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Registered Member #1548
Joined: Mon Jun 16 2008, 09:22PM
Location: Ohio
Posts: 61
Hello,
I am looking to make an inverter for use in a car to convert from 12VDC to 120VAC. I have been looking around the internet for designs of inverters for this purpose. I was thinking a 555 oscillator into some FET drivers to drive a half bridge of MOSFETs. This of course would then power a step up transformer. However, on my hunt I found a little circuit like this:
mod edit: EPIC IMAGE FAIL
I was planning on using a pair of IRFP450s and a rewound MOT. Would this circuit work? And does anyone see any problems with it? Or is this just to easy for it to work right?
(BTW, I'm powering an Xbox 360, a LCD monitor, and a wireless router. These all have a power draw of around 300 watts or so.)
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
- The polarity of the electrolytic capacitors is the wrong way around. - For the circuit drawn, you should put a diode (1n400x) in series with each transistor base because the emitter-base junctions break down with more than 5 or 6 volts reverse bias, and this circuit would give about 24 V reverse bias. - The same applies for mosfets but the breakdown voltage of gate-source is higher so you may get away without diodes, but I would use diodes and a resistor of about 10x R3 or R4 from gate to source/ground. - I would remove D1,D2,R1,R2 and put a zener or TVS across each collector-emitter (drain-source), the tvs should have a voltage clamping rating between 33V and whatever the Vce/Vds rating of your transistors is. - I would use a ready made transformer in reverse, use a 120 : 15-0-15 (or 12 + 12) transformer with a VA rating just above your intended output power. - A squarewave inverter like this may cause too much rfi/emi, if you have rfi/emi problems add an output filter, the simplest (not best) would be something like 0.1 uF 400V across the output to 'soften' the edges of the squarewave.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Doubl3 Helix wrote ...
I was planning on using a pair of IRFP450s and a rewound MOT. Would this circuit work? And does anyone see any problems with it? Or is this just to easy for it to work right?
This wont work with MOSFETs.
If you can get the IC, you might rather try
Sulaiman wrote ...
- A squarewave inverter like this may cause too much rfi/emi, if you have rfi/emi problems add an output filter, the simplest (not best) would be something like 0.1 uF 400V across the output to 'soften' the edges of the squarewave.
This would actually "ring" the output to twice the nominal voltage for a moment, which might be even worse than just leaving the cap out...
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I've used the Mazzilli/ZVS circuit with the DC link choke and resonant capacitor left out, and an iron-cored transformer substituted for the ferrite one. It runs in a ferroresonant mode with the frequency controlled by transformer saturation.
A filament transformer with two 6.3V windings worked for me: I connected them in series to get 12.6V CT, and hooked the mess up to a 12V battery. I could draw about 200V AC from the (nominally 240V) winding. Most gear now has universal 90-260V power supplies.
A rewound MOT might be sketchy, it seems to me that you want a high-quality core that saturates hard, for faster and more efficient switching. A toroidal transformer would probably be best, if you have one. Even so this is about as ghetto as inverters get!
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Doubl3 Helix wrote ...
@Dr. Kilovolt I do not have a IR2153 but I do happen to have a IR2113 on hand.
The datasheet is
I believe this would suffice for a high side/low side FET driver of this application?
This is for a senior project, and right now it's just in the proof of concept stage. Thanks for all of your help everyone!
Here it does not work as a high-side driver, just a push-pull driver. You can use a TL494 or SG3525 too with the advantage that you can make the output into what is referred as modified sine wave (or rather modified square wave).
isnt it more efficient to have a boost converter to 170vdc then an inverter? on the same note could you make a nice sine wave by doing variable pwm on the inverter, with mcu control, then low pass filtering the output?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
More efficient, maybe. That is how most commercial inverters work, but they do it like that because it saves weight and money, not necessarily because it's more efficient.
Registered Member #1548
Joined: Mon Jun 16 2008, 09:22PM
Location: Ohio
Posts: 61
@ Dr. Kilovolt, You wouldn't happen to have any links that have info on the modified square wave would you? I would love to read up on it.
Also, would it not be feasible to have a tl494 feed a max4428( ) which will give me an inverted and a the original output of the tl494 to drive a pair of FETs through a GDT? The max4428 has a maximum output of 1.5 amps. Would this be enough to drive a pair of FETs from 12v at 60Hz?The MOSFETs would be arranged like the circuit you mentioned earlier.
The only reason I ask all of this is because I have all of the necessary parts on hand if that would work.
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Looking to make an inverter...
