Duncan PSU Designer II

Now that you have a general understanding of what goes into a power supply and roughly what each part does, take a look at Duncan PSU Designer II software.  This power supply modeling software takes a lot of the heavy math out of power supply design and will even provide estimates on how much ripple a power supply will pass to your amplifier.

dpsu2

So, how much ripple is too much ripple?  Consider the following.

If transformer coupled output, your B+ flows through the output transformer. Any ripple there is going to be stepped down at the secondary. Say you have a 5k:8 transformer. The voltage ratio is 25:1, so even a few mV of ripple on the B+ becomes pretty tiny reflected on the secondary. You also have the AC impedance of the OPT primary working in your favor.

If the B+ is going to an input stage or preamp (assuming single ended), you want to be a little more careful because ripple is magnified by the amplification of the stage. Here too it is going to be somewhat mitigated, depending on your topology, but I try to minimize it as much as possible in the modeling. Real world performance is probably going to be worse. Luckily, input stages usually run at much lower current, so you can afford brute force filtering.

Note that Duncan’s software is not a replacement for understanding power supplies!  You will need to change the configuration to suit your application and/or parts.  YOU ALSO NEED TO MAKE SURE YOU INSTALL A SWITCH AND FUSE(S).  These are not shown in the modeling.  That said, this tool is seriously indispensable for quick power supply estimates and design.  If you ever see Duncan Munro, buy him a beer.

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