ISO01 - Compact low voltage isolated power supply

Project Status: 
released

ISO01 A00While 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 Full Wave n*Vin STUFF NO STUFF NO STUFF STUFF NO STUFF NO STUFF
Bridge Bridge 1 2*n*Vin STUFF STUFF STUFF NO STUFF NO STUFF SHORT
Bridge Bridge 2 +/-n*Vin STUFF STUFF STUFF STUFF NO STUFF STUFF
Doubler Voltage Doubler +/-2*n*Vin NO STUFF STUFF NO STUFF NO STUFF STUFF STUFF

doubler waveformThe 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.

Manufacturer Part Number Turn Ratio isolation mounting Output Voltage (Vin=5V)
Murata 78250C 1CT:1 1500V PTH 10-18V
Murata 78250VC 1CT:1 4000V PTH 10-18V
Murata 78253/55C 1CT:1.31CT 1500V PTH 5.9-23.6V
Murata 78253/35C 1CT:2.14CT 1500V PTH 9.6-38.5V
Murata 78253/55VC 1CT:1.31CT 4000V PTH 5.9-23.6V
Murata 78253/35VC 1CT:2.14CT 4000V PTH 9.6-38.5V
Murata 782485/55C 1CT:1.5CT 2500V PTH 6.75-27V
Murata 782485/35C 1CT:2.2CT 2500V PTH 10-40V
Murata 782482/33VC 1CT:1.33CT 4000V PTH 6-24V
Murata 782482/53VC 1.14CT:1CT 4000V PTH 3.6-14.4V

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

Manufacturer Part Number Turn Ratio isolation mounting Output Voltage (Vin=5V)
Wurth Electronics 760390012 1CT:1.1CT 2500V SMD 5-20V
Wurth Electronics 760390013 1CT:1.7CT 2500V SMD 7.5-30V
Wurth Electronics 760390014 1CT:1.3CT 2500V SMD 5.75-23V
Wurth Electronics 760390015 1CT:2.1CT 2500V SMD 9.25-37V
Murata 76250ENC 1CT:1 6000V PTH 4.5-18V
Murata 76253/55ENC 1CT:1.31CT 6000V PTH 5.9-23.6V
Murata 76253/35ENC 1CT:2.14CT 6000V PTH 9.6-38.5V
Wurth Electronics 750313734 1CT:1.1CT 5000V SMD 5-20V
Wurth Electronics 750313769 1CT:1.7CT 5000V SMD 7.5-30V
Wurth Electronics 750313638 1CT:1.3CT 5000V SMD 5.75-23V
Wurth Electronics 750313626 1CT:2.1CT 5000V SMD 9.25-37V
Bourns HCTSM80910BAL 1CT:1.11CT 4200V SMD 5-20V
Bourns HCTSM80308BAL 1CT:2.66CT 4200V SMD 12-48V
Design Files
Schematics: 
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