Cap Dump Circuit

[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]

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.

pulsing594parallel.JPG

Mike Ps thanks gentlemen for your continued instruction.

[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

[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

[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

[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

[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

[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

[BroMikey]

Very Well Then

@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

Hello AC

I have never heard of this so yeah. Is this the only part number you have? Any Idea how many 2500pf gate Mosfet's one of those darlin's can handle?

Ill go look see at the ICL 7667 dual mosfet driver ASAP.

Thanks for your comment.

All comments excepted.

Mike

[BroMikey]

Driver testing

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

Yes i learned much from experimenting and I had some tc4420's coming but may try others if I was sure.

Great to see your work in electro-Med. The people need you with all of the planned sickness against the populous.

Looks like you have some slippery handed folks running around outside HUH?

Either way your work is an added help and great for learning by.

Mike

[Allcanadian]

Hello Mike

I have never heard of this so yeah. Is this the only part number you have? Any Idea how many 2500pf gate Mosfet's one of those darlin's can handle?

Ill go look see at the ICL 7667 dual mosfet driver ASAP.

The 7667 is nothing special, a cheap 1-2 amp generic mosfet driver I believe. The key here is to use a driver so the rise/fall is super fast while the 555 output is slow and adding an optocoupler is like watching paint dry.

I use a mosfet driver so the on/off transition or slope is very fast regardless of the transition from the source switching it such as the 555. Then I use the driver to switch another set of mosfets to source/sink the gates of the mosfets actually performing the switching operations. Think of the driver and source/sink mosfets as a very large mosfet driver in itself because it is and it's cheap.

The general rule is to hammer the gate hard and fast which can get a little tricky. For instance switching big current means big losses (I2R) so the on/off transition must be fast and the On resistance(R-DS) of the mosfets as low as possible.

I should mention that if your using PWM at a relatively low frequency with big current then On resistance is huge in my opinion. You can always bump the driver to compensate for a larger gate capacitance but R-DS is a nightmare with low voltage/high current. As well it may sound counter-intuitive but in one project I found it was easier and more efficient to boost the voltage to max, switch it then buck it back down rather than take a major hit with I2R losses when switching.

AC

[BroMikey]

Deeply Descriptive

Hello Mike


The 7667 is nothing special, a cheap 1-2 amp generic mosfet driver I believe. The key here is to use a driver so the rise/fall is super fast while the 555 output is slow and adding an optocoupler is like watching paint dry.

I use a mosfet driver so the on/off transition or slope is very fast regardless of the transition from the source switching it such as the 555. Then I use the driver to switch another set of mosfets to source/sink the gates of the mosfets actually performing the switching operations. Think of the driver and source/sink mosfets as a very large mosfet driver in itself because it is and it's cheap.

The general rule is to hammer the gate hard and fast which can get a little tricky. For instance switching big current means big losses (I2R) so the on/off transition must be fast and the On resistance(R-DS) of the mosfets as low as possible.

I should mention that if your using PWM at a relatively low frequency with big current then On resistance is huge in my opinion. You can always bump the driver to compensate for a larger gate capacitance but R-DS is a nightmare with low voltage/high current. As well it may sound counter-intuitive but in one project I found it was easier and more efficient to boost the voltage to max, switch it then buck it back down rather than take a major hit with I2R losses when switching.

AC

Hello AC

Looks like you got your feet wet a few time doing the tronix. Great pointers.

I am looking at quad drivers now, all of the guys got me thinking.

In your post you talked about gate capacitance and fast switching in a way that made me think the max ratings are there because some switching times are very slow for specific design, but where the MAX speed can be used with multiple fets the capacitance might get shared so more fets can operate safely.

Thanks AC.

Mike

Mike

[BroMikey]

Dump Down Crash

Hello Mike


I should mention that if your using PWM at a relatively low frequency with big current then On resistance is huge in my opinion. You can always bump the driver to compensate for a larger gate capacitance but R-DS is a nightmare with low voltage/high current. As well it may sound counter-intuitive but in one project I found it was easier and more efficient to boost the voltage to max, switch it then buck it back down rather than take a major hit with I2R losses when switching.

AC

Hello Ac and group members

Here is what happened to my 555 timer to opto to 6 mosfet's.

Each mosfet has around 500ohms on the gate and a 10k divider arrangement and what would happen is each time the dump came I could hear a "TICK" that would get louder as the power increased.

My dump down voltages was out of control and as soon as I added atleast 100ohms inline between the opto and the entire set of six gates I regained control of "dump down to" voltage.

As it turns out the entire circuit setup is fully functional without blowing an occasional fet due to out of control crash landings at the bottom of the dump.

The "Tick" Sound is gone and the circuit can handle alot of power with some heat evolution.

IT IS RUNNING NOW AND ALL NIGHT WITH NO PROBLEMS

I am very happy.

I am dealing with RC time constants for charging the bank of caps for the least amount of loss. For instance I use a set of toroidals (ONE is a variable) rated at 2.5kVA to HUGE bridge to 5000UF 200v caps then to an RC charge resistor that is HUGE also.

It gets the job done for now and either way some heat will be lost with any large power circuit. Fans must be used when switching large amounts of power no matter how you cut the cake.

For now as in the past I use heater element wire from a clothes dryer cutting to length for proper resistance so it is only gently warm so a fan is added.

This slows the charge time of the cap bank so hardware and energy loses are minimized.


Dumping down to the battery bank voltage causes an ever increasing "TICK" noise that will smash your junctions.

Case dismissed.

Thank you all for keeping me focused while I experiment. It is your advice that gave me something to go by when I am in the middle of testing a circuit.

Michael

[BroMikey]

Cold solder joints

Hello Group Members



I would like to add that a cold solder joint ignited and I got the entire cap bank dump right across that gap. Needless to say my Fet went up in smoke. But I have plenty of Fets and this is a small price to pay to learn.

I think someone said that each fet is good for 750 watts and will run cool so 6 fets should be good for 4000 watts Plus.

If anyone has noticed the "radiant" chargers are being sold using a conventional 24vdc wall adapter connected to a cap dump. This simple setup will also employ some form of resistor to limit cap charging.

Like AC and others have stated turning off the supply for a few micro-seconds is another option generally acquainted with high quality computerized industrial equipment.

Mike

[BroMikey]

RC source and Cap Dump Ciruit

Hello group

Here is a video of my progress and how I can run over 500 watts of surging power into batteries.

https://www.youtube.com/edit?video_id=tAflPiIM1gc

Mike A special thanks to all my helpers.