The σ24 Power Transformer Board

AMB Laboratories

The σ24 Power Transformer Board

News

The σ24 board is available.

Overview

σ24 ("sigma 24") is a companion circuit board for the σ25 regulated power supply and ε24 power switch driver circuit. It allows a standard EI-30 form-factor miniature transformer to be board-mounted and to supply power to either circuit. Both single-secondary and dual-secondary transformer configurations are supported. The two secondary windings on a dual-secondary unit are connected in parallel.

σ24 can also be used to mount an EI-30 transformer for use with other circuits if such a transformer is appropriate.

The following is a photo of the top and bottom sides of the σ24 circuit board, and a photo of an assembled board.

WARNING: Building the σ24 will require that you work with AC line voltage, which is a lethal shock hazard. If you don't know what you're doing, please ask someone who is experienced to help you.

Wiring

The AC input terminals should be connected to AC mains. The AC output terminals should be connected to the AC IN terminals of the σ25 board, or to the AC1 and AC2 terminals of the ε24 board. There is no need to connect any portion of this board to AC or chassis ground.

Parts list

The following is the parts list to populate the σ24 board. The listed power transformer is appropriate for an ε24 circuit. For the σ25 you should read the "Transformer selection" section at the σ25 website to determine the correct transformer for your application.

Qty	Part	Description	Vendor part numbers				Notes
Qty	Part	Description	Mouser	Digi-Key	Farnell	RS Components	Notes
1	PCB	σ24 printed circuit board	AMB audio shop				-
1	T1	Power transformer 12V, EI-30 encapsulated	673-030-7136-0	567-1031-5-ND	-	-	for 115V AC mains
1	T1	Power transformer 12V, EI-30 encapsulated	-	-	1689049	347-3401	for 230V AC mains
1	J1	Phoenix Contacts 2P .200 screw terminal block 1729128	651-1729128	277-1247-ND	3041440	193-0586	-
1	J2	Molex KK 2P .100 header 22-23-2021	538-22-23-2021	WM4200-ND	1462926	483-8461	-
1	-	Molex KK 2P .100 plug housing 22-01-3027	538-22-01-3027	WM2000-ND	1462825	679-5363	-
2	-	Molex KK .100 crimp terminal 08-50-0114	538-08-50-0114	WM1114-ND	1462641	172-9178	-
-	-	imperial #4-40 or M3 machine screws, standoffs and hex nuts	local or online hardware store				-

Compatible transformers

σ24 is compatible with EI-30 encapsulated transformers with a single primary and and either single or dual secondaries. With a dual secondary transformer, the two secondaries are connected in parallel.

Pulse EI-30 series (115V and 230V AC mains)
Zettler Magnetics BV series (115V and 230V AC mains)
Zettler Magnetics 44000 series EI-30 (115V and 230V AC mains)
Falco L300xx series (115V and 230V AC mains)
Myrra 44000 series (117 and 230V AC mains)
Block VB series (230V AC mains)

Tranformer vendors:

Pulse: Digi-Key, Mouser
Zettler: Allied
Myrra: Farnell
Block: RS Components

The circuit board

The σ24 board is made of high quality FR-4 glass epoxy, single copper layer with top-side silkscreen and bottom-side soldermask. The dimensions of the board is 2.0" x 1.2" (50.8mm x 30.5mm). The thickness of the board is 0.062" (1.58mm). The dimensions and mounting screw locations of the σ24, σ25 and ε24 boards are identical, therefore they can be "stacked" together with 1" long standoffs. The following image shows the board layout: