UC3845 PWM DRIVER
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UC3845, which is a high-performance current-mode PWM controller often used in isolated and non-isolated switching power supplies.
UC3845 Current-Mode PWM Controller Specification
- Key Functional Overview
Parameter | Detail | Notes |
Type | Fixed Frequency Current-Mode PWM Controller | Offers excellent line and load regulation. |
Topology | Optimized for off-line and DC-to-DC converters. | Commonly used in Flyback, Boost, and Forward topologies. |
Output Duty Cycle | Max 50% | Designed for converters (like Flyback) where the duty cycle is inherently limited or needs to be controlled. |
Operating Voltage (V) | 10V to 30V | Uses an under-voltage lockout (UVLO) mechanism for startup/shutdown. |
Start-up Current | < 1 mA | Very low current consumption during initial power-up. |
Pin Function Summary (DIP-8 Package)
Pin No. | Name | Function |
1 | COMP | Error Amplifier Output (Compensation point). |
2 | V_FB | Feedback Voltage Input (Error Amplifier Inverting Input). |
3 | CURRENT SENSE | Input for sensing switch current (sets PWM pulse width). |
4 | R_T / C_T | Timing Resistor / Timing Capacitor (Sets operating frequency). |
5 | GND | Ground Reference. |
6 | OUTPUT | High Current Totem-Pole Output (Drives external MOSFET/Transistor). |
7 | V | Positive Supply Voltage Input. |
8 | V_{REF} | 5.0V Reference Voltage Output (Trims 1%). |
Critical Features
- Current Mode Control: Provides inherent cycle-by-cycle current limiting and easier loop compensation.
- Oscillator: The operating frequency is programmable via external R_T and C_T components.
- UVLO Lockout:
- Turn-ON Threshold: 16V
- Turn-OFF Threshold: 10V
- High Output Current: The totem-pole output is capable of high source/sink currents, suitable for driving power MOSFETs directly.
- Oscillator Frequency: Typically operated up to 500 kHz.