AP3706P-G1 查看數據表（PDF） - BCD Semiconductor

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AP3706P-G1

PRIMARY SIDE CONTROL IC FOR OFF-LINE BATTERY CHARGERS

BCD Semiconductor 

Data Sheet

PRIMARY SIDE CONTROL IC FOR OFF-LINE BATTERY CHARGERS AP3706

Operation Description

Bridge

Vg

VIN

+

C1

VS D1

LM NP

NS IS

VO

+CO

IO

Q1

OUT

AP3706

IP

FB

GND

CS

VAUX

NAUX

RCS

Figure 10. Simplified Flyback Converter Controlled by AP3706

Figure 10 illustrates a simplified flyback converter The energy stored in the magnetizing inductance LM

controlled by AP3706.

each cycle is therefore:

Constant Primary Peak Current

The primary current ip(t) is sensed by a current sense

resistor RCS as shown in Figure 10.

The current rises up linearly at a rate of:

dip(t) = vg(t)

dt

LM

................(1)

See equation 2

Eg

=

1

2

×

LM

⋅

Ipk2

................(3)

So the power transferring from the input to the output

is given by:

P

=

1

2

×

LM

×

Ipk2

×

f SW

................(4)

Where the fsw is the switching frequency. When the

peak current Ipk is constant, the output power depends

on the switching frequency fsw.

Ip

0A

Figure 11. Primary Current Waveform

As illustrated in Figure 11, when the current ip(t) rises

up to Ipk, the switch Q1 turns off. The constant peak

current is given by:

Ipk = Vcs

Rcs

Jul. 2008 Rev. 1.3

................(2)

Constant Voltage Operation

The AP3706 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:

( ) VAUX

=

N AUX

NS

×

Vo + Vd

................(5)

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