Lightning and power surges

[robertpear]

I would like to start this thread because of my observations of the carnage I see at my main job, repairing audio equipment. Most of the terminal failures of currently produced equipment are due to lightning and power surges. The most common is a surge that takes out the input switching ics and then proceedes to the control and DSP CPU ics. This problem is due to the total lack of input protection circuitry and the very bad habit of hooking up components that are pluged into different wall outlets or even different rooms. When lightning strikes nearby a surge is induced into the interconnet wiring that can reach hendreds of volts if not suppressed. I have found that back to back 5 volt zener diodes on signal connectors work well to keep the input circuits safe. I also recomend that a silicon bilateral switch diode rated at a clamping voltage of 220 v be used accross the AC input to your gear after the fuse. This diode will fuse itself to a dead short when a high level surge enters your equipment and then blowes the fuse. You would have to replace the diode if this happens but that is a lot cheaper than the alterative. I first saw this used on a top end laser disk player from Pioneer. In this case the customers amp, preamp, tv, and cd player were all severly damaged but after replacing the diode and fuse the laser player was working just fine. The diode I use is 1.5KE220A availabe at both Newark and Allied Electronics. If your line voltage is 220vac use two of these diodes in series.

[Edited by robertpear on 01-03-2001 at 11:06 AM]

[Eric]

Hi Robert,

Thanks for the post! I'm always looking to protect my equipment from nasty transients! Would you be able to provide more specific details such as the necessary ratings for the zener diodes for line-level input stage protection?

Thanks!

[robertpear]

Since the current is not high 500mw diodes will be fine. The diodes will short out if a really high surge gets to them protecting the rest of the circuitry. I use large pads on my PCBs to make changing them easier.