AP3783R datasheet(9/17 Pages) DIODES

9 / 17 page

AP3783R

Document number: DS37448 Rev. 5 - 2

9 of 17

www.diodes.com

October 2015

AP3783R

Operation Principle Description (Cont.)

Figure 2 shows the typical waveforms which demonstrate the basic operating principle of AP3783R application. And the parameters are defined as

following.

IP---The primary side current

IS ---The secondary side current

IPK---Peak value of primary side current

IPKS---Peak value of secondary side current

VSEC---The transient voltage at secondary winding

VS---The stable voltage at secondary winding when rectification diode is in conducting status, which equals the sum of output voltage VOUT and

the forward voltage drop of diode

VAUX---The transient voltage at auxiliary winding

VA--- The stable voltage at auxiliary winding when rectification diode is in conducting status, which equals the sum of voltage VCC and the forward

voltage drop of auxiliary diode

tSW ---The period of switching frequency

tONP ---The conduction time when primary side switch is “ON”

tONS ---The conduction time when secondary side diode is “ON”

tOFF ---The dead time when neither primary side switch nor secondary side diode is “ON”

tOFFS --- The time when secondary side diode is “OFF”

For primary-side regulation, the primary current ip(t) is sensed by a current sense resistor RCS (as shown in Figure 1).The current rises up linearly

at a rate of:

dip

)

(

)

(



(1)

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 the input to the output is given by:





(4)

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

Constant Voltage Operation

As to constant-voltage (CV) operation mode, the AP3783R detects the auxiliary winding voltage at FB pin to regulate the output voltage. The

auxiliary winding voltage is coupled with secondary side winding voltage, so the auxiliary winding voltage at D1 conduction time is:





AUX







(5)

Where Vd is the diode forward voltage drop.

AP3783R データシート(PDF) 9 Page - Diodes Incorporated

AP3783R データシート(HTML) 9 Page - Diodes Incorporated

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

データシートダウンロード