LED Lamp - Circuit and Graphs

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On Fri, 06 Jan 2012 08:01:48 +1000, David Eather wrote:

I don't use LT spice.

The other thread had a bunch of rubbish about in rush currents and so forth that simply are not problems with this design. This thing is essentially 2 caps and a bridge, dirt cheap and sensible for low wattage LED lighting straight from the mains. Someone asked what circuit was actually used in these lamps - this is.

This works without grief

Do you need the filter cap? As your graphs show, the dynamic impedance of the LEDs is so low that a modest sized cap doesn't filter very well. That's a big cap, and 'lytics are not the most reliable parts.

John

I think you find the cap is the reason you don't need the series resistor to squash the spikes - instead of going through the LEDs it takes several cycles for the filter cap to charge enough for current to flow through the LEDs - and then the current is fairly constant - hence no flicker.

I doesn't look very constant. Is 100/120 Hz flicker very annoying?

John

Without that cap, there could be a huge start transient if power were applied near the cycle peak.

This was a problem with using a capacitor to drop line voltage for an incandescent pilot light. The surges would eventually blow out the bulb.

All i see is the whole URL as given is 110% ad(s) and NO access to the stated file (yes..the _name_ of the file is there, but not useful).

Now THAT works; hopefully V1 is isolated...

Wow! You got that right, Robert. That site is CRAP!

No, it doesn't.

It appears to me that the string of LEDs is being supplied reverse voltage. What am I missing?

John S

Dunno, I saw a string of zeners, I gave up trying to make sense of schematic.

Grant.

Deep Sigh.

All this and today I decide to screw around with my mail and change to opera (I'm on a different PC)

Try this. it is from drop box which was recommended by someone other than me.

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It "worked" for me, but it's still a "crocko" s**t with ads and links=20 begging for money. Then I had to wait for the "slow download" button to=20 activate, and then I had to use a captcha which was very difficult to = read=20 and required a couple of attempts and delays. Then I got a message:

"There is another download in progress from your IP. Please try to=20 downloading later."

Why make someone go through all these hoops just to VIEW a posted image? = All=20 for a stupid GIF of a simple circuit and some waveforms. Sheesh!

Since you insist on posting images of circuits, why not use a photo = hosting=20 site, such as

I won't bother even looking at anything from "crocko" or "dropbox". Not=20 worth the frustration, and, yes, grief!

Paul

Dropbox works well. The bridge on the schematic is backwards.

Ed

Hardly, he's driving a string of low power 4.7V zener diodes, I can't see the LEDs.

LTSpice would be much better, plain text file, no attachments, and quite common for this newsgroup. It's not hard to pickup. Free too, not from some odd website, but rreally truly from LTC, makers offine but expensive chips.

• Download LTspice IV (Update January 5, 2012)
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Grant.

I didn't have a model for a led - in any case whatever I could get wouldn't match the Chinese LED specs anyway

John S Inscribed thus:

Works for me !