5v/3.3v down to 1.5v

Hi guys,

I was wondering if any of you would have any idea how to convert either 5v or 3.3v down to 1.5v? This is so that I can run a flashlight, and so far as I'm aware it must be 1.5v on the flashlight.

Many thanks!

-C

What makes you thnk that this is the voltage needed for a flash light? You are not wanting to make an led one are you? If so you need to use a constant current supply not a constant voltage one as 1.5 is the forward voltage drop across the LED not the voltage you have to supply it with.

You wont find a flashlight that runs on 1.5v (unless it's got a boost circuit, eg running from 1AA)

Basically, what's the flashlight? (if it runs on 3v bulbs, there's probably no circuit) if you're planning on powered an LED, then you'll need 4.2v (or a step up boost circuit)

Hi,

Thanks for your replies!

The flashlight I want to power is this one: http://www.candb-seen.co.uk/flashlightheadlamp/cabs-flashg3.html

It runs from a 1.5v AA battery currently, but I want to control it from an arduino.

Thanks!

you're going to have a hard time, the driver for torch is located (usually) under the head (top down)

best you can hope for is that it screws out, if there's epoxy keeping it glued in, you might need to heat it up before trying to extract it, anyway once you managed to do that you'll see the driver for it (a boost circuit) you're better off buying a Q5 (Cree LED) and using that with an Arduino.

That link said it was a 7W light. So at 1.5V that is going to take a staggering 4.6 Amps you have to supply. I am not sure where you expect to get that sort of current from.

CJdelphi - that torch uses a Q5 Cree LED...

And I don't know either, I'm just trying to figure out if its possible at all?

Those battery claims are porkies as well.

It might help if you tell us exactly what you want to do.

Yes i know it uses a Cree Q5... you're better off buying an LED and a heatsink rather than modify a torch's circuit.

you wont have full control over it, better to write the driver yourself (using analogWrite and a Transistor)

Mike, ALL flashlights / torches (with exception to the higher end ones, Fenix, Thrunite, etc) all claim the magical figure that the LED itself can provide, the Q5 can
supply 7watts…

the boost circuit in the torch however…

Wont. (not even close from an AA)

Okay then, if I remove the LED from the torch, how difficult is it to control from either 3.3v or 5v?

Cheers :slight_smile:

Another option may be to continue powering the flashlight with the current battery, but replace the on/off button with an opto-isolator/relay from the Arduino. That way you can turn it on/off, but you don't have to get into power conversion.

Connor_ward0909:
Okay then, if I remove the LED from the torch, how difficult is it to control from either 3.3v or 5v?

Quite simple. You can use one of these two schematics http://www.electronics-tutorials.ws/diode/diode46.gif with a +5V supply, but design for 100 to 300mA though the LED. For example, the upper circuit using a BC337 transistor with R = 6.8 ohms and Rb = 220 ohms will give about 200mA through the LED

dc42:

Connor_ward0909: Okay then, if I remove the LED from the torch, how difficult is it to control from either 3.3v or 5v?

Quite simple. You can use one of these two schematics http://www.electronics-tutorials.ws/diode/diode46.gif with a +5V supply, but design for 100 to 300mA though the LED. For example, the upper circuit using a BC337 transistor with R = 6.8 ohms and Rb = 220 ohms will give about 200mA through the LED

200ma is pittyful, you can safely drive it near to 1amp with a good heatsink.

Download Cree's datasheet...

Connor_ward0909: Okay then, if I remove the LED from the torch, how difficult is it to control from either 3.3v or 5v?

Easy...but first you have to remove it, connect it up to a battery and measure the voltage and current it's using.

cjdelphi: 200ma is pittyful, you can safely drive it near to 1amp with a good heatsink.

True; but in the original flashlight, it is likely to be getting more like 200mA. The OP's original requirement was to control the flashlight.

Fungus - Thanks for the help, any idea how I should go about connecting it all up? And what parts I need etc?

Thanks!

You could get some AMC7135's and power the light from a 3.7V li-ion cell (preferably one with a protection circuit). It's a great little driver chip for single cell lights.

The AMC is a low dropout constant current sink. It has an enable pin which can be tied directly to an Attiny chip so that you can control the modes via PWM. There's two bins that I'm aware of (350mA and 380mA). You can also put multiple chips in parallel to drive the LED at 700mA, 1050mA, 1400mA etc...

I just built one the other day for a AA light that originally came with a boost circuit. It's now a 3 mode light, which uses two AMC chips for 700mA on High. Medium and Low are pulsed at roughly 16Khz for an average current of ~230mA and ~77mA. I'm also using one of the ADC's to read the battery voltage. At 3.2V there's a visible pulse to let you know that the cell needs to be recharged.

You could always just cut the wire between the battery and switch then splice in a couple of leads and use an external MOSFET to turn it on and off. Once you have those leads spliced in, you can measure the current delivered by a new battery when the light is on, which will give you an idea of what MOSFET you need.

As an aside, I'm guessing you will find out that 7W is wishful thinking on their part. I'm fairly confident that a cheap AA cell does not have in excess of 24 Watt-hours of energy in it. Top rated AA alkaline cells have about 3 Wh max. Cheap carbon-zinc (Leclanche) cells (like EverReady '9-lives') have about .7 Wh.

Connor_ward0909: Fungus - Thanks for the help, any idea how I should go about connecting it all up? And what parts I need etc?

Thanks!

A resistor will do it. But first you need to know how many volts it has to get rid of.

You find that out by measuring the torch battery when it's in use, nobody else can do it for you.