The target was to draw from the line less than 2W over the entire input voltage range with the 28V and

12V outputs unloaded and with the minimum load (0.55 W) on the 5V section. The results of the evalu-

ation are summarized in table 5.

Table 5. 40W Power Supply for inkjet printer. Standby consumption.

Mains Voltage

85Vac

110Vac

160Vac

220Vac

265Vac

Input Power

0.93W

0.97W

1.13W

1.34W

1.87W

Input Power (*)

0.90W

0.93W

1.03W

1.14W

1.57W

Output Power

0.55W

(*) By using start-up circuit of fig. 7c.

APPENDIX

Flyback Basics

Flyback’s operation takes place in a two-step process. During the ON time of the switch, energy is taken

from the input and stored in the primary of the flyback transformer (actually, two coupled inductors). At

the secondary side, the catch diode is reverse-biased, thus the load is being supplied by the energy

stored in the output bulk capacitor.

Vout

VOLTAGE

REFERENCE

Vin

CLOCK

LATCH

R

S

Q

Rs

DRIVER

-

+

ERROR

AMPLIFIER

-

+

2R

R

1V

PWM

COMPARATOR

ISOLATED

FEEDBACK

Ip

Lp

Vcs

Vc

Vc/3

Is

Vdrain

Vac

CONTROLLER

Q

CLOCK

Vcs=Ip

•Rs

Is

Vdrain

Vin

n

•Vout

DCM operation

Q

CLOCK

Vcs=Ip

•Rs

Is

Vdrain

∆Ip

CCM operation

Q

CLOCK

Vcs=Ip

•Rs

Is

Vdrain

TRANSITION

Figure A1. Flyback Topology with peak current mode control and associated waveforms

AN1049 APPLICATION NOTE

17/24