AP3983C datasheet(6/13 Pages) DIODES

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AP3983B/C/D

Document number: DS36784 Rev. 4 - 2

6 of 13

www.diodes.com

July 2016

AP3983B/C/D

Operation Description

RFB1

RFB2

RCS

GND

AP3983B/C/D

NAUX

IOUT

VAUX

VIN

CPC

CCPC

VBULK

Figure 1. Simplified Flyback Converter Controlled by AP3983B/C/D

Constant Primary Peak Current

The primary iP(t) current is sensed by a current sense resistor RCS as shown in Figure 1.

The current rises up linearly at a rate of:

)

(

)

(

BULK



……… (1)

iP(t)

See equation 2

IPK

Figure 2. Primary Current Waveform

As illustrated in Figure 2, when the current iP(t) rises up to IPK, the switch Q1 turns off. The constant peak current is given by:



………(2)

The energy stored in the magnetizing inductance LM each cycle is therefore:





………(3)

So the power transferring from input to output is given by:





………(4)

Where fSW is the switching frequency. When the peak current IPK is constant, the output power depends on the switching frequency fSW.

Constant Voltage Operation

The AP3983B/C/D captures the auxiliary winding feedback voltage at FB pin and operates in constant-voltage (CV) mode to regulate the output

voltage. Assuming the secondary winding is master, the auxiliary winding is slave during the D1 on-time. The auxiliary voltage is given by:

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