1.5 to 3a buck converter?

[justDIY]

Greetings

I'm looking for recommendations on controller / regulator ICs to build a 1.5 amp (minimum) switch mode buck (or buck-boost) converter.

Application will be a constant current source for 1.4a Luxeon III red-orange stars.

Input voltage 12 to 15vdc
Output voltage 6 to 12vdc
Ouput current 1400mA to 1500mA

the biggest feature I'm looking for is the constant current output of course, but I also need some way to dim the output - pwm input preferablly but regular analog is good to (like 100% or 50% output). also a low 'band gap' or refrence voltage is crucial - idea is to get away from burning power resistors. 250mV or less is ideal

I was looking at the HV9910, but it doesn't seem really suited to handle low-voltage DC to DC conversion... but it has all the nice features I need

I found the MIC4682, and it looks interesting - I'll be ordering some samples soon unless someone's tried one already and it sucks? ... none of my US suppliers carry the chip, which turns me off

I found a few on the Linear.com website, but I'm hesitant to order samples since they cost so much, and none of my US suppliers carry the parts, which is a turn off!

Supplier's I've checked: Digi-key (prefered, they're real close), Mouser, Newark, Jameco

Thanks for any input!

 

[Oznog]

Input voltage 12 to 15vdc
Output voltage 6 to 12vdc
Ouput current 1400mA to 1500mA

I was looking at the HV9910, but it doesn't seem really suited to handle low-voltage DC to DC conversion... but it has all the nice features I need

Everything you've mentioned indicates the HV9910 is ideal for what you want to do. Any DC/DC converter other than this type of current mode PWM is way more complicated and less effective.

What did you see as the problem?

 

[justDIY]

sorry for the delay in my reply.

The problem I have with the HV9910 is the step-down configuration requires Vin => 2Vout (according to their datasheet).

That won't work for automotive applications, unless I want to build a largely parallel string of leds.

I have tried their flyback buck-boost configuration, but I'm not able to get it working properly. I setup a breadboard, following the formulas in Supertex App Note AN-H49 "Buck-Boost-based LED Drivers using the HV9910"

The calculations indicate I need a 6uH inductor with a peak current rating of 8 amps (?!)... well, smallest I have is a 10uH inductor rated at 20a

So I plug the inductor in there, and fire up my circuit, dumping the output into a bank of power resistors, measuring the voltage drop, I'm only seeing approximately 600mA into the resistors, less than half the output I configured Rsense to deliver (0.16 ohms)

I'm using a 7 amp hour 12 volt "gel cel" as my power source, voltage at the battery is about 13.2

The other problem I have with the hv9910 ... in the main datasheet, the formula for buck-boost mode are different than the formula in the app-note ... and they yield grossly different inductor sizes. Any idea why this is, and which one is possibly correct?