Hy all
this is my first post on this forum, and i registraded just to explain to you folks how this work's
I was thinking about this problems, and i would like to share with all of you what i have realized.
So, Firstly, i guess manny of you watch the datasheets closly...
As for the mosfet's you need to realize tat thay are a litle diferent constructed then a normal npn transistor.... on the gate yo ucan see the diference... in fact the gate-sourse is charged like a capacitor. in the moment the voltage get's on it it has no resistence and huge current flows (if there is so much current) it behaves like shorted, but, that lasts for a split of a second, and after 5 tau the cup is charged fully, and the gate behaves the same like a cup. so after the gate is charged it draws no current and that's the advantage to the npn's . much less power is needed for driving a mosfet. So you need a driver for a mosfet, you just NEED IT!
And in this schematic: **broken link removed** the mosfet is driven ineficient. that's why the mosfet blows off, after some time... the fact is , the output of a tl494 in that schematic is connected like a pull up driver, and that relly bad.
if you see the funcion block diagram of tl494 you'll see that the gate of the mosfet is connected on the emiter at the pin 9 (and 10) so, it isn't close to be driven correctly . in the fact, the gate charges while the tl494 open's but, after it closes it stay's open, maybe the gate voltage fals a fiew volt's 1 or 2, maybe even 3V, and then the tl494 opens again. and so on... The thing is, the mosfet is opened, while the tl494 is on, it's ok., but it dosen't close just falls a litle bit, ... and while the off time it's floating, and that's why the mosfet blows up and dies! By that said, you realize you should use a driver, and you can use any driver.
The posebilities for driving a mosfet, are a fiew... and thay are all good, some better , some cost more, depending on how much money are you willing to spend...
People mentioned the ucc's and they are great. but, some people can't buy them becose in their countrie, ther isn't a shop, which would have them... but, there are a fiew other good ideas....
you could put the gate of the mosfet on the colector of the tl494 output (puns 8 and 11) and use them like pull down, and that would give the supply current to the gate while charging and the C-E current of the tl494 200mA per chanel, but, i haven't tested this , and there is a big posibility that the discarge current will destroy the tl494, so, that need's to be tested.
i tried to make a driver and it works nice. The mosfet isn't ofcors cold. but, it work's and dosen't blows out... it just works.
**broken link removed** but, you can use any simular pnp and npn transistors. just you need to concidure the charge and discharge current, ofcors the base current.... You need just to put some heatsinks on them... with a 10 ohm resistor the discharge pnp heet's a bit, but it's ok. that means it work's fine and discarges the mosfet fine.
Some other chips are there to buy like the ucc's but thay are the same, but a litle weeker.
And for the half-bridge, and the h-bridge....
they work the same, the only diference is the half-bridge , work's with half of the supply voltage, and that would mean that half of the supply voltage you will bring to the primary. As for the h-bridge, there you bring the full voltage to the primary......
This circuit, :
https://www.instructables.com/files/orig/FVE/I3SC/FR123O01/FVEI3SCFR123O01.png works the sam e like the h-bridge, but without a GDT. or some drivers...and the schematic is verry nice. but you would need to add a gate driver per gate... from the pins 9 and 10
As for the GDT, you need a strong driver for ti, the same like you would drive a singele mosfet,
If you whan't to know something, or you mean i'm saying something wrong, then please Say so,....