# Topology choice for wide-output-voltage-range SMPS

I'm intending on building a off line (230VAC), 50W, isolated, constant-current switch mode power supply. This by itself is not a big challenge with the plethora of application notes and examples available.

However, a particular requirement that I have is i need to provide a voltage range on the output of 1V-100V. For the 50W power level, I would expect a flyback converter to be the best topology, but my understanding of flybacks leads me to believe I cannot achieve that range on the output.

My question is; have I missed something with flyback topology design, and is there a different topology that is more suitable for the requirements?

EDIT: The 50W quote for power is maximum power output. The minimum power output would be ~1W. So to keep the current constant, the supply could go between 1V and 100V.

• 100:1 output voltage range constant power is not possble – Sunnyskyguy EE75 Apr 4 at 2:16
• What is the maximum amperage? $50W/100V = 0.5A$ over all output? – Unknown123 Apr 4 at 2:28
• 1 volt out delivering 50 watts is a current out of 50 amps. Given that you will be running about 50% efficient (or probably less) this means at least 50 watts of internal dissipation AND secondary windings capable of not melting at 50 amps plus diodes rated at 50 amps continuous. Think again unless you like pain. – Andy aka Apr 4 at 7:28
• Thanks for your responses. I've edited the question to clarify the max and min power, and the method of driving the output. – Joe Apr 4 at 21:49

If your only control of the energy-transfer is by the duty cycle of a switch, then 1% to 99% may be in conflict.

The circuit need two periods:

1) storing energy into the inductor

2) removing energy from the inductor

Storing energy with 200 or 300 volts across the inductor: OK its fast

Removing energy with only ONE VOLT across the inductor (or a schottky diode voltage_drop + ONE VOLT): not so fast.

• Yes this would appear to be the problem with trying to design a power supply in this way. Such a large difference in the duty cycle for a fixed frequency. – Joe Apr 4 at 22:09