This may sound like a simple question, but I am wondering about zener diode clipper circuits of the back-to-back anodes type. It involves keeping transients out of test equipment powered by AC wall adapters, which output DC voltage. As we know, TVS diodes are a larger, more powerful version of ordinary zener diode clippers. They can be either unidirectional ( DC ) or bidirectional ( AC ). In an AC circuit, the TVS diode will clip both positive and negative AC peak voltages that it is rated to. For example, a 120 VAC TVS diode might have a clamping voltage of 209 volts peak. The unidirectional DC diode will have a clamping voltage that varies with the reverse stand off voltage ( for example, a 5V TVS diode might clamp at 9V ). Note that of course the breakdown voltages are usually somewhat lower.
However, if I want to protect a Fluke 8040A vintage LED DMM that runs at 7.5 Vdc, how would I connect TVS devices to block both positive and negative DC transients, and AC transients? For example, what voltage ratings of zener diodes connected anode to anode
would I use to block out such transients above say 10 Volts DC negative and positive, and AC as well? What voltage rating of a bidirectional TVS diode would I use also? How are the voltage ratings of devices determined for this application?