I am designing a 30 V 5 A lab bench power supply having SMPS as a pre-regulator for the linear stage which will keep the SMPS output always 4 V higher than the main output voltage. This means SMPS output will be varying from 4 V to 34 V. For SMPS, I have used forward topology and therefore it requires a minimum load to operate properly. After some trial and error in the simulation, I found out that it requires a 1.2 W minimum load at its output and therefore I want to have some margin and want to place a 2 W load at the output. But since the output voltage will be varying from 4 V to 30 V I can not just put a resistor at the output because if it is dissipating 2 W at 4 V then it will be dissipating 144.5 W at 34 V which is obviously not practical.

Is there any simple way that requires only a few components to overcome this problem?

EDIT: Extra details if required:

1. I am using UC3844 as the controller IC. Link to datasheet.

2. I have tried using opamp to maintain a constant voltage across a resistor and hence the power dissipated by it but the rest of the voltage is dropped across a BJT which is carrying the same current as of the resistor and therefore in total around 17 W (BJT and resistor combined) is dissipated at 34 V which is still pretty high.

3. This is my SMPS schematic:

• ”forward topology and therefore it requires a minimum load to operate properly” If implemented correctly, it would be happy with no load. Fix that instead of putting a bandaid on it? Commented Dec 9, 2021 at 10:16
• Maybe you have implemented a flyback converter - they require a minimum load usually. Be clear about this as winny implies. Commented Dec 9, 2021 at 10:23
• Where is the problem with pulse skipping? After implementation the SMPS must maintain constant output with 10k dummy load only.
– user208862
Commented Dec 9, 2021 at 10:23
• @winny Maybe I need to learn more about the forward converter but AFAIK if there is no load at the output, MOSFET will be switching with a very low duty cycle, and next to no power will be transferred to auxiliary winding and the control IC will shut down and will take some time to turn on again due to soft-start circuit. Commented Dec 9, 2021 at 10:25
• @Andy aka No I am pretty sure I have used forward converter Commented Dec 9, 2021 at 10:25