In Progress

Arduino code for voltage sensing and control

Arduino code is hosted here. This code is far from finalized and represent only one of many possible design approaches. Post as many variations or improvements as you can as long as they have advantages.

Next steps: - implement SPI to control digital potentiometer

Design buck/boost converter module

For affordable buck-boost that can change voltage by a factor of five, high frequencies are needed to reduce inductor size. The Arduino has a limited PWM frequency (less than 100 kHz?).

Volt-second balance on the inductor means that the average voltage across it over one switching cycle is zero

Discontinuous mode is when current through the output inductor is zero for part of the switching cycle

Next steps: - simulate main circuit - design PCB - research microcontroller options for voltage control and display

Figure out ways to salvage or build transformers

Investigate ways to use high frequency for more efficiency in power transformation as well as smaller inductors.

With new Silicon Carbide MOSFET technology, maybe feasible to use flyback transformer at high frequency as described here.

A flyback transformer could more compact and cheaper initially, but the lifetime cost of replacing a large input capacitor would likely outweigh the initial savings. It is also more complex than an AC transformer, so probably not the best choice for this application.

Design

Applications

Powering 3D printer

Workbench power supply

Charging batteries

Requirements

At least 360W output (12V at 30A)

Adjustable DC voltage output up to 24V

120Vac input

Microcontroller

~11 I/O pins for 7-segment display

2 I/o pins for rotary encoder and power switch

at least 4 I/O pins for SPI control of digital potentiometer

1 ADC for output voltage sensing

5V output to power other ICs would be nice

minimum requirements: 17 I/O pins, 1 ADC

Research

Voltage Conversion

This page is a great guide.

Astable multivibrator

Buck–boost converter

Understanding Buck-Boost Power Stages

Buck Converter Design

Similar DC/DC converter with isolation but without adjustable output or display: ~$80

Flyback Transformer

The Active Clamp Flyback Converter: A Design Whose Time Has Come

A Comparison of Different Snubbers for Flyback Converters

Inductor and Flyback Transformer Design

1200 WATT FLYBACK SWITCHING POWER SUPPLY WITH SILICON CARBIDE SEMICONDUCTORS

Inductor volt-second balance, capacitor charge balance, and the small ripple approximation

Flyback transformer design considerations for efficiency and EMI

PASSIVE LOSSLESS SNUBBERS FOR HIGH FREQUENCY PWM CONVERTERS (page 41)

Modules

edit

Arduino Power Subcircuit

Flyback Transformer

A flyback transformer would most likely be operated in continuous conduction mode, so transformer size will be limited by core saturation. A toroid with powder core could be a suitable solution.

Switching speeds of MOSFET and diodes should be minimized to reduce switching losses. Winding losses should be minimized as well.

Selecting a Distributed Air-Gap Powder Core for Flyback Transformers

Inductor Design Tool