JPH02273031A - Dc power source device - Google Patents

Abstract

PURPOSE:To intercept a voltage quickly upon service interruption by a method wherein the output voltage of an output power source line, to which a capacitor is connected in parallel, is detected that it is reduced than a predetermined value upon the service interruption to discharge the capacitor through a low resistor. CONSTITUTION:A capacitor 32 is charged by DC current, obtained by rectifying an AC input by a bridge diode 31 through a transformer 2, to supply power to a load not shown in a diagram. A discharging circuit 4 and a control circuit 5 are connected between a DC output line L and an earth. In the control circuit 5, a voltage in accordance with a Zener diode 52 and resistors 53, 54 is generated upon normal time, a transistor Tr 51 is put ON, a collector potential Vc becomes zero and the thyristor 42 of the discharging circuit is being put OFF. When the AC input is interrupted, the capacitor supplies power to the load, however, the voltage of the same is reduced in accordance with the elapse of time. When the voltage is reduced to a predetermined value, the Tr 51 is put OFF, the collector potential Vc is increased, the thyristor 42 is put ON and the capacitor 32 is discharged quickly through a load resistor 41 of a low resistance. According to this method, the supply of power to the load may be intercepted quickly.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a DC power supply, and particularly to a DC power supply in which a smoothing capacitor is connected in parallel with an output power line.

[Prior Art] Conventionally, as a power source for electronic equipment, circuits have been known that connect a commercial AC power source to the primary side of a transformer, rectify and smooth the secondary output of the transformer, and supply it to each part of the equipment. ing.

A diode is used as the rectifying means and a capacitor is used as the smoothing means in the power supply circuit as described above.

A smoothing capacitor is connected in parallel with the power supply line, and in recent electronic devices using semiconductors, the capacitance of this smoothing capacitor is usually extremely large.

Therefore, in a configuration in which power supply is controlled by a power switch on the primary side of the transformer, there is a problem that the voltage of the power supply line does not drop until all the charges in the smoothing capacitor are discharged. For this reason, the device continues to operate even though the power switch is shut off, and to prevent this, a configuration is known in which a load resistor is connected in parallel with the smoothing capacitor.

[Problem to be solved by the invention] The smaller the resistance value of the load resistor, the faster the discharge time of the smoothing capacitor, making it possible to quickly shut off the power supply. The problem was that the capacity of the power supply had to be increased by the load resistance, resulting in poor efficiency.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide a power supply device that can quickly shut off the power supply, reduce the capacity of the power supply, or reduce the power consumption of the device.

[Means for Solving the Problems] In order to solve the above problems, the present invention provides means for detecting the voltage of the output power line in a DC power supply device in which a smoothing capacitor is connected in parallel with the output power line; The configuration includes a control means that connects a load circuit in parallel with the smoothing capacitor to discharge the electric charge of the smoothing capacitor when the detection means detects that the voltage of the output power line has decreased below a predetermined value. did.

[Function] According to the above configuration, when the power of the device is cut off and the voltage of the output power line falls below a predetermined value, the load circuit can be connected to the smoothing capacitor and the electric charge can be promptly discharged.

[Example] Hereinafter, the present invention will be described in detail based on the example shown in the drawings.

FIG. 1 shows the structure of a power supply device for electronic equipment employing the present invention. In FIG. 1, reference numeral 2 denotes a transformer, and a commercial AC power or the like is supplied to the negative side of the transformer through a power switch 1.

A bridge diode 31 is connected to the secondary side of the transformer 2 as a rectifier. One side output of the bridge diode 31 is grounded, and the + side output is connected to the power supply line. A smoothing capacitor 32 is connected between the power supply line and ground. This capacitor 32 is composed of a large capacity electrolytic capacitor or the like. These bridge diodes 31 and capacitors 32 constitute a rectifying and smoothing circuit 3.

Further, a discharge circuit 4 is connected in parallel with the capacitor 32. The discharge circuit 4 includes a load resistor 41 made of low resistance, a thyristor 42 that controls whether or not the load resistor 41 is connected between the power supply line and the ground, and a capacitor 43 connected between the gate of the thyristor 42 and the ground. has been done.

The capacitor 43 is for guaranteeing the corephthal emitter voltage of the transistor 51 for a certain period when the power is cut off, which will be described later.

The operation of the discharge circuit 4 is controlled by a control circuit 5.

The control circuit 5 includes a transistor 51. zener diode 5
2. Consists of resistors 53 to 55. That is, the emitter of the transistor 51 is grounded, and its collector is pulled up via a resistor 55 and connected to the gate of the thyristor 42.

The base of the transistor 51 is connected to the connection point of the resistors 53 and 54. The other end of the resistor 54 is grounded, and the resistor 53
A Zener diode 52 is connected to the other end and the power supply line. The cathode of the Zener diode 52 is connected to the power supply line.

Next, in the above configuration, when the power switch 1 is turned on and AC power is supplied to the transformer, the AC transformed by the transformer 2 is input to the bridge diode 31 and rectified. A rectified output is applied across the capacitor 32;
It is smoothed and supplied to a load (not shown).

At this time, the voltage across the capacitor 32 is applied to the series circuit of the Zener diode 52 and the resistor 53.54, and the ratio of the Zener voltage of the Zener diode 52 and the resistance value of the resistor 53.54 is applied to the connection point of the resistor 53.54. A voltage corresponding to the voltage is generated, and the transistor 51 is turned on. As a result, the collector potential of the transistor 51 becomes 0, so the Zener diode 52 enters the cut-off state, and the discharge circuit 4
No current flows through the load resistor 41.

When the power switch 1 is turned off from the above-mentioned power-on state, the voltage across the capacitor 32 begins to gradually decrease due to power being supplied to a load (not shown). This results in a resistance of 53.54
The voltage at the voltage dividing point also decreases, and when the base voltage of transistor 510 falls below a predetermined value, transistor 51 is cut off and its collector potential becomes equal to the power supply voltage. The power supply voltage supplied via this resistor 55 is supplied from a power supply line to which the capacitor 32 is connected via a path not shown.

When the transistor 51 is turned off, the thyristor 42 is triggered by its collector potential, and the load resistor 41 of the discharge circuit 4 is connected in parallel with the capacitor 32. As described above, since the load resistor 41 has a low resistance, the charge in the capacitor 32 is quickly discharged through the load resistor 41, and the operation of the component circuit of the electronic device, which is a load (not shown), is immediately inhibited.

According to the above configuration, since the load resistor 41 is not connected to the power output under the control of the control circuit 5 while the device is in operation,
The current capacity of the power supply circuit, for example, the transformer 2, only needs to be suitable for the value required for the load (not shown), and there is no need to leave room for the capacity of the power supply part more than necessary, making the configuration of the power supply part simple and inexpensive. It can also be made small and lightweight.

Further, when the power is cut off, the load resistor 41 of the discharge circuit 4 is connected to the power output by the control circuit 5, so that the charge in the smoothing capacitor can be promptly discharged and the power supply to the equipment can be cut off. Since the load resistor 41 is not connected when the device is in operation, it is possible to reduce the resistance value as much as possible and shut off the power more quickly.

In the above, it is determined only by the control circuit 5 whether or not to connect the discharge circuit 4, but as shown in FIG.
By connecting a second control circuit 6 consisting of a resistor 61 to the base of the transistor 63, it is possible to prevent the discharge circuit 4 from being connected to the power supply circuit at a timing other than that required. The transistor 63 of the second control circuit 6 may be controlled to be always conductive during an operation period in which it would be undesirable for the power to be cut off, by software of a control section constituted by a microprocessor or the like of the device.

[Effects of the Invention] As is clear from the above, according to the present invention, in a DC power supply device in which a smoothing capacitor is connected in parallel with an output power line, there is provided means for detecting the voltage of the output power line, and Since the configuration includes a control means that connects a load circuit in parallel with the smoothing capacitor to discharge the charge of the smoothing capacitor when it is detected that the voltage of the power supply line has decreased below a predetermined value, When the power of the device is cut off and the voltage of the output power line drops below a predetermined value, the load circuit can be connected to the smoothing capacitor and its charge can be quickly discharged. In that case, the load circuit is not connected when the device is operating, so the current capacity of the power supply section is reduced and the power supply section or the entire device is connected to i'JI.
L It can be configured to be inexpensive, small and lightweight.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the structure of a DC power supply device employing the present invention, and FIG. 2 is a circuit diagram showing a modification of the device shown in FIG. 1. 1... Power switch 2... Transformer 3... Rectifier smoothing circuit 4... Discharge circuit 5... Control circuit
6... Control circuit 31... Bridge diode 32... Capacitor 41... Load resistor 42...
・Thyristor 43...Capacitor 51...Transistor 52...Zener diode 53-55.61.62...Resistance

Claims (1)

[Claims] 1) In a DC power supply device in which a smoothing capacitor is connected in parallel with the output power line, there is provided means for detecting the voltage of the output power line, and the voltage of the output power line decreases below a predetermined value by the detection means. 1. A DC power supply device comprising: a control means for connecting a load circuit in parallel with the smoothing capacitor to discharge the charge of the smoothing capacitor when it is detected that the smoothing capacitor has been charged. 2) The DC power supply device according to claim 1, further comprising a control means for prohibiting connection of the load circuit as necessary.