Introduction
Switching power supplies play a crucial role in modern electronics, providing efficient voltage conversion for various applications. One such configuration is the boost converter, which steps up a lower DC voltage to a higher level. This article explores the 100W boost converter using the UC3843 PWM controller, covering its design, component selection, circuit analysis, and performance testing.
Understanding the UC3843 PWM Controller
The UC3843 is a fixed-frequency PWM controller commonly used in DC-DC converters. It provides excellent performance in boost, buck, and flyback topologies, offering features such as:
High-speed operation (up to 500 kHz)
Current-mode control for improved stability
Internal voltage reference (5V)
Adjustable duty cycle (up to 100%)
Under-voltage lockout (UVLO)
The UC3843-based boost converter efficiently steps up voltage while maintaining stable output regulation, making it ideal for power supply applications such as LED drivers, battery chargers, and power amplifiers.
Circuit Diagram and Working Principle
Below is the circuit schematic for the 100W boost converter using UC3843:
Circuit Breakdown
The schematic consists of the following key components:
1. Power Input Stage
P1: Input Connector – This is where the low-voltage DC source is connected.
C1 (2200µF, 25V) – A large electrolytic capacitor that filters the input voltage, reducing ripples and ensuring smooth operation.
LED1 (Indicator LED) – Provides a visual indication of power availability.
P1: Input Connector – This is where the low-voltage DC source is connected.
C1 (2200µF, 25V) – A large electrolytic capacitor that filters the input voltage, reducing ripples and ensuring smooth operation.
LED1 (Indicator LED) – Provides a visual indication of power availability.
2. UC3843 Controller Circuit
U1 (UC3843 IC) – The heart of the circuit, which controls the switching of the MOSFET.
R04 (100kΩ) – Provides feedback to the voltage reference.
C4, C5, C6 (1nF each) – Stabilization capacitors for the controller.
R03 (15kΩ) – Sets the voltage feedback ratio for output regulation.
C3 (100nF) – A bypass capacitor for noise suppression.
R05 (330Ω) & R06 (4.7Ω) – Set the frequency and stability of the PWM controller.
U1 (UC3843 IC) – The heart of the circuit, which controls the switching of the MOSFET.
R04 (100kΩ) – Provides feedback to the voltage reference.
C4, C5, C6 (1nF each) – Stabilization capacitors for the controller.
R03 (15kΩ) – Sets the voltage feedback ratio for output regulation.
C3 (100nF) – A bypass capacitor for noise suppression.
R05 (330Ω) & R06 (4.7Ω) – Set the frequency and stability of the PWM controller.
3. MOSFET Switching Stage
Q1 (IRFZ44) – A high-power N-channel MOSFET that switches the inductor current on and off.
R07 (0.1Ω) – A low-value resistor used for current sensing to prevent overcurrent damage.
Q1 (IRFZ44) – A high-power N-channel MOSFET that switches the inductor current on and off.
R07 (0.1Ω) – A low-value resistor used for current sensing to prevent overcurrent damage.
4. Inductor and Diode Stage
L1 (10-100µH) – Stores energy when the MOSFET is on and releases it when the MOSFET is off.
D3 (MBR2045CT Schottky Diode) – Provides fast switching and low forward voltage drop, improving efficiency.
L1 (10-100µH) – Stores energy when the MOSFET is on and releases it when the MOSFET is off.
D3 (MBR2045CT Schottky Diode) – Provides fast switching and low forward voltage drop, improving efficiency.
5. Output Filtering and Regulation
C7 (2200µF, 50V) & C8 (100nF) – Smooth out the output voltage and reduce switching noise.
R08 (6.8kΩ), R10 (1kΩ), R12 (10kΩ) – These resistors form a voltage divider to provide feedback to the controller.
LED2 (Output Indicator LED) & R11 (2.7kΩ) – Provide a visual indication of output voltage presence.
C7 (2200µF, 50V) & C8 (100nF) – Smooth out the output voltage and reduce switching noise.
R08 (6.8kΩ), R10 (1kΩ), R12 (10kΩ) – These resistors form a voltage divider to provide feedback to the controller.
LED2 (Output Indicator LED) & R11 (2.7kΩ) – Provide a visual indication of output voltage presence.
How the Boost Converter Works
When the circuit is powered on, the UC3843 generates a PWM signal to control the IRFZ44 MOSFET.
During the ON phase, the MOSFET conducts, and current flows through the inductor (L1), storing magnetic energy.
During the OFF phase, the MOSFET turns off, and the stored energy in the inductor is released through the Schottky diode (D3) to the output.
The output capacitor (C7) smooths the voltage to provide a stable high-voltage DC output.
The feedback resistors (R08, R10, R12) regulate the output voltage by adjusting the duty cycle of the PWM signal.
When the circuit is powered on, the UC3843 generates a PWM signal to control the IRFZ44 MOSFET.
During the ON phase, the MOSFET conducts, and current flows through the inductor (L1), storing magnetic energy.
During the OFF phase, the MOSFET turns off, and the stored energy in the inductor is released through the Schottky diode (D3) to the output.
The output capacitor (C7) smooths the voltage to provide a stable high-voltage DC output.
The feedback resistors (R08, R10, R12) regulate the output voltage by adjusting the duty cycle of the PWM signal.
Design Considerations for 100W Output
To achieve 100W output power, the following calculations are critical:
1. Input Voltage and Output Voltage Selection
Input Voltage (Vin): 12V DC
Output Voltage (Vout): 24V DC
Output Power (Pout): 100W
Efficiency (η): ~90%
Input Voltage (Vin): 12V DC
Output Voltage (Vout): 24V DC
Output Power (Pout): 100W
Efficiency (η): ~90%
Using the boost converter efficiency equation:
Thus, the input current requirement is approximately 9.3A.
2. Inductor Selection
The required inductor value can be estimated using: For a switching frequency fs = 100kHz, an appropriate inductor value is between 10µH to 100µH.
3. MOSFET Selection
IRFZ44 MOSFET is used due to its low Rds(on) (17.5mΩ) and high current handling capability (49A max).
IRFZ44 MOSFET is used due to its low Rds(on) (17.5mΩ) and high current handling capability (49A max).
4. Schottky Diode Selection
MBR2045CT is chosen for its low forward voltage drop (0.4V) and high current rating (20A), reducing power losses.
MBR2045CT is chosen for its low forward voltage drop (0.4V) and high current rating (20A), reducing power losses.
Testing and Performance Evaluation
1. Testing Setup
To test the converter, the following equipment is required:
12V DC Power Supply
Digital Multimeter
Oscilloscope (to analyze switching waveforms)
Electronic Load (to test performance under different loads)
2. Key Performance Tests
Voltage Regulation Test
Measure the output voltage at different load conditions.
Verify that the voltage remains constant at 24V.
Measure the output voltage at different load conditions.
Verify that the voltage remains constant at 24V.
Efficiency Measurement
Measure input power (Vin × Iin) and output power (Vout × Iout).
Calculate efficiency using:
Measure input power (Vin × Iin) and output power (Vout × Iout).
Calculate efficiency using:
Thermal Performance
Use an infrared thermometer to monitor MOSFET and inductor temperatures.
Ensure adequate heat dissipation with a heatsink if necessary.
Use an infrared thermometer to monitor MOSFET and inductor temperatures.
Ensure adequate heat dissipation with a heatsink if necessary.
Video Here
Conclusion
The 100W boost converter using UC3843 provides an efficient and stable DC-DC voltage step-up solution. By carefully selecting components and optimizing the design, the converter achieves high efficiency with minimal heat dissipation. Real-world testing validates its performance, making it ideal for power applications requiring boosted voltage.
This guide covered everything from circuit design, calculations, component selection, and testing, ensuring a successful boost converter implementation. If you’re looking to build your own high-power DC-DC boost converter, this design serves as an excellent reference.
Further Improvements
Implementing synchronous rectification for improved efficiency.
Adding a soft-start circuit to reduce inrush current.
Integrating microcontroller-based feedback for precise voltage control.
By following this guide, you can confidently design, build, and test a high-efficiency boost converter for your projects!