Servicing Personal Computers, 3rd Edition

146

A.C.

input

from

transformer

secondary

Fl

2A

Tsn

Rl

100

R2

2k7

Cl

4700μ

Width-

modulated

-

pulse train

T

j

R3

2k7

LI

.

C2

'

In

C3

10η

-H3+5V

at 1.8 A

C4

2200/i

D.C. control

input

to

pulse

width modulator

J

470

Set output

Figure 3.42. Basic elements of

a

series-pass switched mode regulator

High-voltage DC.

Noise filter

and fuses

Rectification

and

smoothing

High-

frequency

inverter

Amplitude

control

input

High-

frequency

transformer

Rectification

and

smoothing

Opto-

isolator

Regulated

low-voltage

D.C.

output

Figure 3.43. Alternative switched mode power supply using an opto-isolator

A.C.

mains

supply

O »

input

Noise filter

and fuses

Rectificatio