User:ZyMOS/Howto build a workbench power supply

This is a design for a workbench power supply. Its not recommended for a novice. Its more of a proof of concept for an efficient (small, light weight) power supply, which avoids the need for large heat sinks and very large/heavy transformers.

=Features=


 * General features
 * Output voltage: 0 - 50V
 * Output current: 0 - 3A
 * Current limit control
 * Output on/off switch


 * Protections
 * Current limit
 * Short circuit
 * Over voltage on output
 * Negative voltage on output
 * Overheat protection (maybe added)


 * Displays and indicators
 * Actual output voltage display
 * Actual output current display
 * Set output voltage display
 * Set current limit display
 * Transistor Temp display
 * Fan speed display
 * Overheat indicator
 * Current limit indicator
 * Short circuit indicator


 * Other features
 * PWM Fan speed control dependent on temperature

=Components=


 * Input stage
 * Power socket (optional)
 * Fuse holder
 * 820nF 250V polypropylene Capacitor
 * 680uF 400V electrolytic Capacitor
 * Full wave bridge >5A
 * DPST switch >5A


 * Flyback converter stage
 * IRFP448 NMOS power transistor
 * MUR1560 fast switching diode
 * E42/21/20 (datasheet)

=Input filter stage= The input filter is designed to reduce noise on the AC line. Flybacks are noisy converters. The filters probably aren't necessary, but you don't want to see the noise on the rest of your equipment.




 * Components
 * U3 - fuse holder
 * U1 - Varistor
 * U2 - Full wave bridge >5A
 * S1 - DPST switch >5A
 * C1 - Capacitor - 0.47uF 275V
 * C2 - Capacitor - 1uF 275V
 * C3,C4 - Capacitor - Polypropylene 820nF 250V
 * C5 - Capacitor - Electrolytic 680uF 400V
 * C6 - Capacitor - Electrolytic 330uF 400V
 * C7
 * T1 - Common mode choke

The values for many of the components in the input stage are fairly arbitrary. Since I don't really have to meet any FCC specifications, I didn't really do any calculations on the filters.
 * Design


 * U2, S1, T1 need to be higher than the max input current. 5A or greater should be fine.
 * U2 needs to have a good heatsink. It can share a heatsink with other components
 * C1, C2, C3, C4 values can vary from my design. Just have the voltages large enough for to avoid failure.  It's also better to have C2 > C1
 * U1 varistor needs to have a voltage much larger than 120V
 * C5 + C6 should be as large as possible, it would be fine to just have one capacitor instead of two. If you have the room.

=Flyback Design=


 * Components
 * R1 - Resistor 0.15 5W
 * R2 - Resistor 1.5k
 * Q1 - Transistor IRFP640 500V 18A Rds=0.22
 * D1 - Rectifier - MUR1560 fast switching diode
 * Rs - Power resistor - 15k 15W
 * Cs - Polypropylene Capacitor - 47uF 500V
 * Ds - Rectifier - 1N4007
 * T1 - Transformer
 * Core - E42/21/20 (datasheet)
 * Bobbin
 * 1.3mm gap made from plastic DVD case cut in two (5mm x 20mm) pieces
 * 18 gauge magnetic wire (aka enameled copper wire)
 * 16 gauge magnetic wire
 * copper sheet for shielding
 * Electrical tape for isolation
 * C8 - Ceramic capacitor - 1nF 500V
 * C9 - Electrolytic capacitor - 680uF 200V
 * C10 - Electrolytic capacitor - 470uF 200V
 * L1 - Inductor
 * C11 - Electrolytic capacitor -

Transformer Design

 * Estimated inductance: 500uH
 * turns ratio: 5
 * Air gap: lg = 1.3mm
 * Primary winding
 * turns: 56
 * wire size: 18 AWG
 * Secondary
 * turns: 11
 * wire size: 16 AWG


 * Construction from center outwards
 * Row 1: primary 18 turns
 * tape
 * Row 2: primary 14 turns
 * tape
 * shield
 * tape
 * Row 3: secondary 11 turns
 * tape
 * shield
 * tape
 * Row 4: primary 24 turns
 * tape
 * outside core
 * Shield surrounding core

=Isolated power supply= I wanted to make an isolated power source for each of the sections.

Components

 * 47uF 400V Electrolytic Capacitor
 * 1uF 250V Polypropylene Capacitor
 * Transformer - PQ2620 core and bobbin (datasheet)
 * TNY277PN - Off-Line Switcher IC, with integrated transistor (datasheet)
 * 1N4007 - 1A 1000V Rectifier (datasheet)
 * 10nF 1000V Ceramic Capacitor

Transformer design
=Voltage regulator stage=


 * Components
 * LM723 - Voltage regulator (datasheet)
 * 39V Zener diode - 1N4745 (datasheet)
 * Op-amp - LF356N (datasheet)
 * 6.2V Zener diode - 1N823 (datasheet)
 * TIP142 NPN Power Darlington transistor (datasheet)
 * TIP140, TIP141 can be used as an alternative
 * MJE3055 - NPN power transitor (datasheet)
 * MUR1560 - power Rectifier (datasheet)

=References=
 * Voltage regulator stage
 * 0-50V-3 A - using op-amps
 * 30 volt Bench Top Power Supply is rated at 10 amp - using LM723
 * linear power supply design
 * On-Semi Linear & Switching Voltage Regulator Handbook - amazing textbook like, with practical instructions and guide lines for using real components. See section 4 for designing output stage, and current limiting methods
 * link list of designs, guides, and tutorials - some good some bad
 * http://www.ti.com/lit/an/snva020b/snva020b.pdf