JPH0638359A - Power relay driving circuit - Google Patents

Abstract

PURPOSE:To suppress the temperature rise of relay coil by applying a rated voltage onto the relay coil for controlling connection of a surge current suppressing transistor at the time of starting driving and eventually lowering the applying voltage when an electrolytic capacitor in a timer is charged. CONSTITUTION:Upon turn ON of power, a control power supply 1 rises to turn a microcomputer ON through a photocoupler 6 thus turning a PNP transistor Tr15 and NPNP transistors Tr12, 14 ON. Consequently, rated relay driving voltage is applied, as it is, onto the coil 3 of a relay for connecting a surge current preventive resistor. At the same time, a capacitor 5 is charged through a resistor 8 in a timer circuit 5 and base voltage of an NPN Tr13 rises to turn the Tr13 ON while turns the NPN Tr12 OFF. Since current flows from the coil 3 through a resistor 9 and the NPN Tr14, temperature rise of the coil is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention improves the reliability of a relay by reducing the temperature rise of the coil of an inrush current suppression circuit relay used in a power circuit of an inverter, a servo driver, etc. The present invention relates to a relay drive circuit that can be adopted.

[0002]

2. Description of the Related Art An inrush current suppressing circuit 18 in a power circuit such as an inverter or a servo driver as shown by a dotted line in FIG. 2 has a suppressing resistor for suppressing the inrush current when the power is turned on. When a sufficient amount of electric charge is stored in the electrolytic capacitor 19 by suppressing the above, a steady state is entered by turning on the relay so that the suppressing resistor does not generate heat.

FIG. 3 shows a conventional relay drive circuit that operates as described above. First of all, when the power is turned on,
The power supply for driving the relay 2 rises and the electrolytic capacitor (C)
23 is charged. When the electrolytic capacitor (C) 23 is fully charged, the relay drive voltage is changed to the resistors (R1) 24, (R
2) The voltage is divided by 25 and the Zener diode (ZD) 26 and the base of the PNP transistor (QP) 22 becomes Low, so that the PNP transistor (QP) 22 is turned on and the rated voltage is applied to the relay coil (RY) 3.

[0004]

The causes of the temperature rise of the relay include heat generation in the contact resistance of the relay and heat generation of the coil inside the relay, and the total of the temperature rise in the relay and the ambient temperature is the insulation class of the coil. Exceeds the maximum allowable temperature in.

The present invention solves the above-mentioned problems. By reducing the temperature rise in the coil of the relay, the total of the temperature rise of the relay and the ambient temperature is set to the maximum allowable temperature in the insulation class of the coil or less, and the reliability of the relay is reduced. It is an object of the present invention to provide a relay drive circuit that is highly functional, small in size, and low in cost.

[0006]

In order to achieve the above object, the present invention provides a relay drive circuit for an inrush current suppressing circuit, which is operated at a rated voltage of a coil at the start of driving of the relay to accumulate electric charges in an electrolytic capacitor. The voltage applied to the coil of the relay is set between the open circuit voltage and the rated voltage during steady operation after the voltage is applied.

[0007]

According to the present invention, the temperature rise in the coil of the relay can be reduced by the above structure.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.

As shown in FIG. 1, when the control power supply (V1) 1 is turned on when the power is turned on, a microcomputer (not shown) is turned on.
The ow signal is output and the photocoupler (PC1) 6 is turned on. As a result, since the base potential of the PNP transistor (QP1) 15 is Low, the PNP transistor (QP1)
1) 15 turns on, NPN transistor (QN1) 12
And (QN3) 14 are supplied with the base current, and the NPN transistors (QN1) 12 and (QN3) 14 are turned on.
To do. At this time, the base current IB1 of the NPN transistor (QN1) 12 and the NPN transistor (QN3)
The base current IB3 of 14 is represented by (Equation 1).

[0010]

[Equation 1]

At this time, the current flowing through the relay coil 3 has an NPN transistor (QN3) because of the resistance (R3) 9.
It does not flow to 14, but flows to the ground through the NPN transistor (QN1) 12. The voltage VRY1 across the relay coil 3 is expressed by (Equation 2).

[0012]

[Equation 2]

Meanwhile, the capacitor (C) 5 is charged with electric charges through the resistor (R2) 8 and the NPN transistor (QN).
2) Voltage VQN2 (BE) between the base and emitter of 13
However, when it reaches VBE (SAT), the NPN transistor (QN2) 13 is turned on. NPN transistor (QN
2) When 13 is turned on, NPN transistor (QN1) 1
The base current of 2 flows into the NPN transistor (QN
1) Turn off 12. At the same time, the current flowing through the relay coil 3 flows through the resistor (R3) 9 and the NPN transistor (QN3) 14 to the ground. NP at this time
When the collector current of the N-transistor (QN3) 14 is IC, the voltage VRY2 across the relay coil 3 is expressed by (Equation 3).

[0014]

[Equation 3]

By the above operation, after operating the relay at the rated voltage VRY1, the operating voltage of the relay is lowered to VRY.
By setting it to 2, the temperature rise of the coil inside the relay can be reduced.

However, in the above equation, VQN1 (BE): base-emitter voltage of NPN transistor (QN1) VQN2 (BE): base-emitter voltage of NPN transistor (QN2) VQN3 (BE): NPN transistor (QN3) Base-emitter voltage of VQP1 (SAT): saturation voltage of PNP transistor (QP1) VQN3 (SAT): saturation voltage of NPN transistor (QN3) VRY1: rated voltage of relay VRY2: operating voltage of relay in steady state.

[0017]

As is apparent from the above embodiments, according to the present invention, after operating the relay at the rated voltage, the operating voltage of the relay is lowered to reduce the power consumption of the coil inside the relay. The temperature rise of the coil can be reduced. Therefore, it is possible to use a relay having a low allowable temperature rise among relays having the same rated current, and thus the relay can be downsized and the mounting area of the relay can be reduced in the power circuit of the inverter or the servo driver. .

[Brief description of drawings]

FIG. 1 is a relay drive circuit diagram of an inrush current suppressing circuit for an inverter, a servo driver, etc. according to an embodiment of the present invention.

[Fig. 2] Power circuit diagram for inverters and servo drivers

FIG. 3 is a relay drive circuit diagram of a conventional inverter or servo driver inrush current suppression circuit.

[Explanation of symbols]

 1 Control power supply (V1) 2 Relay drive power supply (V2) 3 Relay coil (RY) 4 Diode (D) 5 Capacitor (C) 6 Photocoupler (PC1) 7 Resistance (R1) 8 Resistance (R2) 9 Resistance ( R3) 10 resistance (R4) 11 resistance (R5) 12 NPN transistor (QN1) 13 NPN transistor (QN2) 14 NPN transistor (QN3) 15 PNP transistor (QP1) 16 three-phase AC power supply 17 diode bridge 18 inrush current suppression circuit 19 Electrolytic capacitor 20 Power transistor 21 Induction motor 22 PNP transistor (QP) 23 Electrolytic capacitor (C) 24 Resistance (R1) 25 Resistance (R2) 26 Zener diode (ZD)

Claims (1)

[Claims] 1. A diode bridge that rectifies an AC input voltage, a capacitor that smoothes an output of the diode bridge, a power element that controls a pulse width of an output voltage of the capacitor, and a resistor that suppresses an inrush current to the capacitor. And a resistor connected in parallel to the resistor, a voltage dividing circuit that switches the voltage applied to the coil of the relay, and a timer circuit that operates the voltage dividing circuit.