inverter circuits

[Jamie Morken]

Hi all,

I just took apart a 12VDC to 120VAC (I believe) inverter and I was surprised
how few components it had inside. I thought that it would be complex
circuitry but there was only a laminated steel EI transformer, two power
resistors, two caps, and two transistors (or at least I think they are
transistors). Could someone explain how these can work!?

cheers,
Jamie Morken

 

[Joerg]

Hi Jamie,

That looks like one of those simple versions that take a power transformer and
just oscillate at 60Hz (plus minus a lot...). I had a radio once that used a
regular transformer for 120V operation and simply used that same transformer "in
reverse" for 12V operation. Not quite reverse, they used the oversized filament
windings to hook up the transistors for conversion. Same thing, a couple TO-3
transistors on a heat sink, a few caps and resistors. It worked.

Regards, Joerg
http://www.analogconsultants.com

 

[Ian Stirling]

Jamie Morken <truespace1@hotmail.com> wrote:

Hi all,

I just took apart a 12VDC to 120VAC (I believe) inverter and I was surprised
how few components it had inside. I thought that it would be complex
circuitry but there was only a laminated steel EI transformer, two power
resistors, two caps, and two transistors (or at least I think they are
transistors). Could someone explain how these can work!?

Posting the number of the transistors might help.
If it's heavy for the wattage, then it probably just does run the transformer
at 60Hz.

 

[John Popelish]

Jamie Morken wrote:

Hi all,

I just took apart a 12VDC to 120VAC (I believe) inverter and I was surprised
how few components it had inside. I thought that it would be complex
circuitry but there was only a laminated steel EI transformer, two power
resistors, two caps, and two transistors (or at least I think they are
transistors). Could someone explain how these can work!?

cheers,
Jamie Morken

The transformer is used as a load for a power multivibrator. The core
saturation sets the on time for each half cycle. Here are some
examples with some explanation:
http://www.repairfaq.org/REPAIR/F_samschem.html#SAMSCHEM_023
http://www.aaroncake.net/circuits/inverter.htm
--
John Popelish