Over Voltage Protection | Power Supply Overvoltage| OverVoltage Protection Circuit l TL431 (ka431) l Auto Cut-Off

The Thyristor or SCR, Silicon Controlled Rectifier can be used to provide overvoltage protection in a power supply circuit. By detecting the high voltage, the circuit can fire the thyristor to place a short circuit or crowbar across the voltage rail to ensure it does not rise to high in voltage.

This overvoltage protection or crowbar protection circuit is used where we need protection against high voltage surge. The circuit has a few components, it is very easy to build and will protect your electric equipment againg overvoltages. The crowbar circuit must be mounted between power supply and the protected device.

Over voltage protection is a power supply feature which shuts down the supply, or clamps the output, when the voltage exceeds a preset level. Most power supplies use an over-voltage protection circuit to prevent damage to the electronic components.

I tried to implement over-voltage protection using a TL431 and either an N-channel or P-channel mosfet. I've been simulating the two circuits in lt spice, which I'm not very proficient at. I'm attaching the circuits. The n-channel MOSFET one is much simpler, but disrupts ground.
One simple way to protect circuits from over voltage is the use of a Shunt Regulator IC TL431 to switch off the load if the voltage increases above the preset level. TL 431 is programmable shunt regulator Zener diodes having three terminals In unregulated power supply, if the voltage in the primary of the step down transformer increases, a corresponding increase in voltage will appears in the secondary also. This may seriously affect the circuit, if it uses voltage sensitive semiconductors.TL431 is an adjustable precision Zener shut regulator and its output voltage can be set between 2.5 volts to 36 volts using a voltage divider. It can functions like a Zener diode but with precision.

It’s a low temperature coefficient Zener diode and can be programmed from reference voltage (Vref) up 2.5 to 36V when it is attached External resistors.
TL-431 can either be used as positive or as negative voltage Reference because it operates as shunt regulator. TL-431 has low Output noise voltage.

Block Diagram, Symbol, Package

Reference Circuit

fig1. When switch contact's Open


As show in fig1, At supply on and the switch is open then the voltage across the D1and ground is 11.44 or the led is on ,then the voltage across (Vref) is 2.39v and MOSFET gate voltage (Vgs) is 10.5v. we can adjust the (Vref) by vary R2. you can calculate the R1,R2 resistor value by the formula { Vout=(R1+R2/R2)Vref }. At this time the tl431 work like open.

fig 2. when switch short circuit (over voltage) 


At second condition the switch is short then the voltage arose D1-GND is 12v. and the (Vref) is above 2.3v to 2.5 then the TL431 work like short and voltage across MOSFET gate voltage (Vgs) become 2v,so the MOSFET turn-off the load(led ) shut down, then the device protect to over voltage.

2) led driver (auto cut-off)

3) variable power supply

4) mobile charger

5) battery charger



Costing for build the circuit

TL431 20rupee

Resistor 10rupee

LED 2rupee

MOSFET 10rupee

Breadboard 70rupee

Jumper wire 10rupee

Switch 2rupee

Warp Up
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