JPS61182325A - Transistor switch circuit - Google Patents

Abstract

PURPOSE:To protect a main switch element of a transistor (TR) switch circuit even when any DC voltage supply source is connected or any load is connected by forming a constant current drooping protection circuit with a resistor and a PNP TR and setting properly the resistor. CONSTITUTION:The constant current drooping protection circuit 7 consists of the resistor R1 and the PNP TR Q2. The resistor R1 is connected in series between the emitter of the TR Q1 and a positive side input terminal 1. The emitter of the TR Q2 is connected to the positive side input terminal 1, the base is connected to the emitter of the TR Q1 and the collector is connected to the base of the TR Q1. In setting properly the resistance value of the resistor R1, an output current I0 does not exceed the current rating of the TR Q1 in any load state.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is provided between a power supply line between a DC voltage supply source and a load, and is capable of turning on and off the DC voltage supplied from the DC voltage supply source to the load. The present invention relates to a transistor switch circuit.

[Conventional technology]

In DC circuits in electronic equipment, power lines are sequence-controlled and DC voltage output is turned on and off using drive signals.
It often happens that it turns off. In this case, it is necessary to configure a switch circuit using a semiconductor switch element such as a relay contact or a transistor. Here, in the case of a switch circuit using relay contacts, there are many disadvantages such as delay in operation time, bounce time, and contact noise, which are undesirable when installed in an electronic circuit. On the other hand, transistor switch circuits are currently widely used because they have low voltage loss between the collector and emitter and are easy to control on and off.

FIG. 5 is a circuit diagram showing the configuration of a conventional transistor switch circuit. In the figure, 1 and 2 are DC input terminals connected to a DC voltage supply source (not shown), 1 is a positive input terminal, and 2 is a negative input terminal. 3,4
is the DC output terminal connected to the load (not shown), and 3 is the positive output terminal.

4 is the negative output terminal. Ql is a PNP type transistor, and its emitter is connected to the positive input terminal 1 and the collector is connected to the positive output terminal 3. The base of the transistor Ql is connected to the negative input terminal 2 and the negative output terminal 4 via the drive circuit 6. The drive circuit 6 includes a resistor Rc and an NPN transistor Q. It has

The transistor Q has an emitter connected to the negative input terminal 2 and the negative output terminal 4, a base connected to the drive signal input terminal 5, and a collector connected to the base of the transistor Ql via a resistor Rc. or.

A resistor Rb is connected between the base and emitter of the transistor Q1.

In such a configuration, when a drive signal is input to the drive signal input terminal 5, the base current of the transistor Q flows, the transistor Q0 becomes conductive, and the transistor Q
The base current of the transistor Q1 flows through the emitter and collector of L and the resistor R, and the transistor Q1 becomes conductive. Since the conduction state of the transistor Q1 is such that the emitter is grounded to the input and output, the saturation voltage is extremely low, and the voltage loss between the collector and the emitter can be reduced. On the other hand, when the drive signal is not supplied to the drive signal input terminal 5, the transistor Qc is in a cut-off state, and the transistor Q1 is also in a cut-off state.

[Problem that the invention seeks to solve]

However, in the transistor switch circuit shown in FIG. 5, when the transistor Ql is in a conductive state, that is, on, and the DC output terminals 3 and 4 are short-circuited, the DC current amplification factor of the transistor Q1 is reduced. 4. If the voltage between DC input terminals 1 and 2 is vin, the transistor Q
1's base current is expressed as v1n/Rc, which is the collector current of transistor Q1.

That is, at the point when the output current 0 becomes hFE1×(vin/Rρ), the transistor Ql shifts from the saturated operating state to the linear operating state, and as shown in FIG. 6, the output voltage appearing between the DC output terminals 3 and 4 vo begins to fall.

At this point, the collector loss increases rapidly or exceeds the collector current rating, and the transistor Q1 is permanently damaged.

Therefore, in order to prevent the above damage, an output current I is applied to the power supply side of the transistor switch circuit. is hF8. ×(vi
The transistor Q1 is always kept within a safe operating area (hereinafter referred to as
It was necessary to make it work within the ASO (abbreviated as ASO).

However, if the DC voltage supply source is passive, the power supply current capacity is sufficiently large compared to the semiconductor rating, so
It has been impossible to provide the above-mentioned electronic current limiting circuit on the power supply side. Also, even if a protective fuse is installed in series between the battery and the transistor switch circuit, the power impedance is sufficiently low that transistor Q1 will exceed the ASO and be permanently damaged before the protective fuses are installed. .

As described above, the conventional transistor switch circuit has the disadvantage that, in the event of an output short circuit or overload, the transistor is permanently damaged due to the narrow ASO of the transistor.

[Means and effects for solving the problems] One of the transistor switch circuits according to the present invention is provided between a power supply line between a DC voltage supply source and a load, and has an emitter on the positive side of the DC voltage supply source. , has a PNP type first transistor whose collector is connected to the positive side of the load side, and the base of the first transistor is connected to the drive circuit for controlling on/off of the first transistor. hand,
In a transistor switch circuit connected to the negative side of the DC voltage supply source and the load side and configured to turn on/off the DC voltage supplied from the DC voltage supply source to the load, a resistor inserted and connected in series between the positive side and the emitter of the first transistor;

an emitter on the positive side of the DC voltage supply source;
The base is on the emitter side of the transistor.

The device is characterized in that it includes a PNP type second transistor whose collector is connected to the base side of the first transistor.

In such a configuration, by appropriately selecting the resistance value of the resistor, when the output current increases, the second transistor becomes active and the first transistor becomes active before the first transistor exceeds the ASO. The base current of the first transistor is suppressed and exhibits constant current droop characteristics to prevent the first transistor from exceeding its current rating.

Another transistor switch circuit according to the present invention is
Provided between the power line between the DC voltage supply source and the load,
A PNP type first transistor has an emitter connected to the positive side of the DC voltage supply source and a collector connected to the positive side of the load side.

The base of the first transistor is connected to the DC voltage supply source and the negative side of the load side via a drive circuit for controlling on/off of the first transistor, and the DC voltage supply source In the transistor switch circuit configured to turn on and off the DC voltage supplied to the load, a first resistor inserted and connected in series between the positive side of the DC voltage supply source and the emitter of the first transistor; an emitter connected to the positive side of the DC voltage supply source, a base connected to the emitter of the first transistor via a first diode, and a base connected to the base side of the first transistor via a second diode. a PNP type second transistor having collectors connected to each other, and an emitter connected to the negative side of the DC voltage supply source;
a third transistor of an NPN type, the base of which is connected to the collector of the transistor through a second resistor, and the collector of which is connected to the base of the second transistor through a third resistor; Features.

In such a configuration, by appropriately selecting the resistance value of the first resistor, when the output current increases, the second transistor becomes active and the second transistor becomes active before the first transistor exceeds the ASO. When the base current of the first transistor is suppressed and the second transistor becomes active, the third transistor becomes conductive, making the second transistor conductive and turning the first transistor off. can.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram showing the configuration of an embodiment of a transistor switch circuit having a constant current droop protection function according to the present invention. Components having the same functions as those in FIG. 5 are given the same reference numerals. It is. In this embodiment, a constant current droop protection circuit 7 is further added to the circuit shown in FIG. This constant current droop protection circuit 7.

It consists of a resistor R, and a PNP type transistor Q2.

The resistor R1 is connected in series between the emitter of the transistor Q1 and the positive input terminal 1. transistor Q
2, the emitter is connected to the positive input terminal l, and the base is connected to the emitter of the transistor Qs.

The collector is connected to the base of transistor Q1.

In such a configuration, when a drive signal is applied to the drive signal input terminal 5, the transistor Q0 becomes conductive and the resistor R
The base current of transistor Q1 is drawn through c,
The transistor Q1, which is the main switch element, is electrically connected to the grounded emitter for the input and output, and the transistor switch circuit is in a conductive state.

In this state, it is assumed that the load impedance decreases and the output current factor 0 increases. At this time.

The current flowing through the current detection resistor R1 can be regarded as IO. Here, since the current limiting PNP transistor Q2 has its emitter and base connected to both ends of the resistor R1, and its collector to the base of the transistor Q1, an increase in the output current IO causes the resistor R1 to
The point where the voltage drop of is equal to the base-emitter level vB2 of transistor Qz, that is, vBE2''Io XR
At the point when it becomes 1.

The emitter and collector of transistor Q2 become active, and the base current of transistor Q1 is suppressed. Therefore, the output current factor 0 is vBE. When XR1 is reached and the load impedance further decreases.

It exhibits constant current drooping characteristics as shown in FIG. Therefore, by appropriately setting the resistance value of resistor R1,
Under any load condition, the output current IO is
The current rating can be prevented from being exceeded.

, Here, in a transistor switch circuit having only a constant current droop protection function as shown in FIG. 1, if the DC output terminals 3 and 4 are continuously short-circuited.

V, xI (1 collector loss occurs continuously n Therefore, some kind of countermeasure is required.

FIG. 3 is a circuit diagram showing the configuration of an embodiment of a transistor switch circuit which has a constant current droop protection function according to the present invention and also has a function of cutting off the main switch element at the constant current droop starting point. Components having the same functions as those in the figures are given the same reference numerals. The difference from FIG. 1 is that the constant current droop protection circuit 7' includes a diode DI+D2 in addition to a resistor R1 and a transistor Q2. The transistor Q2 of this embodiment has its emitter connected to the positive input terminal 1, its base connected to the emitter of the transistor Q1 via the diode DI, and its collector connected to the base side of the transistor Ql via the diode D2. Also 2
In this embodiment, a cutoff circuit 8 is also provided. This cutoff circuit 8 includes an NPN type transistor Q3 and a resistor R2t.
It has R3*R4. The transistor Q3 has an emitter connected to the negative input terminal 2, a base connected to the collector of the transistor Q2 via a resistor R2, and a collector connected to the base of the transistor Q2 via a resistor R3. Resistor R4 is connected between the base and emitter of transistor Q3. Furthermore, transistor Q! Nobe-I-
A diode D is connected between the ashes and the diode D2 and the resistor R8.
3 are connected in series, and a capacitor C1 is connected in parallel with a resistor R4 between the base and emitter of the transistor Q3.

In such a configuration, the drive signal input terminal 5 will be explained below.

In this case, the diode D! When the forward voltage of vF1 is tossed, the base emitter level of transistor Q2 vBE2
At the point in time when VB, = I oX R1 - VFl.

Transistor Q2 becomes active and part of the input current from positive input terminal 1 flows through the emitter, collector and diode D2 of transistor Q2, so transistor Q1 exhibits a constant current drooping function with respect to a decrease in load impedance.

At the same time, when the transistor Q2 becomes active, the transistor Q3's pin is driven from the collector of the transistor Q2 through the resistor R2, and the transistor Q3 draws the base current of the transistor Q2 through the resistor R3. As a result, transistors Q2 and Q3 continue to be completely conductive, and all current flowing through resistor Rc becomes current from the emitter and collector of transistor Q2 and diode D2, and the base current of main switch element Q1 is cut off. Therefore, the 9 transistor switch circuit is.

As shown in FIG. 4, it is shut off.

In this embodiment, the DC output terminals 3, 4
If a short circuit occurs between them, the output current IO is cut off at the point where the constant current droop starts, so that the collector loss of the transistor Q1 can be extremely small.

9 In this embodiment, the base of the transistor Q3.

A capacitor C1 is connected between the emitters.

Therefore, if the load side is capacitive or has a peak current, the transistor Q1 is operated at a constant current by the delay of the time constant determined by the resistor R2 and the capacitor C1, and only if this continues abnormally, the transistor Q
1 can be blocked.

〔Effect of the invention〕

As explained above, according to the present invention, the main switch element of the transistor switch circuit can be protected no matter what kind of DC voltage supply source is connected to the input terminal or what kind of load is connected to the output terminal. It is extremely useful industrially. especially.

When used when the DC voltage supply source is a battery.

The transistor switch circuit of the present invention can exhibit sufficient effects.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of an embodiment of a transistor switch circuit according to the present invention, FIG. 2 is a diagram showing an example of the output current-output voltage characteristics of FIG. 1, and FIG. A circuit diagram showing the configuration of another embodiment of the switch circuit, FIG. 4 is a diagram showing an example of the output current-output voltage characteristics of FIG. 3, and FIG. 5 is a diagram showing the configuration of a conventional transistor switch circuit. The circuit diagram, FIG. 6, is a diagram showing an example of the output current-output voltage characteristics of FIG. 5. 1.2... DC input terminal, 3, 4... DC output terminal, 5... Drive signal input terminal, 6... Drive circuit, 7
．． 7'... Constant current droop protection circuit, 8... Cutoff circuit. Figure 1 Figure 2 Figure V. 8E2 Broom 3 Figure 4 Figure n -2+Vpt R1 Tsuji 5 Figure 6 Figure n

Claims (1)

[Claims] 1. A PNP type provided between a power line between a DC voltage supply source and a load, with an emitter connected to the positive side of the DC voltage supply source and a collector connected to the positive side of the load side. The base of the first transistor is connected to the negative side of the DC voltage supply source and the load side through a drive circuit for controlling on/off of the first transistor. In the transistor switch circuit connected to turn on/off a DC voltage supplied to the load from the DC voltage supply source, a transistor is connected in series between the positive side of the DC voltage supply source and the emitter of the first transistor. a PNP type including a resistor inserted and connected, an emitter connected to the positive side of the DC voltage supply source, a base connected to the emitter side of the first transistor, and a collector connected to the base side of the first transistor. the second of
A transistor switch circuit comprising a transistor. 2. A PNP type first transistor is provided between a power line between a DC voltage supply source and a load, and has an emitter connected to the positive side of the DC voltage supply source and a collector connected to the positive side of the load side. The base of the first transistor is connected to the DC voltage supply source and the negative side of the load side through a drive circuit for controlling on/off of the first transistor, and the base of the first transistor is connected to the negative side of the DC voltage supply source and the load side, and In a transistor switch circuit configured to turn on and off a DC voltage supplied from a supply source to the load, a first transistor is inserted and connected in series between the positive side of the DC voltage supply source and the emitter of the first transistor. a resistor, an emitter connected to the positive side of the DC voltage supply source, a base connected to the emitter of the first transistor via a first diode, and a second diode connected to the base side of the first transistor. a second transistor of PNP type, the collector of which is connected through the transistor, the emitter of which is connected to the negative side of the DC voltage supply source, the base of which is connected to the collector of the second transistor through a second resistor; A transistor switch circuit comprising a third NPN transistor whose collector is connected to the base of the second transistor via a third resistor.