Xenon Photon Torpedo effect?

[HarveyH42]

Couple of weeks ago somebody was looking for an LED circuit for a Star Trek model. Was doing some thinking at work (mindless job), and got an idea...

If I could control the brightness of some blue LEDs in relation to the charge of the capacitor in a disposiable camera flash. Have some unfortunate problems to get past... The flash runs off a 1.5 volt battery, and fries off 3 volts. The blue LEDs I think were 3, maybe 3.4 volts. The flash capacitor is 160 volts (takes about 12 secs to charge).

Wiring up the flash, to make it a strobe is simple (done several, SCR triggered by the neon 'ready' light). An LM317T gets very hot when trying to drop 6 volts down to 1.5 volts.

Anyway, posting this for ideas on get the blue LED's brightness to increase with the capacitor charge, and hopeful be spared getting shocked from poking around too much.

 

[Hero999]

This seems a silly idea.

What are you trying to achieve?

 

[HarveyH42]

Just something to do with parts laying around. Get silly ideas about how to put them together. The Star Trek think has come up a couple of times in the past, figured this might work.

 

[audioguru]

A little blue LED is not a strobe light. It is just a little blue LED.
Your idea won't make it look as bright as a strobe light. It will just blow it up.
Look at the max ratings of blue LEDs on their datasheets. They have a lot less power than a strobe light.

A 5W Lumileds Luxion LED might flash like a strobe light. It is not just a little LED but is 4.2V at 1.2A.

 

[HarveyH42]

A little blue LED is not a strobe light. It is just a little blue LED.
Your idea won't make it look as bright as a strobe light. It will just blow it up.
Look at the max ratings of blue LEDs on their datasheets. They have a lot less power than a strobe light.

A 5W Lumileds Luxion LED might flash like a strobe light. It is not just a little LED but is 4.2V at 1.2A.

The Xenon tube will still flash, bright white... Not looking to replace it. I want the blues to sort of give a visual indication of the charging capacitor, before the Xenon Flash. Obviously driving LEDs directly from a 180 volt capacitor is a great idea. Need some way to read the charge level, and translate it to a voltage range suitable for the LEDs. Also don't want take too much away from charging the capacitor (takes a long time anyway).

 

[Hero999]

I take it you're wanting to use an LED to indicate that the voltage ids high enoug to fire. What's wrong with a comparator and a potential divider on the high voltage output?

 

[HarveyH42]

I take it you're wanting to use an LED to indicate that the voltage ids high enoug to fire. What's wrong with a comparator and a potential divider on the high voltage output?

There is a mini neon lamp for that, and it also triggers the flash...

I'm hoping to have the blues start out dim, and reach full brightness around the same time the flash capacitor's charge is ready to flash the xenon tube.

The main problem is the high (180 vdc) voltage, and probable shock hazzard (hate that). Just wondered if there was a simple safe method of visualizing the charging of the capacitor.

 

[Hero999]

Isn't there a bargraph chip for that?

Can't you just scale the voltage down using a potential divider?

If you really want to vary the brightness of the LED with the varying input voltage, use a transconductance amplifier on the output of the potential divider.

Note, I hope it's obvious that you'll need a separate power supply for the LED circuit, if you're powering this whole thing from a 1.5V cell then use a switching regulator to get 6V or so for the LED circuit.