Isolated variable resistor function?

ain

ier

he

ost

ere

wer

s of

el

ce

one

estate.

tage).

Actually, that's the balanced modulator version. The MC1495 - no longer made - had the extra circuitry to make it a more or less accurate multiplier, which slowed it down a bit.

It wasn't anything like as good as the Analog Devices parts are now, and it was a bit if pig to use - like the MC4024/MC4044 parts for which Jim Thompson also admits responsibility - but it was cheap, as it had to be to sell at all against the much better Analog Devices and Burr-Brown parts.

-- Bill Sloman, Nijmegen

This is another one of your zero context questions. Sounds like you're working on a amplifier with uC controlled gain, and some crazy demod/mod scheme with the couple hundred kiloHz control frequency?

on a amplifier with uC controlled gain, and some crazy demod/mod scheme with the couple hundred kiloHz control frequency?

Like, should be done OTHER than with an optically controlled resistor ?:-) ...Jim Thompson

Give a non-isolated example that does absolutely everything you need, then we'll figure out how to do it, isolated.

I'm sick to death of weaseling.

RL

Yeah, one is a "tiny" 400W boost. I cheated, though, and it's four-phase. ;-) Most of the others are in the 15-20W class.

Or just replacing a pot with a plasic shaft, to go vroom vroom.

When you see resistance-controlled interface, you have to think 'OLD'. You get the gold star if you can do it some other way.

A resistor seldom has to do everything:

- It may be polarized, in it's place.

- It may be used with a fixed voltage - actually modulating branch current.

- It may be used at a fixed current - actually modulating a node voltage.

If a variable resistor did work, then there were acceptable limits of linearity, resolution, minimum and maximum compliance values that would be expressed and passed on.

If it didn't actually work, then there's little point in promoting a substitute that attempts the same degree of basic malfunction.

I hope this isn't another frigging lamp dimmer, with power factor correction. These will likely never see significant North American manufacture, no matter what brand name gets stamped on them.

RL

The above describes quite accurately what's needed. Of course I can't post a schematic.

Only if it costs less.

Yes, it can be.

Unfortunately it can't :-(

I wish, but no.

This was stated in my original post: substitute that attempts the same degree of basic malfunction.

You may be very mistaken there :-)

Amazing! Maybe I should use a F5 series some day.

modulation.

be efficient?

network to gate.

Sure, but that's quite a lot of parts. I was planning on doing it with a single device plus optocoupler.

The MCP4011 series is listed at 15uA when operated at 2.7V. I could live with that :-)

estate.

That was just one example. There are many more, for example RF mixers that can go down to zero even though the datasheet often don't mention it. Typically well under a Dollar. AD makes good multipliers but that's more for precision scientific instruments where cost doesn't really matter. I don't need any precision here.

I gave one, see "b". You can get digital potmeters that are more accurate than 20% and cost more. But it's not isolated. No problem to communicate with one via optocouplers but the whole purpose of this post was to see if there's a more simple one-chip solution. Like the optocouplers that contain a 2nd diode so you can servo out the transfer function tolerance (but that's not resistive).

Then why did you answer?

rtain

rrier

the

most

there

power

ons of

nnel

ance

Done

al estate.

are

oltage).

WM

or

You do need some - you did mention 5% linearity. And multipliers are specified in a way that smears out the non-linearity over the whole of the range, which you can rarely completely exploit.

-- Bill Sloman, Nijmegen

I usually think "fast" and "accurate". You'd need a pantload of fancy parts to make something as linear and low-capacitance as an 0603 metal film. Of course for low performance jobs, something crappy like a

Cheers

Phil Hobbs

Ummmmmh! Larkin will claim that means you're an old hen and can't really design :-)

modulation.

I just got the first boards back a few weeks ago, so haven't, yet. ;-) However, efficient should help. An extruded aluminum case should help, too (the final product will be in a casting).

As I said, it's cheating but it's really four phases, each at 500kHz. It's an advanced development project. One of the groundrules is that switching regulators must be above 2MHz (AM band). This cheating was the only way I found to get there. On another project, I have a couple of other smaller

network to gate.

We don't always get our wishes.

Isn't the tolerance of the 4011 an issue?

modulation.

has

;-)

If you run them at 500kHz that's a bog-standard switcher range. That's not a 2MHz switcher. You won't be above the AM band with that unless you have a super-precise balancing system in there.

Cost

network to gate.

But I want my wishes granted!

:-)

It's exactly borderline but was only an example. I am pretty sure I can find one that is less than 20%. If not we'll have to do an auto-cal on start-up and the SW guys will throw their coffee mugs at me.