UC3843 Current-Mode PWM Controller IC
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Prices updated: 12 Oct 2026
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About this product
The UC3843 is a fixed-frequency current-mode PWM controller used in off-line and DC-to-DC switching power supplies such as flyback converters. It integrates undervoltage lockout with low start-up current, a trimmed voltage reference, a PWM comparator with current limit, and a totem-pole output for driving N-channel MOSFETs. It is widely used in SMPS and converter designs.
Specifications
- Control method
- Fixed-frequency current-mode PWM
- Package
- 8-pin
- Start-up current
- Less than 1 mA
- Undervoltage lockout (UVLO)
- Turn-on 8.4 V / turn-off 7.6 V
- Output stage
- Totem-pole, for driving N-channel MOSFETs
- Current limit
- Built-in PWM comparator with current limit
- Maximum duty cycle
- 100%
Frequently asked questions
What is the difference between UC3842, UC3843, UC3844 and UC3845?
The family differs mainly in UVLO thresholds and maximum duty cycle. UC3842 and UC3844 use 16 V on / 10 V off, while UC3843 and UC3845 use 8.4 V on / 7.6 V off. UC3844 and UC3845 limit duty cycle to 50%. Always confirm with the datasheet of your manufacturer.
Can it start from a 5 V supply?
No. VCC must rise above the UVLO turn-on threshold (8.4 V for UC3843), so it is normally powered from a higher bias supply or an auxiliary winding.
