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/ ROOT / BENCH-PSU    ◂ back to sheet 1

Bench power supply

A linear bench supply I'm building to learn the practical fundamentals of electrical engineering: mains in, a safe isolated low-voltage rail out, set voltage and current limit, protection, and a meter. Rev A, drawn in KiCad, reaches the smoothed but unregulated rail; a fixed regulator comes first, as training wheels.

J1Mains inLNPET118 VAC, 5 A or moreAC1AC2AC1AC2~~+−D1+C110,000 µF 35 VC2100 nF+V RAW0VRegulator stage: not drawn yet.▸ Hover a wire to name its net.NET L line, from the mains inlet to T1's primaryNET N neutral, to T1's primaryNET PE protective earth, bonded at the inletNET AC1 T1's secondary into the bridge, by labelNET AC2 T1's secondary into the bridge, by labelNET +V RAW the unregulated rail across C1 and C2NET 0V the return
24 V22 V20 V0 ms10 ms20 ms30 msΔVpeak 24.1 V

ΔV ≈ I / 2fC = 1.00 V, so the rail dips to about 23.1 V between peaks.

FIG. 1  C1's ripple against load, computed on this page from the design values below: an 18 VAC secondary, two diode drops of about 0.7 V, and the reservoir you pick.

REQUIREMENTS, FROM MY NOTES

Transformer18 VAC secondary, 5 A or more (6–7 A preferred), EI or toroidal core, 50 Hz, mains-rated insulation
Bridge rectifierFull bridge, 10–15 A or more, 100 V reverse or more (200 V safer), rated for ripple current
Reservoir10,000–22,000 µF electrolytic, 35 V or more, 105 °C, low ESR
Bypass100 nF ceramic or film, 50 V or more, beside the reservoir

PARTS, REV A

J1 mains inlet, L, N and PE. T1, one primary and one secondary. D1 bridge rectifier. C1 10,000 µF 35 V reservoir. C2 100 nF.

BUILD CHECKLIST, NONE TICKED YET

  1. Raw DC rail works
  2. A fixed regulator first
  3. Adjustable voltage
  4. Current limiting
  5. Metering: volts and amps
  6. Enclosure, CAD and thermal

SOURCE

A KiCad 9 project: the schematic, a project file, and a board file with nothing on it yet.

REVISIONSREVDATEDESCRIPTIONA2026-01-15Mains to reservoir; regulator not drawn yetB2026-01-20Part requirements and the build checklistTITLEBench power supplySHEET/ bench-psuNO.5 of 7REVBDATE2026-01-20DRAWND. BrownSIZEA3GO TO◂ sheet 4sheet 6 ▸OTHER VIEWSDEVPHYSICSACADEMICee.desmondbrown.me

/ ROOT / BENCH-PSU

Bench power supply

A linear bench supply I'm building to learn the practical fundamentals of electrical engineering: mains in, a safe isolated low-voltage rail out, set voltage and current limit, protection, and a meter. Rev A, drawn in KiCad, reaches the smoothed but unregulated rail; a fixed regulator comes first, as training wheels.

SHEET5 of 7REVBDATE2026-01-20
OTHER VIEWSDEVPHYSICSACADEMIC
J1Mains inLNPET118 VAC, 5 A or moreAC1AC2AC1AC2~~+−D1+C110,000 µF 35 VC2100 nF+V RAW0VRegulator stage: not drawn yet.

Drag sideways to pan the schematic.

24 V22 V20 V0 ms10 ms20 ms30 msΔVpeak 24.1 V

ΔV ≈ I / 2fC = 1.00 V, so the rail dips to about 23.1 V between peaks.

FIG. 1  C1's ripple against load, computed on this page from the design values below: an 18 VAC secondary, two diode drops of about 0.7 V, and the reservoir you pick.

REQUIREMENTS, FROM MY NOTES

Transformer18 VAC secondary, 5 A or more (6–7 A preferred), EI or toroidal core, 50 Hz, mains-rated insulation
Bridge rectifierFull bridge, 10–15 A or more, 100 V reverse or more (200 V safer), rated for ripple current
Reservoir10,000–22,000 µF electrolytic, 35 V or more, 105 °C, low ESR
Bypass100 nF ceramic or film, 50 V or more, beside the reservoir

PARTS, REV A

J1 mains inlet, L, N and PE. T1, one primary and one secondary. D1 bridge rectifier. C1 10,000 µF 35 V reservoir. C2 100 nF.

BUILD CHECKLIST, NONE TICKED YET

  1. Raw DC rail works
  2. A fixed regulator first
  3. Adjustable voltage
  4. Current limiting
  5. Metering: volts and amps
  6. Enclosure, CAD and thermal

REVISIONS

A2026-01-15Mains to reservoir; regulator not drawn yet
B2026-01-20Part requirements and the build checklist
TITLEBench power supply
◂ sheet 45 / 7sheet 6 ▸