# 6 to 2.2 volt DC-DC converter

Discussion in 'General Electronics Discussion' started by aidan, Mar 21, 2012.

1. ### aidan

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Jul 15, 2011
I am getting a couple 1 watt laser diodes, they run optimally at 2.2 volts at 1.2 to 1.3 amps. they will be used in a project where the main supply voltage is 6 volts.

-what would be the best way to get 2.2 volts from this 6 volt supply?
-what would be the most simple way?

Thanks!

2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
In all likelihood they do not.

It is perhaps more correct to say that they operate optimally at between 1.2A and 1.3A, at which current the voltage drop is approximately 2.2 volts.

LEDs of any type are best driven from a current source and almost NEVER should be driven from a voltage source.

Good.

The best (where best = most efficient) way to drive these diodes would be to use a switchmode current source.

The simplest (where simple = cheap and not very good, and inefficient, and needs to be used with care) would be to use an appropriate resistor in series with the laser diode.

edit: it's possible these are laser diode modules and they already have a constant current source built in. If that was the case I'd expect to see a wider range of input voltages. Seeing the datasheet on these devices would be most instructive. As it is I'm making a lot of assumptions.

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Jul 15, 2011
4. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
Perfect!

Although there's no part number or link to a datasheet that I could see, there is a graph of output power against current. You can see that the current is what is important, not the voltage.

And it's clearly a laser diode and not a laser diode module.

If I were you I'd be looking for a suitable constant current source rated around 1A.

You could use something like this (it's actually designed for a LED flashlight, but it should do the trick)

5. ### aidan

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Jul 15, 2011
ah! good ol' deal extreme! and I have just enough money in my paypal! too bad the shipping time is ludicrous....

I guess making one myself would be a large ordeal?

6. ### aidan

29
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Jul 15, 2011
also so this whole current led thing is kind of a big revelation to me.... baiscally the current running through the led or diode is what matters? say I have a run of the mill red led. I feed it 12 volts but as long as only 20mA is running through it will be fine?

7. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
You could make one yourself. Or maybe you could find something on ebay.

If power and heat are no issue, then there are some simple linear constant current sources.

Making your own switchmode current source from discrete components is a bit more complex, but do-able.

If you've looked at the LED guide I pointed you to, one of the first things you would have seen is the voltage vs current curve for LEDs. The key thing to note is that a small change in voltage can produce a massive change in current and that the process is such that it can run away with the result of killing the LED in fairly short order.

The key thing is the current. If you place a resistor in series with the LED, it will drop a greater voltage and the LED current increases, partially of offsetting the runaway problem. You choose a resistor to set the LED current, but in practice you need to know some voltages to do that.

Constant current sources are the best way of driving LEDs and they become "more better" as the power dissipated in the LED increases. Switchmode current sources have an additional benefit that they don't dissipate large amounts of heat themselves.