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Registered Member #4932
Joined: Thu May 17 2012, 01:42PM
Location:
Posts: 59
I want to charge and discharge the capacitors for a multi stage coilgun independently, but this requires a seperate voltage reference for every capacitor. I've modified the schematic for uzzors's cfpr cap charger to be able to do this and came up with this: I do not know for sure if it works or not and I also dont know for sure if the charger has to be disconnected from the caps or turned off when it discharges. That's why I would like you to check if this schematic will work.
Registered Member #11591
Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556
Don't know about the rest of that circuit, but with a 12v supply the open voltage coming of of the flyback is going to be much higher than 1KV, due to the resonant rise in the primary, so you'll need to be careful with that MOSFET!
Registered Member #4932
Joined: Thu May 17 2012, 01:42PM
Location:
Posts: 59
I've tried out the schematic (I've tried it out without that diode I thought wasn't necessary.), but it doesn't work. First of all, the 2n3904 doesn't stay low, but conducts even when the desirable voltage isn't reached by any of the caps. Second, when I connect the 2n3904 to the ground, it does conduct, but when I try the rest of the schematic, the caps just charge as if they are in parallel and are charging very slowly. None of the caps stop with charging when their voltage limit is reached. Can someone please tell my why it doesn't work and what I've done wrong or is the problem the fact that I didn't use the resistor. The mosfet I used was an ndfp03n150cg, the inverter I've used is a 74hc14n and the and gate I've used is a cd4073b. I've checked out the breadboard several times and from what I can tell, it checks out with the schematic I made and gave you, so can someone please explain why it doesn't work if they know why? Thanks in advance, Dehim
Registered Member #191
Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720
Source of MOSFET not at ground, need high side gate driving. Alternatively, if all the stages need to charge to the same voltage, you can just use a properly rated diode for each of the banks to isolate them.
Registered Member #4932
Joined: Thu May 17 2012, 01:42PM
Location:
Posts: 59
Electroholic wrote ...
Source of MOSFET not at ground, need high side gate driving.
I don't believe I have the source of the mosfet at ground, but I also don't believe I understand what You mean.
Electroholic wrote ...
Alternatively, if all the stages need to charge to the same voltage, you can just use a properly rated diode for each of the banks to isolate them.
I've thought of that first, but I don't believe it would work, since the smaller caps would charge faster so they would reach the desired voltage before the other caps would and turn off the cap charger, before the other caps could be Fully charged. The Same thing would happen if the caps would have some charge left after discharging in the coil. That's why I need a separate voltage reference for every cap. It also gives you the extra option of charging the caps to a different voltage, so if anyone can help me out, I would really appreciate it!
Registered Member #191
Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720
To turn on a MOSFET, you need to reach a certain voltage ate the gate pin with respect to source pin of said MOSFET. If source pin is not at ground, you need a way to reference your gate voltage to the varying source voltage.
And believe me, diode method will work. The cap with the lowest voltage will cet charged until all of them reach the same terminal voltage.
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Capacitor charger for multi stage coilgun
