Retrofit UCC28750 EVM to Support Aux Power Application
Abstract
Flyback topology is major used in the low power PSU (<100W), because it is easy to design and cost effective. Most of high power PSU also need the Auxpower to support the Vdd and fan power supply, and the power rating is also under 100W, so flyback topology is used at every PSU.
UCC28750 is a highly-integrated current-mode, continuous-conduction-capable, PWM controller optimized for high performance, low standby power, and cost effective offline flyback converter applications using an opto-coupler.
This application note introduces how to retrofit the UCC28750 EVM to fit the Aux power and also explain the benefit for this application.
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1 Introduction
The UCC28750EVM-071 is a 60-W evaluation module (EVM) for evaluating an off-line power AC to DC flyback converter. The UCC28750EVM-071 converters 85-VRMS to 265-VRMS input voltage down to 24-VDC, capable of delivering 60W of output power. The schematic is shown in Figure 1-1.
However, the PFC stage is in the front end, and the PFC converts the universal AC input voltage to 400Vdc, and the output voltage is 12V for fan power supply, so this application note introduces how to retrofit the UCC28750EVM-071 to support the Aux power application.
Figure 1-1 Original EVM Schematic