Simple self-locking switch circuit

Probe domestic switch needle KG-300K needle head diameter is 3.0mm normally open switch needle

Photocoupler

Ordinary transfer switch or pull switch, long-term use, its action machinery and contacts are easy to wear, at the same time, due to high current impact contacts are also very easy to ablate. A simple circuit can be introduced to replace this switch.

As shown in the figure above, when the AN is not pressed, the SCR1 is not turned on, and the relay or contactor K does not operate, which is equivalent to the "off" state. When the AN is pressed, the 12V voltage provides the trigger current to the SCR1 through R1, AN, and VD1 to turn it on. When K is energized, the contact is connected to the load. Since the voltage across the capacitor cannot be abruptly changed, the SCR2 does not conduct when the AN is pressed, and the current is charged to C through R3 and VD2. If AN is pressed again, the voltage on capacitor C is used as the trigger voltage of SCR2, so that SCR2 is turned on when AN is closed, the anode voltage of SCR1 is lowered, SCR1 is turned off, and K is released. Capacitor C discharges through the control poles and cathodes of R2 and SCR2, and the circuit returns to its original state. Thereby achieving self-locking effect.

Component selection: Relay K selects JRC-5M, its electrical parameter is DC12V, winding resistance is 850Ω, contact capacity is DC27V 1A (can also be selected according to actual load); AN selects jog button, such as LA19-11J for electrical operation Etc; other components are shown in the drawing.

During debugging, the values ​​of R2, R3, and C should be adjusted repeatedly so that when the AN is pressed, the circuit does not malfunction, and after K is released, press AN again for a while, then K can be powered immediately.

Note: Xiaodou thinks that this circuit should be connected to a small load from the cathode of SCR2 to ground, such as 12V small bulb, so that SCR2 will not be damaged when large current (12V voltage is directly applied to SCR2), R1 can also be removed. .