Overcoming a 5 V Input Limitation to Create a 2:1 12 V Power Rail

Push-pull DC-DC converters use a two-switch topology with very high efficiency and require a transformer to transfer power from primary to secondary in each switching cycle. Bourns® HCTSM8 Series transformers are qualified to be used with Texas Instruments SN6501 or SN6505B drivers to generate +/- 15 V to switch IGBTs even though the drivers have a maximum operating voltage of 5 V for isolated power supplies. The common voltage used for interface/bus isolation in industrial applications is 12 V as well as for isolation of digital circuits, and for DC-DC 2:1 12 V power rails in communications interface systems.

Recently we released an app note illustrating how the TI SN6501 driver with our Model HCTSM8 transformer can create a DC-DC 2:1 12 V power rail in a communications interface system. The app note describes the benefits of a push-pull configuration, and explains what makes our HCTSM8 transformer an excellent solution for these converters. The app note also presents a solution along with lab test results to illustrate the feasibility of this application.

Giving you a sneak peak, the app note outlines how we modified our standard design by inserting FETs between the primary winding of the transformer and the TI SN6501 internal FET drains. These new FETs protect the chip from voltages above 5 V without hindering the efficiency of the circuit. Instead of a shared input voltage, a linear regulator from the transformer input voltage supplies the TI SN6501, and a separate supply is used to bias the gates of the new FETs.

We tested this modified design using the same transformer with 1:1 and 2:1 turns ratios and found performance was good in both designs with minimal impact on efficiency. In this configuration, the TI SN6501 can be used above 5 V. Combining our HCTSM8 with this driver provides an ideal solution for isolating a 12 V bus rail in a communication system or as a power supply for IGBT switching.

We provide detailed test results along with crucial tips for FET selection and circuit efficiency in the application note. You will also discover how the Bourns® Model HCTSM8 transformer enables designers to expand on a proven 5 V solution for a 12 V application with minimal impact on efficiency.

Please see the application note to learn more about the benefits that push-pull transformers deliver in terms of electrical and mechanical advantages, maximum creepage and clearance, and enhanced isolation, as well as our detailed test results.

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