Tech Briefs

This is a prototype of power converters for high-temperature applications such as automobile and aircraft engines.

A DC-to-DC power converter, nominally rated for a power of 180 W, an input potential of 28 V, an output potential of 270 V, and a maximum operating temperature of 200°C has been designed, built, and tested. This power converter serves as a prototype for further development of power converters required to be capable of operating in high-temperature environments in diverse settings, including automobile, aircraft, and spacecraft engines, and oil and gas wells.

The Power Stage of the DC-to-DC power converter contains high-temperature-rated components. The circuit topology is chosen in conjunction with the switching cycle so that transformer leakage inductance energy is fed back to the input capacitor and the maximum voltage stress on S1, S2, RD1, and RD2 is limited to the input voltage.
The power stage of the power converter (see figure) includes a transformer (TX), the DC input to which is switched at a rate of 100 kHz by means of two recently developed high-temperature SiC bipolar junction transistors (S1 and S2) that are rated at a maximum potential of 1,000 V, maximum current of 5 A, and maximum operating temperature >300°C. The transformer has a planar core made of a powdered ferrite that has a Curie temperature >300°C. Also included in the power stage are an output filter inductor (Lout) having a core made of the same material as that of the transformer core, two SiC Schottky transformer-reset diodes (RD1 and RD2) and rectifier diodes (D1 and D2), and input and output capacitors (Cin and Cout, respectively). The capacitors contain ceramic dielectrics that conform to an Electronics Industries of America (EIA) standard, called "X7R," that specifies acceptable ranges of dielectric properties as functions of temperature.

During each switching cycle, the power converter proceeds through three successive modes of operation:

  • An energy-transfer mode in which S1 and S2 are on and D1 conducts;
  • A transformer-reset mode in which (1) RD1 and RD2 conduct, applying reverse input potential to the primary winding of the transformer and (2) the output inductor current freewheels through D2; and
  • A dead-time mode in which S1 and S2 are off and RD1 and RD2 are not conducting while the output inductor current is freewheeling through D2.