S.E.D is disappearing

So post a circuit problem.

It isn't the task of those of us who qualify as experts (*) to constantly provide a subject feed.

Ask a *real* circuit problem and you will receive many answers.

(*) I'm sure I'll see a lot of guff over that statement, but, if you'd like to challenge me, bring it on >:-} ...Jim Thompson

-- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at

I'm looking for work... see my website.

Thinking outside the box...producing elegant & economic solutions.

If I'd had a current circuit problem I'd have posted it. Sometimes the solution is to increase the signal, sometimes it's to reduce the noise. Right now I can't do either. But I can always complain!

NT

OK, I'll ask a "real" circuit problem. One I've been thinking about for a little while. I have some ideas but haven't had time to flesh it out.

The problem: A current source to drive two series LEDs (~3V each) at, say 10A with a duty cycle of 2, say 200us on out of 10ms cycle. I want a switcher, to save energy. The input to this circuit is 7V and may draw no more than 250mA at any time, including startup (though startup may be longer than one cycle).

What part of that is proving a problem?

NT

Is the circuit that meets these requirements that trivial? Show me.

How about a buck switcher, current limited, to charge a big cap (polymer or supercap) to just enough voltage to go linear after that?

Poorly specified >:-}

What does "go linear after that" mean? ...Jim Thompson

Makes no sense to run those big LEDs at 2% duty. The idiot is trolling.

Buck from 7V to what? The LEDs are 6V. Then you have the storage issue. It's not a trivial problem. I have a solution but it's not simple.

As always, Blobby hasn't a clue what he's talking about. Not only is it the only way it works but it's the specification. If you're not capable of solving the problem, it's expected.

You should ask that question in sci.electronics.basics.

You don't know that. But it may not make sense to worry about efficiency at 2% duty cycle. So a simple input RC could take care of the peak input current limit. Maybe a depletion fet and a supercap to get fancy.

Sorry, it wasn't clear to me that the prime source is 7 volts.

If 7 volts is enough for the LEDs (no boost needed) all you need is some energy storage and an LED current limiter. That's easy.

Design some kind of electronic bit fence?

If there is a part of it you're not clear how to implement, say so. I wonder from your comment if it's all of it?

A 2% duty cycle switcher is not challenging. An inductor to limit i to 10A with switcher turning off when it reaches 10A is not challenging. So what is? If no straight answer there is no milegae in continuing, and this would turn out to be trolling.

Re the point of it, maybe it's a strobe. Who knows. I've a feeling it's short, brown & hairy & lives under bridges.

NT

You should define the problem more precisely. ...Jim Thompson

It's not my problem!

Mine neither... I'm busy doing a chip design, so problems "presented" by supercilious individuals will be ignored ;-) ...Jim Thompson