DC Boost Converter - A single inductor Joule Thief

How to build a simple Joule Thief style DC boost converter using a few basic components.
This circuit requires just two resistors, two transistors (NPN and PNP), and a small axial inductor. With an additional diode and capacitor it will also run a rainbow flashing LED from a single AA cell.
With a full explanation of how the circuit works.
(Software is LTSpice for those who want to try it themselves.)

[@Elnufo]

so much effort for making the circuit as inefficient as possible, wow.

[@gristlevonraben]

You really are a smart person. You explain things so well. It will take a while before I can fully understand this, though, because I see current as going from negative to positive. And transistors are still new to me. Thank you for making this video and sharing it.

[@andyharsley]

To fully understand transistors you do actually need to think in terms of actual current flow (negative to positive). If you can handle a bit of theory, get a copy of Microelectronics by Jacob Millman. They're very cheap on the secondhand market.

[@christianchow3807]

This is indeed a great learning material. One problem: The capacitor matters! If you simulate this circuit using elec-cap, then the ripple cannot be eliminated.

[@xxJerry19xx]

20% efficiency !!! 100pF in parallel with R1 can improove it...

[@mrdovie47]

I built this circuit using an S8050 NPN (Q2) and S8550 PNP (Q1) , but it would not oscillate for me until I put a 455KHz filter (which I used for a capacitor) across R1. Now it is doing super well. 100pf or so would do as well I think. My alkaline batteries were quite spent and may have had too much internal resistance.

[@charlesdickens6706]

.....good delivery .

[@incxxxx]

good job!

[@ThingsWhichArentWork]

Good vid, and a good explanation of a boost converter, but you need to work on the efficiency of that thing. When you remove the green LED from the circuit (thereby removing the load) the input current drops by just 0.7mA (down from 37.0mA to 36.3mA).

[@andyharsley]

These simple converters are notoriously inefficient. It can be as low 1%, although in a Spice simulation I was able to achieve about 40% using a 2222 and 2907 pair. There are other more practical uses for the circuit, but I'll have to do another video to explain that.

[@andyharsley]

Here's a quick follow-up discussing the efficiency: DC Boost Converter ("Joule Thief") Efficiency Measurement

[@marcisberzins]

IMHO, this is not a Darlington transistor.

[@paradiselost9946]

a...a... a. szzzzxxxzzzslakkkkkxxki pair or summink...