555 relay current reducer

in

Here's your "metaphor":

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--/quote--

I didn't write that. I don't know why you'd try to make it look like I did.

Cheers, James Arthur

engineering accuracy

sometimes it does.

isn't it obvious to any EE that a bistable relay can't have infinite gain, but it's not far off? If not, it may be time to head for sci.electronics.basics.

NT

If a relay had infinite gain it wouldn't require any power to latch OR it would allow an infinite amount of power travel through its contacts.

joe

There are several definitions of gain. RF guys have to worry about differential gain, dPout/dPin as well as average gain, Pout/Pin. If you're building a VCA, the gain changes with time, so you have to worry about instantaneous differential gain.

There are sensible definitions of gain in which a latching relay's gain is indefinitely large after it has latched, while being either zero or mathematically undefined (0/0) at other times.

There are other definitions, such as the one you'd use in calculating battery life, in which you'd concentrate on the total switched energy / total coil energy.

Neither is obviously absurd.

Cheers

Phil Hobbs

That's a good point. Most of us would say this circuit has a gain of -2 because d(Vc)/d(Vin) ~= -2.

Yet for -1 < Vin < -.9V, d(Vc)/d(Vin) ~= 0. So is G -2, or zero?

It's a silly question: G=-2. By convention. We assume it's biased.

Likewise the latching relay. Once 'biased,' d(Pout)/d(Pin) = infinite.

Cheers, James Arthur

...or it would stay latched forever. Ever hear of limits? From his years of whining here, it's apparent Fields hasn't.

What's absurd is Fields years of whining about such nonsense. The statement was perfectly valid in the context given and understood by (almost) everyone.

Our thermostat runs for years on one AA battery, switching 24 volts at ballpark an amp, ON at maybe a 10% duty cycle average. It has a latching relay inside. That's a lot of averaged power gain!

That reminds me, there are all sorts of gadgets around the house that need their annual battery replacement. Amazon sells batteries for about 1/10 the price at a hardware store.

The static power gain of a good mosfet is insane, 1e14 ballpark. The real gain is dominated by charging and discharging the gate capacitance, which depends on the drive frequency. That's pretty similar to the situation with the latching relay.

But it's just words and philosophical blather about the meaning of gain and infinity and such. We need to design circuits that work, and some other people need to debate abstractions for years.

We use the word "infinite" as shorthand for "so big you can't measure it" or "so big it doesn't matter". We're engineers, not barroom philosophers.

rubbish

NT

a point that no EE could possibly have considered anything but 100% obvious.

NT

He's not an EE.

Here's what I wrote:

So, the game is that John needs netcopping for saying latching relays have infinite gain because it's not literally true (even though it's close enough, and we all knew what he meant),

but then you insist he was literally lifted off his feet by an exploding relay, and want to argue over whether world peace *could* literally depend on the exact use of the word 'infinity'?

That just sounds like a lot of pointless word games about things that never mattered. Zero value.

Here's your post:

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----- /quote -----

I did not call you stupid. Nor did I call you any other name. Your first line has been edited to say things I never said.

Cheers, James Arthur