About a PWM power inverter

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#3
Hello

I was looking at a PWM inverter circuit because modified sine inverter are too noisy in TV and audio systems and others things.

I have a 500 w sine inverter schematic, I have the mosfet and few very big ferroresonant transfo, but it would need a very big heat sink and it would lost quite much energies into heat.

Here is the original 500w sine wave circuit.

http://img371.imageshack.us/img371/8734/invertersine500wcc.jpg

Thank

Bye

Gaetan
 
#4
I tried to build this exact circuit almost 20 years ago, back when all the parts were in full production. I never was able to get it to work. I don't know if my choice of transformer wasn't appropriate, or if the negative feedback wasn't correct. Either way, not a very practical circuit. You are definitely better off with a PWM circuit and modern components. I would 86 the XR-2206, for starters. Better ways of generating clean sine waves with current production.
 
#6
That inverter design is not a PWM inverter. It uses a PWM circuit to create a Sinewave output to power switching transistors to create a 60 hz output. The power transistor operate in linear mode instead of switchmode which isn't very efficient.

A PWM inverter will switch the power transistors in the Khz range and alter the duty cycle to simulate a sine wave output. The PWM output from the transformer secondary needs either a rectifying bridge/flipping bridge. A PWM output can also be set up using a BTL (Bridge Tied Load) output circuit.

To give you idea how PWM inverter work, research Class-D Amplifiers:
http://en.wikipedia.org/wiki/Electronic_amplifier (for a starting point).

To create a PWM Sinewave output without a Microcontroller (aka PIC) you can do sometime like this:
http://home.c2i.net/helbue/projects/vfd.htm

I recall an app-note from National that created a digital quasi sinewave PWM output generator using a 555, a TTL Counter (maybe a 74193) and either a multiplexor or a CD4017 or Both. Perhaps you can google for it.

Setting up a simple Sinewave generator in a Microcontroller is the easier solution. You just need a create a delay lookup table to drive either a digital output on the uC, or using a PWM controller that is Built into the uC. The PIC 18F1330 is a small uC with four built-in PWM controllers.

We discussed PWM inverters a year or two ago on this forum. A seach might be useful.
 
#7
I build a couple of inverters with PICs and they were all PWL with hybrid output to mosfets. There are many ways to increase/degrees the output voltage from the transformer to measure the right voltage on the output, in my place 230V ac. They were all not sine wave output but definatly not use square wave. All my amps work perfectly with these with zero noise caused by the PWM on the input of the transformer. Measure the output current on a proper design and it will be sine wave into a inductive load. Google 3rd harmonic injection.

Regards
Chris
 
#8
The circuit is a time bomb. As quickly you start the device, both MOSFET will be carbon and smoke. Look at the diodes in the gate circuit, they will be turned on, but never go off, when second transistor will be on, with the first still on, transformer is shorted out. And great balls of fire will make.
 
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