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
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.
The above circuit can be regulated with a feedback as shown below:
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:
Good evening sir,
very difficult to leave your pages. Your information is always precious.
Transistors in Darligton mode would lift me the current in these joule thief if powered by solar cell?
If not, is there any other way to get a current gain?
If it were a buck converter would there be a way to take advantage of the current of the dissipated voltage?
Thank you very much in advance.
A lot of Swag light
Thank you Marcelo, appreciate your interest very much!
A Darlington may help to increase the current transfer response. However, using many thin wires together for the winding may also help to gain more power from the design. A joule will normally work like a boost converter so not sure how it may be turned into a buck converter…but I don’t think this concept can be used effectively used for charging bigger batteries.
Hello sir
For giving the gate pulse to the BJt can i give it through Arduino?
like pwm technique
Hi Parsiva, you can do that, just make sure that the duty cycle and the frequency are optimally adjusted.
Goodday sir I really want to appreciate you for good work thank you very much please keep up
Sir please I build a boost converter using 555 timer to drive my mosfet, and I use a mosfet in place of the transistor but each time I power it up the mosfet get really hot please what could be the cause I have checked but can find any fault in the circuit
Hello faith, keep the frequency at around 50 kHz, and test by gradually increasing the turns until the MOSFET stops heating, this is perhaps the easiest trial and error way to optimize a boost converter.
Which turns is it the number of turns i.e the inductor
There’s only one component in 555 circuit which has turns, it’s L1
Sir I have seen my mistake all this while the diode was connected wrongly but now is working very well thanks for your assistance
Glad you could solve it!
Sir I did exactly what you said it still the same I noticed that when ever I connect the power supply it like both positive and negative are connected together it al hiways spark and if I try leave it for some second the wire Wil burnt out but if i remove the inductor it will not happen, and the output power is not boost please what could be the cause. The inductor I’m using is wound on a toroid core
How many turns did you use? and what at what frequency did you set your IC 555?
Sir I’m really confused here, I even try building the boost without the 555, i.e the simple circuit were I have just inductor, diode pull button switch and capacitor, when ever I pushed the switch the inductor Wil connect it to ground i.e shorting the circuit why this happening
The switching should be in millisconds, if you hold it even for 0.25 seconds it will create a short circuit. You can read the following article for more info:
https://www.homemade-circuits.com/how-boost-converters-works/
sir I made this circuit but its not working I can’t find 680pf but am using 2A682k then I cant get tip31 and am using tip41 while testing it its just sparking as if I shot the circuit of the battery then the transistor is getting hot please help me
damilare, 2A682k = 6800pf, it’s not 680pF
In your present set up increasing the number of turns to 5 times more than the shown value, and check the results. Wind it on a ferrite rod.
adofo I have 5v 500ma solar panel. can I use your booster convert to run car tape
5 x 0.5 = 2.5 watts that’s too less for a car tape, it won’t work
Hello,
Sir can i use N-channel mosfet instead of transistor? for T1 & BC547?
is there any modifications for this?
Thanks a lot..
Hello Paul, mosfets will require minimum 9V to turn ON fully, so it cannot be in these applications.
Thanks for the reply then can i use 13003 transistor for T1?
I am sorry Paul, for BC547 you can use a mosfet since the gate would be receiving a boosted 12V so no problem.. MJE13003 won’t be suitable here!
I cant find any TIP31 Its hard to find here in our place but i found TIP41 & TIP42, can it be used here in the circuit ?
Thanks…
TIP41 is fine, it will work…
Sir Can I use 100nf cap instead of 680 pf? i cant find that capacitor.. and 1n4007 diode instead of FR107.
thanks again..
Hi Paul, There’s a huge difference between 100nF and 680pF, so it won’t work. You can try the first circuit instead.
Hmm, if Paul been asking about replacing T1 BJT with 13003 it would probably work, since 1300x family is just (high-voltage) NPN BJTs, not anyhow worse than any others. They are pretty typical in CCFLs and dumbest “electronic transformers”, esp these for “halogen lamps” and even some cheap SMPS designs.
It will work but with poor efficiency, that’s the reason we have such a huge range of devices designed for different voltage or current specs, otherwise the manufactures could have designed a single all purpose 1kv transistor : )
Yes, but if one goes for joule thief or 555-driven circuit, especially with BJT as switch and FR107 as diode, they don’t have to expect superb efficiency or awesome output power in compact package, right?
This said, joule thief is funny thing to power small led or so out of 1.5 volt battery. Only few relatively exotic and expensive DC-DC ICs would start up from voltages that make “joule thief” happy.
Actually a joule thief circuit is supposed to be extremely efficient, that’s why it’s called a “joule thief”. Yes, it’s been one of the most interesting inventions so far, considering the fact that it can work even with voltages lower then 0.5 V.
Joule thief key property that makes it interesting is that it runs down to like 0.3V or so, draining 1.5V batteries way below what most of other electronics could afford. Say, most CMOS-based ICs have a problem that 0.3V is way below of threshold voltage. Even “special” boost ICs like NCP1400 would start up from like 0.8V – then it would hold down to like 0.3V as well – because they start up, and then supply self out of own boosted output. However it implies startup problems if battery got below 0.8V and “cold” start happens.
This said, joule thief is kind of “blocking oscillator” – so it got no reasons to be terribly efficient. Waveforms aren’t really perfect, BJT drops some tenths of volt on C-E junction even if current is small, etc (FETs get edge in this regard generally, but most MOSFETs got threshold over 1V, so running less than 1V is a problem, lowest I know have Vg_th=0.8V). However joule thief gets its edge over many other circuits when it comes to using 1.5V batteries, draining them way more completely compared to most other circuits. So it would start and work out of batteries most equipment considers long “dead”. That’s where it gets extra power margin – partially negating its imperfections, so overall performance looks rather good.
p.s. I’ve finally got right one of these 10-year-led-blink, without getting it working I would have felt ashamed way too much – failing such a simple thing is a LOL. Grossly simplifying one (as suggested on youtube comments – just thief, cap and resistor). I’ve used 5.6uF 1206 SMD cercap, 5.1M 0805 resistor, PMBS3904 in sot 23 and hi-eff blue led – overall I’ve got shy 10uA average current while still getting very persuading bright blue flash about once in couple of seconds. I’ve also found funny enclosure for this little cheat, making it look like part of office alarm system, haha. A perfect joke for few vandal-unsafe places, granted most expensive part is battery and enclosure. And according to my computations battery would last … for hell knows how long, at 10uA average it would rather self discharge I guess. That’s probably best use of joulr thief I’ve faced to the date XD
What is the advantage to get add on a transistor BC547 feedback circuit? Please give me reply….
it is for keeping the output voltage restricted to a specified limit, and preventing any rise beyond that limit.
Thanks for yours valuable reply.Yours support in electronic science field really dedicated…god bless
.
It is my pleasure Biju!
Please for the bjt booster , how can I reduce the voltage to 7v instead of 30v as designed to charge a smart phone
sorry, you cannot use a 1.5V AAA cell to charge a smart phone.
Thanks Swag, but can 3.7v lithium battery power the 555ic. You said +5v to 12v input.
Hi Grace, yes you are right, normal 555 ICs will not work with 3.7V but the CMOS version (7)555 can be used which is rated to work with minimum 3V
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!
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.
Thank you sir for replying
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?
Thanks Godson, you can use the same design as shown in the above article
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 (3×1.5 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!
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.
hello, how can i make the Simple Boost Converter using a single BJT circuit work with a solar panel to charge the battery?
Hi, please see the diagram at the bottom of this article, it might be just what you are looking for
https://www.homemade-circuits.com/simplest-automatic-led-solar-light/
thanks for the reply.
however i would like to use 1 battery instead of 3 to keep the circuit as small as possible.
All the circuits referred here use a single battery. So perhaps you can try the first design from the above article