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Ah, I see. then you're right, more volts needed

W

Thank you Wells_C. I did try, even with no resistor it was drawing only ~90mA.

Hi Joe,

You may be able to simply lower the series resistance and get more current. LEDs typically drop a constant voltage across their leads, around 1.5 volts. Subtract that from total circuit voltage, then use V=IR to calculate how much resistance to use to keep the LED under its rated max. current.

Hope that helps,

Wells

Thanks anyway Dinesh. That looks similar to the "front end" of the circuit I'm currently using, with a transistor driving the LED. I'm just looking for a way to boost the 6V from my batteries to around 8 or 9, and still get ~150mA going through the LED.

Oops! Just noticed our admin gave you a good link.

Never mind

If you're trying to boost your 6V dc supply to 9V, you may lose out on the current, entropy being what it is

You need a constant current source because the led will try to draw more current as it warms up, changing the colour characteristics. You could always just configure something loke this (the zener is not necessary):

Thanks. The four AA's are connected in series so I'm only getting the mAh of one, maybe around 2700 mAh, which is plenty since it's only being illuminated for a minute or so at a time.

The first and last are current limited below your requirement. Not sure about the middle one, though.

By the way, one AA battery might yield about 2,000 mAh. Four of them x 1.5V x 2,000 mAh nets you 12,000 mWh of energy. Let's estimate your conversion to 9V efficiency at 67%, so you are at 8,000 mWh on the output side. 8,000 mWh / (9V x 200 mA) is about 4 to 4.5 hours.

Four hours is an eternity if the display is only on briefly for viewing. It is not very long at all if the display is left on for any length of time.

Thanks very much, John. All of those circuits are quite interesting, and I will be studying them.

Is this of any use: http://www.electroschematics.com/6788/3 ... converter/