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I am trying to convert 5v PWM signal to 10v using ULN2803a IC. My target device (a dual channel LED light)expects two 10v pwm signal and GND via a 3.5mm audio connector. The part I am struggling with is ULN2803a is a sink, i.e. all available circuit for LEDs uses ULN2803a's output pin as GND connection to individual LEDs (since its a sink) while the +ve end of the power supply directly connects +ve end of individual LEDS. This does not work in my case, as I have to provide single GND connection and two +ve (PWM) via the 3.5mm audio connector, thus both channels sharing the same GND connection. I am a novice, but I can pick up from a circuit/schematic I am following this post: http://www.haberocean.com/2014/11/simple-circuit-for-controlling-led-strip-using-arduino-mega-and-uln2803/

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  • \$\begingroup\$ That's why you should be using a half-bridge instead. \$\endgroup\$ – Ignacio Vazquez-Abrams Apr 27 '17 at 4:27
  • \$\begingroup\$ You might consider a sourcing driver then (I can't speak about whether they match up with your needs as you haven't specified the "dual" LED device), like the UDN2981 or the LMD18400, to name two. \$\endgroup\$ – jonk Apr 27 '17 at 4:49
  • \$\begingroup\$ Does the LED light really need 10V and 0V, or can you get away with 10V and floating? \$\endgroup\$ – Ignacio Vazquez-Abrams Apr 27 '17 at 6:03
  • \$\begingroup\$ @IgnacioVazquez-Abrams I had initially tried L293D, but for some reason the result was not correct, I built the second circuit with uln2803. \$\endgroup\$ – Ranjib Apr 28 '17 at 5:24
  • \$\begingroup\$ @jonk this is the LED light (kessil.com/aquarium/Saltwater_A80_Tuna_Blue.php) . 10v pwm is only used for controlling intensity, spectrum of the light, it has its own dedicated power supply. This a reef tank light. I am trying to build an opensource/hardware reef tank controller, which includes both software and electronics/housing (github.com/ranjib/reef-pi). I can share all the details. Thanks for your inputs, I'll go through them \$\endgroup\$ – Ranjib Apr 28 '17 at 5:27
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Can I suggest you use a ProFET high-side driver IC. These devices give you a switchable high-side drive with protection from all sorts of things, including output over-current.

You can find and select ProFETs readily enough in distributors. If surface-mount is awkward for you, I'd recommend the BTS50080-1TMB Smart High-Side Power Switch in a TO220 7-lead package. You can drive its control input directly from your ULN2803 outputs. Its output drives your LEDs with your 10 V or high impedance for PWM driving.

If surface-mount parts are no problem, look at the BSP752T which is cheaper, smaller and can be driven directly from 3.3 V or 5 V logic rather than through the ULN2803.

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  • \$\begingroup\$ Thank you. I'll read up on this. I had read about mosfet, but was under the impression that I wont need uln2803, I went with uln2803 because of existing tutorials. You are right, SMD will be bit harder for me. TO220 packaging I can solder easily. My target device wont be drawing too much current, this current will only be used for controlling intensity/color of the LED, it has dedicated power supply of its own. I think I can go with simple N channel power mosfet as well then (adafruit.com/product/355) \$\endgroup\$ – Ranjib Apr 27 '17 at 6:46
  • \$\begingroup\$ @Ranjib, yes, you can use a MOSFET plus the gate drive components. It looked like this would use fewer components and give you short-circuit protection. Good luck and I'll leave you to your choices :-) \$\endgroup\$ – TonyM Apr 28 '17 at 12:08

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