4.5 volt converter

trivergata

Enlightened
Joined
Nov 5, 2004
Messages
438
Location
Huntsville, TX
Who makes a 4.5 volt Converter board - I've got a cheapy light that I want to regulate and improve the led in, and I guess this is the way to go about it. Any help would be greatly appriciated.
Josh
 
IMO, this is not the way to go about it.

LEDs are current devices, drive them with constant current sources. Using constant voltage sources is looking for problems.

What's the light/LED you want to drive? What's the battery?

Doug Owen
 
The light I'm modding had a good housing and a 3 AAA carrier, so I just want to improve it. I've already done some lathe work to the housing to fit my needs, but the electronics are fairly new to me.
That's why I'm here.
Thanks
 
I would suggest an LDO Linear current regulator.

A wizard gets you about 65-75% efficiency. Making some assumptions here:

500mA current,
Vf=3.5V

So using a wizard, input = 4.5V, output = 3.5V, current = 500mA, You will be drawing 555mA from the batteries (if it were in buck mode). So it looks like you actually start out in direct drive or boost mode.

Given the same conditions, with a linear regulator, it'll draw 500mA at the start. So it looks like a wizard would be worse than an LDO Linear.

The linear will start out at 77% efficiency, increasing to 97% when it drops out of regulation.

There are several linear regulator designs that give you less than 0.1V of dropout, meaning you get flat output until the battery voltage drops to 0.1V above the Vf of the LED. At that point, current starts to gradually diminish as the battery voltage drops.


This gives you nice flat output for the majority of battery life, and gives you a nice amount of usable dimming light as the batteries die.

3 Alkaline AAAs can only deliver 500mA for about 20 minutes before they drop down to less than 3.6V. So regulated runtime will depend on current, and Vf of the LED.


Given all of this, your best bet (cost wise) may be to simply use a resistor. 1 ohm should do it.
 
um.. duh why didn't i think of it... trivergata... email me: [email protected] I can send you some chips you can use to make a driver.. here is the link to the driver mr. al and i deveolped for my nano.. the chip i use is good for about 2A and i've run it as high as 1800mA. the efficiency is very high when Vbat is close to Vf, the more distant the less efficient.. has the tradeoff of once Vbat gets to Vf the output will drop exponentially.
 
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