UC3842AN

Ah, now we’re in the power electronics arena ⚡💪 — the UC3842AN is a classic workhorse for switch-mode power supplies (SMPS), like those in adapters, chargers, and LED drivers.

Think of it as the “brain” that controls switching of the power transistor in a flyback, buck, or boost converter.

📦 UC3842AN – Product Description

The UC3842AN is a high-performance current-mode PWM controller IC. It’s widely used for:

Isolated and non-isolated switching power supplies

Battery chargers

LED drivers

DC-DC converters

It includes features for high efficiency, overcurrent protection, and stable switching. The AN suffix is the DIP-8 package.

✨ Key Features

✅ Fixed 500 kHz oscillator
✅ Current-mode control for better line/load regulation
✅ High startup voltage tolerance
✅ Under-voltage lockout (UVLO)
✅ Low startup current (~1 mA)
✅ Thermal shutdown
✅ Pulse-by-pulse current limiting
✅ 8-pin DIP (UC3842AN)

📊 Electrical Specifications
Parameter Typical / Max Value
Supply voltage (VCC) 7.6 V – 30 V
Startup voltage 16 V (typ)
Undervoltage lockout 10 V (typ)
Oscillator frequency 47 kHz – 500 kHz (nominal 100 kHz–500 kHz adjustable)
Output current (source/sink) ±1 A peak
Duty cycle Max ~50 %
Input bias current ~1 mA startup
Package 8-pin PDIP
Operating temp 0 °C – 70 °C (commercial)
🔌 Pin Configuration (DIP-8)
UC3842AN
┌───────────┐
1 COMP VCC 8
2 VFB CS 7
3 RT/CT GND 6
4 OUT VREF 5
└───────────┘

Pin functions briefly:

VCC (8) → supply for IC

GND (6) → ground

OUT (4) → PWM output to MOSFET or transistor gate

CS (7) → current sense input (limits peak current)

VFB (2) → voltage feedback for regulation

COMP (1) → error amplifier output

RT/CT (3) → sets oscillator frequency

VREF (5) → 5 V reference for internal circuits

⚙️ How It Works (Simplified)

Voltage feedback via VFB → compares output voltage to reference

Error amplifier adjusts COMP pin → controls duty cycle

Current sense via CS → prevents overcurrent in MOSFET

PWM signal → drives gate of power switch → regulates output voltage/current

This is current-mode PWM control, which is faster and more stable than voltage-mode for SMPS.

🛠️ Typical Applications

Switch-mode adapters (5 V, 12 V)

LED drivers

Battery chargers

Flyback and boost converters

Small DC-DC converters

💡 Design Tips
✅ Start-up

Use high-value resistor or auxiliary winding to supply VCC until oscillator starts.

✅ Frequency

Choose RT/CT for stable 50–100 kHz (typical for small power supplies).

✅ Overcurrent

Connect CS properly to MOSFET source for pulse-by-pulse protection.

✅ Thermal

UC3842AN doesn’t limit temperature directly, so use heatsink for MOSFET.

✅ Quick Summary

UC3842AN = current-mode PWM controller IC

Perfect if you need:
✔ efficient switching supply
✔ overcurrent protection
✔ reliable PWM control