protection.
鈥?/div>
Simple design as no control-loop compensation is
concerned.
The proposed buck and buck-boost converters are very
similar to each other. Their major difference is that buck
provides a positive output voltage but buck-boost provides
a negative output voltage referring to the input ground.
PRINCIPLE OF OPERATION
Figure 1 shows the proposed buck and buck-boost
converters. The rectifier circuit, which consists of capacitor
C
3
and diode D
3
, is in the front end for AC or DC input
voltage. Then, the NCP1052 is self-powered up from the
rectified input voltage directly with a V
CC
capacitor C
2
.
When the switch inside the IC is opened, there is a voltage
across Drain (D) and Source (S) pins of the IC. If this voltage
is greater than 20 V, an internal current source I
start
= 6.3 mA
(typ.) inside the IC charges up C
2
and a voltage in C
2
is built
up for the operation of the IC. Comparing to the switching
frequency, the V
CC
voltage level is in a lower-frequency
7.5-8.5 V hysteresis loop. This V
CC
hysteresis loop is for
frequency jittering features to minimize EMI and
short-circuit fault timing function.
D
2
Z
2
FB
D
V
CC
C
2
(a) Buck
D
2
Z
2
FB
D
V
CC
C
3
C
2
(b) Buck-boost
S
D
1
C
1
D
L
R
1
C
Z
1
Output
S
D
1
C
1
R
1
L
D
3
Input
C
3
D
C
Z
1
Output
D
3
Input
Figure 1. Proposed Circuit Using NCP1052
In Figure 2a it is noted that in the buck topology the input
voltage powers up the IC through the path across the
inductor L and capacitor C. This charging path passes
漏
Semiconductor Components Industries, LLC, 2003
1
June, 2003 - Rev. 1
Publication Order Number:
AND8098/D