It seems the arduino cannot supply enough current to switch the IGBTs properly.
No, it takes virtually no current at all to turn a FET on. Not enough voltage perhaps but current no.
If your design was on paper instead of your head maybe we could help you with it.
But if a MOSFET or IGBT is switching high voltage and current at high frequency (PWM basically) the gate does
need large currents to charge up and down fast enough to reduce switching losses to acceptable levels.
Also if switching high voltages with MOSFETs you may need a low-impedance gate driver or protection circuitry
to prevent capacitive coupling from the drain to gate burning out your microcontroller. Especially true for
inductive loads at switch-off.
Grumpy_Mike:
It seems the arduino cannot supply enough current to switch the IGBTs properly.
No, it takes virtually no current at all to turn a FET on. Not enough voltage perhaps but current no.
If your design was on paper instead of your head maybe we could help you with it.
I will draw something up here in a bit.
The arduino controlls the optocouplers, and how i have it setup is on pins 2,3,4,5 goto 2 optocouplers each.
the optocouplers are setup in a push-pull mode. When a pin goes HIGH the output from the two optos will put out +12v and -12 when the pin is low. now, when the gate of the IGBTs are not connected everything is ok.
but when i connect the gate, only the pins 2, and 4 actually switch the IGBT. 3, and 5 give odd values like +13 on high, and +8 on low, while the the other pins(2,4) continue to put out +/-12v.
sloppy but thar u go for now. I will be redrawing the design after I get some sleep.
just to clear some things up, on all the opto leds at the bottom, there is a resistor between the leds and ground.
same with a resistor between the other rail for the leds and +3.3v of the arduino.
As for the the opto connected to the transformer, the opto actually drives a mosfet that is fed from +12v. the opto itself is driven from +5v from the arduino supply.
Common ground is the tie point between the 12v cells. The capacitor, arduino, IGBTs, opto leds, and the mosfet are all grounded to this point.
MarkT:
But if a MOSFET or IGBT is switching high voltage and current at high frequency (PWM basically) the gate does
need large currents to charge up and down fast enough to reduce switching losses to acceptable levels.Also if switching high voltages with MOSFETs you may need a low-impedance gate driver or protection circuitry
to prevent capacitive coupling from the drain to gate burning out your microcontroller. Especially true for
inductive loads at switch-off.
Mark, chill out, this is a H-bridge.
This one is much cleaner.
I have to ask, why aren't you using a gate driver? When I played with a HV project (~400V) and an IGBT, I had to use a gate driver to prevent the IGBT from overheating, but I was PMWing the transistor.
afremont:
I have to ask, why aren't you using a gate driver? When I played with a HV project (~400V) and an IGBT, I had to use a gate driver to prevent the IGBT from overheating, but I was PMWing the transistor.
dont have one yet, and it will be some time before i can afford some. I still need some bolts for my capacitos, 3 more A123 20AH cells, 1200v diodes, the IGBT drivers, more IGBTs, and some mosfets. >.<
I also need to figure out how in the world i can drill threaded screw holes into a larger heatsink. and eventually I plan to use water cooling for the system, but google search does not turn up much. i have to machine all this crap myself, or find someone who can.
The reason I ask is that it takes Amps of current to switch the transistor at its rated speed. A micro pin or opto is just not going to cut it if you are switching it quickly. I think I used the TC4451 from Microchip as the gate driver chip. I don't think it was very expensive. It's been several years so I don't recall if that's the exact part I used or not.
I also need to figure out how in the world i can drill threaded screw holes into a larger heatsink.
Not sure what you are asking but on the face of it all you have to do is to drill a hole of the tapping diameter for the thread you want. And then use a tap to cut the thread. If it is a blind hole you need three taps, a starting tapered tap, a bottoming tap and finally if you are doing it correctly a plug tap for that last turn.
http://www.amazon.co.uk/dp/B000PJDN9Q/?tag=hydra0b-21&hvadid=9557944389&ref=asc_df_B000PJDN9Q