Power Electronics Europe Issue 4 - November 2022

www.vicorpower.com POWER MODULES 17 www.power-mag.com Issue 4 2022 Power Electronics Europe switching frequency and the use of smaller magnetics with lower intrinsic losses. The resulting increase in efficiency means less power is wasted during conversion, easing thermal management and allowing for more output current and a larger power density from a smaller package. Faster operation transfers energy to the output more often, improving the transient response to dynamic load changes to a few cycles. Vicor is planning to bring to orbit a range of DC-DCs. Parts have already been de- risked and designed-in by Boeing for an O3b satellite offering space-based internet. Initially four rad-tolerant DC-DCs will be offered: A 300W, 9A, 849W/in 3 , isolating, ZVS/ZCS, SAC bus converter module (BCM3423PA0A35C0S), which accepts a DC source from 94 to 105V and outputs a fixed load voltage 1/3 of the input, ranging from 31 to 35V. Its maximum ambient efficiency is specified at 94% in a package size of 33.5 23.1 7.4mm weighing 25.9g. A 200W, 7.7A, 797W/in 3 , non-isolating ZVS buck-boost regulator, (PRM2919P36B35B0S), which accepts an input from 30 to 36V and outputs an adjustable load voltage from 13.4 to 35V. Its maximum ambient efficiency is specified at 96% in a package size of 29.2 19.0 7.4mm weighing 18.2g. A 200W, 50A, 1204W/in 3 , isolating, ZVS/ZCS, SAC DC-DC (VTM2919P32G0450S), which accepts a line voltage from 16 to 32V and outputs a fixed load voltage of 1/8 of the input, ranging from 2 to 4V. Its maximum ambient efficiency is specified at 93% in a package size of 29.2 19.0 4.9mm weighing 11g. A 150W, 150A, 903W/in 3 , isolating, Figure 2: The full-bridge, SAC series-resonant topology offers advantages over existing space-grade DC-DCs. gives you more flexibility when deciding where to place the PRM, less worries about area congestion at the load and more freedom to size power planes for maximum current density. This floor- planning is very different to the traditional brick approach, which requires the isolated DC-DC and POLs to be close together to minimize I 2 R distribution losses. Present space-grade, isolated DC-DCs and buck POLs are PWM-based devices with the output power proportional to the duty cycle of the switching frequency. These hardswitched converters use a square wave to drive an inductor or transformer with the MOSFET dissipating energy as it is turned on and off. A square wave contains lots of harmonics that must be filtered or they will conduct or radiate throughout the system. The VTM’s topology uses a sinusoidal current in the primary winding, producing a cleaner output noise spectrum requiring less filtering. Existing space-qualified buck regulators and forward/flyback DC-DCs specify efficiencies in the range of 67 – 95% and 47 – 87% respectively. Today, there are 12 suppliers of space- grade switching POLs offering almost 30 nonisolated convertors. Input voltages range from 3 to 16V, load voltages and currents from 0.785 to 9.6V and 4 to 18A respectively, with switching frequencies from 100kHz to 1MHz. Previously, I described the theory of conversion for the buck topology, what criteria to consider when selecting space-qualified parts, and how to choose values for the inductor, input, and output capacitance. There are seven vendors of space- qualified isolating DC-DCs offering over 30 families of parts generating single, double, or triple standard voltages, or in some cases, adjustable, regulated, stepped-down intermediate outputs. Power ratings range from 2.5 to 500W. Previously, I described the theory of conversion for the forward and flyback topologies. To meet the power-distribution and low- voltage, high-current needs of future NewSpace constellations, Vicor is qualifying its novel, Sine Amplitude Converter Figure 3: Vicor will offer these new BCM, PRM, and VTM rad-tolerant DC-DCs. (SAC™) topology for space applications. This patented, ZCS/ZVS technology offers higher efficiencies, larger power densities, and lower EMI emissions than existing space-grade DC-DCs. SAC is a transformer- based, series-resonant, forward architecture that operates at a fixed frequency equal to the resonance of a primary tank circuit as shown in Figure 2. The FETs in the primary side are locked to the natural resonant frequency of the series tank circuit and switch at zero- voltage crossing points, eliminating power dissipation and increasing efficiency. At resonance, the inductive and capacitive reactances cancel minimizing the output impedance, which becomes purely resistive reducing droop. The resulting very-low output impedance allows the VTM to respond almost instantaneously (< 1 s) to step changes in the load. The current flowing through the tank is a sinusoid that contributes less harmonic content, resulting in a cleaner output noise spectrum, requiring less filtering of the load voltage. The SAC has a forward topology with the input energy passing to the output. The leakage inductance of the primary is minimized since it is not a critical storage element. The unique operation of the SAC forward topology enables a higher