How this inverter works? urgent, please


Joined Apr 27, 2007
Indeed, it didn't occured to me, but it is indeed an hartley oscillator. It's positive feedback is made via the transformer. In simple terms, any variation of current in the 6 turn coil induces current in the 17 turn coil. This current biases the base of the transistor, which by its turn starts cunducting, having more current to the 6 turn coil. This stays that way until the capacitor is charged. This happens until it saturates the transistor (saturation is desirable here). Then the current going to the 6 turn coil starts to decrease (a transistor in saturation doesn't have as much gain as when it is in its active region), and the current induced in the 17 turn coil shifts direction. As a consequence, the oposite behaviour happens until the transistor cuts. Once the transistor cuts, the cycle repeats itself. The capacitor provides DC blocking, which is essencial because we don't want the 17 turn coil to be fixed to the ground, but floating in accordance with the current drawn by the same coil (so, essencially AC passes). If you notice, the capacitor will allow negative voltages in that node.


Joined Sep 21, 2007
could anyone explain how this inverter circuit works?
Both coils are coupled and provide positive feedback. As collector current grows it induces more base current. This process continues until the coil is saturated when base current ceases and the process is reversed. The process depends on the orientation of the turns of the coil so that they provide positive feedback. A couple of dots in that diagram are essential and missing although they can be deduced.

This circuit has the advantage of being very simple but has several disadvantages. One of them is that the flux in the coil only flows in one direction and if we use a circuit which is simetric we can get more power. The attached circuit does just this and is very common in small inverters used for things like powering small fluorescents, etc. One initial problem with this circuit is that there is a small overlap in the conductance time of both transistors which creates almost a shortcircuit. This is solved by the choke in series which stores energy and then returns it in the form of higher voltage.

I have ZIPped the attached file to get around the (IMHO unreasonable) pixel size for PNG graphics. As we all know there is no compression scheme which can reduce the size of all files and some files will become larger after "compression". In this case the original file is 1114 bytes and the ZIPped file is 1240 bytes.



Joined Nov 9, 2007
Looks very much like ones we used to build using the audio output transformer from an old tranny radio.

If you are actually going to build this be aware that the output can provide quite a nip!
The actual output achieved will depend very much on the characteristics of the transformer used. You would be lucky to get 450 volts, 150 - 250 more like. The frequency of operation is also rather less predictable than we might like.

This circuit has often been used to drive a camping flourescent light from a battery. The 2N4401 would be inadequate for this purpose, however.