ISO01 - Compact low voltage isolated power supply

While working in the lab it's often useful to have a small isolated power supply handy. Depending on the circuit configuration, ISO01 can generate galvanically isolated unipolar and symmetric voltages from a single 3.3V or 5V rail. The circuit is based on the Texas Instruments SN6501 transformer driver and uses an easy to obtain off the shelf transformer.

Schematics

The circuit is a simple push-pull topology without feedback. Thanks to the integration of the SN6501 the primary side is trivial. The integrated circuit contains an oscillator and power drivers to directly drive the transformer windings. The board can also accept the higher current capability SN6505.

Multiple rectification topologies are supported on the secondary side to obtain different voltages without the need for custom transformers. For more stable output voltages, and option to add linear regulation is achieved with a pair of 78Lxx and 79Lxx.

The board accepts input voltage from a terminal block or from a mini USB connector.

Schematics	Topology	Output	D2	D3	D4	R1	R2	C6
	Full Wave	n*Vin	STUFF	NO STUFF	NO STUFF	STUFF	NO STUFF	NO STUFF
	Bridge 1	2*n*Vin	STUFF	STUFF	STUFF	NO STUFF	NO STUFF	SHORT
	Bridge 2	+/-n*Vin	STUFF	STUFF	STUFF	STUFF	NO STUFF	STUFF
	Voltage Doubler	+/-2*n*Vin	NO STUFF	STUFF	NO STUFF	NO STUFF	STUFF	STUFF

The scopeshot on the right shows the board in action. Ch1 and Ch2 are the driver pins of the SN6501. The switching frequency is 420KHz as expected. Dead time also matches the datasheet. Ch3 is the transformer output for the voltage doubler topology using a 1:1 Murata 78250C transformer.

Transformer Selection

The design can use many off the shelf transformers. There are some optimized specifically for the SN6501 but most center tapped transformers designed for other isolated DC-DC converters will also work.
The following table has some of the tested transformers with the associated approximate output voltage range.

The following table has additional transformers that work with the SN6501 but have not been tested due to footrpint mismatch with the ISO01.