variable output bench supply

Hi, a flyback is not a good choice for variable supply, forward converter is better. The output range you want is hard to achieve (as you have allready noted) with any kind of single swithced coil. Another way that works, needs more components, is to drive each end of the primary with 1:1 square wave and change the phase shift betwwen them to change your output voltage. There are several psu chips that use this method, and it makes the transformer design very easy. To get 200W at low voltages means a heavy secondary so you would be better to use a second switching regulator after your main output to lower the output voltage and boost the current.

Yes, flyback will work for this but no matter how you go about it, you should expect trouble because of the wide output voltage range.

For wide output voltage ranges, it is usually easiest to give up on trying to make the switcher run at a constant frequency. When you work out the ideal inductance for the high voltage end, you will find that that value leads to continuous mode operation at a lower voltage. Both continuous and discontinuous mode can be designed for but making the circuit work right at the boundary is real trouble.

If instead, you always wait to some short time after the load side inductor current stops, you end up with a frequency that decreases at the lower voltages and at the higher currents. This is electronically easy but not the ideal case. You do not want a large change in frequency with load current.

Assuming you are using a current mode circuit, you can use the control voltage to set both the turn off point and to shorten the dead time. With that included, the system's loop gain stays in a narrow enough of a range that you do have some hope of a simple controller being stable.

Typically all of the smarts of the servo circuit are connected to the load side circuit. A small transformer and bridge supply the power to run the control electronics.

If you hoping to hand wire all of this, you are asking for even more trouble. For hand making the circuit, cutting bits of copper clad with tin snips and gluing them down on a larger sheet is the best way to go. You can use a Motor Dremel tool to cut out areas of copper. The stuff from

All that said this is not a project for first timers. Off line switchers, which is what this sounds like, are hazardous to debug and troublesome to design.

All topologies are typically used at constant output voltages. It is more a question of whether the flyback is more trouble than forward in this case.

For very wide range conversions you might consider a synchronous step down buck regulator with hysteretic current mode control. The frequency changes depending on the output voltage (being maximum at 50% duty), and as a bonus you can simple implementation of current limiting. The down side is output ripple is more difficult to filter at the extreme low output voltages because of the reduced frequency.

Assuming you want isolated output then you would also need a DC-DC converter that steps 170VDC to 200VDC unregulated. This could be a simple fixed frequency square wave drive using H bridge, a gate driver transformer and 200W isolating 170V200V transformer.