500W inverter circuit not working properly

[aamir1]

Hi !! i have made the attached circuit hardware but the circuit does not give proper voltage at output the output should be 220vac while the circuit just gives16vac at output. please some one guide me what is the mistake ??

 

[colin55]

R6 R7 should be 1R

 

[alec_t]

What is the VA rating of your transformer? If it's too low the core will saturate and the output voltage will be low too.

 

[johansen]

can you upload a photo of what you built?

 

[ChrisP58]

I see a couple of things wrong.

1) You have 100 ohm resistors in what needs to be very high current paths. Most of your input voltage will be dropped across them, instead of the transformer.

2) There is no resistance between the op-amp outputs and the TIP122s. Without something to control that current, the op-amp outputs will be clamped to the the poing where the transistors are just barely on. But not enough to provide sufficient base current.

 

[colin55]

There are so many voltage drops that the circuit will hardly work.
It's just a very bad design with 4 voltage-drops amounting to more than 5v with even a 3amp current.

 

[colin55]

What is the VA rating of your transformer? If it's too low the core will saturate and the output voltage will be low too.

This is totally untrue.

 

[ChrisP58]

R6 R7 should be 1R

Even 1 ohm is way to much. At 500W the current through each leg of the push-pull will peak at over 50 amps during each half cycle.

You really should have multiple TIP35s in parallel. I would guestimate at least 4 per side. Each should have it's own emitter resistor. But the value should a fraction of an ohm.

I don't see what purpose D1 and D2 have.

 

[colin55]

Even with R6,7 at zero ohm, the primary of the transformer is getting less than 10v. The circuit is completley unworkable.

 

[Nigel Goodwin]

Even with R6,7 at zero ohm, the primary of the transformer is getting less than 10v. The circuit is completley unworkable.

True, it's appallingly poorly 'designed', but simply altering the driver arrangements would cure most of the issues. First off you don't want the collectors of the TIP122's connecting to the transformer, they need conencting to the main 12V rail - then you need current limiting resistors feeding the bases of the TIP35's - this will make the 35's switch correctly, and give maximum voltage to the transformer.

However, 2xTIP35 are FAR short of 500W.

 

[aamir1]

thanx guys what should i alter in the design to make it perfect for about 100watts and please tell me what values of resistors should i use at the base of tip122 (output of opamps) and r the emitter resistors of tip122 correct ??

 

[audioguru]

The output is a square-wave at a voltage that is reduced by all the losses.
What do you have that works when fed a square-wave with a voltage that is too low?

 

[johansen]

thanx guys what should i alter in the design to make it perfect for about 100watts and please tell me what values of resistors should i use at the base of tip122 (output of opamps) and r the emitter resistors of tip122 correct ??

there is no reason to have any resistors.

 

[Nigel Goodwin]

there is no reason to have any resistors.

I think almost everyone else here would disagree with you

 

[johansen]

I think almost everyone else here would disagree with you

so the emitter resistors are there to keep the magic smoke in?
please explain

 

[Nigel Goodwin]

so the emitter resistors are there to keep the magic smoke in?
please explain

They are - essentially for current limiting - however also for current sharing when you parallel the devices (and for 100W I'd really like to see two pairs of TIP35's). But base resistors are essential as well.

Personally I'd also replace the TIP122's with PNP's, to give much better base drive to the TIP35's.

 

[johansen]

They are - essentially for current limiting - however also for current sharing when you parallel the devices (and for 100W I'd really like to see two pairs of TIP35's). But base resistors are essential as well.

Personally I'd also replace the TIP122's with PNP's, to give much better base drive to the TIP35's.

there's only one transistor.

now granted you could make the argument that the resistors are there to combat flux walking.. but i'd expect the resistance of the transformer to be sufficient

 

[Nigel Goodwin]

there's only one transistor.

now granted you could make the argument that the resistors are there to combat flux walking.. but i'd expect the resistance of the transformer to be sufficient

I'd be far happier with extra current limiting resistors, output transistors fail often enough as it is

 

[aamir1]

They are - essentially for current limiting - however also for current sharing when you parallel the devices (and for 100W I'd really like to see two pairs of TIP35's). But base resistors are essential as well.

Personally I'd also replace the TIP122's with PNP's, to give much better base drive to the TIP35's.

which PNP`s should i use and how can they perform better because the beta of the transistor will also decrease i just chose the tip122 for better beta and current amplification to give proper base drive to tip35`s.........and 1 more thing if i remove the emitter resistors of tip35 will the transformer resistance be enuf or it will create a smoke condition ??

 

[aamir1]

The output is a square-wave at a voltage that is reduced by all the losses.
What do you have that works when fed a square-wave with a voltage that is too low?

i dont know please stop the quiz program and help me