching transistor 2. It

When the load current of the load R _L is within the predetermined range, the collector-emitter voltage V _CE of the switching transistor 2 is low,
The transistor 13 is controlled to the off state, and the switching transistor 2 is controlled to the on state.

Next, when the load R _L decreases and the current flowing through the switching transistor 2 increases, the voltage V _CE sharply increases as in the characteristic example of the collector current vs. collector-emitter voltage V _CE shown in FIG. This voltage V _CE is the voltage of transistor 13
_{When the BE (ON)} voltage is exceeded, the transistor 13 is controlled to be on. As a result, the base and the emitter of the switching transistor 2 are short-circuited by the transistor 13, the switching transistor 2 is controlled to the off state, and the voltage supply to the load R _L is cut off. Once the switching transistor 2 is turned off, the transistor 13
Is kept on, the switching transistor 2 does not generate heat even in the off state.

In order to turn on the switching transistor 2 once turned off as described above, the control terminal C is once set to a low potential and then set to a high potential again so that the switching transistor 2 is turned on as described above. Turns on.

When the control terminal C is set to a low potential, the transistor 4 is turned off, the bias of the switching transistor 2 is cut off, the switching transistor 2 is controlled to the off state, and the voltage of the power supply B _AT of the load R _L is not applied. Be cut off.

Next, when the load R _L is short-circuited, the voltage of the power supply B _AT is applied between the base and the emitter of the transistor 13 through the resistor 14, so that the switching transistor 2 is surely turned off.

Here, the capacitor 12 is connected to cut off the oscillation loop formed by the switching transistor 2 and the transistor 13. Furthermore, the diode 19 is connected for the purpose of accelerating the discharge of the capacitor 18 when the transistor 4 is turned off, and it may be omitted.

However, since the switching transistor 2 is only connected between the power supply B _AT and the load R _{L as} described above,
The loss in the voltage supply path from the power supply B _AT to the load R _L is only V _{CE (ON)} of the switching transistor 2 and the current detection resistor 1
There is no voltage drop due to, and it is smaller than the conventional example.

Further As for causes of when to quenching transistor 2 is broken, (b) I _CMAX V _CE is increased by disruption (ii) I _C increased by more than, P invites a sharp increase in collector loss P _{C CMAX} Damage due to exceeding

Regarding (a), it is often not actually destroyed because it is limited by the base resistance of the switching transistor 2 and the reduction of the current amplification factor h _fe in the large current region.

With respect to (b), since V _CE of the switching transistor 2 is relatively small and can be suppressed to about V _{CE (ON)} of the transistor 13, V _{CE of} the switching transistor 2 is reduced _.
Is suppressed, which is advantageous for thermal destruction,
Further, once V _CE of the switching transistor 2 exceeds V _{CE (ON)} of the transistor 13, the control terminal C is set to a low potential after the load R _L is in a normal state, and then it is set to a high potential again. Since it does not re-operate, it is also advantageous in terms of heat, and the destruction due to (b) is eliminated. Therefore, it is not necessary to provide a radiator for the switching transistor 2, and the space factor is improved.

Further, even in the case where the power supply B _AT is applied via the switch by the start-up circuit, even when the high potential is first applied to the control terminal C and the voltage of the power supply B _AT is applied with a delay. The transistor 13 can be activated by being turned off by the transistor 15 as described above.

Further, in the above-mentioned embodiments, the case of the bipolar transistor is illustrated, but it is also possible to replace with a FET or other element. Further, a plurality of switching transistors may be connected in parallel.

According to the present as described (invented effect) or devised only provided when to quenching transistor in series between the power source and the load, to detect the V _CE of when to quenching transistor with a second control transistor, the detection voltage When the voltage exceeds the predetermined value, the switching transistor is turned off. Therefore, the current detection resistor is not necessary, the voltage drop due to the current detection resistor does not occur, and the voltage drop is reduced.

Further, since the OFF state of the switching transistor by the second control transistor has priority over the control of the switching transistor by the first control transistor,
When the switching transistor is turned off by the control transistor, the switching transistor is surely protected because the first control transistor does not restart unless it is turned off once, and the switching transistor generates less heat. No radiator is needed.

Furthermore, the second control transistor surely acts on the short circuit of the load, and the switching transistor is surely protected.

Further, since the voltage between the collector and the emitter of the switching transistor is detected, it is easy to limit the collector loss.

Furthermore, since the third control transistor is configured to control the second control transistor to be in the OFF state for a predetermined period after the power supply to the load is started, the power supply voltage to the load and the power supply voltage to the load are cut off. The effect is that the re-application can be surely performed.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention. FIG. 2 is a diagram for explaining the operation of one embodiment of the present invention. FIG. 3 is a circuit diagram of a conventional example. B _AT ... power supply, R _L ... load, 2 ... switching transistor, 4 and 13 ... transistor.

Claims (1)

[Scope of utility model registration request] 1. A switching transistor in which an emitter and a collector are connected in series between a power source and a load, and a switching transistor which is connected to the base of the switching transistor via a first resistor and is on / off driven by a control voltage. Connecting the collector to the base of the switching transistor and the emitter to the emitter of the switching transistor,
The base is connected to the collector of the switching transistor through the second resistor to detect the collector-emitter voltage of the switching transistor, and when this voltage exceeds the base-emitter on-voltage, the switching transistor is turned on and the switching transistor is turned on. And a second control transistor for turning off the first control transistor in preference to the control by the first control transistor, a collector connected to the base of the second control transistor, an emitter connected to the emitter of the second control transistor, and a power supply to the base. A transistor switching circuit, comprising: a third control transistor that supplies a voltage through a time constant circuit and keeps a second control transistor in an off state for a predetermined period after power supply to a load is started.