DP2525F datasheet(7/11 Pages) DEPUW

7 / 11 page

DP2525F

Quasi-Resonant PSR CC/CV PWM Power Switch

www.depuw.com

Rev.1.1

7-/11

PERATION DESCRIPTION

DP2525F is a high performance, multi mode, highly

integrated

Quasi

Resonant

Primary

Side

Regulation (QR-PSR) power switch. The built-in

high precision CV/CC control with high level

protection features makes it suitable for offline

small power converter applications.



System Start-Up Operation

Before the IC starts to work, it consumes only

startup current (typically 3uA) which allows a large

value startup resistor to be used to minimize the

power loss and the current flowing through the

startup resistor charges the VDD hold-up capacitor

from the high voltage DC bus. When VDD reaches

UVLO turn-on voltage of 12V (typical), DP2525F

begins switching and the IC operation current is

increased to be 0.8mA (typical). The hold-up

capacitor continues to supply VDD before the

auxiliary winding of the transformer takes the

control of VDD voltage.

Fig.1

Once DP2525F enters very low frequency FM

(Frequency Modulation) mode, the operating

current is reduced to be 500uA typically, which

helps to reduce the standby power loss.



Quasi Resonant PSR CV Modulation

(QR-CVM)

In Primary Side Regulation (PSR) control, the

output voltage is sensed on the auxiliary winding

during the transfer of transformer energy to the

secondary. Fig.2 illustrates the timing waveform of

CV sampling signal, demagnetization signal (DEM)

and quasi-resonant (QR) trigger signal in DP2525F.

When the CV sampling process is over, the internal

sample/hold (S&H) circuit captures the error signal

and amplifies it through the internal Error Amplifier

(EA). The output of EA is sent to the Quasi

Resonant PSR CV Modulator (QR-CVM) for CV

regulation. A valley is selected to trigger new PWM

cycle by the output of the QR-CVM bock, which is

determined by the load. The internal reference

voltage for EA is trimmed to 2V with high accuracy.

Fig.2

During the CV sampling process, an internal

variable current source is flowing to FB pin for

Cable Drop Compensation (CDC). Thus, there is

a step at FB pin in the transformer

demagnetization process, as shown in Fig.2.

Fig.2

also

illustrates

the

equation

for

“demagnetization plateau”, where Vo and VF is

the output voltage and diode forward voltage; R1

and R2 is the resistor divider connected from the

auxiliary winding to FB Pin, Ns and Na are

secondary winding and auxiliary winding

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