Power supply

Notes on power supplies

• https://www.youtube.com/watch?v=nbKwUSH9NiY : Good series on SMPS
• http://www.powerelectronics.com/content/guide-selecting-inductors-switching-regulators Inductors

Stages

I would like a 2 stage design. The first stage is a switching supply that gets it a few volts above the target, then the second stage is a linear regulator to get it down to the target. The current regulator should probably be attached to the first stage.

IC

I can use something like a lm2596 but, it comes with a pretty low current limit. It may be possible to overcome that with something like an external transistor.

The lm723 has built in current regulation and can be used in switching mode.

Discrete

Not exactly sure how to do this, but I could built it handle whatever current I wanted.

Transformer and Rectification

The current is rectified, then converted to a high frequency signal then passed through a transformer, then rectified back to DC. I think I want 10v, 40v and 160v taps on the transformer.

I'm curious about using mosfets instead of diode for the rectification.

Switch Mode

For the switching regulator; you've got the basic switching layout with the inductor, capacitor and switch. I need a control signal. In theory, a frequency square wave with a duty cycle equal to V_out/V_in will work. I think I'll use the inverting buck boost converter. It only needs one more part and it would give me access to higher voltages. It's most efficient in then 0.5-2x range so we can switch what tap we're using from the transformer.

I think the easiest way to do that is feed either a triangle or sawtooth wave into the - and a reference voltage into the + of an op-amp. Here's a simple sawtooth circuit with 3 transistors, 1 cap and a few resistors.

While that will work in theory, I don't think it will be precise enough in practice. Instead, use an op-amp with + as the reference voltage and - as the output to the load. This just sets the whole thing up as a voltage follower.

Then we need low-pass filter on the output.

Current Limit

FINISH THIS

Get a beefy 1Ω resistor between the switching regulator and linear regulator. This provides our current sense. I need to work through the logic, but that gets fed into the switching control to lower the voltage if the current draw gets too high.

Linear Regulator

This should only be shaving a volt so I don't think I'll need anything too beefy. A simple regulator might do or an op-amp with a transistor. The goal is really to smooth the output.

Basic

I'd like to build a basic version around a buck-boost module.

I have two ideas for current regulation; either linear regulation or a circuit breaker. Linear regulation is pretty simple. But I'm really only concerned with current regulation to protect against accidental short circuits.

Here's one, but I don't like it. I don't want a relay because it's going to be slow and the current limit will be relative to the voltage.

Modular Build

These are common

• DC power supply (ATX or flyback)
• DP50V5A regulator

DC Supply Mod

Get one of the cheap DC modules and modify it to accept feedback.