the easiest and simplest inverter

Thread Starter


Joined Dec 10, 2011
_An inverter is a circuit that converts dc voltage to ac voltage, The circuit uses two power transistors, two power resistors, and the transformer.

_The transistors determine how much power the inverter can supply, and the transformer determines the input and output voltage, also it should handle the needed power, so more power means bigger transformer, The least expensive and the easiest way to get a big transformer is to re-wind an old microwave transformer, they supply at about 1KW.

_You can choose any high power transistor, according to your needed current for exemple 2N3055 2SC5200 2N3773 MJ2955 2sd1047 2SC2922 2SA1943...
_A good 12v battery should be used to supply the wanted power, Remember, when operating at high powers, the circuit draws big amounts of current. so be careful not to let your battery go dead!!!

This image shows some of the caracteristics of the circuit:



Joined Mar 24, 2008
I notice there are no components to set frequency, nor do you mentioned a frequency associated with it. Given that most appliances care a lot about something this basic I suspect this is not going to be a very usable project. It may power a light bulb, but I would not want to use anything very expensive on it. The waveform you show is nothing but spikes, which is also not a good thing.

Merely creating a high voltage AC signal is not generally a worthwhile goal. It needs to be usable. What have you used this circuit for?

Just curious, did you measure its operating frequency?


Joined Dec 20, 2007
The 680 ohm resistors provide a max base current of 34mA then the collector current is about 1A. The input power is 12V x 1A= 12W and the output power is about 9W.

The video showed it driving three little compact fluorescent light bulbs for a few seconds.


Joined Oct 26, 2011
The base drive goes negative and zeners the base-emitter junction--recommend antiparallel diodes. This is a saturating transformer topology--will run at whatever the transformer volt-seconds determine. The 1nf capacitor is so minimal in size that this probably accounts for much of the spike amplitude. Crude at best.


Joined Dec 20, 2007
I don't think the base drive goes negative in that extremely simple circuit because the other transistor's collector slams to 0V.

I betcha the voltage regulation of the circuit is horrible.


Joined Aug 21, 2008
Letting the base drive draw current on negative swings can be a good thing as it helps sweep minority carriers from the junction, speeding up the turn-off, thereby reducing turn-off losses in the transistor.

The frequency is set by either the time the core saturates or one of the transistors runs out of drive -mostly determined by L/R of the drive winding and the base voltage.

This kind of inverter can run fine for a long time, and then suddenly drop dead. The reason is "flux walking" in which the core becomes magnetized because of unbalanced waveforms (unequal volt-seconds on the two collector windings) and eventually saturates. Therefore, it is important to use matched transistors and to make sure that the load looks the same to the transformer on both halves of the cycle.