kalaman

hi,
i have charged one ni-mh battery and used 3v led. I'd like to make 1,2v to 3v dc/dc converter which is not include any IC. Because I couldn't find that type ICs where i live.

Actually i found a circuit and it worked nicely but it waste source when i don't connect load.

Hero999

That circuit is fine for powering LEDs, I don't understand why you should want anything better.

For a simpler circuit Google Joul thief.

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kalaman

Firstly, thanks you for help.

It works properly but I measure 60mA standby situation. It spends 60mA when i disconnect LED. Is it normal ?

By the way my English so bad. I'm sorry.

Nigel Goodwin

Then don't disconnect the LED - and yes, I would imagine that is perfectly normal.

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Hero999

Does the capacitro blow up when you remove the LED too?

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kalaman

blow up = explode ?

Hero999

Yes, there's nothing to control the maximum output voltage from this thing so fi you're not careful the capacitor will explode as it's maximum voltage rating will be exceeded.

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kalaman

Yes absolutely right. Because i remove the led electrolitic cap's voltage goes 11-12V.

Allright. this circuit eat 60mA from my poor battery without led. any idea alternative circuit?

thanks for replies

Nigel Goodwin

You don't appear to be listening?, WHY ARE YOU REMOVING THE LED!!

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kalaman

Hi Nigel. You are angry with me. I'm so sorry. But I supposed that something is wrong in my circuit. Maybe there might be an alternative circuit.
Anyway thank you.
Best regards

Nigel Goodwin

You still haven't answered the question?.

There's nothing wrong with the circuit, just don't disconnect the LED - and why would you want to?.

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kalaman

My electronic knowledge is a little bad. So according me any circuit spends more watts when you use load. When you remove the load every circuit's standby current decreases. But this circuit surprised me in this case.

As a result i'm wrong. I will use this circuit with solar energy and any mA will be important for me.

This was just curiosity.

I won't remove the led forever.

Best regards

Hero999

I haven't analysed the circuit in detail but from a quick glance:

This circuit is a flyback step up converter.

It works by suddenly interrupting the current through an inductor so the large back EMF charges a capacitor.

When you disconnect the LED the current in the inductor decays faster so the gap between the inductor being turned on and off is shorter causing it to draw more current.

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justDIY

come on guys, lets not be too dense here

the OP talks about disconnecting the led. perhaps they mean they're turning off the led, upstream of the converter. not exactly a good solution, since it leaves the converter running.

I don't know if you're interested in making things more complex, but the TPS61040 from Texas Inst is a very small boost converter with some nice features. 28 uA quiescent current with no load and 1uA current in shutdown.

I built a flashlight based on one of these long ago, powering eight white leds (in series) off a pair of aaa batteries. My ammeter can't measure the current draw from the batteries when it is "off", it doesn't show up on the 2mA (lowest) scale.

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