audioguru2
- Apr 6, 2004
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- Apr 6, 2004
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The "500W" inverter schematic now on our site does not have enough output transistors for 500W output. Also its output transistors must be matched.
500W output.
83% efficiency is an extra 100W of heating. Total= 600W.
600W/12V= 50A.
The output transistors must conduct 20A-25A each but their absolute max rating is 15A and they operate poorly at 10A and above.
My corrected inverter had twice as many output transistors so that their current was 10A-12.5A each.
The output transistors used emitter resistors to reduce the current gain of high gain ones for better matching.
It had diodes to arrest voltage spikes.
It had resistors to turn off the transistors.
It had correct values for the frequency determining R and C.
500W output.
83% efficiency is an extra 100W of heating. Total= 600W.
600W/12V= 50A.
The output transistors must conduct 20A-25A each but their absolute max rating is 15A and they operate poorly at 10A and above.
My corrected inverter had twice as many output transistors so that their current was 10A-12.5A each.
The output transistors used emitter resistors to reduce the current gain of high gain ones for better matching.
It had diodes to arrest voltage spikes.
It had resistors to turn off the transistors.
It had correct values for the frequency determining R and C.
audioguru2
- Apr 6, 2004
- 12,026
- Joined
- Apr 6, 2004
- Messages
- 12,026
Hi Photoar,
You made my corrected circuit that has been on the site for nearly 3 years until it was changed recently.
Look at the changed one in POWER CIRCUITS in our PROJECTS section. It is missing important parts and its frequency determining parts values are wrong.
The transformer is a 220VAC to 2x12VAC power transformer rated for 500VA or 600VA. The 2x12VAC windings can also be 24VAC center-tapped.
You made my corrected circuit that has been on the site for nearly 3 years until it was changed recently.
Look at the changed one in POWER CIRCUITS in our PROJECTS section. It is missing important parts and its frequency determining parts values are wrong.
The transformer is a 220VAC to 2x12VAC power transformer rated for 500VA or 600VA. The 2x12VAC windings can also be 24VAC center-tapped.
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The one now on the site is designed just like any other square wave inverter. The one you built is designed just like an audio amplifier with heat generating resistors to ground. Something you would expect to be designed by a stereo technician or audiophile. It consumes way too much energy from the battery. Others have emailed me to let me know they had to make serious changes to get it to work properly for them. It was after these emails that the one you made was removed from the site.photoar said:
MP
audioguru2
- Apr 6, 2004
- 12,026
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With a 500W load, each 0.1 ohm emitter resistor dissipates 10W half the time. Their total power dissipation is only 40W (8% of the load's power). Then the transistors don't need to be matched to have the same current gain. Remove the resistors if you can buy matched transistors.MP said:
With less load then there is less power in the equalizing emitter resistors.
Mosfets are much better than old transistors in a simple square-wave inverter. This circuit is old and is used where Mosfets are not available.
They didn't e-mail me and I developed the modification. But they e-mail you?
