JPH01133565A - Power unit - Google Patents

Abstract

PURPOSE:To prevent damage positively by detaching an AC power from a power unit when overvoltage continues and the temperature of a Zener diode is elevated. CONSTITUTION:In a power unit, an AC power P is connected to power terminals T1-T2, and an input terminal 4a on one side of a rectifier bridge 4 is connected to the power terminal T1 through a switch 1 and a current limiting resistor 2. The anti-series connecting circuit of two Zener diodes 3 is connected between input terminals 4a, 4b for the bridge 4, and the series circuit of a coil 10c for a relay 10 with a normally closed contact 10b and a thermistor 9 detecting the temperature rises of the Zener diodes 3 is connected. Load 6 is connected between output terminals 4c, 4d for the rectifier bridge 4 through a smoothing capacitor 5. Consequently, when the AC power P reaches overvoltage and continues for a prolonged time, the temperatures of the Zener diodes 3 are elevated. Accordingly, the relay 10 is energized, and the normally closed contact 10b is opened and the currents of the Zener diodes 3 are interrupted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a power supply device, and more specifically, it proposes a power supply device that protects a load connected to the power supply device from overvoltage.

[Conventional technology]

FIG. 2 is a circuit diagram of a conventional power supply device.

The power terminal T2 of the power terminal T2 to which the AC power source P is connected is connected to an input terminal 4a on one side of the rectifying bridge 4 via a switch 1 and a current limiting resistor 2. Power terminal T
2 is connected to the input terminal 4b on the other side of the rectifying bridge 4. Between the input terminals 4a and 4b of the rectifier bridge 4,
An anti-series connection circuit of two Zener diodes 3.3 is connected.

The rectifier bridge 4 connects in parallel a series circuit of diodes D and D2, and a series circuit of diodes D and D4, and connects intermediate points between the diodes D, D2, and D4, respectively. Input terminals 4a and 4b, diodes D,
and D3, and the respective connection intermediate points of D2 and D4 are output terminal 4.
c, 4d. A smoothing capacitor 5 is connected between the output terminals 4c and 4d of the rectifying bridge 4, and a load 6 is also connected thereto.

In this power supply device, DC voltage is supplied to the load 6 by closing the switch 1. When the voltage of the AC power supply P connected between the power supply terminal 'rl + T2 exceeds a predetermined value, the voltage exceeding the predetermined value is cut off by the Zener diodes 3, 3, and input terminals 4a, 4b of the rectifier bridge 4. No overvoltage is applied between the output terminals 4c of the rectifier bridge 4.
, 4d is protected from overvoltage.

Further, the current limiting resistor 2 limits the current flowing through the Zener diode 3.3 to prevent damage to the Zener diode 3.3.

[Problem that the invention seeks to solve]

The above-mentioned power supply device disconnects the Zener diode 3 when the voltage of the AC power supply P connected to it becomes significantly overvoltage.
, 3 becomes large, and its power consumption also becomes extremely large. If the overcurrent continues for a long time, the Zener diode 3.3 may generate heat, resulting in an abnormal temperature rise, which may cause damage to the Zener diode 3.3. If the Zener diodes 3 and 3 are damaged in an open circuit state, there is a problem that the protection function against overvoltage is lost, and the rectifier bridge 4, smoothing capacitor 5, and load 6 are exposed to the overvoltage and may be damaged. .

In view of the above-mentioned problems, the present invention provides a power supply device that can prevent damage to a Zener diode when the voltage of an AC power supply connected to the power supply device becomes abnormally high and the temperature of the Zener diode increases. With the goal.

[Means for solving problems]

The power supply device according to the present invention connects a series circuit of a temperature sensor that detects the temperature of a Zener diode and a relay between input terminals of a rectifier bridge, and can switch on/off the voltage applied to the Zener diode and the input terminal. The circuit includes a normally closed contact operating in conjunction with the relay.

[Effect]

When an overvoltage is applied between the input terminals of the rectifier bridge, the Zener diode cuts the overvoltage.

When the temperature of the Zener diode rises due to overvoltage, a temperature sensor detects this and a normally closed contact operating in conjunction with the relay opens, cutting off the voltage applied between the Zener diode and the input terminal.

Therefore, the Zener diode will not be damaged.

〔Example〕

The present invention will be described in detail below with reference to drawings showing embodiments thereof.

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

A power terminal T1 of the power terminals T, , 'r2 to which the AC power source P is connected is connected to an input terminal 4a on one side of the rectifying bridge 4 via a switch 1 and a current limiting resistor 2. The power supply terminal T2 is connected to the input terminal 4b on the other side of the rectifier bridge 4.

An anti-series connection circuit of two Zener diodes 3, 3 is connected between the input terminals 4a, 4b.

Further, a series circuit including a relay coil 10c of a relay 10 having a normally closed contact 10b and a thermistor 9, for example, for detecting a temperature rise of the Zener diodes 3, 3 is connected between the input terminals 4a, 4b. The rectifier bridge 4 includes a series circuit of diodes D1 and D2, and diodes D and D4.
The series circuit with diodes D and D! are connected in parallel, and the diodes D and D! The connection intermediate points of D4 and D4 are connected to input terminal 4a.
, 4'b, and the connecting intermediate points of the diodes D1 and D3 and Dz and D4 are output terminals 4c and 4d, respectively.

A smoothing capacitor 5 is connected between the output terminals 4c and 4d of the rectifying bridge 4, and a load 6 is also connected thereto.

In the power supply device configured in this way, by closing the switch 1, the voltage of the AC power supply P connected between the power supply terminals T's and Tz is applied between the input terminals 4a and 4b of the rectifier bridge 4. A DC voltage that has been full-wave rectified by the rectifier bridge 4 is generated between the output terminals 4c and 4d, and this DC voltage is smoothed by the smoothing capacitor 5 and applied to the load 6, so that the load 6 is in a power supply state.

When the voltage of the AC power supply P rises above a predetermined value in such a power supply state and the voltage between the input terminals 4a and 4b of the rectifier bridge 4 exceeds the Zener voltage of the Zener diode 3.3, the overvoltage period will be Zener diodes 3, 3 become conductive and cut off the overvoltage. In this way, the voltage between the input terminals 4a and 4b of the rectifier bridge 4 is always maintained at a predetermined voltage by the Zener diode 3.
A constant DC voltage is applied to the load 6. Note that the current flowing through the Zener diode 3.3 is limited by the current limiting resistor 2.

However, if the voltage of the AC power supply P becomes significantly overvoltage and continues for a long time, as described above (a large current continues to flow through the Zener diodes 3, 3, the temperature of the Zener diodes 3.3 increases).

Then, the thermistor 9 is heated due to the temperature rise of the Zener diode 3.3, and the resistance M of the thermistor 9 is increased.

value decreases.

Therefore, current flows through the relay coil 10c of the relay 10, energizing the relay 10, and opening the normally closed contact 10b. Then, by opening the normally closed contact 10b, the AC power source P is disconnected and the current flowing through the Zener diodes 3, 3 is cut off, thereby preventing damage to the Zener diodes 3.3. In this way, when the current of the Zener diode 3.3 is cut off and the temperature of the Zener diode 3.3 decreases, the resistance value of the thermistor 9 increases.
Relay 10 is deenergized. Therefore, the normally closed contact 10b is closed again, the AC power source P is connected between the input terminals 4a and 4b, and the load 6 is returned to the power supply state. Note that if the overvoltage of the AC power source P has been resolved when the normally closed contact 10b is closed again, the temperature of the Zener diodes 3, 3 will not rise and the power supply state to the load 6 will continue. but,
If the overvoltage has not been resolved, the temperature of the Zener diode 3.3 will rise again, and the AC power supply P will rise again as described above.
will be separated.

In this way, if the Zener diode 3.3 rises in temperature, its current is cut off and the Zener diode 3.
．． 3 damage can be prevented.

Therefore, since there is no risk of damage to the Zener diodes 3, 3, the rectifier bridge 4, smoothing capacitor 5, and load 6 can be reliably protected from overvoltage.

Note that although a thermistor is used as the temperature sensor in this embodiment, a bimetal switch may also be used.

〔Effect of the invention〕

As described in detail above, according to the present invention, when the overvoltage of the AC power source continues and the temperature of the Zener diode exceeds its temperature, the AC power source is disconnected from the power supply device. Therefore, it is possible to prevent damage to the Zener diode, and to reliably prevent damage to the rectifier bridge, smoothing capacitor, and load due to overvoltage.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a power supply device according to the present invention, and FIG. 2 is a circuit diagram of a conventional power supply device. 2... Current limiting resistor 3... Zener diode 4...
・Rectifier bridge 6...Load 9...Thermistor 1
0... Relay 10b... Normally closed contact In the drawings, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] 1. A power supply device in which a Zener diode is connected between the input terminals of a rectifier bridge, an AC voltage is applied between the input terminals, and a DC voltage is obtained between the output terminals of the rectifier bridge, comprising: A series circuit consisting of a temperature sensor for detecting a temperature rise of the Zener diode and a relay is connected between the input terminals, and a circuit that can switch on and off the voltage applied to the Zener diode and the input terminal is connected to a circuit that operates in conjunction with the relay. A power supply device characterized by having a closing contact interposed therein.