Input protection for the regulator

[Murugesh_89]

Hi,
I want to have the following circuit to be
a. Short circuit protected at the input (If Vcc - 12V and Vss - 0V are shorted)
b. If the polarities are interchanged ( Negative supply, Vss to Vin and positive supply,Vcc to Gnd) the circuit should not affected.



I give 12V DC as input from the SMPS.

What should i do?


Thanks,
Murugesh

 

[kripacharya]

Hi,
I want to have the following circuit to be
a. Short circuit protected at the input (If Vcc - 12V and Vss - 0V are shorted)

your smps probably already has a short-circuit (or over current) protection builtin.

b. If the polarities are interchanged ( Negative supply, Vss to Vin and positive supply,Vcc to Gnd) the circuit should not affected.
I give 12V DC as input from the SMPS.

Use a diode in series

 

[Jackwin]

Hi，i think you can use a IC to protect your circuit and this kind of IC is based on MOS.
If you need more, please contact with me.

Good luck!

 

[FvM]

Standard linear regulators like 7808 are already overload- and short-circuit protected. They need addition protection against input reversal, like already suggested series diode. There's also a risk to damage the regulator by discharging output capacitors backwards through an input short, but it would be also handled by the series diode.

 

[Murugesh_89]

I saw a circuit like this one.



What is the function of D1 and D2.

 

[iukhan]

I saw a circuit like this one.

View attachment 85998

What is the function of D1 and D2.

D1 is for protection against input reversal, if the input is reversed the D1 will conduct and fuse will blow, resulting in protection of regulator.
D2 is for protection against input short circut. Normaly it will not conduct but if input is shorted D2 will discharge the output capacitor. Regulators with outputs exceeding about 7V need this protection to prevent base emitter reverse breakdown.

 

[Murugesh_89]

I am giving the 12V input to this circuit. If i use a diode then after drop the input voltage to the 7808 would be 11.3 V. Is it enough for it to have an output of 8V.
Is there any low drop out 0.2V diodes? If any give me its part number.

 

[iukhan]

Yes, 11.3V is enough.

I am giving the 12V input to this circuit. If i use a diode then after drop the input voltage to the 7808 would be 11.3 V. Is it enough for it to have an output of 8V.