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audioguru
Nobel Prize Winner
Canada
4218 Posts |
 Posted - Sep 12 2008 : 1:33:54 PM
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The circuit is a transistor multivibrator. Look in Google but there are a few circuits shown with backwards capacitors (like this one).
Please keep Muhammed out of here.
Please turn off the CAPITALS. |
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almaleky
New Member
2 Posts |
Posted - Sep 12 2008 : 4:01:41 PM
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ok,i willnot write capital..
sorry,prophet muhammad is my leader and prophet .he is in my heart.this is freedom!!!
very thanks the circuit start to be unterstanded |
I LOVE PROPHET MUHAMMAD |
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audioguru
Nobel Prize Winner
Canada
4218 Posts |
Posted - Sep 12 2008 : 8:27:40 PM
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Please keep Muhammad away from here.
We talk about electronic circuits, not about your religion.
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julep
New Member
3 Posts |
Posted - Sep 21 2008 : 11:02:34 PM
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Hi,moderator,hi audioguru, im julep from Philippines, i want to ask for your help, i have read a lot in this forum about inverter, and it seems that you have i broad knowledge about this, i would like to ask if there is a working circuit of inverter here,12vdc-230ac atleast 500watts, it doesn't matter to me what output waveform it produce. i planned it also to have it a low battery cut-off device. i have search the entire net, and i'm afraid to gamble in making it,it will waste my budget. Please help me to have a working circuit. thankyou in advance.. and Godspeed... |
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julep
New Member
3 Posts |
Posted - Sep 21 2008 : 11:05:08 PM
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| Hi moderator, hi audioguru.. you can email me at julep_roxas@yahoo.com regarding with my above request. i really need your help.. wish u all luck and good health.. thankyou in advance and morepower to your site.. Godspeed... |
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dragan
New Member
2 Posts |
Posted - Sep 30 2008 : 08:30:48 AM
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i need convertors 12v=/220v~
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gim
Apprentece
5 Posts |
Posted - Oct 01 2008 : 06:55:56 AM
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Hi. I am by no means an expert on these things but...
I love the simplicity of this circuit, also its symmetry. It has some imperfections though. As someone else said, the thing is a multivibrator. That is, two oscillators that are interdependent.
One of the problems with this circuit is that there is no way to control the frequency. The impedance of a capacitor decreases as the frequency increases. If the thing oscillates at high frequencies, very high currents will flow through the capacitors. That probably explains the propensity of the capacitors to explode.
It probably also explains why some people have reported low voltages on the output. Iron cored transformers are not designed to work at high frequencies.
I think that someone, with more knowledge than myself, could make a fairly simple modification to this circuit, to make it run at about 60 Hz. That should (I think) solve the other problems. |
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pebe
Nobel Prize Winner
United Kingdom
1078 Posts |
Posted - Oct 01 2008 : 07:21:32 AM
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quote:
Originally posted by gim
I think that someone, with more knowledge than myself, could make a fairly simple modification to this circuit, to make it run at about 60 Hz. That should (I think) solve the other problems.
Don't bother. The circuit is CRAP!
It should have been removed from the board a long time ago! |
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audioguru
Nobel Prize Winner
Canada
4218 Posts |
Posted - Oct 01 2008 : 11:24:25 AM
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There is only one oscillator, not two. Tt is a multivibrator. Look at it in Google. It probably operates at exactly 60Hz.
The polarity of the capacitors is backwards.
The transistors have avalanche breakdown of their emitter-base junctions (max allowed voltage is 7V) because the capacitors are charged to about 23V then they try to drive the base of the transistor to negative 22V. Therefore the capacitors have a very high discharge current which overheats them even if their polarity is correct.
The transistors do not have enough base current for a powerful inverter so the output power is very low. |
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gim
Apprentece
5 Posts |
Posted - Oct 02 2008 : 10:24:25 AM
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Thanks for the detailed analysis.
According to Wikipedia, for a multivibrator, "The period will also depend on any current drawn from the output..."
So maybe it won't run at exactly 60 Hz?
The circuit of this inverter is slightly different from the basic multivibrator, because the +V feed to the collectors of the transistors passes through the load, which is variable. |
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gim
Apprentece
5 Posts |
Posted - Oct 09 2008 : 09:01:45 AM
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quote: Now the schematic is confusing.
D3 and D4 connect to pin 5-and-a-half on the CD4017.
EDIT:
Thanks again Juan for fixing the schematic.
Can someone please direct me to the schematic referred to here? I can't find it. Thanks. |
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gim
Apprentece
5 Posts |
Posted - Oct 09 2008 : 09:12:34 AM
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I have built a modified square wave inverter according to the schematic I found at http://www.discovercircuits.com/C/co-dctoac.htm (Third circuit in the list).
This inverter works fine, at low power. I have not tried it at high power yet. It does not require a centre tapped transformer. I have used 12amp MTP3055E MOSFETs rather than the 0.5amp BS170s.
Audioguru, if I may ask you a question. In a previous post you stated that the gates of MOSFETs should be fed through a (47 ohm) resistor, to prevent high frequency oscillation. The schematic I have used does not have any such resistors. How necessary are they? |
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audioguru
Nobel Prize Winner
Canada
4218 Posts |
Posted - Oct 09 2008 : 10:45:34 AM
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quote:
Originally posted by gim
I have built a modified square wave inverter according to the schematic I found at http://www.discovercircuits.com/C/co-dctoac.htm (Third circuit in the list).
This inverter works fine, at low power. I have not tried it at high power yet. It does not require a centre tapped transformer. I have used 12amp MTP3055E MOSFETs rather than the 0.5amp BS170s.
Audioguru, if I may ask you a question. In a previous post you stated that the gates of MOSFETs should be fed through a (47 ohm) resistor, to prevent high frequency oscillation. The schematic I have used does not have any such resistors. How necessary are they?
The BS170 is a tiny low power Mosfet. Its input capacitance is only 60pF max so it probably doesn't oscillate without a resistor in series with its gate.
Real power Mosfets have an input capacitance almost 200 times higher so they oscillate at a high frequency if the gate doesn't have a series resistor mounted closeby. |
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4396459saad
New Member
Pakistan
1 Posts |
Posted - Oct 11 2008 : 11:22:02 AM
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hi i am making a ups for my project
i need a ckt diag of a ups that could drive a load of 100w for 10min |
SAAD SARDAR |
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yunusu
New Member
Rwanda
1 Posts |
Posted - Oct 12 2008 : 11:17:39 AM
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It's possible to adjast the output fo an inverter
by using a simple variable resustor in it's
oscilator ? how |
Hello |
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12/120V inverter again
