Polarity flipping circuit ...

[DeepCut]

Hi.

I've googled for hours now and can't find an answer, i hope someone can help me

Is there a simple circuit that can take a DC input and flip it's polarity at a specific frequency ?


Thanks,

Gary.

[fritznien]

depends, how much voltage and currant at what frequency.
try looking up an H bridge.

[Bob Smith]

DeepCut,
The remarks by Jesus and others re the 555 timer chip circuit and polarity switching in the Lee Crock thread might be of help:
http://www.overunity.com/index.php?topic=9123.msg260166#msg260166
Bob

[TinselKoala]

Also depends on what you consider "simple".

The H-bridge is very versatile and can be used from DC on up to many megaHertz depending on components and construction.

My TinselKoil uses 2 H-bridges: one made with 2 NPN and 2 PNP silicon RF power transistors, to take the low-current positive pulse output of the TL494 controller chip and boost the current while flipping polarities. The output of this stage drives 2 toroidal phase transformers, which make oppositely-phased outputs to drive the gates of the second H-bridge.The second bridge is made of all N-channel MOSFETS, which take the higher input voltage to the coil primary and chop it into sharp positive and negative pulses to produce the fast dB/dt that makes the secondary swing like a quarter-wave whip. IGBTs can also be used here.

The high-power H-bridge is a bit more complicated as it requires diodes for surge and overvoltage protection for the transistors.

In this video I am driving the H-bridges at about 800 kHz and the high-power section is switching about 6 amps at that frequency.  This is about the top of the frequency range for the kind of construction I am using: busswire and breadboard. To go higher in frequency or power, a well-designed circuit board with low-inductance current paths is necessary.

http://www.youtube.com/watch?v=3DjcRPSljB4

[DeepCut]

Thanks very much chaps, that's plenty to be getting on with.

Cheers,

Gary