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Surge current protection

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E

eepty

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As shown in the attachment in the link, a motor control circuit in which a surge current protection circuit is included.



Basically, the motor speed is controlled by changing the value of the variable resistor "R4", different value of R4 will trigger the diac and triac at different voltage level. It is also called phase control.

However, I do not understand the part for surge current protection. Suppose when there is a sudden change of high current, the relay will close so that the triac will be disconnected. Anyone know the working principle of this circuit?

Thank you very much
 

Hi,
Are you sure that the circuit is a working one? With a 56 K in series with the motor, I do not find any scope for a surge voltage developing across 3 ohms R3. Also does C1 get charged to 24 V relay voltage , being in series with a capacitor (0.22uF), about 1/100 th of its value?

Regards,
Laktronics
 

Yes, this circuit is working. It is a circuit of one of the home appliance selling in the market.
 

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