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Grounding for Bicolor LED driver

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Hackpenguin

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Im trying to build a Bicolor LED flasher, I know i need to have the polaruty to swap with it and I want to be ab le to handle more than 200mA. My first design used 4 Power Transistors and 1 low power transistor to make a invertor fror the push pull. I would like to see about making 1 with just a 555,a few resistors,capacitors and just 2 transistors making a push pull.now on instructables i saw that on a tv scope amplifier they used 2 capacitors for making the virtual ground. Will that work with my driver? Also i'm planing on using 12v and not 9 as you see in the schematic. I would rather not use resistors to make the virtual ground. CN1 is the string of LEDs in parallel with resistors
 

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Tony Stewart

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You are going about this the wrong way.

The NE555 can easily drive 100mA witha 2V drop from either supply rail. The LED will have some internal resistance.
If you use Red Yellow which is around 2.1V and want to drive many LEDs up to 100mA , then you only need 2.1V +2V + If*Rs =V+ for current regulation. Thus 5.0V is ideal not 9 or 12V unless you drop more LEds in series.

The changing the duty cycle will change the colour from one to the other at high freq like 1kHz or alternate if you use a low frequency.

So the transistor are not needed. absolute max is +-200mA.

If you choose White, Green or Blue it is around 3.1-3.3V nominal and if 5V is well regulated, then Rs can approach 0-10Ohms or less.

If using only 20mA this raises the value for Rs.
 

MrAl

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Most Helpful Member
Im trying to build a Bicolor LED flasher, I know i need to have the polaruty to swap with it and I want to be ab le to handle more than 200mA. My first design used 4 Power Transistors and 1 low power transistor to make a invertor fror the push pull. I would like to see about making 1 with just a 555,a few resistors,capacitors and just 2 transistors making a push pull.now on instructables i saw that on a tv scope amplifier they used 2 capacitors for making the virtual ground. Will that work with my driver? Also i'm planing on using 12v and not 9 as you see in the schematic. I would rather not use resistors to make the virtual ground. CN1 is the string of LEDs in parallel with resistors

Hi,

With 2200uf caps you might only be able to get a max pulse width of about 20ms. That may or may not be long enough.
You might also add some series resistance.
The equation is:
dv=i*dt/C

where C will be twice the value of one cap if they are both the same value for this circuit.
You also dont want dv to be too large or else the LED will dim.

If you switch too fast you'll get the combination of the two colors and wont be able to see both colors individually.
 

ronsimpson

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I would rather not use resistors to make the virtual ground.
You said 12V.
I don't know what type of battery.
Can you use two 6V batteries? 6+6=12 and the center is the virtual ground.
Or use a bunch of 1.5V batteries. Tap off at the 1/2 point.
 
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