Please see the simple SMPS buck circuit below (24V to 12V)
Notice the load on the 'first' secondary coil is about 100mA (marked 'fb' This coil is used as the feedback to the MC43063 to regulate the switching duty cycle.
The other secondaries have different loads. One has a 120 ohm resistor (100mA) and the others have 10K resistors applying less load.
Now please see this output voltage plot :
Notice that FB (green) rises to 12V and remains steady.
Notice that one (blue) rises to just above 12V and remains steady.
And notice that the other outputs with smaller loads, raise to above 12V and keep slowly rising.
I notice that if I use a smaller load on the feedback output, then the outputs still drift.
What is causing this drifting in the secondary output voltages, and how can I stop it?
I realise I can use a voltage regulator (78L12 etc.) but until I know what is causing this drift I'm reluctant to try and regulate it.
Also what will happen if I apply a variable load to the output coils, will the output voltage fluctuate?
Thank you in advance.