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AN-6067

Design and Application of Primary-Side Regulation (PSR) PWM Controller

Fairchild Semiconductor 

AN-6067

Frequency Hopping Operation

A frequency hopping function is built in to further improve

EMI system performance. The frequency hopping period is

no longer than 3ms and the PWM switching frequency range

is 42kHz +/- 2.6kHz.

APPLICATION NOTE

42kHz frequency, the MOSFET’s on-time is determined by

VCOMI to modulate the output current.

CC Regulation

CV Regulation

decreasing output impedance

4.5V

VCOMV

VCOMI

44.6KHz

39.4KHz

+/- 2.6KHz

Frequency Hopping Period → 3mS

Figure 15. Gate Signal with Frequency Hopping

CV / CC Regulation

Battery chargers are typically designed for two modes of

operation, constant-voltage charging and constant-current

charging. The basic charging characteristic is shown in

Figure 16. When the battery voltage is low, the charger

operates on a constant current charging. This is the main

method for charging batteries and most of the charging

energy is transferred into the batteries. When the battery

voltage reaches its end-of-charge voltage, the current begins

to taper-off. The charger then enters the constant voltage

method of charging. Finally, the charging current continues

to taper-off until reaching zero.

Vo(V)

Charging Sequence

Deep Green Mode

Figure 17. CV/CC Regulation Charging Sequence

Temperature Compensation

The PSR controller has built-in temperature compensation

circuitry to provide constant reliable voltage regulation even

at a different ambient temperature. This internal positive

temperature coefficient (PTC) compensation current is used

to compensate for the temperature due to the forward-

voltage drop of the diode output. Without temperature

compensation, the output voltage is distinctly higher in high

temperatures than in lower temperature condition, as shown

in Figure 18.

Vo

high temp.

after compensation at high temp.

room temp.

CV Regulation

Charging

Sequence

Io(mA)

Figure 16. Basic Charging V-I Characteristic

As mentioned in the CV regulation region section, the VCOMV

modulates MOSFET’s on-time and PWM frequency to

provide enough power to the output load. As shown in

Figure 17, as the output load increases, VCOMV gradually

rises until the system shifts into the CC regulation region. At

the same time, VCOMV increases to 4.5V and the MOSEFT’s

on time is controlled by VCOMI. However, when power

system operates in the CC regulation region at a fixed

Io

Figure 18. Output V-I Curve with Temperature

Compensation

As shown in Figure 19, the accuracy value of R1 and R2

determines the voltage regulation amount. The suggested

deviation for R1 and R2 is a +/-1% tolerance.

Temperature

Compensation

PTC

Vs

S/H

Auxiliary

Winding

Vref

PSR

Controller

Figure 19. Temperature Compensation

© 2008 Fairchild Semiconductor Corporation

Rev. 1.0.1 • 1/26/10

7

www.fairchildsemi.com

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