How to make a power input protection ?

[ahgu]

Re: power input protection

I have power input that goes into the LDO.
I want to make sure the circuit does not go bad if somebody plug in 15 volts, or negative voltage?

What do I have put in the front of the circuit to make sure of that?
I thought about zener, But I guess I need a big zener. I don't want to put a fuse. it is too big.

thanks
ahgu

Added after 43 minutes:

Normal power input is 6.5VDC. I want make sure the circuit does not get blown when user put in like 24v and negatieve voltage.

 

[trigger74]

power input protection

Ususally, I will put a diode in series to the positive supply in order to prevent a reverse polarity.

 

[IanP]

Re: power input protection

In addition to the reverse polarity diode you can use a PolySwitch for over-current protection in combination with a transient voltage suppressor (instead of a zener diode) rated for 7.5V or higher..

 

[tanuki]

Re: power input protection

You might try:

1) series self resetting fuse (Raychem Polyswitch)
2) shunted by a power zener
3) series schottky diode

Fuse (1) opens if Zener (2) voltage reached or reversed voltage. Schottky diode (3) protects LDO circuit from small reversed voltage (~ -1 volt) if negative voltage is applied.

Take a look at http://www.circuitprotection.com

 

[ahgu]

Re: power input protection

can I use a polyswitch that is rate for 60V 0.2amp?

even though my voltage is arround 7v? but I don't want the current to go over 0.2 amp? I guess I don't undertand the voltage rating, does it matter? or just don't exceed that so it does not break the polyswitch?

 

[IanP]

Re: power input protection

I don't think you need such a high voltage..
Anyhow, here you can select a polyswitch by current ratings:
http://ps.circuitprotection.com/poly/index.php#results