Need Op Amp for design

beware lesser performance though.

ginal suggestion is definitely the front runner. I've ordered a couple of Op Amps, including a 324, from Mouser for testing. They should arrive Mond ay.

I love the 324, it's cheap & very useful. Crossover is easily avoided. Don' t buy Motorola or bias the output.

But I do wish there were even cheaper opamps with even more corners cut. Th ere must be plenty of uses for opamps with major compromises, eg poor gain. Trouble is things start expensive and drop in price, which would make crud er opamps uncompetitive in the early days. And who wants to sell an even ch eaper chip when they can introduce a high ticket one.

NT

NJR seems to make a business of it. There's always someone who wants junk. And someone who will buy it.

The ST variant exemplifies why you don't see those; a different op amp has to compete for the bottom dollar, which is a slow-to-pay-back plan. So, different or not, a low-end quad op amp gets "LM324" name attached to it, which is how one advertises the low-end amp while not using an advertising budget.

It has to show up in a quick search for that part number...

d up with anything powering them up with a live input.

The LM709 had a conventional NPN long-tailed pair as it's input. If you put more than 5V across the inputs one or other base-emitter junction broke do wn - the voltage is a bit high for a pure Zener breakdown, but reverse-bias sing a base-emitter junction to breakdown down damages the base-emitter jun ction even if it doesn't destroy it.

The data sheet was perfectly explicit about the voltage difference limit be tween the inputs - it might not have been a feature, but it definitely wasn 't a quirk.

Bob Widlar got more ingenious later, and subsequent op amps either used an input stage that could take more volts, or protected the input stage with i nverse parallel diodes.

The Diodes Inc version of the LM324 is 6.5 cents, Digikey price by the reel. Under 2 cents per opamp.

What does Digikey pay? 5 cents? Why does anybody bother to make and package a quad opamp for 5 cents?

When these were new, one cost about as much as a couple of bicycles.

Probably less. You can buy the AS324 for around 4 cents.

Oh yeah. And people with a good meter to match tubes or transistors could still make a buck.

nce op amp that can withstand up to 25V when power is shut off?

ls, and this is especially true of Li batteries. There are physics based co nsiderations that dwarf the triviality of the electronics interconnection t opology.

monitor LiPo batteries during use. These are extremely common in the Radi o Control hobby sector, and are readily available at very low cost. Below is an example. The only problem is these are designed to be manually disco nnected when not in use. The reed relays work perfectly, but are too large to be able to shrink the design down to a desirable size for a lower power version of the light. The 100W version uses a battery that is nearly 4" x 4" x 12", so a smaller board is not of any value, but I would like to crea te a few 20W lights with a smaller footprint and less weight.

Looks like that one is quite popular. One forum convo talked about killing the current draw by opening the GND lead in the off state, all the inputs r emain connected. That might be worth exploring.

One amp-hour divided by one microampere is a million hours.

Leslie was looking for nanoamps, no idea why. Even a few tens of uA should be ok with 18650 and similar cells. Milliamps, not so much. Had my comeuppance there with bicycle lights where a standby LED is always lit. Silly design and draws 5-10mA. When I used the road bike for several weeks and then wanted to ride my mountain bike I hopped on, click, no lights.

I don't know what a LM324 draws with the input 25V or so above V+. She could find out.

If it was my projects I'd first look for complete battery management ICs with ship mode or similar low power modes. Less space, less parts, approved design, cheap, no hassle.