paigioph:
I am searching for a cheap constant current driver/circuit. I have four of this kind that takes 12V input voltage and gives 900mA at 12V (unfortunately it is not working with 5V input).

I need a circuit that takes 5V input (from a 5V/20A power supply) and produces around 1A constant current.
Is there such a device out there? Which parts would I use to build one on my own? Thanks.

You will need to step up the 5 volts to 12 (or more) volts. Then, use this classic circuit:

The constant current is defined by R and the formula is `[b]R = (1.2 / I)[/b]`

So, for 900 mA, you would do R = 1.2 / 0.9 = 1.33 ohms.

Of course, for 12 volt compliance voltage, you need at least 2 to 3 volts more on the input, so your 5 volt up-converter should provide 15 volts DC minimum.