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Topic: Help with schematic (changing GND to 6v) (Read 1 time) previous topic - next topic

Pancra85

Ok, I needed a driver for a 12v led and did this:
(full article explaining everything: http://www.tbideas.com/blog/build-an-arduino-shield-to-drive-high-power-rgb-led/
Vcc connected to 12v and of course GND to 0v.

It works fine, but now I need the same thing but instead of driving a 12v led I need it to be 6v, but the thing is that because of design Vcc still needs to be connected to 12v.
My question is: Can I connect GND to 6v so the voltage difference of the led is 6v??? (12v-6v=6v)
Also do I need to change anything on the circuit??

Thanks!

cjdelphi

question is...

how much current to power the led is required?

that circuit is overkill... and yes the same circuit would be fine, r2 is doing the work to protect the diode.

DVDdoug

Quote
My question is: Can I connect GND to 6v so the voltage difference of the led is 6v??? (12v-6v=6v)
What?   I'm pretty sure the answer is No.  But, I'm not sure I understand.  Where's the 6V coming from?  If you have a 6V supply, why don't you use it directly instead of trying to subtract?

If the 6V & 12V power supplies share a common ground and you ground the 6V supply, you are shorting it out.

You can measure the voltage difference between two power supplies (if they have a common ground), but if you try to pull power (current) from the difference you might have trouble (because you'd be trying to run current "backwards" into  the low-voltage supply.)


Pancra85

Quote
question is...

how much current to power the led is required?

that circuit is overkill... and yes the same circuit would be fine, r2 is doing the work to protect the diode.

Ok, the led is this one: http://www.alibaba.com/product-gs/712130845/10_Watt_RGB_LED_high_power.html
it is a high power RGB and as you can see on the table you need around 12v for BLUE and GREEN but you need around 6v for RED, and also the leds have a common positive pin.
As this is the case, I need to connect 12v on the positive side, and I was thinking that I could connect 6v on the negative side of RED instead of 0v so it has the required voltage.

Quote
Where's the 6V coming from?  If you have a 6V supply, why don't you use it directly instead of trying to subtract?

I only have a 12v power source and I was thinking getting 6v from it with a voltage divisor (resistors), the question is if it will work connecting the RED driver to Vcc->12v and GND->6v.

The schematic I referenced on the first post is a led driver and I need one for each color (RGB, so three of them)

CrossRoads

Why so convoluted?
Just drive with 3 logic level, low Rds, low Gate capacitance, N-channel MOSFETs
http://www.digikey.com/product-detail/en/NTD5867NL-1G/NTD5867NL-1GOS-ND/2401422
10k pulldown resistor to hold gate off while arduino starts up.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

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