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 12/120V inverter again
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tim
Mad Scientist

198 Posts

Posted - Dec 15 2006 :  4:37:10 PM  Show Profile  Reply with Quote
no i wish i could.
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tim
Mad Scientist

198 Posts

Posted - Dec 15 2006 :  5:19:49 PM  Show Profile  Reply with Quote
so is the npn rated lower or higher then the pnp in a pwm circuit.i dont know if its a typical for voltages within these 2 transistors to be the same only that they are pnp and npn.
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tim
Mad Scientist

198 Posts

Posted - Dec 17 2006 :  11:10:30 AM  Show Profile  Reply with Quote
hey people, how critical is it to replace glass zener diodes as far as exact numbers? or can they be matched by use of multi meter ohms or otherwise. these zeners are in a mosfet driver section i guess for voltage spikes.
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audioguru
Nobel Prize Winner

Canada
4218 Posts

Posted - Dec 17 2006 :  12:04:21 PM  Show Profile  Reply with Quote
You can't measure the voltage rating of a zener diode with an ohm-meter. Just look at its datasheet.
Many Mosfets have "a zener diode" built-in from drain to source. It has a very high avalanche current rating.
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tim
Mad Scientist

198 Posts

Posted - Dec 17 2006 :  12:27:32 PM  Show Profile  Reply with Quote
the inverter im working on had a few zeners that were bad and replaced them with what looked the same and i took them from a circuit that also runs on 12 volts.
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tim
Mad Scientist

198 Posts

Posted - Dec 17 2006 :  12:31:12 PM  Show Profile  Reply with Quote
these zeners are in paralle with regular 1n4007 diodes so would the zeners be added protection for the circuit?
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cyclopsitis
Nobel Prize Winner

Canada
732 Posts

Posted - Dec 17 2006 :  2:37:09 PM  Show Profile  Click to see cyclopsitis's MSN Messenger address  Reply with Quote
Ok I've got a question... I've seen on some high current inverter circuits and on some DC PS circuits the transistors' emitter and collectors are put in parallel and the bases are connected to each other. Or in PS transistors are put in parallel again to make the supply able to carry 20 or 30 amps. Does this kind of connection similar to putting batteries in parallel to increase their current capacity?

I have another question too. I was looking at one inverter:
http://www.electronics-lab.com/projects/power/033/index.html
Why does it say "collector is shorted to collector in order to prevent heating"? Why does this stop heating??? I donít understand this. Those are my questions, thanks!

Ken
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tim
Mad Scientist

198 Posts

Posted - Dec 17 2006 :  3:46:59 PM  Show Profile  Reply with Quote
both the 3055s will be working as one , so less work on the part of 1. i would assume
yea i was looking at that inverter as well.
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audioguru
Nobel Prize Winner

Canada
4218 Posts

Posted - Dec 17 2006 :  8:36:32 PM  Show Profile  Reply with Quote
2 years ago I fixed that inverter so it worked very well. My fixed schematic was recently deleted and the circuit shown now will blow up.

The output transistors in a 500W inverter must pass 25A each. The 2N3055 has a max current rating of only 15A. My circuit had 4 2N3055 transistors on each side passing only 12.5A each. I added resistors to turn off the transistors quickly. I added protection diodes.

The text in the project is a bad translation. I think the collectors "are as one" because the transistors on one side can be bolted to a heatsink without insulators then they are cooler. Their case is their collector terminal.
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cyclopsitis
Nobel Prize Winner

Canada
732 Posts

Posted - Dec 18 2006 :  09:42:01 AM  Show Profile  Click to see cyclopsitis's MSN Messenger address  Reply with Quote
audioguru,

Are you able to re design that circuit again?

How does the input DC (how many ever volts) effect the output of the inveter? maybe this question was already asked I havnt had time to read all 20+ pages of this topic. its huge!

I have another question. Lets say that I wanted to use a power supply that rectified the voltage to a higer voltage then the standard 12 or 24. how would one of these circuits have to change to invert the DC to AC.? How would this change the gate circuit.? How would you bias this so that the transistor actually works?

Tim and audioguru, thanks for your help so far i have learned alot!!

ken
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tim
Mad Scientist

198 Posts

Posted - Dec 18 2006 :  09:54:03 AM  Show Profile  Reply with Quote
well i could tell you ken that todays inverters, most, are 12 volts and are stepped up to between 140- 147 volts then rectified sent to large value caps then off to mosfet transistors where it is cut in half to get ac. but these other home made inverters rely on big transformers , npn transistors, and alot of luck that they will work after building them . not really sure about your saying 12, 24 volts but use 24 volt power on 12 volt components then expect them to fry or use a voltage regulator 24 to 12 volts.
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audioguru
Nobel Prize Winner

Canada
4218 Posts

Posted - Dec 18 2006 :  10:32:08 AM  Show Profile  Reply with Quote
quote:
Originally posted by cyclopsitis

audioguru,

Are you able to re design that circuit again?

It is on my hard drive. But I can't attach it on this site.

quote:
How does the input DC (how many ever volts) effect the output of the inveter?

The circuit is designed for a certain DC supply voltage then the transformer steps up the AC voltage to whatever you want.

quote:
Lets say that I wanted to use a power supply that rectified the voltage to a higer voltage then the standard 12 or 24. how would one of these circuits have to change to invert the DC to AC.? How would this change the gate circuit.? How would you bias this so that the transistor actually works?

I wouldn't be difficult to modify a square-wave inverter circuit to work from any DC voltage.

Edited by - audioguru on Dec 18 2006 10:35:41 AM
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cyclopsitis
Nobel Prize Winner

Canada
732 Posts

Posted - Dec 19 2006 :  12:59:43 PM  Show Profile  Click to see cyclopsitis's MSN Messenger address  Reply with Quote
Hey Tim,

Thanks for the information! I wonder why it is so hit or miss for normal people with alot of knowledge of how circuits work to get their circuits to work.

Audioguru, Would you be able to email me the circuit you have on your HD?

Thanks
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cyclopsitis
Nobel Prize Winner

Canada
732 Posts

Posted - Dec 19 2006 :  1:02:03 PM  Show Profile  Click to see cyclopsitis's MSN Messenger address  Reply with Quote
quote:
Originally posted by tim

well i could tell you ken that todays inverters, most, are 12 volts and are stepped up to between 140- 147 volts then rectified sent to large value caps then off to mosfet transistors where it is cut in half to get ac.



How do you step up a DC voltage?
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tim
Mad Scientist

198 Posts

Posted - Dec 19 2006 :  4:49:37 PM  Show Profile  Reply with Quote
oh ken im no electronics whiz really , this stuff can be very difficult i do alot of guessing and i do get lucky sometimes , but what the hell its fun. the step up in these inverters are done within with small transformers powered by a PWM circuit with mosfets.
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