JP2002041151A - Power unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power unit capable of improving production efficiency by a simple constitution, making it unnecessary to exchange components for protecting electric elements at the time of testing the safety specification of an electric product. SOLUTION: A switch circuit 3 equipped with plural terminals 3a-3d for outputting different voltages through switch elements Q1-Q4 is connected to the output side of a voltage supplying part 2, and an electric element C2 which is set so as to be non-conductive in a normal state is connected between the output terminal 3d side whose potential level is the same as the level of an ON command signal from a control means for ON/OFF controlling the switch circuit 3 and a ground side in this power source unit 1. In this case, a forward conductive element D2 is interposed between wiring A installed from the control means to the switch circuit 3 and wiring B installed from the output terminal 3d, to which the electric element C2 is connected, to a load side so that the ON command signal of the control means can be guided to the ground side according to a potential difference generated between the both wiring A and B when the electric element C2 is set so as to be conductive.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device incorporated in an electric device such as a TV or a VTR, and more particularly, to a problem that an electric element constituting a circuit can be prevented from being heated or burned out during a safety standard test. Power supply.

[0002]

2. Description of the Related Art A power supply unit for suppressing the problem of destruction and heat generation of an electric circuit element when a load of a home appliance is short-circuited and causing a fire or an electric shock and for the safe use of the appliance. Has been proposed (see JP-A-5-49240). In this device, a current flowing to a load is monitored by an output current detection circuit, and when the load is short-circuited or an abnormality occurs and the output current increases, the second switch control circuit activates the second switch circuit. , The operation of the first reference voltage generating circuit is stopped, and power is not supplied to the capacitor and the load. Therefore, this power supply device can suppress an increase in power consumption and prevent an electric element from generating heat, but has a circuit configuration that does not use a transformer, and the electronic circuit is not insulated from a commercial power supply. Limited to those. For this reason, a power supply device having a transformer is not a target. Therefore, for example, when the load side is short-circuited by a VTR power supply device as shown in FIG. 2, a problem in which elements of an electric circuit generate heat cannot be prevented.

[0003] That is, in a power supply device 10 shown in FIG. 2, a commercial AC voltage is supplied to a primary coil of a transformer 2.
Voltages having different levels are output from the respective output sides of the first to third coils 2a to 2c to the load side.
The first to third coils 2a to 2c include a transistor Q
An output terminal 3a via a switch circuit 3 comprising 1 to Q4.
To 3d are connected, and voltages such as 44V, 12V, 9V and 5V are supplied to the loads connected to these terminals. The input port of the microcomputer is connected to the third coil 2c via the connection terminal 4a.
An output voltage of 5 V is supplied. On the other hand, the connection terminal 4b has
The output port of the microcomputer is connected, and a 5 V ON command signal is sent from the microcomputer to the transistor Q2. A fourth output terminal 3d is connected to the emitter of the fourth transistor Q4 via a fuse F for preventing heat generation, and a noise reducing capacitor C2 having one end connected to the ground side.

The microcomputer turns on and off the switch circuit 3 based on an operation signal from a key operation unit. When a power-on signal is input to the microcomputer, the microcomputer outputs an on-command signal from an output port 4b and outputs a switch command signal. First
This is applied to the transistor Q2. As a result, the transistors Q1, Q3, Q4 are turned on, and a required voltage is supplied to each load via the output terminals 3a to 3d. Thereafter, when the user performs an arbitrary key operation with the key operation unit, an operation according to the input content is started.

[0005]

However, a VTR incorporating this type of power supply has a problem in that, when used, a short circuit on the load side causes the electric element to heat up, causing burnout and the like. The safety standard test must be performed by short-circuiting both ends. If both ends of the capacitor C2 are short-circuited in this test, an output voltage of 5V of the third coil 2c is applied between the collector and the emitter of the transistor Q4, so that the transistor Q4 generates abnormal heat and eventually burns out. For this reason, in the power supply device, the fuse F is connected to the transistor Q4 side as described above, or a conventionally known IC protector is connected in place of the fuse F so that the transistor Q4 is blown before the transistor Q4 is burned out. I was However, when the fuse F or the IC protector is blown out every time such a safety standard test is performed, it must be replaced with a new one at all times, so that there is a problem that it is troublesome and production efficiency is reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has a simple structure, which eliminates the need to replace protective components for electric elements during a safety standard test of electric products, thereby improving the production efficiency. It is intended to provide a device.

[0007]

In order to achieve the above object, according to the first aspect of the present invention, there is provided a power supply unit comprising a plurality of terminals comprising switch elements for outputting voltages having different levels. A switch circuit with
A load is connected to each output terminal of the switch circuit, and a potential between the output terminal side of the switch circuit and the ground which is the same potential as the level of the ON command signal from the control means for controlling ON / OFF of the switch circuit. In a power supply device in which a normally non-conductive electric element is connected, and the switch element is turned on by an on command signal of the control means to supply a voltage to each load side from the switch circuit, Wiring from the means to the switch circuit side;
The order in which the ON command signal of the control means is guided to the ground side by a potential difference generated between the wiring and the output terminal connected to the electric element and a wiring to the load side when the electric element is conducted. It is characterized in that a direction conducting element is interposed. Further, according to a second aspect of the present invention, when the switch element is a transistor, the forward conducting element is a diode, and the electric element is a capacitor, and when both ends of the capacitor are short-circuited, an ON command from the control means is issued. A signal is guided to the ground via the diode, and the transistor is turned off.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an electric circuit diagram of a power supply device according to the present invention. This power supply 1
It is built into a popular VTR, and its basic configuration is substantially the same as the conventional example shown in FIG. In FIG. 1, reference numeral 2 denotes a transformer, and a commercial AC voltage is supplied to a primary coil. The secondary coil of the transformer 2 includes first, second, and third coils 2a to 2c, and can output voltages having different levels from each output side.

The output side of the first coil 2a outputs 44V, the output side of the second coil 2b outputs 12V, and the output side of the third coil 2c outputs 5V, respectively, and is connected to a switch circuit 3 comprising transistors Q1 to Q4. A voltage is supplied to each load via output terminals 3a to 3d. The output side of the first coil 2a is connected to the emitter of the first transistor Q1. The collector of the first transistor Q1 has
The first output terminal 3a is connected, and a voltage drop circuit is connected. The collector of the second transistor Q2 is connected to the base of the first transistor Q1. The emitter of the second transistor Q2 is connected to the ground, and the base is connected to the connection terminal 4b.
The voltage dropping circuit reduces the output voltage of the second coil 2b and outputs the reduced voltage. The voltage dropping circuit includes a resistor R1, a zener diode D1 and a capacitor C1, and a connection point of these is connected to the base of a third transistor Q3. ing.

A second output terminal 3b is connected to the output side of the second coil 2b, and a third transistor Q
3 collectors are connected. A third output terminal 3c is connected to the emitter of the third transistor Q3, and the base of the fourth transistor Q4 is connected via a resistor R2. A connection terminal 4a is connected to the output side of the third coil 2c, and a collector of the fourth transistor Q4 is connected. A fourth output terminal 3d is connected to the emitter of the fourth transistor Q4, and a noise reducing capacitor C2 having one end connected to the ground is connected. The connection terminal 4b is connected between the wiring B from the fourth transistor Q4 to which the capacitor C2 is connected to the fourth output terminal 3d side and the wiring A from the connection terminal 4b to the second transistor Q2 side. The diode D2 is connected with the anode and the fourth output terminal 3d side as the cathode.

Although not shown, the first output terminal 3a has a VTR tuner, the second output terminal 3b has a motor, the third output terminal 3c has a hi-fi IC, and the fourth output terminal 3d has Y / Y. C / A separation circuits are respectively connected. The input terminal of the microcomputer is connected to the connection terminal 4a, and the output port of the microcomputer is connected to the connection terminal 4b. This microcomputer is a control unit that controls the operation of the entire VTR, and receives the output of a key operation unit. Then, when the user inserts the plug of the power cord connected to the power supply device 1 into an outlet, the transformer 2
Is output from the third coil 2c side, and the connection terminal 4a
Is sent out to the input port side of the microcomputer via. Thereafter, when the key operation section is operated by the user to input a power-on signal to the microcomputer, an ON command signal having a voltage of 5 V is supplied to the second transistor Q2 of the switch circuit 3 from the output port of the microcomputer.

As a result, the first and second transistors Q1
, Q2 are turned on, and the output voltage 44 of the first coil 2a is turned on.
V is supplied to the tuner through the first output terminal 3a. When the output voltage of 44 V is led to the voltage drop circuit side, the voltage is reduced by the operation of this circuit and sent to the third transistor Q3. Then, the third transistor Q3 is turned on, the output voltage 12V of the second coil 2b is reduced to 9V, and the high voltage I3 is output through the third output terminal 3c.
It is supplied to the C side. The output voltage 1 of the second coil 2b
2V is supplied to the motor side via the second output terminal 3b. Further, the output voltage of 9 V is supplied to the fourth terminal via the resistor R2.
When guided to the transistor Q4 side, the fourth transistor Q4 is turned on, and the output voltage 5V of the third coil 2c is supplied to the Y / C / A separation circuit side via the fourth output terminal 3d. At this time, 5V is also applied to the capacitor C2 side, but the ON command signal output from the connection terminal 4b is also 5V.
Since the potential is the same as V, no current flows through the diode D2. Therefore, no trouble occurs after the switch circuit 3 is turned on, and when the user performs an arbitrary key operation on the key operation unit, an operation according to the input content is started.

By the way, in order to prevent a problem that the load side is short-circuited during use and the electric element is heated to cause burnout or the like, a predetermined safety standard test is performed before shipment of the electric product incorporating the power supply device 1. There is a need. In this safety standard test, both ends of the capacitor C2 are short-circuited in the power supply device 1 using the transistors Q1 to Q4 for the switch circuit 3. Now, when both ends of the capacitor C2 are short-circuited, the cathode side of the diode D2 has the same potential as the ground side, that is, 0 V. Therefore, the connection between the wiring B to the fourth output terminal 3d and the wiring A from the connection terminal 4b side. Causes a potential difference of 5V. For this reason, the ON command signal from the microcomputer is guided to the diode D2, which is connected in the forward direction between the wirings A and B, and flows to the ground. Therefore, the transistors Q1 to Q4 of the switch circuit 3 immediately turn off. Therefore, the third coil 2c is connected to the fourth transistor Q4.
Since the output voltage of 5 V is not applied, the problem that the fourth transistor Q4 abnormally generates heat and burns out during the safety standard test is avoided. When this safety standard test is completed,
Since the short circuit of the capacitor C2 is released, the VTR can be used without any trouble.

[0014]

As described above, according to the first aspect of the present invention, the wiring from the control means to the switch circuit and the wiring from the output terminal to which the electric element is connected to the load are connected. A forward conducting element is interposed between them, and when the electric element is turned on, the ON command signal of the control means is guided to the ground side by the potential difference between both wirings, and the switch circuit is turned off to apply a voltage to the switch element. As a result, the switching element and the like do not generate abnormal heat during the safety standard test as in the prior art, and there is no need to replace the protection component every time this test is performed, so that there is an effect that the production efficiency of electrical products can be increased. . Further, the invention according to claim 2 has an advantage that the electric element can be protected with a simple configuration because the transistor is used for the switch element, the diode is used for the forward conduction element, and the capacitor is used for the electric element.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram of a power supply device according to an embodiment of the present invention.

FIG. 2 is an electric circuit diagram of a power supply device according to a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power supply device 2 Voltage supply part (transformer) 3 Switching circuit 3a-3d Output terminal A wiring B wiring C2 Electric element (capacitor) D2 Forward conduction element (diode) Q1-Q4 Switch element

Claims (2)

[Claims] An output side of a voltage supply unit is connected to a switch circuit having a plurality of terminals which are composed of switch elements and output voltages of different levels, and a load is connected to each output terminal of the switch circuit. A normally non-conductive electrical element is connected between the output terminal side of the switch circuit and the ground side, which are at the same potential as the level of the ON command signal from the control means for controlling ON / OFF of the switch circuit, In a power supply device in which the switch element is turned on by an on command signal of the control means and a voltage is supplied from the switch circuit to each load side, a wiring from the control means to the switch circuit side, and the electric element Between the connected output terminal and the wiring to the load side, an ON command signal of the control means is generated by a potential difference generated between the two wirings when the electric element is conducted. Power supply being characterized in that interposed a forward conduction element is guided to serial ground side. 2. The switch element is a transistor, the forward conducting element is a diode, and the electric element is a capacitor. When both ends of the capacitor are short-circuited, an ON command signal from the control means is transmitted through the diode. The power supply device according to claim 1, wherein the transistor is turned off to turn off the transistor.