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Need an IDEA for the following circuit..!

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Greatbuddy

New Member
Dear friends,
I need to design an LED DRIVE CIRCUIT and atleast it must drive 10 leds at a time. Can anyone suggest any circuit?

I have designed a reference circuit. Can you design taking that as reference? and i need resistors values and transistirs current and base resistor may be 10k.
 

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dknguyen

Well-Known Member
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Use individual current limiting resistors for each LED, not one common one. THe forward voltage drop for all LEDs and diodes are slightly different and your circuit depends on them all being exactly the same. THe way your circuit is, these differences will make one LED on and all other ones off.
 
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nike6

Banned
you'd waste a great amount of energy.

you could use a simple booster circuit, based on single transistor.
then you put all the LED in series!

the booster will act as current source (in my simple circuit there is no regulation at all).

small 2n3906 can drive 5 or 6 low-current LEDs from 2.4 volts.

if you need more current use a different transistor.

i mean, something like this (in the attachment). they are all in series!
parallel connection can result in brightness variation.

but you do not write the type of LED.

the booster also will waste energy. but you can use 5 LEDs or 7 LEDs, and it will work, without modification. while if you use 12 volts, you still get a limit of 5 or 6 LEDs.

i found some circuits on talkingelectronics.com
and then tried modified variations of them for some months.
but I am not really a complete expert.
I just needed to step up 5 volts to 6 volts, without to have complicate ICs or regulation schemes.

maybe such a booster would be a solution for your task.
you can not connect LEDs of different color in parallel, as you maybe already know.
 

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dknguyen

Well-Known Member
Most Helpful Member
Use a separate resistor in series with each LED instead of your one resistor in series with all the LEDs. LEDs can't share resistors.
 
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audioguru

Well-Known Member
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You have the HFE of the transistor written down. Why?
The HFE is used when the transistor is a linear amplifier. It is spec'd at 75 for the 2N2222 transistor when the collector to emitter voltage is 10V.

Don't you want the transistor to saturate with a low voltage loss and light the LEDs? Then look at the "collector to emitter saturation voltage" spec in the datasheet where they say to use a base current that is 1/10th the collector current. I have Philips' datasheet.

So for 10mA in your 10k base resistor its input voltage must be (10k x 10mA) +0.7V= +100.7V. If you reduce the value of the base resistor to 430 ohms then ANY 2N2222 transistor will saturate well with a 100mA load and a +5V input.
 
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