DIY Boost Converter: High Voltage Without Special ICs

Boost converters, which step up a low DC voltage to a higher one, are widely available for around $16 on Amazon. However, building your own is not only rewarding but also lets you customize performance. Inspired by a simple circuit from Circuits DIY, I designed this boost converter to deliver voltages above 9V using MOSFETs instead of BJTs for stable voltage under varying loads. No specialized ICs are required—just common components and a Variable Frequency PWM (Pulse Width Modulator). Follow this guide to build a versatile, high-voltage boost converter and tweak it to your needs!

Note: You’ll need a Variable Frequency PWM circuit. Check out my Instructable for building a precision VF-PWM to pair with this project.

Here’s everything you need to build the boost converter:

1. Power Supply: 12 VDC
2. Tools:
3. Oscilloscope (to monitor frequencies, voltages, and waveforms)
4. Digital Multimeter (DMM)
5. Prototyping:
6. Solderless breadboard
7. 18 AWG PVC-insulated wire (for inductor coil)
8. 22 AWG PVC-insulated wire (for hookups)
9. Hot-melt glue gun (optional, to secure inductor wire)
10. 4x Alligator clips (for large capacitor connections)
11. Variable Frequency PWM: Pre-built circuit (see my Instructable). I am using 2.2 nF for the frequency and 4.7 nF for the pulse width.
12. Inductor:
13. 1x DS400060 Mn-Zn-Fe toroid (23 mm ID, 40 mm OD, 15 mm height) or similar toroidal core (eBay is a great source)
14. Connectors:
15. 1x 3-pin screw terminal block, larger (for TO-247 MOSFET)
16. 2x 2-pin screw terminal blocks (for coil and Schottky diode)
17. 1x 3-pin screw terminal block, smaller (for TO-220 MOSFET)
18. ICs and Transistors:
19. 1x CD40106BE Inverting Schmitt Trigger (cleans gate drive signal)
20. 1x MC34152P Dual Gate Driver (with totem poles to clear gate charge)
21. 1x IRFP250N MOSFET (N-channel, TO-247; swap for IRFP460 for outputs >160–170 VDC, rated for V_DS 500 V
22. 1x FB38N20D MOSFET (N-channel, TO-220)
23. Diodes:
24. 1x D10S120 Schottky Diode
25. Resistors and Potentiometers:
26. 1x 47 Ω, ½ W (gate drive for TO-220 MOSFET)
27. 1x 100 Ω, ½ W (gate drive for TO-247 MOSFET)
28. 2x 100 kΩ, 2 W (for voltage divider and load resistor)
29. 1x 5 kΩ potentiometer (for voltage divider)
30. Capacitors:
31. 1x 1000 µF, 16 V (stabilizes power rails)
32. 1x 1000 µF, 450 V (captures output power)
33. Optional (Recommended):
34. Finned heat sink for TO-247 MOSFET
35. Cooling fan for heat sink

This boost converter uses a Variable Frequency PWM (VF-PWM) to generate pulses that control a MOSFET, driving an inductor to produce high voltages. Here’s the breakdown:

1. Inductor Charging: The inductor, connected to the 12 V (+) rail, stores energy as current flows through it.
2. MOSFET Switching: The VF-PWM sends pulses to the IRFP250N MOSFET via the MC34152P gate driver. When the MOSFET turns on, it connects the inductor to ground, allowing current to build a magnetic field. When it turns off, the collapsing field induces a high voltage.
3. Output Storage: The induced voltage passes through the Schottky diode to charge the 1000 µF, 450 V capacitor, which stores the output voltage.
4. Voltage Control: The pulse width from the VF-PWM determines the output voltage. Wider pulses increase the voltage by allowing more energy to build in the inductor.
5. Safety Feature: A second MOSFET (FB38N20D) and a voltage divider (5 kΩ potentiometer + 100 kΩ resistor) monitor the output. If the voltage exceeds a threshold (when the divider outputs ~1.57 V), the second MOSFET turns on, grounding the gate of the main MOSFET to halt power conversion and prevent runaway voltage spikes.

This design ensures stable, adjustable output voltages up to 180 VDC (with caution; use an IRFP460 for safer high-voltage operation).

Before assembling, build or obtain a Variable Frequency PWM. I recommend my VF-PWM design for precision. Ground yourself to prevent electrostatic discharge (ESD), which can damage MOSFETs and ICs. I use a copper foil connected to Earth ground, placing my bare foot on it.

Inductor Winding:

1. Use the DS400060 toroid with 25 AWG copper, enamel-insulated wire.
2. Wind 32 turns counterclockwise from the center tap in one direction, then 32 turns counterclockwise from the center tap in the opposite direction (total 64 turns). This configuration balances voltage output with controllability; fewer turns (e.g. 34 turns with 18 AWG) readily produce higher voltage for the same PWM settings, but the voltage requires a lot of fine tuning.
3. Calculate wire length: account for leads, center tap, and add 600 mm extra. Secure with hot-melt glue if needed.
4. Attach a 2-pin terminal block to the inductor for easy connection.

Component Checklist (as listed in Supplies):

1. Ensure MOSFETs, ICs, and capacitors are rated appropriately.
2. Use terminal blocks to protect the breadboard from large pins and thick wires.

Place components on the solderless breadboard as follows (refer to the original photos for layout):

1. Power Rails: Connect upper and lower rails (red to red, blue to blue) with 22 AWG wire.
2. ICs and MOSFETs:
3. Insert the MC34152P gate driver IC.
4. Place the IRFP250N (TO-247) and FB38N20D (TO-220) MOSFETs in their respective terminal blocks.
5. Resistors:
6. Place the 47 Ω resistor at pin 7 of the gate driver (for FB38N20D).
7. Place the 100 Ω resistor at pin 5 (for IRFP250N).
8. Place one 100 kΩ resistor across the breadboard’s central channel (right of MOSFETs) for the voltage divider.
9. Place the second 100 kΩ resistor to the right of the diode (load resistor).
10. Other Components:
11. Insert the inductor’s terminal block.
12. Place the 5 kΩ potentiometer below the central channel (below the inductor).
13. Insert the Schottky diode.
14. Place the 1000 µF, 16 V capacitor along the power rails (ensure correct polarity: (+) to red rail, (-) to blue rail).

Wire the breadboard using 22 AWG wire (refer to the original photos for clarity):

1. Connect the 100 Ω resistor from pin 5 of the gate driver to the IRFP250N gate.
2. Connect the 47 Ω resistor from pin 7 to the FB38N20D gate.
3. Connect the gate driver IC’s power pins to the (+) and (-) rails.
4. Connect the FB38N20D drain to the IRFP250N gate.
5. Connect the FB38N20D source to ground.
6. Use a jumper to connect the inductor’s left pin to a nearby breadboard column (due to multiple connections).
7. Connect the IRFP250N drain to the inductor’s left pin.
8. Connect the IRFP250N source to ground.
9. Connect the inductor’s right pin to the (+) rail.
10. Connect the inductor’s left pin to the diode’s anode (right pin).
11. Connect the diode’s cathode (left pin) to the (+) side of the 1000 µF, 450 V capacitor (use alligator clips).
12. Connect the capacitor’s (-) side to ground.
13. Connect the diode’s cathode to the top of the first 100 kΩ resistor (voltage divider).
14. Connect the resistor’s bottom to pin 1 of the potentiometer.
15. Connect potentiometer pins 1 and 2 together (making it a variable resistor).
16. Connect potentiometer pin 3 to ground.
17. Connect potentiometer pin 1 to pin 2 of the gate driver IC.
18. Connect the diode’s cathode to the second 100 kΩ resistor (load resistor).
19. Connect the load resistor’s other end to ground.
20. Connect the VF-PWM output to pin 1 of the CD40106BE Schmitt Trigger. Jumper pins 2 and 3, and connect pin 4 to pin 4 of the gate driver IC.

The output voltage is taken from the junction between the diode’s cathode and large capacitor's (+) terminal.

Setup:

1. Attach oscilloscope probes to:
2. Pin 4 of the gate driver IC (input signal).
3. IRFP250N gate (gate drive signal).
4. IRFP250N drain (inductor waveform).
5. Connect the DMM to the diode’s cathode to monitor output voltage.
6. Turn the 5 kΩ potentiometer fully counterclockwise to minimize startup voltage.

Power On:

1. Apply 12 VDC to the power rails.
2. Set the VF-PWM to ~11 kHz with a 5–10% duty cycle. Note: Increasing frequency widens the effective pulse width, so adjust carefully.
3. Slowly turn the potentiometer clockwise to increase the voltage divider’s output, watching the oscilloscope for stable waveforms.
4. Adjust the pulse width to achieve the desired output voltage (up to 160 VDC safely with IRFP250N; use IRFP460 for 180 VDC).
5. Fine-tune the potentiometer to set the safety threshold, ensuring the FB38N20D MOSFET activates if voltage spikes occur.

Tips:

1. I’ve run this circuit at 160 VDC for hours without issues. At 180 VDC, it’s riskier unless you use an IRFP460.
2. Monitor the main MOSFET for heat; use the heat sink and fan if needed.

Two photos show different waveforms for 160 V. One is with this resistor that got way too hot, and one is with only a 100 kΩ resistor.

This boost converter is a game-changer: it steps up 12 VDC to 180 VDC without transformers or specialized ICs! The adjustable pulse width makes voltage control intuitive, and the safety MOSFET prevents catastrophic voltage spikes. Here’s what I learned:

1. Inductor Winding: Fewer turns (e.g., 34) yield higher voltages at lower duty cycles, but more difficult to control.. More turns (e.g., 64) reduce ringing but require higher duty cycles for the same voltage.
2. Safety First: The voltage divider and secondary MOSFET are critical to prevent runaway voltages, which can burn out the main MOSFET or damage the capacitor.
3. Tuning: Voltages jump quickly with pulse width changes. Use the voltage divider to stabilize the circuit before fine-tuning.

Build this circuit, experiment with pulse widths, and watch the voltages climb on your oscilloscope and DMM. Share your builds, mods, or questions in the comments—I’d love to see your results! If you find this Instructable helpful, give it a Heart (Favorite). For corrections or suggestions, drop a comment to help improve this design.

Notes:

1. In photos, the green trace is the main MOSFET’s drain, yellow is the gate driver input, and blue is the MOSFET’s gate.
2. Use the voltage divider to manage startup and avoid blowing components. I’ve only lost a main MOSFET so far—learn from my mistakes!

Credit: Thanks to Grok, created by xAI, for editorial help in refining this Instructable’s clarity and flow.