Product Overview
Off-Line Switch-Mode Power Supply Integrated Circuit
Condition
Unused new old stock (NOS). Package face stamped UC3845N with Unitrode logo and date code 9504. Pin 1 orientation dimple is clean, and through-hole leads are straight and untinned post-manufacture.
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Product Overview
The Unitrode UC3845N is an off-line or DC-to-DC current-mode pulse-width modulation controller optimized for low-voltage power supply applications. It incorporates a trimmed oscillator for precise duty-cycle and frequency control, an undervoltage lockout circuit tailored for low startup thresholds, and a high-current totem-pole output suited for driving power MOSFET gates directly. With an internal toggle flip-flop restricting duty cycle to 50%, it provides robust operation in flyback, forward, and boost power conversion stages.
Key Features
- Current-mode architecture for fast line and load transient response and inherent cycle-by-cycle current limiting
- Maximum 50% duty cycle clamp via internal toggle flip-flop to prevent core saturation
- Operating switching frequency up to 500 kHz
- High-current totem-pole output capable of 1.0 A peak source and sink currents
- Undervoltage lockout circuitry with 8.4 V typical turn-on and 7.6 V typical turn-off thresholds
- Internally trimmed 5.0 V precision reference
- Standard 8-pin plastic dual in-line package (PDIP-8) for through-hole PCB assembly
- Operating ambient temperature range from 0°C to +70°C
Applications
- Bench power supply builders prototyping flyback and forward converter topologies
- Industrial maintenance technicians repairing legacy switched-mode power supplies in factory automation hardware
- Amateur radio operators and electronics hobbyists assembling custom DC-DC step-up and boost regulators
- Field service engineers replacing failed PWM control ICs on vintage industrial equipment boards
Frequently Asked Questions
What is the difference between the UC3845 and the UC3843 or UC3844?
The UC3845 features an internal toggle flip-flop that limits the maximum output duty cycle to 50% and has undervoltage lockout (UVLO) thresholds set to 8.4 V on and 7.6 V off. By comparison, the UC3844 shares the 50% duty cycle limit but uses higher 16 V on and 10 V off thresholds, while the UC3842 and UC3843 allow duty cycles up to 100%.
What package format is this IC?
This chip is in a standard 8-pin plastic dual in-line package (DIP-8) designed for through-hole mounting or socketed installation on printed circuit boards.
Can I purchase multiple units or just what is needed for a single repair?
You can order the exact quantity required for your build or keep extra spares on hand for the shop bench. More pieces cost less each, and the price-break table on this page shows what each quantity costs. Orders ship for an $8 flat rate, with free shipping once the order passes $28, leaving our Idaho warehouse the same or next business day.
Before switchers got overly complicated, the 384x family taught a generation of power supplies how to behave. Drop this Unitrode original into your board and bring that switching stage right back to life.
