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Digital PFC Description

12.3 EVM Hardware – Introduction

12.3.1 PFC Pre-Regulator Input

The power entry section, PFC pre-regulator input, as shown in Figure 31, consists of EMI input filter, AC

voltage sense circuit and inrush relay control circuit. The series resistor R3 limits the inrush current. The

inrush control relay K1, controlled by the UCD3138 controller, is used to bypass this resistor. The

controller measures input and output voltages and decides the appropriate time for closure of this relay.

Input AC voltage is scaled and conditioned, and the sensed signal is applied to the UCD3138 ADC input

AD_07 and AD_08. Figure 31 also shows a DC voltage regulator D3, which converts the 12 V into 3.3 V

to provide the bias for on-board 3.3 V.

Figure 31. AC Power Filtering, Inrush Current Limit and AC Voltage Sense

SLUU885B–March 2012–Revised July 2012 Digitally Controlled Single-Phase PFC Pre-Regulator

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