EV020-5-S-00D

– UNIVERSAL INPUT, DUAL OUTPUTS FOR SMALL APPLIANCES

EV020-5-S-00D Rev.1.0

www.MonolithicPower.com

5

4/1/2013

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CIRCUIT DESCRIPTION

The

EV020-5-S-00D

is

configured

in

a

single-stage

Flyback

topology,

it

uses

primary-side-control which can mostly simplify the

schematic and get a cost effective BOM. It can

also achieve accurate constant voltage and

acceptable cross regulation.

FR1 and CR1 compose the input stage. FR1 is

used to protect for the component failure or some

excessive short events, also it can restrain the

inrush current.

C1, L1 and C2 compose π filter to guarantee the

conducted EMI meet standard EN55022. R1

paralleled with L1 is used to damp resonant

between L1 and C1, C2. R2, R3, D1 and C3

compose

the

snubber

circuit

to

reduce

drain-source voltage spike.

R4, C5, C6 and D2 are used as Vcc power supply.

C5 is high frequency decoupling capacitor and

should be placed with Vcc pin as near as

possible.

R5 and R6 are resistor divider for detecting output

voltage by sampling voltage on primary auxiliary

winding.

CY1 is Y capacitor lowering common mode noise

to make sure there is enough EMI margin. T1 is

power transformer, the structure of which is also

very important to pass EMI test.

D3 is rectifier for 18V output. Schottky diode is

recommended

for

better

efficiency

and

regulation.C7 and R7 are composed snubber for

D3, which is to restrain the voltage spike between

D3.

C8 and C11 are output capacitors for 18V output.

C8 should be low ESR electrolytic capacitor for

better load regulation. C11 is ceramic capacitor to

reduce high frequency voltage ripple. R9 is

dummy load to lower the output voltage of 18V

rail at no load condition.

D4 is rectifier for 5V output. Schottky diode is

recommended for better efficiency and regulation.

Due to the output current is low at this rail and

there is no obvious spike on D4, so no RC

snubber is needed.

C9 and C10 are output capacitors for 5V output.

C9 should be low ESR electrolytic capacitor for

better load regulation. C10 is ceramic capacitor to

reduce high frequency voltage ripple. R8 is

dummy load to lower the output voltage of 5V rail

at no load condition.