Alarm when the supply to rack with 1N4001

To use such circuits.If you have identified the polarity of the power supply or power supply connector on the wafer is not clear.The wrong polarity can cause damage and range.But when using this circuit with active circuit, it can be Protect And show a correct polarity.
Operation of the circuit is not complicated. When the supply terminals to make LED1, D1 has been bias direct. It makes LED1 light, and The piezo speaker PZ1 emit noise.The lamp LED1,it would be R1, assist current limiting and voltage.To prevent LED1, no damage.But if the supply polarity is LED1, D1 will be actuated bias. D1 is not bias the LED1 is not lit.And piezo speaker PZ1 not emit noise. The D2 works, The D2 works, because it was direct bias.Make a power supply circuit as usual.

Over voltage and low voltage protection circuit
This is an electrical circuit protection device sound disappeared, when too much voltage 220V, and protection, when pressure is too low with Using the relay cut off power when voltage problems. From the circuit when the voltage is 220 volts AC through a transformer T1. It serves to reduce t ...
Switch off delay circuit by 2N4871
This circuit prevents surges. From the opening - is switched off or power failure. The damage to electrical appliances. The circuit will switch to use a short period before Power raising circuit to go. When raising the power supply 9-volt circuit then. Circuit delay. The duration of chargin ...
Over load protection for a transformer
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. ...
Overload protection circuit
Generally the level of a signal that departs output of sound signal generator the all. The that get fix have standard same score be 1Vrms. But in now audio signal generator the all the that may produce come to exceed limitation standard of the level input of stereo power amplifier. Thus ha ...
Solar battery charger with overcharge protection
This circuit is formed maintain one's position voltage from solar cell with , shunt regulator circuit. For protect voltage not too until much destroy battery. Because of something charger too much. The D2 be for protect current flow turn back from battery during nighttime. The circuit mainta ...