Protecting a CMOS gate input

Pimpom · 2020-05-15T10:53:57+00:00

I'm going to use a CMOS bistable chip (not a uP) that's to be manually triggered from time to time by a mechanical switch. It has a debouncing circuit but since the switch is to be connected by a removable jack-and-cable set and operated by non-techno savvy users, I thought I'd include a few extra components as a precaution. The input will have a series resistor followed by a capacitor to ground and schottky diodes to Vdd and Vss. Do you think any of this is superfluous since the chip already has similar protection built-in?

May 15, 2020 41 Replies

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Tom Del Rosso 6 years ago

It looks like you could make it oscillate when the button is held, or not, by changing the resistor ratio.

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Ricky C 6 years ago

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Not sure what the issue is with protection, but the debounce I suggested re quires a schmitt trigger clock input which I stated. If it has that, the c ircuit will work.

Input protection depends on the input spec. We don't have one, so of cours e there will be input conditions that will not be met. State an input spec and perhaps I can suggest input conditioning circuits to protect the circu it.

What makes you think this circuit will work reliably? While it may have a schmitt trigger input that is not enough to assure the idle level will be c lose enough to the threshold voltage to sit in the state given rather than revert to a default state. The threshold value is specified as a wide rang e that can vary with process and temperature.

Definitely the R values need to be tweaked to achieve anything like "low" p ower when on. But I guess in comparison to 15 amps even many mA is "low".

Rick C. ++- Get 1,000 miles of free Supercharging ++- Tesla referral code - https://ts.la/richard11209

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