參數(shù)資料
型號(hào): CS52845
廠商: ZF Electronics Corporation
英文描述: Current Mode PWM Control Circuit with 50% Max Duty Cycle
中文描述: 電流模式PWM控制電路的最大占空比為50%
文件頁(yè)數(shù): 4/6頁(yè)
文件大?。?/td> 142K
代理商: CS52845
Undervoltage Lockout
During Undervoltage Lockout (Figure 1), the output driv-
er is biased to sink minor amounts of current. The output
should be shunted to ground with a resistor to prevent
activating the power switch with extraneous leakage cur-
rents.
PWM Waveform
To generate the PWM waveform, the control voltage from
the error amplifier is compared to a current sense signal
which represents the peak output inductor current (Figure
2). An increase in V
CC
causes the inductor current slope to
increase, thus reducing the duty cycle. This is an inherent
feed-forward characteristic of current mode control, since
the control voltage does not have to change during
changes of input supply voltage.
When the power supply sees a sudden large output cur-
rent increase, the control voltage will increase allowing
the duty cycle to momentarily increase. Since the duty
cycle tends to exceed the maximum allowed to prevent
transformer saturation in some power supplies, the inter-
nal oscillator waveform provides the maximum duty cycle
clamp as programmed by the selection of OSC compo-
nents.
4
Figure 1: Startup voltage for the CS52845.
Circuit Description
Test Circuit Open Loop Laboratory Test Fixture
V
REF
V
CC
V
OUT
1k
1W
0.1
μ
F
0.1
μ
F
V
REF
V
CC
V
OUT
Gnd
V
FB
Sense
OSC
COMP
5k
100k
4.7k
1k
Error Amp
Adjust
4.7k
Sense
Adjust
R
T
2N2222
C
T
Gnd
A
V
CC
V
ON
= 8.4V
V
OFF
= 7.6V
ON/OFF Command
to reset of IC
<15mA
<1mA
V
ON
V
OFF
I
CC
V
CC
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