electronics help needed

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Joe Farina
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electronics help needed

Post by Joe Farina » Fri Feb 26, 2016 9:07 am

Hi, I would like to ask a question about electronics. My display system for holograms uses a circuit based on four AA batteries. I want to use a new LED which uses a bit more power, my old voltage level of 5 or 6 volts isn't enough, about 8 or 9 volts is probably needed. To keep the system compact, with a decent battery capacity (mAh), I want to keep the same kind and quantity of batteries. The new LED will draw about 150 to 200 mA. So, I'm looking into ways of boosting the voltage. This is the option I'm considering:

http://www.mouser.com/ds/2/405/mc34063a-443483.pdf

It also requires an inductor and a few resistors and capacitors to function as a booster. My knowledge of electronics is at the tinkerer level, so I was wondering if there are simpler ways to raise the voltage. Thanks.

Ed Wesly
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Re: electronics help needed

Post by Ed Wesly » Fri Feb 26, 2016 9:16 am

You might have better luck with the advice on the PhotonLexicon site.
"We're the flowers in the dustbin" Sex Pistols

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admin_jsfisher
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Re: electronics help needed

Post by admin_jsfisher » Fri Feb 26, 2016 1:43 pm


Joe Farina
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Re: electronics help needed

Post by Joe Farina » Fri Feb 26, 2016 1:49 pm

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

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admin_jsfisher
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Re: electronics help needed

Post by admin_jsfisher » Fri Feb 26, 2016 2:03 pm

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.

Joe Farina
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Re: electronics help needed

Post by Joe Farina » Fri Feb 26, 2016 2:11 pm

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.

Din
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Re: electronics help needed

Post by Din » Fri Feb 26, 2016 2:14 pm

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):
LEDcircuit024.jpg
LEDcircuit024.jpg (27.18 KiB) Viewed 4964 times

Din
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Re: electronics help needed

Post by Din » Fri Feb 26, 2016 2:16 pm

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

Never mind

Joe Farina
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Re: electronics help needed

Post by Joe Farina » Fri Feb 26, 2016 2:25 pm

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.

Wells_C
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Re: electronics help needed

Post by Wells_C » Fri Feb 26, 2016 2:41 pm

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

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