Not so easy led driving.

Mar 29, 2007 7 Replies

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Fred Bartoli 19 years ago

I've a situation where a string of 5 Leds (2mA) has to be powered from

48V up to 1kV (HV safety indicators). That's about 20mW for the leds, and 2W heat under 1kV.

The system ATM is a simple CC source (1BJT + 2 mosfets) but we now need as less heat generation as possible and a more compact design.

The first idea was a resistive drop down to 50V or so, and from there have a small step down switcher current regulator providing the 2mA current. At 50% efficiency that would have been 0.8mA for 1.2W saving, and possibly more.

...but all the little switchers I could find either have huge current draw or low max input voltage, or something.

Before I start rolling my own, which seems not so simple (first attempts show a serious lack of 'efficiency') I have to ask if I missed the good IC? (or idea)

Thanks, Fred.

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martin griffith 19 years ago

anything here

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martin

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colin 19 years ago

"Fred Bartoli" wrote in message news:460c093a$0$6436$ snipped-for-privacy@news.free.fr...

how about more leds in series using less current for the same light output ?

Colin =^.^=

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Fred Bartoli 19 years ago

colin a écrit :

One Led is also an opto (visual feed back for the operator and to the calculator too). And all that is doubled for redundancy :-(

Thanks, Fred.

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Fred Bartoli 19 years ago

martin griffith a écrit :

Thanks. LNK302 looks promising.

Thanks, Fred.

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James Arthur 19 years ago

Must you power the LEDs from the 48-1kV? If not, you could make an isolated supply to power the LEDs, and a separate circuit to sense the high voltage: (warning: crude sketch)

+15v (isolated) | +HV >------. +--+--+ | | | | | LED1 R1 | | : | | LEDn +---------|\\ | | | >----' R2 Vref >-|/ | | -HV>-------+----------+

The isolated supply could be very simple, and unregulated.

That would solve the heat problem, and could also be smaller than the space otherwise needed to dissipate 1-or-2 watts.

Cheers, James Arthur

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Terry Given 19 years ago

or just a self-oscillating flyback converter driving the LED, using a suitably high voltage device. just let it clag out naturally when Vin gets low enough.

I built a 1W 100V - 1kVdc flyback with an emitter switched BU508 once. and it was harder to do than the 100W version.

Cheers Terry

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joseph2k 19 years ago

maybe buy one of these?

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JosephKK Gegen dummheit kampfen die Gotter Selbst, vergebens. --Schiller

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