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/
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.