26 NETWORKING DESIGN www.ti.com Issue 3 2023 Power Electronics Europe www.power-mag.com holdup time is extended by 17ms. The test data in Figure 7 shows that the flyback voltage rose from 9V to 40V during the energy transfer and the holdup capacitor voltage dropped from 58V to 43V. Both voltages depleted to supply the flyback converter for 17ms. Conclusion To meet the increasing holdup time requirement using a capacitor bank, two major considerations are energy density and the energy utilisation. An input-side holdup solution saves 50% board space compared to an easy-to-implement output-side holdup design, by taking advantage of the energy density and utilisation rate of a high voltage capacitor. A backup circuitry designed to minimise insertion losses uses a small auxiliary boost converter to pump up the high voltage capacitor and a fast acting, current limiting switch to relieve stress during power dump. This proposed “pump-anddump” solution maintains system efficiency, while the conventional twostage solution takes a 5% efficiency hit because of the additional boost converter stage. The implementation of this backup circuitry in a 60W IoT application achieves a 17ms holdup time with a single 1,200µF holdup capacitor. This option is suitable for a wide input DC/DC converter where efficiency, space and cost are top design priorities. It also reduces the costly and bulky capacitor banks and significantly extends the holdup time of the energy storage capacitor. Figure 7. Test data shows the energy transfer: holdup capacitor voltage (blue), flyback input voltage (olive green) and flyback output voltage (light green). VISIT US AT PCIM BOOTH #9-450 XFlux® Ultra POWDER CORES Same great DC Bias and high saturation found in XFlux while providing a 20% improvement in core loss. www.mag-inc.com Flux Density (Tesla) 0.01 0.1 1 100 10 10,000 1,000 Core Loss (mW/cm3) 10 kHz XFlux Ultra 25 kHz XFlux Ultra 10 kHz XFlux 25 kHz XFlux 50 kHz XFlux 50 kHz XFlux Ultra 26μ Core Loss Density
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