ebay power supply

[ecat]

Adding up the costs of a diy cnc machine continues to make my eyes water so finding these makes for a refreshing change :)

In theory the output from the opto isolator should be wired to a feedback pin on the main PWM controller chip. If memory serves me correctly and the chip follows convention then the function of this feedback pin is very simple:

if the voltage on this pin is above a certain threshold value (around 2.5v perhaps) the PWM controller switches off and if the voltage on this pin is below said threshold the PWM controller switches on - this is how the output voltage is regulated.

As the PSU already has some way of varying the output voltage there may be some additional complications but all that should be needed to decrease the output voltage is a change to a single resistor such that the voltage on the feedback pin is increased by about 20% for a 40v to 47v output range (ish).

Disclaimer: I know enough to hurt myself and nothing more :)

[HankMcSpank]

I'd have thought the way they do this is to modify the duty cycle of a PWM stream. I'm tempted to order one - it appeals to the lazy mountaineer side of me ("I want to climb it because it's there" or transposed to this particular situation "I can't be arsed to climb a mountain, so I want to get the voltage down on this 50V PSU because erhm it's not 45V")