Small Voltage Surge Protection

[compuguru]

I'm working on project that will turn some LEDs on and off. The status of the LEDs will be controlled by a rather expensive piece of equipment essentially opening and closing the circuit. What I would like to do is put something inline before the wires get to the equipment to protect it from overvoltage or something that could damage the equipment if something goes wrong with the system.

The equipment has a max current of 50 mA and a max voltage of 3.5V. Any idea of what I could put to protect the equipment?

 

[Photon]

Relay? Optoisolator?

 

[gatchel]

Couldn't have said it better myself. Very inexpensive to do.

 

[compuguru]

Thanks for the suggestions. I found a diagram of how the hookup is going to work. I don't know if relays would work with this?

 

[Digger]

Thanks for the suggestions. I found a diagram of how the hookup is going to work. I don't know if relays would work with this?

Could you put an MOV across the line? Something rated 16 V etc.

 

[mustangcoupe]

Could you put an MOV across the line? Something rated 16 V etc.

I'd also add a small fast acting fuse in series with the LED on the 3.5 V side so if the MOV opens it will draw current though the MOV and blow the fuse.

 

[compuguru]

Thanks for the suggestions. Any idea where I can get those? I checked the website I get most of my electronic parts from (AllElectronics.com) but couldn't find the right parts.

I also heard that a Zener Diode (http://www.reuk.co.uk/What-is-a-Zener-Diode.htm) may do the almost the same thing. Any opinions?

 

[Spanky]

Three suggestions:

1. Two diodes, 1N4001 upto a 1N4004. Banded side of one diode to the 3.5 VDC. Unbanded side to the transistor collector. Diode 2: Banded side to transistor collector, unbanded side to negative. This dumps the positve or negative transients to the power supply, protecting the transistor.

2. TVS, transient voltage protector, like a Transorb. 5 VDC rating. Banded side to transistor collector, unbanded side to negative. Transorbs turns on in about 1 nano second. MOV's take 5 to 10 nano seconds to turn on and require a higher voltage to breakdown.

3. Divide the resistance and put a resistor in series with the line at the collector to the transistor. Put a .1 uf cap on the LED side of the resistor to negative. The capacitor diverts small transients to negative.

Unless you are running a long wire, from the LED to the transistor, generally you can get by without protection. You are trying to protect against induced lightning or transients into the wire that could damage the transistor.

Check the LED rating, many LED's have a max current of 20 milliamps unless you are using the high brightness LED's.