Mosfet bidirectional switch

bidirectional switch

Hello, I know this issue has been raised many times in this forum but neither of responses was practical or at least understandable for me.
I want to switch on-and-off an analog voltage that is a sine wave(and sometimes DC, I can't use Triac) between -15V to +15V with mosfet power transistors. Current of this line is about 1A. I want to control the bidirectional mosfet switch with TTL logic. The question is How?
I read in 4016 datasheet and elsewhere that two complementary N and P Mosfets are used in such switches BUT there is literally no information about how gate should be driven apart a few triangles and circles! Well I understand that P and N should be driven by a complementary signal but the trouble is how they should be driven so that Vgs be always in on state or off state? Source could be anywhere between -15V to +15V. my trouble is how gate should follow that voltage so that Vgs be always 10V(On state) or 0V(Off state).
Thank you very much!

bidirectional mosfet switch

You can build a bilateral switch with N-and-P channel MOSFETS, but the trick is in the supply of this switch ..

If you look at the attached picture, you can see that the Input/Output signal shouldn't be higher/lower then the supply of this switch ..

As you plan to switch +/-15V (30V rail-to-rail) signals, I would say the supply shoud be something like +/-18V (36 rail-to-rail) ..

Drivers (inverters) can be made of optocouplers, so you will be able to control the switch of TTL/CMOS logic ..

Regards,
IanP

bidirectional mosfet

Thanks IanP, You always help me when I'm in great troubles. Unfortunately my IQ is not as high as you expect so I have to bother you with two more questions.
1-From supply voltage do you mean, optocoupler voltage(gate voltage)? If so how +-18V in gate can turn on and off the switch? Let's say signal voltage is +15V then gate needs to be about +25V for N-Channel(Vgs = +10V) to turn the switch on and +15V(Vgs = 0V) to turn the switch off.
2-In your schematic and also analog switches like 4016 mosfets have not protection diode and have an extra substrate pin. But all Mosfets that I can buy have this annoying diode. So does it mean it can't be implemented with mosfets that have protection diodes? Is it possible to use two N channel mosfets in series(drains connected to each other) instead of one and also two P channel mosfets(diodes back to back) instead of one to overcome this problem?
Thank you very much!

mosfet bidirectional switch

If you can't get hands on MOSFETs without diodes and with Vgs below 2V than the whole concept falls appart ..

Can you use reed relay?

Regards,
IanP

mosfet bidirectional

Hello IanP, thanks again. Unfortunately Reed Relays are too slow for me. I need faster than 1us. There was a documentary series in BBC a few years ago (I don't know if they continue to broadcast it now) called "Rough Science" where a bunch of scientists (Physicists, chemists, engineers,…) were abandoned in a remote island where they even couldn't find a few meter of wires let alone transistors and then they were asked to build some staff like radio or … Sometimes I find myself with similar challenges

bidirectional fet switch

Maybe this idea will be of any use to you:

Because the combination of one MOSFET and negative VGS would allow current flow in the off state (because of forward bias on the MOSFET's internal parasitic diode), the circuit in Figure 1 connects the two MOSFETs source to source. Their internal diodes then oppose each other, which blocks unwanted current flow to either polarity in the off state.

Click to expand...

More details at:
https://www.edn.com/archives/1997/071797/15di_03.htm

bidirectional switch mosfet

It is a good idea, I am thinking that because N-FETs On resistance is voltage dependent, it can be compensated to some degree by paralleling it with P-FETs, so maybe this idea can be expanded to use four MosFETs(two Ns and Two Ps) connected source to source. Thanks