AND8031 Datasheet, PDF (1/12 Pages) ON Semiconductor – Isolated Precision Regulation of a Single 1.8 Volt Output from a Universal Line Input

AND8031/D
Isolated Precision
Regulation of a Single
1.8 Volt Output from a
Universal Line Input
Prepared by: Jason Hansen
ON Semiconductor
http://onsemi.com
APPLICATION NOTE
INTRODUCTION
The following Application Note describes an off–line
switching power supply utilizing a precision programmable
reference to regulate a 1.8 volt output. The center of the app
note is the MC33363B, a monolithic SMPS controller with
a 700 volt power switch, and the NCP100, a sub–one volt
precision programmable reference. The system design and
analysis will be described in detail.
The design requirements are for a universal off–line
converter with a 1.8 volt, 1.0 ampere single output with less
than 50 millivolts ripple and operates at 100 kHz. Most of the
components selected are surface mount. This design is
separated into the generic circuit of the off–line converter
and the feedback network.
Generic Off–Line Conversion Circuit
To reduce the total number of components and thus
minimize circuit board area, an SMPS controller with an
integrated power switch is selected. With the low output
power requirement, the MC33363B is selected as the control
and power switch IC. The MC33363B contains an externally
programmable frequency and current limit, internal startup
circuit and can handle up to 8 watts of output power.
The basic off–line conversion circuit is illustrated in
Figure 1. The line input is filtered through the EMC circuit
then rectified and filtered. The rectified voltage is converted
to a lower voltage via the transformer and the MC33363B.
The secondary of the transformer is rectified to a DC voltage
and filtered. The output voltage controls the duty cycle of the
switcher via the isolated feedback network. The calculated
values are a starting point and do not replace bench testing.
R1
4.7
Universal C1
Input
1n
R2
4.7
D1
D2
4.7 µ
D3 ^{400 V}
D4
1N4005
R4 _C5
3.9 k 47 p
C6
10 µ
U1
1
16
U2 CTX22–14966
D5
MURS160
D7
MBRD835L
D6
MURS120
C7
C8
820 µ 820 µ
R12
120
Q1
BC858ALT1
+
C12
1µ
1.8 V
–
C9
R9
12 k
0.1 µ
3
4
13
5
12
R3 30 k
6
11
C3 390 p
7
10
C4 1 µ
8
9
MC33363B
C10
1µ
R11
10
U4
NCP100 R10
7.5 k
R6
2.7 k
U3
SFH615–4
Figure 1. MC33363B Basic Flyback Circuit Schematic
© Semiconductor Components Industries, LLC, 2000
1
October, 2000 – Rev. 1
Publication Order Number:
AND8031/D