JPH0380314A - Power supply circuit - Google Patents

Abstract

PURPOSE:To protect a power supply transistor by inverting the power supply transistor to a nonconductive state by the inversion of a detecting transistor to a conductive state when the voltage drops at the collector side of the power supply transistor. CONSTITUTION:When a load 1 has an accident such as a short circuit, etc., the voltage of a power supply circuit 11 serving as the collector of a power supply transistor (TR) 2 drops. When the voltage of the circuit 11 drops down to a set level, a detecting TR 9 whose emitter is connected to the circuit 11 is forward biased and the TR 9 is inverted to a conductive state. Then the bias current is cut to the base of the TR 5 and the TR 5 is inverted to a nonconductive state. As a result, the TR 2 is inverted to a nonconductive state and therefore an excessive current never flows to the TR 2. Thus the destruction of the TR 2 can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Industrial Application Field The present invention relates to a power supply circuit used in audio equipment such as a tape recorder with a radio.

(b) Prior Art Audio equipment called a tape recorder with radio, which is a combination of a radio receiver and a tape recorder, has become widespread. Since the device is portable, batteries are used as a power source. In addition, when such a tape recorder with a radio is used indoors, it is possible to connect a converter called an AC adapter and use commercial power as a power source, but recent tape recorders with a radio Some devices have a power transformer built into the device itself. Such devices are generally equipped with a constant voltage circuit that supplies constant voltage power to loads such as amplifier circuits, but in preparation for accidents such as short circuits in the load, they are equipped with fuses that disconnect the circuit when excessive current flows. It is incorporated into the power supply circuit, and examples of such technology include
The method using such a fuse, which is disclosed in Japanese Patent No. 523, not only has the problem of a long time required to disconnect the power supply circuit, but also has the problem of being expensive. One way to solve this problem is to use a transistor to detect an increase in the current flowing to the load, and to reduce the current flowing to the load by the action of the transistor. Such a technique is described, for example, in Japanese Unexamined Patent Publication No. 139018/1983. Something has been disclosed.

<C> Problems to be Solved by the Invention The technology disclosed in the above-mentioned Japanese Patent Application Laid-open No. 139018/1983 has a resistor inserted into the power supply path for detecting an increase in current, so the load The present invention aims to provide a power supply circuit that improves this problem.

(2) Means for Solving the Problems The power supply circuit of the present invention has an emitter connected to a power source, a collector connected to a load, and a power supply circuit that supplies power to the load when the collector is connected to the load and is in a conductive state. a transistor, a transistor connected to control the operation of the power supply transistor and to cause the power supply transistor to conduct when in a conductive state; and a control transistor for controlling a base bias of the control transistor; Detection in which the collector is connected to the base circuit of the power supply transistor, the emitter is connected to the power supply path on the collector side of the power supply transistor, and the base current is supplied from the tR supply path on the emitter side of the power supply transistor. It consists of a transistor for

(*) Function The present invention is such that when the voltage on the collector side of the power supply transistor decreases, the detection transistor is inverted to the conductive state, thereby inverting the power supply transistor to the non-conducting state.

(F) Embodiment The illustrated circuit is an embodiment of the power supply circuit of the present invention. In the same figure, (1> is a load such as an amplifier circuit, (2)
is a power supply transistor whose emitter is connected to a power source and whose collector is connected to the load, and when in a conductive state, has the function of supplying power to the load (1). (3 ) is a timer switch whose opening/closing operation is controlled by the action of the timer circuit (4), and the first terminal (3a> and the second terminal connected to the power supply)
The terminal (3b) has a collector connected to its base via a resistor (6) and an emitter grounded to control the operation of the power supply transistor (2). The base is connected to the second terminal (3b) of the timer switch (3) via resistors (7> and (8). (9> is the control transistor (5)). Tsuma-791 on the base! Kayusu x
The collector is connected to the base circuit (10) of 5>, and the emitter is connected to the power supply transistor (2).
This is a detection transistor connected to the power supply path (11) on the collector side of the
> and (13) to the second terminal (3b) of the timer switch (3). (14> is connected between the common connection point (A> of the resistors (12> and (13)) and the ground, and the resistor (13> and the time constant circuit (
15>, and has the function of maintaining the base potential of the detection transistor (9) at a low level for a predetermined period of time when power supply starts upon closing of the timer switch (3>). (16> is a resistor connected in parallel to the capacitor (14), and has the function of discharging the charge of the capacitor (14). (17> is a resistor connected to the capacitor (14)). Power supply path (11
) and ground. In such a circuit configuration, the voltage of the power supply path (11) on the collector side of the power supply transistor (2) is the load (1) L5
The value of each resistor is set so that the detection transistor (9) is biased and reversed to a conductive state when 1 is turned on.
The power supply circuit of the present invention is constructed as described above, and the operation of this circuit will be explained next.

When the timer switch (3) whose operation is controlled by the timer circuit (4) is in the open state, no bias current is supplied to the base of the control transistor (5), so the control transistor (5) is in a non-conducting state. , the power supply transistor (2>) connected so that its operation is controlled by the control transistor (5>) is not biased and is in a non-conducting state;
Power is not supplied to the load (1). In this state, when the set time comes, a switching signal is output from the timer circuit (4) and the timer switch (3) is closed. ) is closed, a bias current is supplied to the bases of the control transistor (5) and the detection transistor (9) through the timer switch (3), but a resistor is connected to the base circuit of the detection transistor (9). Since a time constant circuit (15> consisting of a capacitor (13) and a capacitor (14) is provided, the detection transistor (9>) does not immediately turn on. Therefore, the control transistor (5) is connected to the timer When the switch (3> is closed, the resistors (8> and (
Since a bias current is supplied to its base through 7〉, it immediately turns into a conductive state. When the control transistor (5) is reversed to a conductive state, the power supply transistor (2) is biased and becomes conductive;
Power is supplied to the load 1) through the emitter-flefter and the power supply path (11), and the decoupling capacitor (17) is charged. After such an operation is performed, the charging operation of the capacitor (14) connected to the base circuit of the detection transistor (9) is completed, but at this time, the emitter of the detection transistor (9) becomes a high potential. Therefore, the detection transistor (9) is in a reverse-biased state and never turns into a conductive state.As mentioned above, when the timer switch (3) is closed by the action of the timer circuit (4), Since power is supplied to the load (1) by conduction of the power supply transistor (2), it is possible to perform a so-called absentee recording operation in which, for example, a broadcast signal received by a radio receiving circuit is recorded on a magnetic tape. In such a state, when a predetermined time has elapsed, the timer switch (3) is opened by the action of the timer circuit (4). When the timer switch (3) is opened, the bias to the base of the control transistor (5) is reduced. Since the current is cut off, the control transistor (5) is reversed back to the non-conductive state. When the control transistor (5) is reversed to the non-conductive state, the power supply transistor (2) is reverse biased and becomes non-conductive. Because of the inversion, the power supply operation to the load (1>) is no longer performed.In the end, the electric charge stored in the capacitor (14) is quickly discharged through the resistor (16>).

As described above, the normal power supply operation and power cutoff operation are carried out, but next time an accident such as a short circuit occurs in the load (1) at 54-t.
We will explain the operation when If an accident such as a short circuit occurs in the load (1) during the above-mentioned operating state, the voltage of the power supply line (11), which is the flipter of the power supply transistor <2>, decreases.

When the voltage of the power supply path (11) decreases to the set value, the detection transistor (9) whose emitter is connected to the power supply path (11) becomes forward biased, and the detection transistor (9) > is reversed to a conductive state. When the detection transistor (9) is reversed to a conductive state, the bias current to the base of the control transistor (5) is cut off, and the control transistor (5> is reversed to a non-conductive state. As a result, the power supply transistor (2
) is reversed to a non-conducting state, so an excessive current does not flow and damage to the power supply transistor (2) can be prevented.

In this embodiment, the case where the power supply operation is controlled by the timer circuit (4>) has been described, but it can also be implemented when the power supply operation is controlled by the opening/closing operation of a normal power switch. A resistor (
If a constant voltage element such as a Zener diode is used instead of 7), the operating point etc. can be set accurately.

(g) Effects of the Invention The power supply circuit of the present invention protects the power supply transistor by detecting a drop in the voltage on the collector side of the power supply transistor using the detection transistor. It has the advantage that the operation can be performed immediately and that the power supply voltage can be used effectively since no resistor for current detection is required.

[Brief explanation of drawings]

The illustrated circuit is one embodiment of the power supply circuit of the present invention. Explanation of main drawing numbers (1>...Load, (2>...Power supply transistor (5>...Control transistor (9>)
...detection transistor (good)...base circuit, (weird)...time constant circuit.

Claims (1)

[Claims] (1) A power supply transistor whose emitter is connected to a power source and whose collector is connected to a load, and which supplies power to the load when in a conductive state, and is connected to control the operation of the power supply transistor. a control transistor for making the power supply transistor conductive when the power supply transistor is in a conductive state; a collector is connected to the base circuit of the control transistor to control a base bias of the control transistor; a detection transistor connected to a power supply path on the collector side of the power supply transistor, and whose base current is supplied from the power supply path on the emitter side of the power supply transistor; When the voltage decreases, the control transistor is made non-conductive by reversing the detection transistor to a conductive state, thereby causing the power supply transistor to be reversed to a non-conductive state. Power supply circuit.