AN-6756 Datasheet, PDF (1/13 Pages) Fairchild Semiconductor – Applying FAN6756 to Control a Flyback Power Supply

AN-6756
Applying FAN6756 to Control a Flyback Power Supply with
Ultra-Low Standby Power
1. Introduction
Requirements for low standby power consumption are
increasing due to the environmental impact of the energy
wasted by idle electronic devices. Fairchild’s new-
generation green-mode PWM controller, FAN6756,
incorporates innovative mWSaver™ technology, which
dramatically reduces the standby and no-load power
consumption of a power supply with minimum external
components.
The AX-CAP^® innovation, one of the mWSaver™
technologies, removes the X-capacitor bleeder resistor and
its loss in EMI filter stage through intelligent detection and
discharge methods. At no-load or extremely light-load
conditions, Standby Mode dramatically reduces the
switching losses by minimizing the switching frequency
while maintaining the controller supply voltage at the
minimum level. Combined with ultra-low operation current
in Standby Mode, the power consumption of PWM
controller itself is also minimized.
This application note presents the step-by-step design with
an example of applying FAN6756 to a flyback power
supply. It covers designing of the transformer and selecting
the external components.
VAC
C_X
BD1
C_DO R_DO
TF1
L_P
+
C_SN
R_SN
D_O
C_O
C_P
V_O
1N4007
C_IN
D_SN
-
1N4007
Q₁
PC817A
(primary-
side)
R_HV
C_FB
FAN6756
1 GND GATE 8
2 FB
VDD 7
3 NC SENSE 6
4 HV
RT 5
R_A
R_NTC
R_LPF
R_SENSE
C_LPF
D_DD
C_DD
R_D
PC817A
(secondary-
R_F
side)
R₁
C_F
KA431
R₂
Figure 1. Typical Application
© 2011 Fairchild Semiconductor Corporation
Rev. 1.0.1 • 2/21/13
www.fairchildsemi.com