JPH07210112A - Residual charge discharging circuit - Google Patents

Abstract

PURPOSE:To prevent a plasma display panel (PDP) easy to be destroyed with a rush current from being destroyed even when a connector for supplying power source for the PDP are inserted/ejected by rapidly discharging a charge on a smoothing capacitor in a power source when the power source is turned off. CONSTITUTION:Since the smoothing capacitor 5 is large capacity, a voltage (High-B) at a B point is delayed in voltage drop by residual charge on the capacitor 5, and an emitter voltage of a transistor 6 is also delayed in voltage drop. On the contrary, the voltage (Low-B) at a A point is lowered rapidly when the power source is turned off, and the base voltage of the transistor 6 connected through a resistor 7 is also lowered rapidly, and the transistor is biassed in the forward direction to be turned on. Thus, the collector voltage of the transistor 6 becomes the value nearly dividing the B point voltage with the resistors 9 and 12, and since a gate voltage of a thyristor 14 connected to the collector is made the voltage being turned on the thyristor 14, the residual charge on the capacitor 5 is discharged rapidly through the thyristor 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a residual charge discharging circuit, and more particularly to a residual charge discharging circuit for discharging residual charge of a smoothing capacitor of a power source in a short time when the power source of a device using a PDP (plasma display panel) is turned off.

[0002]

2. Description of the Related Art A PDP emits light by discharging a cell.
A pulsed current for this discharge flows into the PDP, and as the current, for example, a current of up to several amperes flows in about 5 microseconds. For this reason, a large-capacity smoothing capacitor is used for the power supply circuit of the PDP so that a large current can be supplied in a short time. By the way, PDP
In some cases, a power supply circuit and a PDP circuit are connected to each other by a connecting line using a detachable connector in order to be separated from the main body of the apparatus due to the necessity of the configuration of the apparatus. When removing the PDP, the power switch is turned off and then the connector is pulled out. However, the PDP is easily destroyed by the inrush current. Moreover, as described above, a large-capacity smoothing capacitor is used in the power circuit. Therefore, if the operation from turning off the power to removing the connector is performed in a short time, the connector will be removed before the charge accumulated in the smoothing capacitor is completely discharged. In this case, if the contact / disconnection between the contacts of the connector / socket is repeated, or if it is reconnected immediately after the removal, the residual charge of the smoothing capacitor is
However, there is a problem that the PDP is destroyed and the PDP is destroyed.

[0003]

SUMMARY OF THE INVENTION In view of the above problems, the present invention quickly discharges the residual charge of the smoothing capacitor of the power source when the power source is turned off, and the connector of the power supply wiring after the power source is turned off. An object of the present invention is to provide a device that prevents current from entering the PDP even when the PDP is inserted or removed to prevent the PDP from being destroyed.

[0004]

In order to solve the above-mentioned problems, the present invention solves the above-mentioned problems by providing a first power source for supplying a DC power source smoothed by a capacitor and a load which is supplied with power from a connection line detachable from the first power source. A circuit comprising a base electrode connected via a first resistor to a second power supply whose DC voltage is lower than the voltage of the first power supply and whose voltage rapidly drops when the power is off. A PNP transistor having an emitter electrode connected to a connection point of a second resistor and a third resistor connected in series between a power supply and ground, and a collector electrode grounded via a fourth resistor; and an anode connected to the first power supply. A thyristor in which an electrode is connected, a cathode electrode is grounded, and a gate electrode is connected to a collector electrode of the PNP type transistor. When the power is turned on, the thyristor includes a second resistor and a third resistor. The voltage of the serial PNP transistor nonconductive and provides a residual charge discharging circuit which is to configured to be applied to the emitter electrode.

[0005]

With the above construction, in the residual charge discharging circuit according to the present invention, the base of the PNP transistor is connected to the power supply whose voltage drops rapidly when the power is turned off, but the emitter is connected. The voltage of the PDP power supply is slow to drop. Therefore, when the power is turned off, the base voltage of the transistor drops, the base-emitter is forward biased, the transistor is turned on, and the collector voltage rises. As a result, the voltage of the gate of the thyristor connected to the collector rises, the thyristor becomes conductive, the anode-cathode is turned on, and the residual charge of the PDP power supply connected to the anode is discharged through the thyristor. To do.

[0006]

Embodiments of the residual charge discharging circuit according to the present invention will be described below in detail with reference to the drawings. FIG. 1 is a circuit connection diagram of essential parts of an embodiment of a residual charge discharging circuit according to the present invention. In the figure, 1 is a transformer, for example, a transformer of a switching power supply. Reference numeral 2 is a diode, which rectifies the output of the winding for Low-B of the transformer 1 and outputs Low-B voltage (A
Point, for example 5 volts). Reference numeral 3 denotes a smoothing capacitor, which has a small capacity and whose electric charge is rapidly discharged when the power is turned off. 4 is a diode, High- of the transformer 1
High-B voltage (B point, for example, 20
Output 0 volt). A smoothing capacitor 5 has a large capacity and is used in order to supply a sufficient current to a load circuit such as a PDP in which a large current flows in a short time.

Reference numeral 6 is a PNP type transistor, which applies a Low-B (point A) voltage to the base through a resistor 7 (resistor 8 >> resistor 7 is set, and a voltage of approximately point A is applied to the base). High-B by the resistor 9 and the resistor 10 in which the emitter is connected in series between High-B (point B) and the ground.
It is connected to the voltage divider of the B voltage and the collector is grounded via diode 11 and resistor 12. 13 is a capacitor. 14 is a thyristor, the anode of which is connected to High-B,
The cathode is grounded via a resistor 15, and the gate is connected to the connection point of the diode 11 and the resistor 12.

When the power supply is turned on, the base voltage of the transistor 6 is approximately a Low-B voltage. Transistor 6
A voltage obtained by dividing the High-B voltage by the resistors 9 and 10 is applied to the emitter of the resistor 9. The resistor 9 is set so that the emitter voltage becomes a voltage at which the transistor 6 does not turn on.
And the value of the resistor 10 are set, and when the Low-B voltage drops to turn on the transistor 6, the diode 11 and the resistor 10
The values of the resistor 9 on the emitter side and the resistor 12 on the collector side are set so that the voltage at the connection point of 12 becomes the gate voltage for turning on the thyristor 13. The diode 11 and the capacitor 13 generate a voltage across the resistor 12 when the transistor 6 is turned on (gate voltage of the thyristor 14).
However, it is held for a while even after the transistor 6 is turned off. The resistor 15 is set so that the current value of the thyristor 14 is within the allowable current value.

With the above circuit settings, since the capacitor 5 has a large capacity, the voltage (High-B) at the point B of the power source of the PDP has a slow voltage drop rate when the power is off, as in the example shown in FIG. , The emitter voltage of the transistor 6 also drops gently. However, the voltage at point A (Low-B) drops rapidly when the power is turned off, the base voltage of the transistor 6 also drops rapidly, and forward bias is applied between the emitter and the base. As a result, the transistor 6 is turned on, and the collector voltage becomes substantially the voltage obtained by dividing the B point voltage by the ratio of the resistor 9 and the resistor 12. As a result, the thyristor 14 is turned on, and the electric charge remaining in the capacitor 5 is discharged through the thyristor 14 and the resistor 15. In this discharge, the voltage at the point B drops, the emitter voltage of the transistor 6 becomes the required voltage, that is, the Low-B voltage + α (value obtained by adding the bias voltage to the base voltage of the transistor 6) or less, and the charge of the capacitor 13 is reduced. Will be discharged until thyristor 14 can no longer be turned on.

[0010]

As described above, according to the residual voltage discharging circuit of the present invention, when the power supply is turned off, the residual charge of the smoothing capacitor of the power supply of the PDP is rapidly discharged through the thyristor. Even if the connector of the power supply wiring is inserted or removed, there is no inrush of current that destroys the PDP.
Since the connector for connecting the PDP and the power source can be easily attached and detached, work efficiency is improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a main part of an embodiment of a residual voltage discharge circuit according to the present invention.

FIG. 2 is a diagram showing a voltage change when the power is turned off for explaining the operation of the residual voltage discharge circuit according to the present invention.

[Explanation of symbols]

 1 Transformer 2 Diode 3 Smoothing Capacitor 4 Diode 5 Smoothing Capacitor 6 PNP Transistor 7 Resistor 9 Resistor 10 Resistor 11 Diode 12 Resistor 13 Capacitor 14 Thyristor

Claims (2)

[Claims] 1. A first power source for supplying a DC power source smoothed by a capacitor, and a load circuit for receiving power from a connection line detachable from the first power source, the voltage of which is higher than the voltage of the first power source. A base electrode is connected via a first resistor to a second power source whose voltage drops rapidly when the power source is turned off at a low DC voltage, and a second resistor and a third resistor connected in series between the first power source and ground. A PNP type transistor in which an emitter electrode is connected to a connection point of a resistor and a collector electrode is grounded through a fourth resistor, and an anode electrode is connected to the first power source and a cathode electrode is grounded, and the PNP type transistor is connected. And a thyristor having a gate electrode connected to the collector electrode thereof, the second resistor and the third resistor are used to generate a voltage for turning off the PNP transistor when the power is turned on. A residual charge discharge circuit configured to be applied to the electrode. 2. A diode in which an anode electrode side is connected to a collector electrode is inserted between a collector electrode and a fourth resistor of the PNP transistor, and a capacitor is connected in parallel to the fourth resistor. 1. The residual charge discharging circuit described in 1.