Regulated Positive Voltage Booster

Outputs 1/4 Watt, up to +60V DC Max

Accepts any input voltage (1V minimum)

Uses a simple, flexible circuit

Warning: If you don't follow the instructions carefully, wiring this circuit wrong can damage your Arduino. The output voltage of this circuit must not be applied to the digital IO of the Arduino.

Arduino Project and Schematic Download



The Arduino 5V boosted to 40V, with a hand made inductor.

The same circuit, with the Arduino regulating at 9V instead.

Circuit Theory

Inductors resist changes in current. When Q1 is active, a larger current begins to flow through L1 to GND. When Q1 is switched off, the current through L1 trys to remain the same as it was, causing an increased voltage. By varying the PWM duty cycle, the current through L1 and output voltage can be controlled.

There are many ways to explain the relationship between PWM (analog output) and output voltage. The simplest way to put it, is that as PWM duty cycle increases, the voltage also increases. This is true when the output load remains constant. What the PWM does is control power, and if output current remains constant, then the voltage increases (P=VI). Alternately, at any given PWM if the output current is reduced, the voltage will increase. Without regulation, the output voltage would change as the load changed.

Don't worry about the gain of the transistor. (I've tested 2N3904, 2N2222, 2N4124, etc.) Connecting it correctly, is all that's important. When the circuit is powered by batteries or the Arduino, the gain of the transistor will have little effect on ouput power. Also note that even though the transistor is rated for 30Vdc (in most cases), it should be safe to use up to 60Vdc for two reasons. 5V logic on the transistor base doesn't saturate it, so the voltage drop across the transistor is generally less than 1/2 the circuit output voltage. The second reason is that the voltage rises when the transistor is off and not conducting. By the time the transistor is turned back on, the voltage should have dropped back down closer to the input voltage. This is why most 30V NPNs can handle generating 60V.

The exact inductance of L1 doesn't matter. The circuit is capable of using almost any inductor. Any insulated wire wrapped at least 16 times around metal should work, regardless of the wire's guage (thickness). I don't even own an inductance meter, and this is the first time I've used inductors in a project. I randomly wrapped wire around metal, and had a working inductor on my third try. It's easy, my advice is don't let it intimidate you. Just remember the important parts: insulated wire (not bare wire) wrapped tight around a smooth metal object (sharp edges could cut the insulation), and wrap the wire around the metal more than a dozen times. Take a look at the pictures below, try making your first inductor about the same size as them.

If you're trying to get more than one watt, then use a darlington pair. With BJT power transistors, the most you'll get is about 4 watts, efficiently. With N-Channel power MOSFETs, it's possible to get 25 watts at about 70% efficiency with a good power inductor (it's very difficult). To get past 30 watts, you'll lose efficiency, need a different frequency PWM, or an elaborate/expensive switch.

Software Summary

The Arduino ATMega168 regulates the output voltage. Regulation is important when the output load varys. The software senses changes in the output voltage, and adjusts the PWM to compensate. The output voltage depends on load and input voltage, which are "unknown" variables, so the mathematical relationship between PWM duty cycle and output voltage are "guessed" by the program. If the input voltage and output load were constant, the Arduino analog input wouldn't be necessary. Because of regulation, almost any load and input voltage can be used to make an accurate output voltage.

The program was written for both the ATMega8 or ATMega168. However, the ATMega8 might not work with as many inductors, since its PWM frequency is lower.

Inductors that work

Each inductor behaved a bit differently. The ones with thick wire didn't regulate well, and the barrel/can shaped inductors in the top row generally wouldn't go above 24V.

The bottom row has two hand made inductors. One is an aluminum heatsink, the other is a torroid. Two different guages of enameled wire.

The quarter is there to show the image's scale.

Inductors that don't work

The top two inductors were hand made, but didn't work. The washer had sharp edges that probably scratched enamel off the wire, shorting it. The screw just doesn't have enough turns.


THE #1 RULE: Do not charge large capacitors to high voltages. Capacitors can discharge instantly, and that can be hazardous.

Voltages exceeding 60V may be possible

  • Wear safety glasses
  • Don't lean over your circuit while it's powered
  • Don't wear loose fitting jewelry
  • Keep liquids, flammable or loose debris away from the circuit
  • Do not leave the circuit operating unattended
  • Never power the circuit from negative voltages, AC or directly from a wall outlet



  1. Assemble and check the circuit components, without the Arduino connected

Power Up Check (Don't connect PWM pin 10, or analog in (ADC) pin 0 until instructed to)

  1. Connect Arduino GND to circuit GND (this is called common ground)
  2. Connect Arduino 5V to circuit voltage input (the voltage input of L1)
  3. Measure circuit Voltage Output is less than 5V (minus the D1 voltage drop), and more than 0V (check inductor)
  4. Measure circuit analog out (Aout) voltage is less than 400mV (5V/15=0.333mV, Aout is a 15:1 voltage divider)

Power Down Check (still, do not connect pin 10 or 0)

  1. Disconnect 5V, your circuit output voltage will gradually fall to 0V.
  2. Repeat the power up check again, and then move on to Operation.


  1. Choose a low voltage in the setup routine, where "power_level=SetVoltage(v)" chooses the voltage.
  2. Upload the project to the Arduino.
  3. Connect ADC pin 0 to circuit Aout, which is between the 1.5M and 100K resistors shown in the schematic. Make sure ADC pin 0 is connected correctly, or your output voltage wont be regulated.
  4. Attach your Voltmeter to circuit Vout
  5. Watch your Voltmeter while you connect pin 10 to the circuit PWM (disconnect pin 10 if the voltage is wrong)

    You can turn off the voltage booster by disconnecting pin 10 from the circuit.
    All power can be shut off by disconnecting Arduino 5V from the circuit


Shut off the circuit before touching, removing or replacing components or wires (see above)

Power Up Check Step 3
The voltage wasn't between 0V and 5V

  • Check diode D1 is inserted with the correct polarity, your inductor is securely connected and conducting,
  • NPN transistor Q1 is connected according to the schematic (collector to L1, emitter to GND)

The voltage was 5V

  • Check your diode D1 is inserted correctly (5V minus its voltage drop, is what you should be measuring at Vout)

The voltage was above 5V

  • At this step, the arduino ADC pin 0 and PWM pin 10 shouldn't be wired.

Power Up Check Step 4
The analog out voltage was above 400mV

  • The resistor voltage divider is not wired correctly (check 1.5M and 100K resistors weren't swapped)

The analog out was 0V (or open and floating)

  • Make sure the Arduino GND is connected to the circuit GND.
  • Check the voltage divider is wired to Vout properly, and the resistors are good.

Operation Step 4
The voltage dropped slightly

  • Your inductor doesn't have enough turns (A PWM frequency of 62KHz isn't high enough)

The voltage increased only slightly

  • The inductor doesn't have enough turns, or your transistor (Q1) isn't working right

The voltage increased beyond the chosen voltage by more than 1V

  • Ensure your load resistor is 100K, filter capacitor is between 0.1uF (100nF) and 47uF
  • or reduce the SetVoltage() 12.41 multiplier.

Nothing happened; the voltage didn't change

  • Your inductor wont work try another one, or transistor Q1 isn't working right

Further Troubleshooting
Different circuit output voltages are off by a relatively constant amount

  • Adjust the 12.41 multiplier constant in the SetVoltage() function

The circuit has poor regulation, it varys by more than half a volt

  • Regulation needs a minimum load and filter capacitance, however at high voltages the regulation wont work as accurately.
  • At high loads, the output voltage will decrease.
  • Check your circuit analog out (Aout) is your output voltage divided by 15.
  • There might be a problem with your resistor voltage divider.
  • Try a different inductor to see if that's limiting the output.
  • If you rapidly change the output load, the output voltage may bounce around.

The circuit wont generate a voltage above 6V.

  • Try a different inductor, check your Q1 transistor is wired correctly, replace D1


Created 12/17/2008 by Amp, last updated 2011