Riccardo

The control electronics will be powered form that 12V regulator and another 5V regulator attached to the same supply. Good point, Do you think I'll need a diode rated for more current? I haven't picked one yet, but yes probably a few amps to be on the safe side. I see your point. So maybe I could reduce the value of R1 since the diodes could take a surge. The relay would have to have higher ratings though right, so the contacts don't get fused. (although maybe I could use some sort of ZVS arrangement) I'm trying to make the pulse width very narrow, as narrow as the IGBT will let me. I want the pulse to be short, but it must be long enough to allow significant current to start flowing in the coil. Ideally though I also want to be able adjust it, but if this is impractical, the pulse transformer method may be best. Peak current would be limited to about 1750A by R4. The IGBT is rated for a 10ms pulse current of 1800A. If I use an isolation transformer, it is safer (because of limited current) , but heavier, more tricky to trigger, and more expensive? If not, I can keep the grounding as it is in the diagram, and the triggering is easier? In what sort of condition are the parts you guys are offering? Can you send me pics?

Oh, I don't know why I put the MOSFET (actually it will be an IGBT) like that, I should have noticed before I posted! I'd also forgot to add a resistor. Revision attached. Its not a coil gun, but it is for pulsing a coil. I cant use a Thyristor because it would not switch off until the cap is discharged. I want to control the pulse time precisely. I'm wanting to use it with various coils really, but generally it will be very low inductance, maybe just 2 loops of cable around a diameter of 0.5 - 1m in air. For Q2 I was planning to use a SEMIX603GAR066HDS. It is pretty large and it's internal diode is too. Not sure about leaving the power side floating. Wont that change the gate voltage requirements?

Thanks. Yes, I saw the isolation transformers would be about 5kg ! I will avoid that if possible The attached circuit shows the power electronics that I have in mind. Another question. Should I make all my GND common with mains earth?

Ok, Thanks for your help :)

I like tomatoes.

The link below shows a diagram with a simple charger based on a LTC4060 http://freecircuitdiagram.com/2008/08/28/autonomous-fast-nimh-battery-charger-using-single-chip-ic/

Yes, I looked at some isolation transformers but I wasn't sure if they would actually limit the current. What do I need to look for in the specs? Maybe I can just use a 100W transformer as the peak load would be brief enough not to overheat it :-\ Since the high currents would only be brief, I suppose the resistor wont need to be rated for 500W. How might I calculate what rating would be ok? I get the feeling that may be a more complex answer than it seems.

Wow, Is it hot in here ;) I don't want to get into the argument so I'll just answer the original questions. I was looking to use a VNH3SP30-E as is it a H-Bridge device that makes things easier but it was not powerful enough for me. I'll now be making my own h-bride. Its a lot more effort, but I'll gain good experience and it will do what I want. Hero999 was very helpful to me in working out what to do. I had some custom software from these guys, but they also do electronics. http://www.rmcybernetics.com/shop/custom-electronics-programming.htm PWM adjustable from low frequency to MHz wont be cheap though. Not sure it is even possible in any realistic way. 0Hz to 100kHz might be more reasonable.

The capacitor will be about 1000uF. I'd discharge it before it reached full voltage. Hoping this could be done every second or so. It's UK voltage so the rectified voltage could be over 300V. I'm wanting to limit the supply to 500W. If I use a 200 ohm resistor the power dissipated would be 450W right? That is a lot! Is there a transformer I could use for this?

I've got some STP40NF10L, and IRF5210PBF MOSFETs handy so I think I will use those as they are N and P type respectively and both rated for 100V and 40A. I also have some comparators, so I will just use those for the level shifting. Thanks

Hi, I'm making a circuit that in part will charge a capacitor from the mains. When the cap is empty the current would be very large. I want to limit the current to about 1.5A so that the rectifier is not damaged. Should I just use a resistor on the rectifier output, or should I use a capacitor in series with the AC input to limit the current reactively? Cheers!

I would expect they had them custom made for the experiments they were doing. There should be some contact information for the authors of the paper on the first page or something in the references. I think that would be the best place to look.

:-[ I thought 5V would be too low to switch the mosfet properly. I was thinking of using some comparators to convert the voltage level to around 12V. I chose 10V zeners because that is high enough to allow the mosfets to switch on but low enough to protect them against any transients. I made them bidirectional because I'm concerned that transients of either polarity could occur since the load would be inductive and the current is being alternated. Is that wrong? I just connected the mosfets like in your diagram, but yes, I see now that they (and the diodes I added) should be the other way around. Don't know how I missed that!

Yes, you are going to need more ODC15 units if you want independent control over the LEDs

Thanks again. I really appreciate your help. Does this diagram look ok? I've not found an appropriate pair of mosfets yet. I find one type, but then can't find its equivalent of opposite polarity. I'll update when I find them.

It will be to drive coils / electromagnets so I was thinking that an IGBT would be better for 2 reasons. 1. They can have a high voltage rating and be more tolerant of voltage spikes. 2. They don't get as hot for a given current. The supply voltage to the load will be variable (although there will be a constant 12V source available for the control electronics). Different coils would also be used so the output current could vary quite a lot. For those potential dividers, would it be ok to just add some back to back zenner diodes to prevent over voltage on the gates?

Wow, you made that diagram just for me! Thanks! I have a few more questions ::) Will I need to change those resistor values if the supply voltage drops to 25V ? Just to confirm: The high site MOSFETs are ordinatry P-Type, and the low side ones are logic level N-Type ? They must not have reverse diodes built in? Can I use IGBT's instead of MOSFET's?

Yes, a schematic would be great thanks. Do you also know of a control IC that can be used to simplify the driving if it. e.g, prevents shoot through or other fault conditons?

Hmm. I was hoping to avoid that as I'd need to make a high and low side driver too. Those IC's also have fault indicators and other useful stuff It only needs to go at 50Hz or less.

Hi, I'm looking for an integrated H-Bridge IC like those used in motor control applications. I've seen the VNH3SP30-E (http://www.st.com/stonline/products/literature/ds/12688.pdf) but it is only rated for 36V. The current rating it has of 30A is just enough but ideally I would like something higher. This IC looks just what I need except for the voltage rating (I need at least 50V). I've been searching for hours but can't seem to find what I need. Does anyone know of an equivalent for this? I must be using the wrong search terms because I'm sure something like this will exist. Cheers