Cap Dump Circuit

[Allcanadian]

@BroMikey

There is an easier option I think, I was using a ICL 7667 dual mosfet driver and only using one channel (A) to drive both a P ch mosfet and an N ch mosfet as a half bridge with a common gate. It's basically a flip flop however the half bridge current can be very large so it can drive a huge number of mosfet gates.

Basically the mosfet driver doesn't allow a slow transition, when it crosses the turn on threshold it switches at max speed as well as the turn off threshold. So why buy a bunch of mosfet drivers when we can use one to make a half bridge switch just as fast and handle big amps to drive other switching mosfet gate capacitance(s). It's stupid simple and can be upgraded to handle 100+ amps to drive the switching mosfets... if that's your thing, lol.

I do this because circuit boards suck and so does soldering. So I want the least number of components to get the job done.

AC

[blackchisel97]

Hi V

Just looking at your expression that would be 350vdc X 2000uF Cap = 120J

I am only dumping 500J or 90vdc X 120,000uF cap = 480J

I dump 3-5 times per second all the way to 80 percent duty cycle at high frec's of my 555 timers using the SG Oscillator.

With the DC box charging the cap bank, I don't know yet.

I have one that is smaller and it is dumping 70vdc X 65,000uF using 5 150watt parts and she needs a cooler even being so small.

With your comment I am now gaining a prospective on things I have lost track of again.

I see your work V. Big flash is awesome.

I'll Be Back

Mike

Actually, I operate at 85VDC and >30,000uF but my pulse is only 2.5-3ms. For what you do some cooling will be necessary. Your duty cycle seems quite high. Is this something you figured out experimentally?
I was going to build cap pulser controlled by microchip with 6 pairs of Fet's but got busy with my other projects a.t.m. Besides, I got rid off all batteries except two and I have couple other ways to charge them using solar power.
I sent you PM.

Regards
V

[BroMikey]

Mixing Ciruits

Hi Mike,



I'm not sure I understand what you mean here. Your oscillator is triggered by the trigger wire correct? I thought you use the tl594 for the cap dump section? I don't see why you would want to use the trigger winding to trigger the cap dump chip?

About your driver schematics, I not an electronics engineer, (I had to learn learn this stuff by experiment over the last years, and with help from a few people, just like you but I think as long as you follow the SOA curves and look at the data sheet specs you should be in the ball park.

regards,
Mario

Hi Mario

No you are right I am getting you mixed up on circuits. The oth one is all the same parts and drive circuits running at higher frec's.

Stay with me I will be back to show results and you guys can see better what's up.

Mike

[BroMikey]

120j

Hi Mike,

You could probably run two Fet's on each output of double driver but this is something I never tried. When I need to parallel several Fet's together I use double drivers. I have one device dumping 120J into inductive load (approx 100A pulse) using two Fets and one driver. They don't need heatsinks - STP165N10F4 STMicroelectronics | Mouser.
In my device I need to invert the output from pulse generator but you can use non inverting driver here.

V

Hi V

Just looking at your expression that would be 350vdc X 2000uF Cap = 120J

I am only dumping 500J or 90vdc X 120,000uF cap = 480J

I dump 3-5 times per second all the way to 80 percent duty cycle at high frec's of my 555 timers using the SG Oscillator.

With the DC box charging the cap bank, I don't know yet.

I have one that is smaller and it is dumping 70vdc X 65,000uF using 5 150watt parts and she needs a cooler even being so small.

With your comment I am now gaining a prospective on things I have lost track of again.

I see your work V. Big flash is awesome.

I'll Be Back

Mike

[Mario]

Hi Mike,

On this Oscillator with multiple modes I also have another question about the trigger wire on the Bedini coils.

Can using the trigger wire as feedback to the tl594 improve resonant quality.

Or will the trigger wire just hang there as it is no longer needed?

I'm not sure I understand what you mean here. Your oscillator is triggered by the trigger wire correct? I thought you use the tl594 for the cap dump section? I don't see why you would want to use the trigger winding to trigger the cap dump chip?

About your driver schematics, I not an electronics engineer, (I had to learn learn this stuff by experiment over the last years, and with help from a few people, just like you but I think as long as you follow the SOA curves and look at the data sheet specs you should be in the ball park.

regards,
Mario

[blackchisel97]

Hi Mike,

You could probably run two Fet's on each output of double driver but this is something I never tried. When I need to parallel several Fet's together I use double drivers. I have one device dumping 120J into inductive load (approx 100A pulse) using two Fets and one driver. They don't need heatsinks - STP165N10F4 STMicroelectronics | Mouser.
In my device I need to invert the output from pulse generator but you can use non inverting driver here.

V

[BroMikey]

TL594 and TC4420

Hi Mike,

Check the data sheets of your devices, how many pf is the capacitance of your mosfet gate, how many pf can your driver handle? If one driver is not enough run a few of them in parallel.

Also check the SOA curve (safe operating area) on your mosfet data sheet, it tells you how many amps at how many volts for a given on time is safe so you won't blow it.

regards,
Mario

Hello Mario

Here is what I think is a parallel arrangement would be. I am asking you if this is right.

According to the TC4420 data sheet can do 6A surges also the voltage input for a TC4420 is 2v at 10uA.

While the TL594 can output 100ma on the upside for a max 200ma.

It seems reasonable that using this arrangement for the cap dump is okay.

Also V says he uses dual 4amp drivers and for the 12 mosfet oscillator array maybe I will use 6 drivers.



Mike Ps thanks gentlemen for your continued instruction.

[BroMikey]

What's Wrong With Me

Hi Mike,

Check the data sheets of your devices, how many pf is the capacitance of your mosfet gate, how many pf can your driver handle? If one driver is not enough run a few of them in parallel.

Also check the SOA curve (safe operating area) on your mosfet data sheet, it tells you how many amps at how many volts for a given on time is safe so you won't blow it.

regards,
Mario

Hi Mario

Thank you pointing this out as it had somehow escaped my thoughts.

My fet is 2500pf gate capacitance.

SOA I did not see. I will look now.

Super, Thanks Mario

I am proceeding with caution.

The thing is I am building 3 large power handling devices at once and will give you all a peek. One needs to run a pulse per second (Approx) and the other is the Bedini / Rene battery circuits running at 7k-15khz.

I want my cake and eat it too. I will be switching modes with this device.

Rene Mode, GenMode and Spike Mode.

Also this time I need to find a circuit that stops the device from running should the unit exceed 90vdc, some kind of shutdown.

On this Oscillator with multiple modes I also have another question about the trigger wire on the Bedini coils.

Can using the trigger wire as feedback to the tl594 improve resonant quality.

Or will the trigger wire just hang there as it is no longer needed?

Thanks from me to you Mario and all of the great inventors here on this site.

Mike

[BroMikey]

Dual 4A Mosfet Drivers

Hi Mike,

I would use double drivers for each pair of Fet's. Check the Mouser site and search for double gate non inverting drivers - gate driver dual Integrated Circuits - ICs | Mouser

Regards
V

Hello V

SO each dual driver chip will handle one mosfet for each channel. So I need to parallel 6 dual chips together, driven by a single tl594? Non-inverting.

My circuits now run fine using non inverting TC4420 and run 2 large Mosfet's.

Can you tell me the benefit of going to Non inverting dual??

Paralleling must occur for both arrangements.

I feel bad today but I may run upstairs and show you all my work anyway in a minute.

I have been working day and night.


Sounds like it would make a big flash

I hold your entry in high regard so when you get time let me know what you found. I am going to guess that that many fets run cooler and this means less conflict.

Am I right?

Mike

[blackchisel97]

[ATTACH]14238[/ATTACH]

Here is a circuit that I have 3 of. What do you think about that? All comments excepted.

The only question I need to ask is how can I use this circuit to drive 12 IRFP250 fets all at the same time the same way. In unison.

The TC4420 will not have enough power to run 12 mosfets this size I don't think.

Thanks for each of your comments.

All comments will be treated with high regard.

Mike

Hi Mike,

I would use double drivers for each pair of Fet's. Check the Mouser site and search for double gate non inverting drivers - gate driver dual Integrated Circuits - ICs | Mouser

Regards
V

[Mario]

Hi Mike,

Check the data sheets of your devices, how many pf is the capacitance of your mosfet gate, how many pf can your driver handle? If one driver is not enough run a few of them in parallel.

Also check the SOA curve (safe operating area) on your mosfet data sheet, it tells you how many amps at how many volts for a given on time is safe so you won't blow it.

regards,
Mario

[BroMikey]

Here is a circuit that I have 3 of. What do you think about that? All comments excepted.

The only question I need to ask is how can I use this circuit to drive 12 IRFP250 fets all at the same time the same way. In unison.

The TC4420 will not have enough power to run 12 mosfets this size I don't think.

Thanks for each of your comments.

All comments will be treated with high regard.

Mike

[BroMikey]

Great Answers

To properly turn on and off a mosfet quickly and sharply a certain current and
voltage is required, the reason is that the gate of the mosfet is basically a
capacitor and to turn the mosfet full on requires the gate be charged to 10 volts
as quickly as possible, for logic level the gate only need be charged to 5 volts.

The higher value resistor to the gate of the mosfet does indeed slow down the
mosfet turn on time. For a regular mosfet the "threshold" voltage is around 4 volts
but that is only when the mosfet begins to turn on, to get the lowest "on"
resistance the mosfet needs to be turned fully on, the quicker it is turned fully
on and off the less power is dissipated by the mosfet.

The mosfet gate has a very high resistance (effectively infinite) but the
capacitance allows the gate to charge via displacement current just like any
other capacitor.

I usually use TC4420 mosfet driver chips which are 6 amp peak current parts.

If the mosfet turns on and off slowly it will dissipate more power and heat up.

You should be able to turn on the mosfet with a "rise" time of nS, the delay
time is irrelevant to power dissipation the rise and fall time is the time it take
to turn the mosfet on or off.

For example an IRF740 mosfet has an input capacitance of 1400pF, so to
charge that capacitance quickly requires a relatively high peak current. That
current is displacement current, just like charging a capacitor, if you try to
charge a capacitor through a resistor it will charge slower and so if you try to
charge a mosfet gate with a resistor the higher the value of the resistor the
slower the mosfet will turn on. Similarly if the drive signal to the mosfet gate
cannot supply sufficient peak current the mosfet will turn on slower as well.

Typically I don't use a resistor between the driver and the gate unless the
mosfet is switched at high frequency > 500 Khz, in the case of HF switching
the mosfet driver can get hot due to the current it is required to deal with if
the mosfet driver gets hot then a resistor of fairly low value 10 Ohms or so
maybe more or less between the driver and the gate will alleviate that but not
too high so as to restrict the drive current too much .

The resistor between the gate and circuit ground/mosfet source typically
between 2 to 10 K is mainly to ensure the mosfet remains off when not driven,
preventing it turning on when not wanted, it is not really necessary with
dedicated driver chips or even some oscillator chips like the SG3525.

Driving power mosfets.

http://ww1.microchip.com/downloads/en/AppNotes/00786a.pdf

A quote from the PDF linked above.



Don't believe anyone who says you don't need current to switch a mosfet properly.

To switch the mosfet on and off quickly a drive voltage of at least 10 to 15 volts
and sufficient drive current to charge the gate capacitance at the desired
rate is required.

The easiest and most reliable way to do that is with a dedicated mosfet driver.

Cheers

Hello Farmhand

Thanks A Million, this is a good answer for me because I have been needing to collect my thoughts about the way to turn these fets on and off.

So far I have been using a 555 timer to triger a OPTO and from the OPTO I am using a buffer transistor that cam handle more power to drive 12 IRFP250 fets.

My on time does not need to be in the nS but it is a great confirmation that the possibility does exist. Looking at the Bedini patent for his energy pump sg3524 he states that 100mS is the target.

So rise time and fall time and ON TIME???? HUmm ...........................

I am not sure what 100mS is for, maybe ON TIME?

Then I am wondering if a quicker rise time helps and just how much help.

Of course there is the stability of the parts operating within their design perimeters so as not to over heat them and burn them out.

Thank you for putting forth special effort to help me think this through.

I better go back and read your post again.

Well i read it again now and I think I am going to order. I will do it my way for now and see the difference. Been working all night on the 3 components I will be showing you guys. Huge dump, Modified Energizer convertor Oscillator and power supply made from 2 toroidal transformers one variable 0-70vdc @ 30amps 95 percent efficient power conversion.

You guys are cool. Thanks

Mike

[Farmhand]

To properly turn on and off a mosfet quickly and sharply a certain current and
voltage is required, the reason is that the gate of the mosfet is basically a
capacitor and to turn the mosfet full on requires the gate be charged to 10 volts
as quickly as possible, for logic level the gate only need be charged to 5 volts.

The higher value resistor to the gate of the mosfet does indeed slow down the
mosfet turn on time. For a regular mosfet the "threshold" voltage is around 4 volts
but that is only when the mosfet begins to turn on, to get the lowest "on"
resistance the mosfet needs to be turned fully on, the quicker it is turned fully
on and off the less power is dissipated by the mosfet.

The mosfet gate has a very high resistance (effectively infinite) but the
capacitance allows the gate to charge via displacement current just like any
other capacitor.

I usually use TC4420 mosfet driver chips which are 6 amp peak current parts.

If the mosfet turns on and off slowly it will dissipate more power and heat up.

You should be able to turn on the mosfet with a "rise" time of nS, the delay
time is irrelevant to power dissipation the rise and fall time is the time it take
to turn the mosfet on or off.

For example an IRF740 mosfet has an input capacitance of 1400pF, so to
charge that capacitance quickly requires a relatively high peak current. That
current is displacement current, just like charging a capacitor, if you try to
charge a capacitor through a resistor it will charge slower and so if you try to
charge a mosfet gate with a resistor the higher the value of the resistor the
slower the mosfet will turn on. Similarly if the drive signal to the mosfet gate
cannot supply sufficient peak current the mosfet will turn on slower as well.

Typically I don't use a resistor between the driver and the gate unless the
mosfet is switched at high frequency > 500 Khz, in the case of HF switching
the mosfet driver can get hot due to the current it is required to deal with if
the mosfet driver gets hot then a resistor of fairly low value 10 Ohms or so
maybe more or less between the driver and the gate will alleviate that but not
too high so as to restrict the drive current too much .

The resistor between the gate and circuit ground/mosfet source typically
between 2 to 10 K is mainly to ensure the mosfet remains off when not driven,
preventing it turning on when not wanted, it is not really necessary with
dedicated driver chips or even some oscillator chips like the SG3525.

Driving power mosfets.

http://ww1.microchip.com/downloads/en/AppNotes/00786a.pdf

A quote from the PDF linked above.

1. MOSFET gate drive rise and fall times must be symmetrical,
and as short as possible. A driver like the TC4427 has a
specified tR and tF of approximately 19nsec into a 1000pF
load. A higher peak output current driver may be selected to
achieve more aggressive rise and fall times if so desired.

Don't believe anyone who says you don't need current to switch a mosfet properly.

To switch the mosfet on and off quickly a drive voltage of at least 10 to 15 volts
and sufficient drive current to charge the gate capacitance at the desired
rate is required.

The easiest and most reliable way to do that is with a dedicated mosfet driver.

Cheers

[BroMikey]

Voltage dividing and voltage driven gate

If you know this already just disregard but I thought it might be helpful.

The MOSFET's used at the cap-dump are voltage controlled devices. The voltage applied to the gate determines when and how fast they turn on.

We'll call the resistor connected to the gate R1 and the resistor connected between the gate and the drain R2.

R1 acts as a current limiting device between the power from Wiley and the MOSFET.

I = R / V

So raising the resistance decreases the current which isn't important to the MOSFET since it is voltage driven but does affect how much power will be drawn from the driving circuit.

The two resistors that you show at each MOSFET (R1 and R2) results in a voltage divider. These will affect the MOSFET switching since they affect the voltage. Vout will be the voltage between R1 and the gate. Vin is the volatage from Wiley to R1.

Vout = Vin * (R2 / ( R1 + R2))

The transistor you show in the 555 circuit is a BJT (Bipolar Junction Transistor) and it is driven by current rather than voltage. So the current limiting resistor in this circuit does affect the turn-on time of the transistor. It affects how much current is available to turn the circuit on and how fast that current accumulates in the transistor.

This may help you do some calculations to determine the switching you need. You compare the values calculated to the device datasheets to attain the results you want. If the device you are using won't give the results you desire just look for another device.

Hello thx1138

Say on. I am in need up these refresher talks. I have not given much of my life to this work and while I am hard at it now, information like you have offered is perfect for quick and easy practical application.

This is the kind of rehearsal I need.

Mike