I am working on a circuit that transmits ~1MHz sine wave(20V amplitude) in RLC based circuit scheme, also transmits high-frequency signals(pulses(non-periodic)) ~20MHz(10 %DS)(20V) in a CR-based circuit scheme. The circuit involves 'disabling' of inductor for ~20MHz signal transmission for a short amount of time(say 10% of the enabled time). I'm having problems in suppressing the voltage spikes(~ +-100 V) which are generated the moment I disable the inductor AND after I connect the wire, while the rest of the time the circuit behaves alright. NOTE: I'm measuring the differential voltage across Resistor(275ohm) circuit

XFG3: 20MHZ, 10%DS +- 20V square wave

XFG2: 1.58MHz(RLC resonant), 50%DS, +- 20V square wave

XFG4,1: 500KHz, 10%DS

Desired output: Maximum power transfer at 275ohms(after rectification, filter) + High-speed data transmission(to be demodulated later from 275ohms)

So, to tackle that, I came up with an idea to temporarily enable the pair of opposite Zener diodes which would act as a voltage limiter(say +-20V) right after the switch S1, but it found to be unsuccessful. I can still see the surges. Also, I've read that Zener has high capacitance, so it won't be effective in a high speed temporarily switching(Note that I want to enable the voltage suppression device momentarily for the initial surge protection(~10ns)) with zener surges

I also have an idea to make my switch kind of a hybrid-relay based, where there will be a state for a very short period of time (just after inductor open-circuit and before connecting the wire) to absorb the surges. But, I'm not getting effective ideas.

I also have heard about MOVs. But I'm not sure about its effectiveness as they also possess capacitance. It's not available in NI Multisim, so I am not sure if it's good.

I need some suggestions/ways to tackle the problem. NOTE: C1 capacitor is an instrument that is very delicate and it's a must to suppress any kind of spike just before it

  • \$\begingroup\$ Surely the voltage spike suppressor would be right before S1, on the left side? \$\endgroup\$
    – user253751
    Feb 16, 2021 at 17:34
  • \$\begingroup\$ also can you explain why you have this circuit? Maybe there is a better way to do whatever you're doing \$\endgroup\$
    – user253751
    Feb 16, 2021 at 17:34
  • \$\begingroup\$ Be it on the left of S1 or on the right, the effect would be the same, isn't it? However I've tried every possibility with the Zener pair, it doesn't work well. I'm using the circuit for power(low freq)+data(high freq) in an application. So, right now, the modulation scheme is fixed here \$\endgroup\$
    – deadplasma
    Feb 16, 2021 at 17:40
  • \$\begingroup\$ I don't see any circuit that is shorting the inductor. \$\endgroup\$
    – Andy aka
    Feb 16, 2021 at 17:43
  • \$\begingroup\$ @deadplasma Well if you put your spike suppressor on the right of S1 then when you disconnect the inductor, it's not connected to the spike suppressor any more, so how could it suppress the spike? \$\endgroup\$
    – user253751
    Feb 16, 2021 at 17:44

1 Answer 1


Have you tried something like this configuration:
When S1 is bypassing L1, SW3 is closed.
When S1 is in series with L1, SW3 is open.


simulate this circuit – Schematic created using CircuitLab
It should quickly quelch any energy in the inductor, and keep it local to that loop.

  • \$\begingroup\$ I tried it, but it isn't effective !! \$\endgroup\$
    – deadplasma
    Feb 18, 2021 at 11:13

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