The working principle of the circuit. Start step, dc voltage power from the secondary coil of the transformer will be charged to C1. through D1.When the switch S1 to the circuit, current flows through relay contact at the NC,And flowing through the load, R1 and VR1. The integrated parallel. by VR1 controls the power of the load and it is set the SCR1 to run, when the load current exceeded.
When overload occurs, SCR1 is triggered to work or inductor,The relay is running and contacts of relay are in NO position so The LED1 light . by the R2 reduces the current of LED1. The load is disconnected from the transformer. So now we have a current flowing through the coil of the relay SCR1, R1 and LED1 only.
After the relay function,If desired, the protection circuit is ready to work again, simply move S1 to the off position and move on again, or unplug it. Then reconnect. Protection circuit is ready to work the same.Do not forget, VR1 to adjust the load current is equal to the current transformers only. The D1, you will be using LED instead.Equipment to the power supply circuit with a maximum of 10 volts (no load). No filters to smooth flow, the use of a 1 amp transformer.