I think diodes D1,D2 and resistors R1,R2 are superfluous to basic design. They are no doubt included as the guy is driving Microwave oven transformers rather than little 2-4 amp secondaries.
Doc
I remember making such an inverter years ago (1968?) basically like this:
12V to 120V Inverter
It used smaller caps for a higher frequency of operation, and was housed in a cardboard tube with Al foil covering the ends. A micro-switch mounted on the bottom kept it turned off until someone picked it up. It used a very small transformer for little power transfer.
Looks like I type slower than you.
The problem at 50Hz is the size of the components.
Try looking at the TL497 datasheet.
It's old but its simple and straightforward.
No. Single primary just fine. Dual needed to series them to make a tube HV supply. Single nets 161 VDC from 120 AC , Dual 339 VDC from 240 AC. For timing see Wiki entry on multivibrator but basically t=.7 RC (or rather half timing for each RC pair. at symetrical drive -50%- cycle.)
Doc
Used to be a local surplus house that got a lot of surplus from Sperry Univac (Now... Lucent? Whatever.) Used to get these loaded power supply boards with 10" x 3.5" finned heatsink and 3055-2955 tab packs Strip off trannies, use heatsink for amp builds. Throw the rest of the board away... except maybe a few caps. I recall them being maybe a buck a piece. Ahh the good old days when local surplus houses abounded....
Doc
frequency
I guess I was looking for a frequency of 50 - 60 Hz to be able to make it seem like an older tube amp with a little hum. But after thought tells me maybe I should just run it at the frequency the transformer works best at and get rid of hum. Seems to be my problem with used transformers is they all seem to work better at different frequencies. I need to try and find the transformer that works in the 265 volt 12ax7 power supply diagram. Or the core to wind it on. I stuck with the 555 since it is rugged and takes some abuse. What happens is I end up with a lot of power wasted in heat in the transformer and the output transistor and no real power I can use. I feel my problem lies within either my duty cycle or the output tranformer. Should I go with a 50/50 duty cycle? What is your experience on this? I still am thinking about just buying an inverter, seems to be a good thought. maybe a 75 watt plug in and dissect the unit from the housing and install in my unit. 20 KHz would be fine. what toroid size or number would work for this?
I guess I was looking for a frequency of 50 - 60 Hz to be able to make it seem like an older tube amp with a little hum. But after thought tells me maybe I should just run it at the frequency the transformer works best at and get rid of hum. Seems to be my problem with used transformers is they all seem to work better at different frequencies. I need to try and find the transformer that works in the 265 volt 12ax7 power supply diagram. Or the core to wind it on. I stuck with the 555 since it is rugged and takes some abuse. What happens is I end up with a lot of power wasted in heat in the transformer and the output transistor and no real power I can use. I feel my problem lies within either my duty cycle or the output tranformer. Should I go with a 50/50 duty cycle? What is your experience on this? I still am thinking about just buying an inverter, seems to be a good thought. maybe a 75 watt plug in and dissect the unit from the housing and install in my unit. 20 KHz would be fine. what toroid size or number would work for this?
design boo boo
I found my error why all types of configurations wouldn't work. I am embarrassed. I tried transistor drivers, ic drivers, lm 386, lm741 to drive my mosfet, all worked great but the results were always the same. It turns out that My protection diode was killing my output. I had it hooked up across my primary with the cathode to the positive. I since moved it to (anode gnd and cathode to drain on mosfet. Senior moment I guess. Transformer is kicking up now. I can reach my goal now. Will follow up with final design. Thanks for the ideas, as I will use them.
I found my error why all types of configurations wouldn't work. I am embarrassed. I tried transistor drivers, ic drivers, lm 386, lm741 to drive my mosfet, all worked great but the results were always the same. It turns out that My protection diode was killing my output. I had it hooked up across my primary with the cathode to the positive. I since moved it to (anode gnd and cathode to drain on mosfet. Senior moment I guess. Transformer is kicking up now. I can reach my goal now. Will follow up with final design. Thanks for the ideas, as I will use them.
I've purchased one of the cheap car "pseudo sinewave" inverters to play with. I've hacked it apart, and it runs at about 50 KHz. Being in the UK it's designed to approximate our 230V mains at "300watts RMS", 50Hz. The 12VDC is chopped at 50 KHZ, and fed to a sensibly-sized transformer, where it's stepped up and rectified to about 350VDC. There's a 100uF capacitor as a reservoir. This is then fed to an H-bridge which reconstitutes the DC into a stepped approximation of a sinewave. It has current feedback, and an overload trip on the output and low voltage warning on the input (both of which work, even with the mods). I've tapped off the 350V to use as the HT, and sent it for some more smoothing and filtering. The pseudo AC I've sent to a small 240V - 2x 24V transformer to obtain the negative bias supply. I did try stealing the 50KHz output, via a 0.01 cap in an attempt to make the negative supply, but this upset the regulation of the unit, and the HT rose to over 500V before I hit the kill switch. The unit is compact, and cheap at £30 (bias transformer and extra filtering have added £5). I'll add more when I've got a working amp.
300 watts ... allegedly ....
300W DC 12V to AC 230V Power Invertor with USB Charging Socket : Invertors : Maplin Electronics
The H-bridge something like an IRF740. I'll look when I get home.
Well I found the 12v center tapped transformer to try the inverter linked.
I sat down and went over the article again, noticed there was a forum on it so I thought I would read it.
It was 60 pages of people having problems with it, like exploding caps etc. I don't think they ever did get it sorted which way the polarized caps went, or which caps will stay intact.
Too bad, I thought it was a novel circuit.
I sat down and went over the article again, noticed there was a forum on it so I thought I would read it.
It was 60 pages of people having problems with it, like exploding caps etc. I don't think they ever did get it sorted which way the polarized caps went, or which caps will stay intact.
Too bad, I thought it was a novel circuit.
Try here : Harry's Homebrew Homepages click on projects and power circuits , then navigate to DC-AC 10w to 10KW. Simple circuit , which works. The trouble is with filtering out the 50/60Hz buzz. It's not a nice sinewave, but lumps of DC. That's why I went for the 50KHz inverter idea. At least I can't hear that high ! Of course I will need to well-filter the -ve bias supply, but it's easier at -60 volts than +350.
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GloBug: Cap polarity is clearly marked on the link I posted. http://upload.wikimedia.org/wikipedia/commons/6/6a/Transistor_Multivibrator.svg
Not really important if you just use mylar caps. < 1uf for 400 Hz opperation. As I recall I used like .47uF caps. The timing R info is on the wikipedia article.
Doc
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