I am using this voltage regulator.
Following this example:
For input power source, I am using old SATA convertor power adapter, which produces 12V 1.5A max (I tried various power supplies, all similar result).
With no load, everything works as expected, instead of R2 I have potentiometer 0 – 5k OHM. I can easily configure any voltage range from 1 to 10V using the potentiometer.
The problem happens when I connect any load. My understanding of voltage regulators is, that you can configure them to provide certain voltage, and they will hold it as long as you don't exceed the maximum current they can provide (3A in this case). But that isn't happening in my case.
I connected Vout to a simple (strong) LED light, that draws 0.2A at 4.5V just to test it out, and while the LED is working, the Vout immediatelly dropped down to 3.3V (Vin also dropped from 12V to 11.5V, but VR should provide same Vout no matter of Vin according to manual, as long as Vin is at least 1V higher than required output). Measured Il was max 0.2A, never more than that.
Is this a normal behaviour? Why is VR not capable to provide stable voltage on output? I would like to use it to power some USB device, which expects stable 5V output, this doesn't seem very stable to me. My expectation is that it will provide stable Vout as long as I don't exceed 3A Il.
Best Answer
The voltage drop in this regulator circuit from 12V to 4.5V is 7.5 Volts.
For a linear power supply, the power dissipation is \$V_{drop}*I\$.
At 0.2A this will cause the regulator to dissipate 1.5 Watts.
With 50 C/W to ambient this means an 75 degree increase in temperature.
If you did not use a proper heatsink, you're most likely running into the thermal overload protection.