The UC3845 Current-Mode PWM Controller IC DIP-8 is a high-efficiency, fixed-frequency control IC designed for use in switch-mode power supplies and DC-DC converters. It combines all essential power control functions, including an oscillator, precision 5V reference, error amplifier, current-sense comparator, and a high-current totem-pole output stage capable of directly driving power MOSFETs. The UC3845AN features current-mode operation that provides superior line and load regulation, fast transient response, and inherent cycle-by-cycle current limiting. With its low start-up current and high switching frequency, it is ideal for compact and energy-efficient designs. Packaged in a standard 8-pin DIP, this controller is widely used in off-line power supplies, battery chargers, motor control circuits, and DC-DC converter modules.
Features
- Fixed-frequency current-mode PWM control for superior performance.
- High-speed totem-pole output for driving power MOSFETs or BJTs.
- Low start-up and operating current for improved efficiency.
- Accurate 5V ±1% reference voltage for stable operation.
- Adjustable oscillator frequency for flexible design options.
- Cycle-by-cycle current limiting for overload protection.
- Undervoltage lockout (UVLO) with hysteresis for safe startup.
- High efficiency and fast transient response.
- Wide operating voltage range: 7.6V to 30V.
- Standard 8-pin DIP package for easy integration in SMPS and converter circuits.
Pinout Configuration
| Pin No. | Symbol | Function |
|---|---|---|
| 1 | COMP | Compensation input – error amplifier output for loop compensation |
| 2 | VFB | Feedback input – voltage feedback to internal error amplifier |
| 3 | ISENSE | Current sense input – detects switch current for PWM control and protection |
| 4 | RT/CT | Timing resistor and capacitor – sets oscillator frequency |
| 5 | GND | Ground |
| 6 | OUTPUT | Output driver – controls external power MOSFET |
| 7 | VCC | Supply voltage input (7.6 V – 30 V) |
| 8 | VREF | 5 V precision reference output (up to 20 mA) |
Specifications
| Parameter | Specification |
| Product Type | Current-Mode PWM / DC-DC Converter Control IC |
| Part Number | UC3845AN |
| Datasheet | UC3845 |
| Manufacturer | TDSEMIC |
| Package Type | DIP-8 |
| Operating Voltage Range | 7.6 V – 30 V |
| Reference Voltage | 5.0 V ± 2% |
| Oscillation Frequency | 500 kHz |
| Output Type | Adjustable |
| Topology Supported | Buck, Boost, Flyback, Forward |
| Number of Channels | 1 |
| Switch Type | External MOSFET |
| Undervoltage Lockout (UVLO) | Start: 7.6 V – Stop: 6.9 V |
| Output Drive Capability | ±1 A peak |
| Optimization | Optimized for multi-topology power supplies including buck, boost, and buck-boost |
| Maximum Duty Cycle | 50% |
| UVLO Thresholds (Start/Stop) | Lower thresholds, suitable for specific design constraints |
| Design Flexibility | Provides limited duty cycle for improved control and efficiency |
| Control Method | Fixed-frequency peak current-mode PWM |
| Main Application | Boost or buck-boost converters, discontinuous flyback converters |
| Operating Temperature Range | 0 °C – +70 °C |
