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Help with step-up converter

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iamweasel

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Hi folks,
I'm in need of a step up converter to increase car's power supply (around 10v-14v) to 36v at 3A.

I've found a few on eBay, which appear to do what I need:
1) **broken link removed**

2) **broken link removed**

I actually bought this one already: **broken link removed**
before realising it's a step-down. I thought it could just dial in the output.

What I'd like is if I could get some input from you as to whether any of these will meet my requirements.

The application is to drive a series array of 10 CREE xml LEDs (Vf 3.6v at 3A).

Thanks in advance
Adam
 
If you put 3 in series with either a current limiting circuit or constant current, you don't need to go to the expense of creating a high voltage supply.
 
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Thanks Colin. I have 10 though, so 3x 3 in series, would leave 1 spare...

2 arrays of 5 could work, but that's 18v 3A.

Any opinion on the links I posted?

Thanks
 
If the LED fv is '3.6V' remember that's a 'typical' figure. You need to allow some voltage margin for production tolerance plus current-limiting circuitry (which may be no more than a resistor, depending on the power supply characteristics). So if you're putting ten LEDs in series, 36V won't be enough. IMHO you would need at least 38V. But as Colin says above, you can do without the extra supply by using LED strings of 3 + 3 + 3 (+1 if you really need 10 altogether). I'd use a respective constant current source for each string (not constant voltage, because the LED vf may change as the LED heats up) .
 
Thanks Alec
Yeah constant current is what I'm after. the reason I need 10 is because I'm making 2 sets of 5 (2 spot lights for my Jeep).

Currently I have a 36v 3A constant current driver, but it needs a 220v input. I have a 220v inverter, but going from the car's power to 220v back to 36v is obviously not ideal. It's my last resort at this point.

What I really need is a DC-DC converter that can generate a constant 3A from the car's power. It doesn't have to be 36v - I'm quite happy to have series/parallel arrays, but to maintain the 10 LEDs, it would need to be 5s2p or 2s5p.

The reason I wanted the 36v was so that I only needed one converter...
 
Look for an LED switching driver. The primary difference is the switcher feedback is based on regulating current versus voltage output. You also need massive heat sinks for the LED that are dissipating 10 watts of heat.

If you can identify the switcher controller IC in the boost switcher you might be able to modify it by putting a sense resistor for current and moving the voltage feedback to the sense resistor. A good LED driver has both voltage limiting and current limiting so if there is a broken connection to LED's or a burned out LED the switching voltage does not go wild and cause damage to switching MOSFET or rectifier diode.
 
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