Low voltage relay pull-in measures working principle circuit diagram

Photocoupler

It is often impossible to operate normally because the power supply voltage is lower than the pull-in voltage of the relay. In fact, once the relay is engaged, it can work reliably at about half of the rated voltage. Therefore, it is possible to start the relay with a starting voltage to pull it in and then let it operate at a lower supply voltage, as shown in the circuit shown.

The working principle of the low voltage relay pull-in measures: as shown in the circuit diagram of the relay application above. V1 is a single junction transistor BT33C, which forms a relaxation oscillator with R1, R2, R3 and C1. The SCR is a unidirectional thyristor. After pressing the start button AN1, the circuit is energized. Because the SCR has no trigger voltage, it is not guided. Pass, relay J does not operate, the power supply quickly charges capacitor C2 through R4 and VD1 to near the power supply voltage (Vcc-VD1 voltage drop). At the same time, the power supply charges capacitor C1 via R1. After a few seconds, the voltage on C1 is charged to the trigger voltage of V1, C1 immediately discharges through V1, and a positive pulse is formed on R3. The pulse is applied to the base of V2, so that V2 is rapidly saturated and turned on, and the V2 collector is also the capacitor C2. The positive pole is close to ground. Since C2 is charged with a positive polarity voltage that is positive and negative, the C2 negative electrode, that is, the J coil has a negative potential at one end. The positive pulse on R3 passes through VD2 and C3 to trigger the thyristor conduction, and the SCR cathode, that is, the other end of the J coil, approaches the power supply voltage. At this time, the J coil actually receives about twice the power supply voltage, so J1-1 is closed, and after releasing AN1, J1-1 is self-protected. J1-2 cuts off the power supply of V1 and V2, and the relay works close to the power supply voltage. In the upper relay application circuit diagram, AN2 is the stop button, press AN2, J is de-energized, J1-1 is disconnected, and the entire control circuit is de-energized.

When making the circuit diagram of the working principle of the low voltage relay pull-in measure, the rated voltage of the relay can be generally about 1.5 times of the power supply voltage. Under normal circumstances, any type of unidirectional thyristor (or two-way thyristor) can satisfy this. The circuit needs. The withstand voltage of V2, C1, and C3 is selected depending on the power supply voltage. The C2 withstand voltage is preferably not less than twice the supply voltage.