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UC3843BN 数据手册 - ST Microelectronics（意法半导体）
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ST Microelectronics（意法半导体）
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PWM控制器
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PDIP-8
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PWM 控制器，STMicroelectronics脉冲宽度调制器 (PWM) 控制器可支持隔离和非隔离交流-直流和直流-直流开关模式电源。 它们在单端配置（如回扫、正向或准谐振控制器）和双端配置（非对称半桥，用于开关模式电源 (SMPS)）基于最常用的拓扑。 PMW 控制器还集成了全面保护，用于增强坚固性和可靠性。### PWM (Pulse Width Modulation) Controllers, STMicroelectronics
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UC3843BN数据手册
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UC2842B/3B/4B/5B
UC3842B/3B/4B/5B
March 1999
HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER
.
TRIMMED OSCILLATOR FOR PRECISE FRE-
QUENCY CONTROL
.
OSCILLATOR FREQUENCY GUARANTEED
AT 250kHz
.
CURRENT MODE OPERATION TO 500kHz
.
AUTOMATIC FEED FORWARD COMPENSA-
TION
.
LATCHING PWM FOR CYCLE-BY-CYCLE
CURRENT LIMITING
.
INTERNALLY TRIMMED REFERENCE WITH
UNDERVOLTAGE LOCKOUT
.
HIGH CURRENT TOTEM POLE OUTPUT
.
UNDERVOLTAGE LOCKOUT WITH HYSTER-
ESIS
.
LOW START-UP AND OPERATING CURRENT
DESCRIPTION
The UC384xB family of control ICs provides the nec-
essary features to implement off-line or DC to DC
fixed frequency current mode control schemes with
a minimal external parts count. Internally imple-
mented circuits include a trimmed oscillator for pre-
cise DUTY CYCLE CONTROL under voltage lock-
out featuring start-up current less than 0.5mA, a pre-
cision reference trimmed for accuracy at the error
amp input, logic to insure latched operation, a PWM
comparator which also provides current limit control,
and a totem pole output stage designed to source
or sink high peak current. The output stage, suitable
for driving N-Channel MOSFETs, is low in the off-
state.
Differences between members of this family are the
under-voltage lockout thresholds and maximum duty
cycle ranges. The UC3842B and UC3844B have
UVLO thresholds of 16V (on) and 10V (off), ideally
suited off-line applications The corresponding thresh-
olds for the UC3843B and UC3845B are 8.5 V and 7.9
V. The UC3842B and UC3843B can operate to duty
cycles approaching 100%. A range of the zero to <
50 % is obtained by the UC3844B and UC3845B by
the addition of an internal toggle flip flop which blanks
the output off every other clock cycle.
BLOCK DIAGRAM (toggle flip flop used only in UC3844B and UC3845B)
UVLO
S/R
5V
REF
34V
INTERNAL
BIAS
VREF GOOD
LOGIC
2.50V
T
S
R
OSC
R1V
CURRENT
SENSE
COMPARATOR
2R
+
-
PWM
LATCH
7
5
4
2
1
3
8
6
ERROR AMP.
Vi
GROUND
RT/CT
VFB
COMP
CURRENT
SENSE
VREF
5V 50mA
OUTPUT
D95IN331
Minidip
®
SO8
UC3842B
1/15
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