Adjustable Power Supply v18.08
- 1 In Progress
- 2 Design
- 2.1 Applications
- 2.2 Requirements
- 2.3 Research
- 2.4 Modules
- 2.5 Calculations
- 2.6 Conceptual Design
- 2.7 Software
- 2.8 Possible Parts
- 3 Bill of Materials
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.
Powering 3D printer
Workbench power supply
At least 360W output (12V at 30A)
Adjustable DC voltage output up to 24V
- ~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
Existing Open-Source Projects
This page is a great guide.
Similar DC/DC converter with isolation but without adjustable output or display: ~$80
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.
These designs may not be safe or functional. Use at your own risk.
DRAFT, values are not correct
10 gauge wire for secondary winding. Primary has 8.5 turns, try 3 or 3.5 for secondary.
Output Capacitor: Aluminum (cheaper but more lossy), organic semiconductor (good overall), tantalum (best for surface mount) 
Output Inductor: Bobbin or rod-core cause more noise 
Isolator: DGTL ISO 2.5KV 2CH GEN PURP 8DIP
Synchronous Rectifier IC: SOT-23-5
Digital Potentiometer: IC DGTL POT 10BIT NV 14-TSSOP
Voltage regulator: IC REG BUCK 12V 1A TO220-5
Inductor: FIXED IND 33UH 30A 1.9MOHM SMD (would require 2.5 MHz switching frequency)
Rectifier Diode: DIODE SCHOTTKY 250V 40A TO220AB
555 Timer: IC OSC SINGLE TIMER 3MHZ 8-SOIC
Input/Output Capacitor: CAP CER 15UF 100V X7S SMD
High-side gate driver: IC HIGH-SIDE DVR HS HV 8-MSOP
Gate driver bootstrap diode: DIODE GEN PURP 100V 200MA SOD80
Oscillation setting: CAP CER 47PF 50V C0G/NP0 0201, 4.7 kOhm resistor
Short circuit protection timer: CAP CER 0.47UF 100V X7R 0805
Error Amp Feedback: CAP CER 0.068UF 100V X7R 0805, 100 Ohm resistor
Op amp for voltage buffer: IC OPAMP GP 1MHZ RRO SOT23-5
Rectifier: RECT BRIDGE FAST 3PHASE I4-PAC-5
Switching Transistor: MOSFET N-CH 40V 95A TO-220AB
Cost of components ~$80
Input Capacitor: CAP ALUM 18000UF 20% 160V SCREW
Snubber Diode: DIODE SCHOTTKY 250V 40A TO220AB
Snubber Capacitor: CAP CER 0.18UF 250V X7R 1812
Active Snubber Control: Active clamp flyback controller UCC28780D
Integrated Gate Driver: IC DRIVER HI/LO SIDE 600V 14-DIP
Output Diode: DIODE SCHOTTKY 45V 60A TO247AD
Synchronous Rectifier IC: SYNC RECTIFIER FLYBACK
Synchronous Rectifier Transistor: MOSFET N-CH 40V 95A TO-220AB
Bill of Materials
Buck/Boost Converter Module