JPH02290127A - Power supply circuit - Google Patents

Abstract

PURPOSE:To obtain a power supply circuit with a protective function by connecting a diode making the input terminal side of an anode between an output point short-circuiting with an earth and the input terminal, and making the diode reverse-biased in the event of normal operation. CONSTITUTION:In the event of normal operation, an input of AC plug 25 is converted into DC by a DC conversion circuit 26, and a power input pin of a power IC 11, a control transistor 23, a reproducing switch 24 and an auxiliary connecting terminal of a function switch 7-1 are applied to a radio terminal to make a protective circuit diode 10 reverse-biased. In the event of such abnormal operation that an output line (a) of the control transistor 23 short-circuits with an earth, the cathode of the protective circuit diode 10 is connected to the output line (a) of the control transistor 23 to make an earth, and powers of the control transistor 23 and power amplifiers 12, 13 are turned OFF. According to the constitution, a power circuit with a protective function can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a power supply circuit with a protection function used in electronic equipment such as radio receivers and tape recorders.

Conventional technology Conventionally, in the power supply circuit of audio equipment, in order to comply with the safety standards of each country and to ensure the safety of the equipment in the event of component failure, a power supply circuit is connected in series to the output line in case the output line of the power supply circuit is short-circuited. It was equipped with a protection circuit using fuses, IC protectors, and control transistors.

Problems to be Solved by the Invention However, the fuses and I
A protection circuit using a C protector or a control transistor has disadvantages in that it is very expensive and requires a large amount of mounting space. In addition, there were many problems such as the fact that it was sometimes difficult to implement it due to the safety standards of each country.

The purpose of the present invention is to solve the problems of the conventional technology, take advantage of the fact that the power supply circuit has a standby function, and use a simple circuit configuration such as adding a diode and a voltage setting resistor to reduce the cost and the amount of electricity required. This is an attempt to realize a power supply circuit with a protection function within the mounting space.

Means for Solving Problems The power supply circuit of the present invention uses a standby circuit that turns on and off large current circuits such as power amplifiers and constant voltage output lines depending on the presence or absence of input voltage. The present invention is characterized in that a diode is connected between the output point to be detected and the input terminal for input voltage detection, with the input terminal side serving as an anode, and the voltage is set so that the diode is reverse biased during normal operation.

According to the present invention, with the above configuration, it is possible to realize a protection circuit that turns off the large current output circuit and cuts the output by lowering the input voltage of the standby circuit when the output line is short-circuited to the ground. Therefore, for safety reasons without affecting normal operation, the input terminal voltage of the standby circuit is divided by the diode VF by a resistor to lower the input voltage only when the power output line is shorted to the ground, and the input voltage is reduced to standby. Turns the circuit off and cuts the output circuit. As a result, a protection circuit that ensures the safety of equipment can be realized with an inexpensive and simple circuit configuration.

Example An embodiment of the present invention will be described based on the drawings.

The figure uses the standby circuit of the present invention, and adds a diode between the input terminal and a line that is shorted to ground for safety reasons, with the input terminal as the anode, and a diode added during normal operation. The same figure shows the electric circuit of a radio-cassette player that has a power supply circuit that operates as a protection circuit that does not affect normal operation by setting the voltage so that it is reverse biased, and cuts the output when the output line is shorted to ground. 1 and 2
3 and 4 are external connection terminals for connecting CDs, etc.; 5 is a tuner circuit for radio reception; 6 is a pre-amplifier circuit that amplifies the signal input from the recording and playback head 1.2; 7-1 to 7 -4 is a function switch that switches the signal line and power supply in conjunction with each function of tape, radio, and external lease, 8 and 9 are volume controls, 10 is a protection circuit diode, and 11 is a power IC with a built-in standby circuit. 12 and 13 are power ICII
14 is a standby circuit that detects the 4-bin input voltage of the power IC; 15 is a constant voltage circuit that operates when the comparator 14 is turned on and stabilizes the power output circuit voltage; 16 is a regulator circuit that controls the output control transistor 23 with the output stabilized by the constant voltage circuit 15, 17.18 is a left and right speaker, and 19 and 20.21 are reverse biased protection circuit diodes 10 during normal operation. When the output line of the output control transistor 23 is shorted to ground, the protection circuit diode 1
A resistor is used to further lower the Vf of 0 by resistor division (R, /R,) and set to ensure that the input voltage of the comparator 14 becomes an off voltage. 22 is a motor that operates a mechanism for recording a cassette tape. , 23 is a control transistor that turns on and off the power output under the control of the regulator circuit 16; 24 is a regeneration switch that turns on the electric circuit and motor 22 in conjunction with the regeneration operation of the mechanism;
5 is an AC power plug, and 26 is a DC conversion circuit for converting AC voltage into DC voltage.

Next, to explain the operation, in normal operation, the AC input input from the AC plug 25 is converted into AC voltage by the AC transformer, and the current is converted to DC by the DC conversion circuit 26. The voltage is applied to the bottle and control transistor 23, the regeneration switch 24, the A external lease of the function switch 7-1, and the radio terminal. In this state, when the playback button of the mechanism is next pressed and the playback switch 24 is turned on, since the function switch 7-1 is in the tape position, the resistor 19 is connected to the input terminal 4 bin of the converter l4 of the standby circuit. , resistor 20, and resistor 21. Since this voltage is above the specified value, the comparator l4 is turned on and the voltage is made constant by the constant voltage circuit 15, and the control transistor 23 is turned on by the regulator circuit 16, so that a constant voltage output is applied to the function switch 7-4. Function switch 7-1~
Since function switch 7-4 is interlocked, function switch 7-2
~7-4 is in the holding tape state, and voltage is supplied to the preamplifier circuit 6 at the same time as the signal line is switched. At the same time, the power to the power amplifiers 12 and 13 of the power ICII is also turned on.

In addition, since the playback switch 24 is turned on, voltage is supplied to the motor 22 and it rotates, so the mechanism enters the playback state, and the set receives the source recorded on the cassette tape, the playback heads 1 and 2, and the preamplifier circuit 6. street,
Power amplifier 1 of power ICI 1 via function switch 7-2.7-3 to volume volume 8.9
2.13, is amplified and then output, drives the subwoofers 17 and 18, and is reproduced as sound. At this time, since the protection circuit diode 10 is reverse biased, it does not affect this operation. Next, in the event of an abnormal operation in which the output line a of the control transistor 23 is short-circuited to ground due to safety reasons, the cathode of the protective circuit diode 10 is connected to the output line of the control transistor 23 as shown in the figure. Since it is connected, it is grounded. Therefore, the potential at the midpoint between the resistors R and R is held at IV by the protection circuit diode 10 and becomes low b. Therefore, the input voltage of the comparator 14 is IV,
is divided by resistor R and resistor R and becomes even lower, the comparator 14 is turned off, the power supply of the control transistor 23 and the power amplifier i2.13 is turned off,
Safety problems such as smoke and fire caused by excessive current can be prevented. In addition, function switches 7-1 to 7-
Even when 4 is other than tape, the power protection circuit operates in the same manner as described above, and safety can be ensured.

Effects of the Invention According to the present invention, by utilizing the fact that the power supply circuit has a standby function, the power supply output point that is shorted to earth in the event of an abnormality due to safety reasons and the input terminal for detecting the input voltage of the standby function are connected. By connecting a diode with the input terminal side as the anode and setting the voltage so that the diode is reverse biased during normal operation, it will not affect the output line during abnormal operation and will not affect the output line during normal operation. When shorted to ground, the standby function is turned off, the power output line and power amplifier are cut off, and smoke is generated due to overcurrent. Safety problems such as ignition can be prevented. A protection circuit can be realized. In this way, a power supply circuit with a protection function can be realized at low cost and with a small mounting space by using a simple circuit configuration with only a few additions of diodes and resistors, and its practical effects are extremely large.

[Brief explanation of the drawing]

The figure is a circuit diagram of a cassette tape recorder with a radio using a power supply circuit according to an embodiment of the present invention. 1, 2... Recording/playback head, 3, 4...
...External connection terminal, 5...Tuner circuit, 6.
...Preamplifier circuit, 7-1 to 7-4...
・Function switch, 8.9...Volume volume, 10...Protection circuit diode, 1
1...Power IC, 12, 13...Power amplifier, 14...Comparator, 15...
... Constant voltage circuit, 16 ... Regulator circuit, 17.18 ... Subika, 19.20.2
1...Resistor, 22...Motor, 23
...Control transistor, 24...P
I. A Y switch, 25... AC power plug, 26... DC conversion circuit.

Claims (1)

[Claims] In a power supply circuit with a standby function that turns on and off large current circuits such as power amplifiers and constant voltage output lines depending on the presence or absence of input voltage, input between the output point that is shorted to ground and the input terminal for input voltage detection. A power supply circuit characterized in that a diode is connected with the terminal side as an anode, and the voltage is set so that the diode is reverse biased during normal operation.