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Hi,
The setup will be:
12VDC > Inductor > Capacitor Bank > 12V DC Power
12V DC Power > TL494 > Push-Pull MOSFETs > Ferrite Transformer > Bridge Rectifier > Inductor > High Voltage DC Bus Output of around 300v for 220vac required output.
12V DC Power > 50Hz Oscillator > MOSFET Hi-side, Lo-side Driver > H-bridge > Inductor-Capacitor Filter > Required output voltage.
Hope that's cleared.
For 50Hz oscillator, I don't think you should use TL494 as it would be outside the specified frequency range in the datasheet. Instead use KA3525(!not SG3525) or SG3526. It has two outputs. Connect these to two hi,lo side MOSFET drivers(IR2110/IR2113/L6384/L6385/L6387).
Take a look at the circuit and carefully go through the datasheet of the hi/lo drivers.
I've done plenty of switching inverters like this. If you have any questions/queries, you can ask over here.
Hope this helps.
Tahmid.
Thanks for ur answer tahmid, but i still dont understand y i cant used tl494 for this application, i have reverse engineered an inverter, and the h bridge i dont understand
Ok,
You're using SMPS, and here you're using a ferrite transformer instead of the bulky iron core ones.
Ferrite transformers only work in high-frequency, not low-frequency.
So, usually around 30 to 50kHz frequency is used to step up the battery voltage from 12v to 300v by using TL494 or any PWM IC and MOSFETs in push-pull or h-bridge configuration. This 300v is high frequency alternating current (AC), usually 30 to 50kHz. So, you can't use this to power your devices.
So, this high frequency AC is converted to DC using ultra-fast recovery diodes and capacitors and inductors for filtering.
The DC needs to be converted to 50Hz AC so that you can use this for your appliances.
To convert this DC to AC, the H-bridge is used.
The H-bridge is driven by the 50Hz clock. I said not to use TL494 here as the datasheet states minimum safe operating frequency of TL494 is 1kHz. You can use KA3525, it's quite similar.
Right wait... so u mean i can still use the tl494 in the circuit BUT, to use the ka3525 to drive the gates on the H-bridge (min 60hz) on the datasheet, is this correct ?
A step-down transformer works as a step-up transformer by swapping the primary and secondary windings. The ratio stays the same of course because that is determined by the number of turns on each winding. You may not get exactly the voltage you expect though for these reasons:
1. There are losses in the power transfer of the transformer so you may have to feed more current into the low voltage side than you think. Bear in mind that the extra current will cause more loss through the wire resistance.
2. Step down transformer output voltage is specified under load, it will typically be 5% to 10% above the rated voltage if not loaded. This will influence the voltage you get out when running it in step-up mode.
Also consider that in normal use, power transformers are fed with fairly clean sine waves but all the inverters mentioned so far use square wave switching. This will result in higher loses in the transformer core and hence more power will have to be fed in to overcome it.
If I was designing a square wave inverter like the one using the crystal oscillator mentioned earlier, I would remove all the 50Hz generating circuit and replace it with a PIC10F202. It has a built in oscillator which is quite accurate and stable and a very simple program can generate the bi-phase 50Hz signals. It would even be simple to introduce a dead period between cycles which might improve efficiency.
Hi KRYCHEK,
You can use the TL494, and I've seen it being used, but it's better not to.
KA3525 better.
I use a small microcontroller here.
You can also use a 4047.
But for 30kHz to 50kHz, you need to use either TL494 or KA3525 or any PWM IC.
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