Waveforms, Figures 1, 2, 3, and 4, taken from products delivered to customers are samples of the actual performances.

Functional block diagram shown in Figure 5 represents the design topology for the MA and MB platforms. The shaded blocks highlight the differences. They include the primary power stage, power transformer and output rectification scheme. While triple output designs are common for most applications, the platform can be configured to accommodate any number of outputs with the limitation being the total combined output power requirements.

The MA and MB designs deploy dual voltage regulation stages, one in the primary and one in the secondary. Regulation in the primary uses current-mode control topology to maximize efficiency. The topology offers inherent current regulation and primary overcurrent protection. Regulation in the primary is built around a standard PWM controller with known performance characteristics in the targeted radiation environments. Voltage regulation is performed on the internal 10 V supply via a bootstrap winding of the power transformer (XFMR). All primary circuitries including the PWM controller and gate drive circuitry are powered by an internal 10 V linear regulator upon power up. The internal 10 V supply takes over all biasing responsibility upon achieving regulation. All primary input circuitries are galvanically isolated from the secondary output via a power transformer. Secondary voltages of the transformer are stepped down, rectified and filtered feeding downstream output regulators. All outputs are independently regulated by linear voltage regulators, which offer inherent excellent noise and regulation performances. The regulators use discrete components with a bipolar transistor as a pass element to minimize voltage headroom and maximize efficiency. The regulator circuit is a proprietary design that has been used successfully for many design applications. Extremely low output noise and high CS rejection are possible with the dual-stage regulation scheme. Guaranteed end of life performances for voltage accuracy and regulation can be demonstrated through worst- case and aging design analysis.

The single-switch flyback and two-switch half bridge can accommodate a wide range of input voltages. The switch elements are selected based on the operating input bus voltage and dynamic transient conditions. Transformer design and turn-ratios are adjusted accordingly. The output rectifiers may require different voltage and current ratings. MA and MB assembly outline designs have taken into account all the changes in component footprints due to the deviations in input and output requirements. The established PCB layouts and dimensions can normally be maintained for most design applications.

The Mx platform also includes an input filter design that yields very low reflected line noise and is expected to satisfy EMI/EMC requirements of most major satellite power buses. While the design will change to accommodate different input bus voltages, the change in the filter components have little or no impact on the assembly layouts.

The TC/TLM interface will accommodate a standard high-level pulse command using latching relay to provide the necessary isolation. The telemetry on/off status is bi-level. The TC/TLM interfaces are isolated from one another and from any other functional and input/output terminals within the converter. Temperature telemetry is available and can be included as required.

1. U.S. Patent No. 4 899 271.
2. U.S. Patent No. 5 335 163.

Tiva Bussarakons is marketing director for International Rectifier. He joined the company in 1999 as field application engineer. He has been marketing director for the dc-dc converter product line of the HiRel Product Group since 2002. Bussarakons holds a BSEE and an MSEE from California State Polytechnic University at Pomona, and an MBA from Pepperdine University at Malibu, Calif.

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