# high current switch-mode driver?



## justDIY (Feb 6, 2006)

greetings everyone!

I am hoping someone knows a source for high current switch-mode drivers, for LEDs. Either preassembled, kit or just plans.

I'm looking for these attributes:

1) current handling 1.4 to 3 amps
2) buck (step-down), buck-boost (flyback) or sepic mode
3) analog or digital dimming control input
4) preferably low-dropout, like 2v or less

This seems to be a tall order - looking through google, I find lots of drivers in the 350 to 700mA range, and some as high as 1 amp, but nothing past that. Same goes for driver-ic's, in a DIY fashion... TI and Linear have some nice chips for "up to" 1 amp, but nothing over that.

I have a couple applications on the drawing board, some automotive, some residential accent lighting ... and I need to be able to safely, reliably and efficiently drive the 4 watt Red Luxeon III leds.


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## markus_i (Feb 7, 2006)

Hi justDIY,

you might want to take a look at Maxim's MAX1640/1641 or 1772. Buck converter controller, uses external MosFETs for switching and synchronous rectifier and external current sense resistors. The 1772 has a few additional options you probably won't need. Not as simple as the switchers with integral transistor, but very versatile - it's actually supposed to be a multi-chemistry battery charger, but as long as it's putting out a regulated current with low feedback voltage, I'm not fussy. Layout is not too bad if you're using IRF's dual MosFETs in SO-8.
I'm currently (well, it's ongoing, ok?) trying to set up a bicycle light controller around a few of those beasts - at the moment. I'm setting up a programming system for the PIC that's going to control the stuff (actually, I'm waiting for a mechanical kvm switch that's supposed to be in the mail while soldering the ICSP/ICD).


Bye
Markus


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## meteor (Feb 7, 2006)

Hi justDIY,
I'll soon be introducing a new driver which is a hybrid constant current/PWM. It supplies _regulated current limited_ pulses to the LEDs. You adjust the brightness by varying the duty cycle of the pulses with an on-board (or external) pot. The amplitude of the pulses can be set from 1000mA to 3000mA with an on-board trimpot. You'd set the trimpot once for your application and use the "brightness" pot to vary the intensity of the LEDs. It's a buck (step-down) configuration that runs on an input voltage of 4.5 - 14.5 VDC. The internal PWM runs at about 3KHz which avoids any "flicker" effects seen with other PWM drivers. Since the output is a constant current pulse no limiting resistors are needed. This driver is intended to eliminate the color shift seen when varying the brightness of white LEDs. A prototype is now in the hands of another CPF'er for evaluation. I'd like to line up some other members with sufficient knowledge and basic equipment to properly evaluate the unit's performance. The circuit is unique in that it limits the output pulse amplitude to a level safe for your LEDs. Simply switching a constant current source on and off will give large current spikes through the LEDs until the regulator "syncs up". This is where this driver is unlike any others I've seen. I'll probably make a new post next week to formally introduce the circuit to CPF.

Frank


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