PWM lighting quest!

The filament in a lamp has something called, latency. You can think of latency as when you take your foot of the gas of a car, the car keeps rolling, the duration of the rolling is the latency. The filment acts the same way, you can remove the power source from it, and the duration of how long it emits light for is its latency. This is why 60Hz AC works.

The PWM concept that you describe is used on remote controls, it allows the IR LEDs to use up to 1 Amp (1000mA) and not burn out, because it is only on for microseconds at a time. You might be able to get around this and instead use the latency concept in combination with a PWM frequency. Check out

for simple PWM setups using 555 timers.

** Groper alert !!

** Complete bullshit where filament lamps are concerned. ** You said it.

....... Phil

If you can't drive both together, and want to, you need to find out why and then determine what can be done.

There's no such thing as a free lunch. You can operate both at reduced light output maybe - but you are lacking in real world numbers. Capacity of the source volts/amps, need of each load, volts amps. Then determine what you want to do with what you have. Likely as not, you have to compromise . . .

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Explain? Are trying to connect them in parallel or series? When something like PWM is used, you will get less effective power to the lights instead of more.

I would guess you're talking about something like this (view in fixed font or M$ Notepad):

| | ___ \\.-./ | .---|___|---. .--( X )-VCC | | R | |\\ | /'-'\\ | | | .---|H>O----. |-+ | | |\\ | |\\ | |/ | ___ | | o---|H>O----o-| >O-o o-|___|-->|-+ | | |/ | |/ | |\\ | 100 | | | | '---|H>O----' === | C --- | |/ GND | --- | | | | | === | | GND | \\.-./ | | .--( X )-VCC | | |\\ | /'-'\\ | | .--|H>O----. |-+ | | | |/ | ___ | | '-------o o-|___|-->|-+ | | |\\ | 100 | | '--|H>O----' === | |/ GND (created by AACircuit v1.28.6 beta 04/19/05

Lets assume Vcc is +12VDC. The IC is a 74C14 hex inverter with Schmitt trigger input.

The first inverter with R and C creates a square wave oscillator. The other inverters are used to drive the two FETs. Only one FET is on at a time, so you're suggesting you might be able to get away with using only one power supply instead of two.

The answer is, it might work. A lot depends on the specifics of your power supply and lamp -- details you haven't provided. The question is, will you be satisfied with the greatly reduced light output? You might want to try it and see.

I would think using both power supplies might be a better idea.

Good luck Chris

And by the way, this has just about the same effect as placing both bulbs in series.

| | .-. .-. | .--( X )-( X )--. | +| '-' '-' | | --- | | - | | | | | '---------------' | | (created by AACircuit v1.28.6 beta 04/19/05

Chris

Not really, Ad. That trick with persistence of vision works with LEDs, but not with incandescent bulbs. You're depending on the thermal time constant to determine rate of rise of light output, which is much slower than your PWM. If you switch every second, it will work, but you'll just have two blinkers, then. That's why the PWM really won't work any better than just putting the two bulbs in series.

By the way, please bottom post. Since you're a Google person, please read Google Groups Help Topic "What's good 'netiquette' when posting to

Usenet?"

Good luck Chris

Ad,

No one seems willing to say "it won't work".

But guess what? It won't work. You can drive both together as much as you want, but you won't get enough brightness.

Ed

"ehsjr"

** I did ,day ago:

" ** Complete bullshit where filament lamps are concerned. "

** The OP should repost his bizarre crap on " alt.magic-tricks " .

....... Phil

Ed,

I wanted to multiplex the lights one on one... so that the peak lighting will be there! Dnt'u think t'will work bright now?

ehsjr wrote:

No, not with incandescent lamps and especially not with halogen lamps. The heating time constant is in the human perceivable range - there is no peak brightness to speak of.

You need a more efficient light source or bigger power source, or settle for less light.

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No. Use one lamp or a bigger supply.

Got it, got it, i'll find some other way to it!!!

Anyways thankz everyone....!!!!!