Re: relay switching circuit

Feb 13, 2024 Last reply: 2 years ago 3 Replies


>


>>>>> for relay switching circuit which transistor is perfer
>>
>>if i'm getting 3.3v/0v input signal for base terminal
>
> What's the coil voltage and current?
>
> You could probably use a logic-level n-channel mosfet, something like > FDV301.
>
> I'm designing a board that needs about 125 relays. Turns out that
> modern nfets don't need flyback clamp diodes, which will save me some
> room I need for routing traces.

They don't? I guess I'm not using "modern" NFETs then ... :(


Or are you just gonna rely on the body diode?

Body diode doesn’t come into play. Some modern fets have published avalanche energy ratings, so exceeding Vbvds can be permitted.

Even when fets are specified for avalanche energy, there is seldom a hint of what the avalanche voltage might be.

I don't mind helping beginners. Their questions sometimes evoke interesting issues.

My pcb designer thinks he can route out 134 available balls of our FPGA, and I think I can drive all those relays with just one sot23 fet under each relay.

We'll selective-solder the thru-hole relay pins and the solder nozzle will just barely not desolder the fet.

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