This induces a negative pulse on the Base (Blue trace) which is 3-times greater. The base drive disappears, the field collapses, producing the pulse. This stops when the supply cannot drive the coil any more. The top (yellow) trace shows the voltage slowly growing, which increases the drive on the Base, forcing the transistor to conduct harder. The circuit cannot start at this voltage, but, once given a jump (with a 1v jolt), it is very stable, drawing a measly 7-milliAmps from the supply.Ī look at the scope's reading tells us how it works. Remember the tester can only be used to compare similar JT circuits and LEDs!Īn entry from acmefixer's blog brings us this strange beast - it's a Joule Thief type circuit that runs on 200mV! That's a fifth of a volt! And all it uses is the plain old MPS2222 silicon transistor!Ī few changes allow this to happen: First, the coil must have a Secondary with at least 3 times as many turns as the Primary, and the LED is connected between the Base (-) and the Collector (+) of the transistor. Another hint is the +Duty: it is over 25% longer than the basic JT (34% vs 27%). First, Although V_amp is only 3.52v, its wave-form is a more rounded peak instead of a quick drop. A look at the last Oscilloscope display (CH2, blue) gives us some hints. It also illustrates one of the weaknesses of the measuring tool - despite its low QS reading, its output seems very bright. The last circuit is a faux-JT in that it replaces the secondary winding with a capacitor and another transistor, which lets us use off-the-shelf inductors instead of winding our own. The relevant numbers are the V-amp (Amplitude) and +Duty (-cycle) the higher they are, the more light is produced. Only the inductor (coil) is changed.īasic Oscilloscope readouts are included, with the top (CH1 / yellow) trace always displaying the output pulse of the 'standard' circuit (#2, which has one of the 'matched' 100uH inductors). Each circuit consists of an MPS2222 (Motorola's number for the 2N2222 transistor), 1k base drive and Nichia LED. Starting with the four lights we used at the beginning. To test the effectiveness of the QS meter, we're going to build some basic JT circuits. For example, the first coil on the left is half the size of the larger one to its right, yet it has an impedence (magnetic reactance) 8-times greater, even with the same number of turns on it. One advantage is that it is easily duplicated: just take some thin wires and wind it around a form - as long as the number of turns and the size of the coil are the same, it produces the same results.įerrite cores, often specified in the making of the JT, depend almost entirely on the material used to make it, and it is impossible to guess its performance at a glance. In fact, in some ways, it is superior to the ferrite.

It's called an air-core coil and obviously, it works. Oh, and yes, the big green thing is a coil - just without the ferrite core. In future installments, we'll go deeper into the more advanced concepts. Here, in this Instructable, we will give you the basic information on what goes into a Joule Thief, its technical aspects and offer tools to help optimize the design. This circuit uses a single-transistor blocking-oscillator which features a coil with a secondary winding to generate timing signals to maintain oscillations. Many of us are interested in the Joule Thief, the common name for a voltage boosting converter which allows a 1.5-volt or lower battery source to operate an LED which requires upwards of 3-volt to light.

Datathief add hint