Hi,
I built a simple robot platform that uses 11.1 lithium 1100mah battery. The two motors take 1.5 - 4.5 volts at 350ma load, 1amp stall, each. My idea is to use two voltage regulators, a 9v and a 5v, rated for 1amp. So my arduino pulls around 200ma and with the motors thats 900ma for the 8v reg, the 4v reg won't have to power the arduino, so 700ma.
900ma x 2.1v = 1.89watts - 8v regulator
700ma x 3 = 2.1watts - 5v regulator
Will the regulators be ok with a heat sink?
Are my calculations correct? :-?
Your text says 9V and 5V regulators and then 8V and 4V regs and then 8V and 5V (equations). I am not sure which numbers you are using. You also do not mention
the regulator you are using.
The power dissipated (Pd) is (Vin - Vout) * Iout.
The junction temperature (Tj) is Pd * Rja + Tamb
Rja is the thermal resistance junction to ambient (regulator datasheet)
Tamb is the ambient temperature
For a typical TO-220 regulator the thermal resistance is apx
70degC/W (no heatsink, no airflow) and the maximum
junction temperature is 150degC.
Using an ambient temperature of 25degC you can have an
absolute maximum rise of 125degC. Adding some design margin
I would make the acceptable rise 100degC.