Simple Variable Voltage Strobe Circuit

either a 555 or a 3909 (depending on how fast you want it to flash) driving the gate of a MOSFET should fill the bill.

What's this bit about "no caps" mean?

I think it means "no capacitors" (either that or he's telling us he's not shouting) which, with a 555 timing circuit, wouldn't be possible.

No Capacitors. No need for energy discharge storage.

I built some pulse width modulated halogen lights for Christmas - about an amp each. I used an N-channel 100V MOSFET controlled by a PIC microcontroller, but you could substitute a 555.

One thing to look at though - is there any electronics inside the 36V LED bulb? Often they will have their own little dc/dc converters inside to maintain a constant current. If they do, a MOSFET will still work but you need to take the start up time of the dc/dc circuit into account. If not, a MOSFET is your best friend. They take almost no power to drive, and you can find them that have gates that work off of 5V.

You should be able to build this with a single 555 chip and a single MOSFET. Just google "mosfet 555 circuits".

have fun!

Takes only one PowerMosfet, controlled. If your normal control of the LED cannot take it, it is simply bad. Good ideas going bad? NO, bad ideas going badder.

MOSFET. Perfect.

I'm looking for a flash rate of around 300/s or so. Any idea on a part list?

555
-555 regulation parts (resist, cap, etc.)
V Reg
Power MOSFET

I was hoping someone knew of a 555 chip that could pass the extra power I needed. I'm really pressed for space with this project.

Surface mount components and solid tantalum caps for the higher value caps should keep the space small, but you will be dissipating about 50-75W so dealing with the heat is going to be an issue. consider using an ICM7555 variant which can deal with Vcc's as high as 18V which should make driving the MOSFET (not all will turn on completely at 5V of gate drive, and those that do tend to be more expensive.) much easier and allow your regulator to dissipate less heat.

So it's small that you need?

555-type ICs cannot drive more than 0.1A directly, nor can they work to 36V. But they are available in 8-pin smt packages. Since the mosfet is used in switching mode, and dissipating little power, you can use one in a small package. For example, the NDT3055** has Ron=0.1 ohms, is rated at 60V and comes in a small SOT-223 package. It's 50¢ at Mouser (link).

[It'd be nice to use a mosfet in a TO-92 package, but the lowest Ron you'll be able to find is about 0.3 ohms (a Supertex VN3205N3), and its heat dissipation will be on the marginal side.]

There are some high-voltage mosfet-driver ICs with an integral 555-sryle oscillator, I'm thinking of parts IR makes, like the IRS2153, etc. These can work to 600V, and they'd be happy working at 36V, but they can only provide about 0.2A max output, enough to drive the gates of external mosfets.

** Some will remember the venerable 2n3055 bipolar power transistor, popular about 40 to 50 years ago. In the years since, many parts with similar power-handling capability have come out, all bearing a '3055 type part number, for easy recognition. Most have slightly-improved specs. The NDT3055 is a small easy-to-use mosfet meant to take on '3055 style tasks.

SOT-223 rated at 60V/25A pulsed looks like a fit. You think I should try this?

absolutely! combined with a SOIC-8 7555 and a SOT-89-3 18V linear regulator and you are in like flynn

What do you think would be needed for 36v in and 36v out for the LED bulb?

Maybe run the circuit through a bimetallic strip that alternately heats up, breaking contact; and cools down, making contact. (Similar to a stove burner switch, but lower current.)

Might make noise no? But brilliant thinking. Tinkering with this idea...

No, I meant That the already existing pulse control to regulate the LEDs current consumption is simply not designed with any other input in mind. In all likelihood, I am sorry to say, it will fail or blow up for that simple reason. Low power circuits may tolerate such abuse. No telling, without trying, sorry.

Interesting challenge. Bimetallic strip could be a solution. But the 300 times per second is probably blows that solution out of consideration. That rate implies some sort of photosensitive device which might want evenly spaced pulses or perhaps synchronization. Modern photography uses 18 to 24 frames per second to synthesize motion so it seems that 300 events per second would have other requirements as well. And a 555 can not provide 1 Amp.

Christmas lights that flash use a low voltage bimetallic strip device. The heat to activate it comes from voltage applied to the coil so you have some options up to 12 volts. A small wattage compact lamp has a bimetallic device (starter) but it won't work under 60 VDC and you might have issues with polarity for DC operation.

Even turn signals use bimetallic switches and their speed is load dependent. But getting 300 pulses per second will be difficult if you need any precision. Can you throw us another bone? Perhaps some more information?

Ooops. I meant 300/minute.

The project has space and weight limitations. This is why the number of parts is of relevance.

Can I use a 555 to pulse a MOSFET to pass +30V?

Sure, that is what I was saying before. the 555 will need a regulator to bring the voltage down to it's safe working voltage (18V MAX for the CMOS 7555 types. 5v MAX for the original LM555 NMOS design. most quality MOSFETs have an on resistance around .1-.2 ohms (lower is ALWAYS better, reduces power dissipation when on and reduces voltage drops too.), some can be driven fully on by a 5V gate voltage, others need a higher voltage which is another reason to recommend the 7555 version since you can get it's output almost to 18V with an 18V Vcc input which should be PLENTY to drive the MOSFET fully on.

If you didn't want to use a regulator you could simply put a 15V Zenier diode in series with the 555. That would give you a much smaller two terminal device instead of a three terminal device.