## DIY boost converter calculator

For many small projects, its cheaper and easier to DIY a boost converter than to buy a specialty chip. DIY converters are usually not as efficient but they’re quick & cheap!

The above schematic section shows how I designed a 30-60V vacuum fluorescent tube display driven from a microcontroller pin.
Tubes such as VFDs, Nixies, Decatrons, etc require high voltage to light the gas in the tube. In order to reduce cost, we use a microconrtoller to make a boost converter and avoid paying \$5 for a seperate chip. We can do this because we don’t need a precision output and the current draw is mostly constant. The boost regulator is run open-loop there is no feedback resistor divider as it isn’t necessary as long as the input voltage is within a reasonable range…

The microcontroller runs at 8MHz so the 8-bit PWM output is 31250 Hz. The inductor and output capacitor is calculated below. The diode is a standard Schottkey type. The switch just has to be able to handle the max voltage plus some for safety. Note that this design is meant for ‘static’ output currents, not for variable current draw designs. There is no feedback and its very approximate! This is not for precision electronics!
The boost circuit works by connecting the power inductor L1 to ground that current can flow through it by turning on Q2. After a little bit of time, we disconnect the from ground (by turning off Q2) this means that there is no longer a path for the current in L1 to flow to ground. When this happens, the voltage across the inductor increases (this is the electric property of inductors) and charges up C6 . When the voltage increases to the level we want it to be (30V+) we turn on Q2 again which allows the current in L1 to flow back to ground. If we do this fast enough, and C6 large enough, the voltage on C6 is smoothed out and we get a nice steady high voltage.

The timing of turning off/on Q2 allows us to modify the output voltage. Normally there is a feedback resistor to the microcontroller but it is not here because we are running it open-loop. To drive Q2 we use the PWM output from the microcontroller and adjust the duty cycle to vary brightness.

These sorts of designs can be easily made with a 555, once you have the PWM output, connect it up to Q2! For this simple calculator, enter in the freqency, voltage ranges and current ranges and the duty cycle, inductor and current requirements will be displayed!

More on the calc page!

Adafruit publishes a wide range of writing and video content, including interviews and reporting on the maker market and the wider technology world. Our standards page is intended as a guide to best practices that Adafruit uses, as well as an outline of the ethical standards Adafruit aspires to. While Adafruit is not an independent journalistic institution, Adafruit strives to be a fair, informative, and positive voice within the community – check it out here: adafruit.com/editorialstandards

Stop breadboarding and soldering – start making immediately! Adafruit’s Circuit Playground is jam-packed with LEDs, sensors, buttons, alligator clip pads and more. Build projects with Circuit Playground in a few minutes with the drag-and-drop MakeCode programming site, learn computer science using the CS Discoveries class on code.org, jump into CircuitPython to learn Python and hardware together, TinyGO, or even use the Arduino IDE. Circuit Playground Express is the newest and best Circuit Playground board, with support for CircuitPython, MakeCode, and Arduino. It has a powerful processor, 10 NeoPixels, mini speaker, InfraRed receive and transmit, two buttons, a switch, 14 alligator clip pads, and lots of sensors: capacitive touch, IR proximity, temperature, light, motion and sound. A whole wide world of electronics and coding is waiting for you, and it fits in the palm of your hand.

Have an amazing project to share? The Electronics Show and Tell is every Wednesday at 7pm ET! To join, head over to YouTube and check out the show’s live chat – we’ll post the link there.

Join over 36,000+ makers on Adafruit’s Discord channels and be part of the community! http://adafru.it/discord

CircuitPython – The easiest way to program microcontrollers – CircuitPython.org

Maker Business — “Packaging” chips in the US

Wearables — Enclosures help fight body humidity in costumes

Electronics — Transformers: More than meets the eye!

Python for Microcontrollers — Python on Microcontrollers Newsletter: Silicon Labs introduces CircuitPython support, and more! #CircuitPython #Python #micropython @ThePSF @Raspberry_Pi

Adafruit IoT Monthly — Guardian Robot, Weather-wise Umbrella Stand, and more!

Microsoft MakeCode — MakeCode Thank You!

EYE on NPI — Maxim’s Himalaya uSLIC Step-Down Power Module #EyeOnNPI @maximintegrated @digikey

New Products – Adafruit Industries – Makers, hackers, artists, designers and engineers! — #NewProds 7/19/23 Feat. Adafruit Matrix Portal S3 CircuitPython Powered Internet Display!

1. Does this let you vary the brightness of the fluorescent tube by varying the PW?

2. Durr.

“To drive Q2 we use the PWM output from the microcontroller and adjust the duty cycle to vary brightness.”

3. Hi,

I follow your blog having recently got into Arduino’s and that. A brief comment about the circuit:

1N5817 diode only has a reverse breakdown of 20V (see http://www.fairchildsemi.com/ds/1N%2F1N5818.pdf). So whenever the MOSFET is turned on, the anode of the diode is at ground and the cathode is at the +UB output voltage.

This would mean that any voltages above 20V on the output would cause the diode to breakdown and be damaged. The voltage rating of the diode must be at least rated for the output voltage of the boost converter circuit.

So for higher voltages, you could use a 1N5819 which goes up to 40V reversed. You could also use a conventional fast rectifier like a UF4001 or UF4002 (http://www.fairchildsemi.com/ds/UF%2FUF4004.pdf) to get 50V and 100V reverse voltage respectively or just select a higher voltage Schottky.

Also, a resistor divder from the output and fed back to the input (with a little decoupling) could be used for feedback and control (albeit with a slow response) of the PWM driving the circuit.

Perhaps some of this could be included in the calculations page?

B. Regards,
James

4. James, good point, thank you for reminding me! I will update that. MBR160 are nice and stocked at our fav. suppliers 🙂