How to Make Simple Boost Converters

A couple of simple boost converter circuts are explained in this post, whch can be build and applied by any hobbyists for their own specific requiremenet.

What is a Boost Converter

A boost converter circuit is a design intended for stepping-up or boosting a small input voltage levels to a desired higher output voltage level, hence the name "boost" converter.

Although a boost converter circuit may involve many complex stages and calculations, here we will see how the same could be built using minimum number of components, and with effective results.

Basically a boost converter works by oscillating current though a coil or inductor, wherein the voltage induced in the inductor is transformed into a boosted voltage whose magnitude is dependent on the number of turns and PWM of the oscillation frequency.

Simple Boost Converter using a single BJT

simple boost converter circuit using BJT

Parts List

R1 = 1K 1/4 watt

D1 = 1N4148 or a Schottky diode such as FR107 or BA159

T1 = any NPN power BJT such as TIP31, 2N2222, 8050 or BC139 (on heatsink)

C1 = 0.0047uF

C2 = 1000uF/25V

Inductor = 20 turns each of super enameled copper wire on a ferrite torroid T13. Wire thickness can be as per the output current requirement.

1.5V to 30V Converter

In the above design a single BJT and an inductor is all that's needed for visualizing an incredible 1.5V to upto 30V boost.

The circuit works using a joule thief concept and utilizes an inductor in the flyback mode for generating the specified high efficiency output .

Using a flyback concepts allows the two side of the transformer isolated and ensures better efficiency, since the load is able to operate during the OFF time of the BJT, which in turn prevents the BJT from overloading.

While experimenting I found that adding C1 drastically improved the performance of the circuit, without this capacitor the output current did not look too impressive.

3.7V to 24V Converter

A simple boost converter circuit can be also built using an IC 555 circuit for boosting USB 5V to 24V, or any other desired level. The same design can be used for boosting a 3.7V to 24V from a Li-Ion cell.

555 boost converter circuit

The idea looks quite straightforward. IC 555 is configured as an astable multivibrator whose frequency is decided by the values of resistors and capacitor at pin#7 and pin#6/2.

This frequency is applied to the base of a driver transistor TIP31 (incorrectly shown as BD31). The transistor oscillates at the same frequency and forces supply current to oscillate within the connected inductor with the same frequency. The selected frequency saturates the coil and boosts the voltage across it to a greater amplitude which is measured to be around 24V. This value can be tweaked to even higher levels by modifying the turns of the inductor and the frequency of the IC .

Video Links for the above boost converter circuits are provided below:

Need Help? Please send your queries through Comments for quick replies!


g said…
hello, how can i make the Simple Boost Converter using a single BJT circuit work with a solar panel to charge the battery?
Swag said…
Hi, please see the diagram at the bottom of this article, it might be just what you are looking for
Shigida said…
Good afternone sir!
I would like to use this boost converter (the first picture) to lit the LED at night and
as a charger (at day) of 4.5 v cell (3x1.5 cell) .The LEd position will be also the position of cells .And on the position of the cell (on the above picture) will come a small solar panel.can you show me how to do a current limiting that can be used for both task (maybe by useing poti?).
Thankyou in advance!
Swag said…
Hello Shigida, I think for this low current application you could probably limit the current with a resistor in series with the battery positive or negative terminal. The resistor value could be calculated using Ohms law:
R = V/I
where V will be output voltage minus battery voltage and I will be the safe charging current of the battery. Make sure the max output is slightly lower than the battery's full charge level.
ge said…
thanks for the reply.
however i would like to use 1 battery instead of 3 to keep the circuit as small as possible.
Swag said…
All the circuits referred here use a single battery. So perhaps you can try the first design from the above article
Godson said…
Hello sir Swagatam,
Thanks a lot for this post.
I would like to use the IC555 version to boost 3.7V Li ion battery to 12V. What modifications do I need to make to achieve this?
Will the output be suitable for powering circuits that have ICs in them?
Swag said…
Thanks Godson, you can use the same design as shown in the above article
Raghavendra said…
Thank you sir for replying
Norman Kelley said…
Hi Swagatam! I have tested the above circuit which uses a 555 timer and the output is 38.6 volts using a 100uH through hole fixed inductor. I tried changing the pin 6 to pin 7 resistor to 10K with no change. I have 22uH, 47uH, 68uH, 100uH, 220uH, 330uH 470uH, 1MuH inductors. I tried 47uH inductor and the output voltage was 38.9v. I tried 220uH and the output voltage was about 37.8v. I tried 3v, 6v, 9v, 12v input with almost the same results. It just takes longer to reach max voltage as the supply voltage is reduced.What should I modify to get 20-24v output? I only have 20volt 1/2 watt Zener available. I looked at other posts which use a Zener to control the output voltage but they require a 1-watt Zener. Thanks!
Swag said…
Hi Norman, you can adjust the voltage either by changing the number of turns of the inductor or simply by adjusting the 1K value between the pin#6 and 7.

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