Author Topic: Switching Speed  (Read 990 times)

Offline thedoc298

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Switching Speed
« on: May 22, 2021, 06:49:19 PM »
  Ok, say my srsgtc is running at 120  presentation per second,  120hz. And the coil resonate at 200khz
Now I sub in an Hbridge with igbt's, Are not the igbt going to switch at 120 presentation  or bps, if my controller is set for that.

So in my mind the coil  rings at 200khz and the igbt are switching at 120hz or whatever I have it set to. Is this correct...?
>
>
>
> What im getting at, is I see people say, you will have to construct
> your coil to resonant at a much slower, 35 to 75 khz to accommodate the
> slow switching speed of the IGBT's>
>
> So what am I not understanding is it looks like the igbts are
> already switching slow (120 in this example) and the coils is what is ringing at the fast speed of 200khz

I just see people running drsstc at higher frequency than 200khz with the same IGBT I want to use but people say they can't switch that fast. But are they already switching slow....?

So in this example I build the coil, its resonant freq is 200khz why would the IGB's have to switch at the 200khz....?

Someone straighten me out on this. Thanks anyone

I posted on the tesla list, but I don't think people under stood what I was asking.

(Say my coil is resonate at 200Khz what speed are the igbt switching at)

 Thank you very much


« Last Edit: May 22, 2021, 07:12:05 PM by thedoc298 »

Offline davekni

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Re: Switching Speed
« Reply #1 on: May 22, 2021, 07:42:57 PM »
120Hz switching works if you have a 10kV IGBT (or whatever voltage your spark gap used).  Lower voltage IGBTs require multiple cycles at 200kHz to build up primary voltage to 10kV.
David Knierim

Offline thedoc298

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Re: Switching Speed
« Reply #2 on: May 22, 2021, 08:09:03 PM »
120Hz switching works if you have a 10kV IGBT (or whatever voltage your spark gap used).  Lower voltage IGBTs require multiple cycles at 200kHz to build up primary voltage to 10kV.

If you have a drsstc and its resonate frequency is 200khz, what is the switching speed of the igbt. This is the question
I have been told if the drsstc runs at 200khz then I need igbt's that run at that speed or better.

Offline thedoc298

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Re: Switching Speed
« Reply #3 on: May 22, 2021, 08:31:15 PM »
120Hz switching works if you have a 10kV IGBT (or whatever voltage your spark gap used).  Lower voltage IGBTs require multiple cycles at 200kHz to build up primary voltage to 10kV.

If you have a drsstc and its resonate frequency is 200khz, what is the switching speed of the igbt. This is the question
I have been told if the drsstc runs at 200khz then I need igbt's that run at that speed or better.

I just can't get the question across .

Offline T3sl4co1l

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Re: Switching Speed
« Reply #4 on: May 24, 2021, 12:45:51 PM »
The IGBTs turn on and off hundreds of times per burst, and there are hundreds of bursts per second in the example.  Depending on exactly what settings you've configured.

The rate at which the IGBT change state, from off to on or vice versa, is on the order of 200ns, one five-millionth of a second.

Tim

Offline thedoc298

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Re: Switching Speed
« Reply #5 on: May 25, 2021, 01:54:25 AM »
The IGBTs turn on and off hundreds of times per burst, and there are hundreds of bursts per second in the example.  Depending on exactly what settings you've configured.

The rate at which the IGBT change state, from off to on or vice versa, is on the order of 200ns, one five-millionth of a second.

Tim

My problem was I thought that the igbt when used in place of a srsg only had to switch  at 120 bps.
My srsg switches at 120, so replacing the srsg with igbt, i thought they only had to switch at the same rate of 120. But, they dont work like I had envisioned.

Thanks for your time
 

Offline thedoc298

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Re: Switching Speed
« Reply #6 on: November 04, 2021, 09:56:57 PM »
120Hz switching works if you have a 10kV IGBT (or whatever voltage your spark gap used).  Lower voltage IGBTs require multiple cycles at 200kHz to build up primary voltage to 10kV.

If you have a drsstc and its resonate frequency is 200khz, what is the switching speed of the igbt. This is the question
I have been told if the drsstc runs at 200khz then I need igbt's that run at that speed or better.

Thanks for reply, just did not quite understand the switching. At 120hz would be way, way to long of on time.

Offline thedoc298

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Re: Switching Speed
« Reply #7 on: November 04, 2021, 09:58:47 PM »
The IGBTs turn on and off hundreds of times per burst, and there are hundreds of bursts per second in the example.  Depending on exactly what settings you've configured.

The rate at which the IGBT change state, from off to on or vice versa, is on the order of 200ns, one five-millionth of a second.

Tim

My problem was I thought that the igbt when used in place of a srsg only had to switch  at 120 bps.
My srsg switches at 120, so replacing the srsg with igbt, i thought they only had to switch at the same rate of 120. But, they dont work like I had envisioned.

Thanks for your time

Thanks again, I was way off in my thinking.

Offline klugesmith

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Re: Switching Speed
« Reply #8 on: November 12, 2021, 02:51:17 AM »
Now if we were talking about MOSFETs, which conduct with low R in both directions when On, the answer could be different.

I bet you could do a low voltage test of actual TC, using DC charging supply and a MOSFET in place of the spark gap.  Every 1/120 of a second, turn the FET on for a few hundred microseconds and watch the primary circuit ring at 200 kHz.   The On resistance must be much lower than sqrt(L/C).

I once did that with full size can crusher, using a 9-volt battery as charging supply for about 1 millionth of maximum shot energy. The "firing" switch was a SO8-size N-FET, with gate driven directly from a 555 timer IC.

Offline thedoc298

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Re: Switching Speed
« Reply #9 on: December 29, 2021, 05:27:42 AM »
Now if we were talking about MOSFETs, which conduct with low R in both directions when On, the answer could be different.

I bet you could do a low voltage test of actual TC, using DC charging supply and a MOSFET in place of the spark gap.  Every 1/120 of a second, turn the FET on for a few hundred microseconds and watch the primary circuit ring at 200 kHz.   The On resistance must be much lower than sqrt(L/C).

I once did that with full size can crusher, using a 9-volt battery as charging supply for about 1 millionth of maximum shot energy. The "firing" switch was a SO8-size N-FET, with gate driven directly from a 555 timer IC.

That was what I was thinking, thanks

High Voltage Forum

Re: Switching Speed
« Reply #9 on: December 29, 2021, 05:27:42 AM »

 


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