Home made inverter...

[cjdelphi]

I started out with the intention to build a standard no frills 240ac from 12v ... i have an old toroidal transformer (ac 240 down to 12v/10v - 0 - /12v/10v) 150w from a cheap amplifier

simple enough... so i thought maybe i could go one step further and get a sinewave...

Now the bit i'm unsure of... the 8038 produces 0v to ?v there wont be say 0v to -10v only 0 to 10v i'll only be getting half the power i should on output...

is it worth the effort to shift the voltage down or just use as is?

i'm only after 40watts or so to power 240ac wall chargers for mobile phones...

 

[ramussons]

If the idea is to charge mobile phones from a 12 volt battery, why go through this complicated process?

You can buy mobile chargers working of 12 volts (look for car phone chargers) that serves your purpose.

If you drive the FET's with a Square wave, your transformer will have Eddy Current losses and the Laminations will heat up. On the other hand, if you drive the FET's by a Sine Wave, the transformer is safe, but the losses in the FET's will be much higher. You need to do a PWM switching.

But yes, the original idea will work.

 

[cjdelphi]

it's not about charging a phone, i'm doing it as a project / learning aid...

i've built so many power supplies i thought i'd step it up..

yes, it did occur to me about the losses across the fets but at 50hz... i figured a large enough heatsink should do if i did try it...

but, is it worth it... i've seen ups's with modified square wave, power computers ok, so why not build that and avoid the losses then

modified square wave it is...

 

[cjdelphi]

actually. ..

this got me thinking, maybe i could exploit the zener effect to block the voltage below 5v etc.... ensuring less wastage as heat? how's that sound?

(funny wave form though)

 

[AnalogKid]

There is a fundamental and very large difference between driving two power transistors as saturated switches (your first schematic) and driving them as linear amplifiers from your second schematic. You are correct that the 8038 sine output has to be level-shifted, but that's the easy part. Basically, you are talking about a 40 W audio power amplifier, like a sub-woofer amp, to drive a center-tapped transformer instead of a speaker. This is a throwback to the 50's, when solid-state amplifiers were clones of tube designs with transistors worked in. An "interstage" transformer takes single-ended audio and drives two common emitter stages driving a center-tapped output transformer. See figure 7.1:

http://www.angelfire.com/planet/funwithtransistors/Book_TS_CHAP-7.html

This is not a part-for-part schematic for your application, but it shows the idea, level of complexity, etc.

ak

 

[ramussons]

There is a fundamental and very large difference between driving two power transistors as saturated switches (your first schematic) and driving them as linear amplifiers from your second schematic. You are correct that the 8038 sine output has to be level-shifted, but that's the easy part. Basically, you are talking about a 40 W audio power amplifier, like a sub-woofer amp, to drive a center-tapped transformer instead of a speaker. This is a throwback to the 50's, when solid-state amplifiers were clones of tube designs with transistors worked in. An "interstage" transformer takes single-ended audio and drives two common emitter stages driving a center-tapped output transformer. See figure 7.1:

http://www.angelfire.com/planet/funwithtransistors/Book_TS_CHAP-7.html

This is not a part-for-part schematic for your application, but it shows the idea, level of complexity, etc.

ak

Yes, and you design a Class D power amp - that's basically a PWM switching.

 

[AnalogKid]

Actually, there is nothing in the original question or in my response that mentions or implies class D operation. While his first schematic has two transistors operating in their saturation region, they are approximating a low frequency sine wave with a stepped square wave approach. There is no high frequency carrier, no modulator, and no high frequency magnetics.

If you are saying that a class D amplifier might work in his application, that might be correct. But the OP's question is about modifying the original circuit to produce a true sinewave output using a low frequency power transformer already in hand.

ak

 

[ramussons]

Sorry AnalogKid, I was'nt contesting you . I agree with what you say. I was only suggesting to the OP that the Amplifier needs to be PWM based to take care of losses as mentioned in my first post.

Invertors of 50 or 60 Hz are basically Class D amplifiers.

 

[mayank tanwar]

Homemade inverters is a device that provides battery backup when the electrical power cuts or fails to an unacceptable voltage level. Inverters can also be used with transformers to change a certain DC input voltage into a completely different AC output voltage (either higher or lower) but the output power must always be less than the input power.

 

[cjdelphi]

Mayank... that is correct, well done!