Switch AC Signal - Low Impedance (<1ohm) 50Vrms 1-100Khz

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Discussion Overview

The discussion centers around designing a switch for an AC signal with specific requirements: low impedance (less than 1 ohm), a voltage of 50 Vrms, and a frequency range of 1-100 kHz. Participants explore various switching technologies and their suitability for this application.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses difficulty using MOSFETs for switching the AC signal, noting they do not block the signal completely and questioning their appropriateness for AC control.
  • Another participant suggests the CD4066BC Quad Bilateral Switch as a potential alternative if a lower voltage (around 10 volts) is acceptable.
  • A participant inquires about the rejection of simple relays, prompting considerations of factors like switching time and contact bounce.
  • One participant mentions that the method of switching may depend on the maximum signal current and asks whether the signals are in coaxial cables or twisted pairs.
  • A proposed solution involves a “T” structure switch, which uses two series switches to block the signal and another switch to ground the midpoint when off, potentially reducing feedthrough.

Areas of Agreement / Disagreement

Participants present multiple competing views on the best approach to switch the AC signal, with no consensus reached on a single solution or method.

Contextual Notes

Limitations include the dependence on specific signal characteristics such as maximum current and the type of cabling used, which may affect the choice of switching technology.

EE4life
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Hi all,

I would like to make a switch for an AC signal (on off ,ie, high impedance and low impedance). The switch should have less than 1 ohmn impedance. The signal can range from 1-100Khz and the signal will be 50Vrms.

I tried to use mosfets, but they do not block the signal completely, and I do not think they are meant to control AC signals like this.

Thanks in advance.
 
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EE4life said:
Hi all,

I would like to make a switch for an AC signal (on off ,ie, high impedance and low impedance). The switch should have less than 1 ohmn impedance. The signal can range from 1-100Khz and the signal will be 50Vrms.

I tried to use mosfets, but they do not block the signal completely, and I do not think they are meant to control AC signals like this.

Thanks in advance.

You have probably considered simple relays -- could you say why you rejected them? Switching time, bounce, etc?
 
There are many ways of doing it, but it will depend on the maximum signal current.
Are the signals in a coaxial cable or a twisted pair?

Often a “T” structure switch is used. Two series switches in the top of the “T” are used to block the signal while another switch in the stem of the “T” grounds the midpoint when the switch is off to greatly reduce feedthrough. Perhaps you can use that structure with mosfets.
 

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