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Ben Solon

Tue Aug 07 2012, 01:32AM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600

a brick simply cant get up to those speeds with its delays alone. then you have to deal with gate capacitance:

-- 2uC @ 24

-- 2uC/24V = 8.333e-8F = 83.33nF

-- P = C*V^2*f = .00000008333*24^2*200000 = 9.59962W/gate

-- 9.59962*2 ~= 20W per half bridge

you need a pretty chunky transformer to supply your "logic" now. almost an amp per half bridge at 24v.

another thing is why use a brick for a 500W coil? to247's can handle this power no problem. i wouldn't use bricks until you get into the kw range.

Mads Barnkob

Tue Aug 07 2012, 08:59AM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

As Terry once said:

I only had time to skim through this, but it looks interesting and might help you calculate:

Also, about the DRSSTC3, progress is slow, but changes to the design have been made as I got home some CM600s instead, so have been redesigning the bridge and will likely be putting it together this coming weekend, rest of the coil is still some miles from completion :)

Dr. Dark Current

Tue Aug 07 2012, 09:33AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Dr. ISOTOP: Nope. The delay times are for the current waveform. During the "turn off delay time", the drain (collector) voltage actually starts rising and reaches supply voltage, but the current still stays at its maximum. During the "fall time" the voltage has already reached full supply voltage, but the current falls to zero. For the turning on this is similar.

Mads Barnkob

Tue Aug 07 2012, 04:55PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

ben123324 wrote ...

a brick simply cant get up to those speeds with its delays alone. then you have to deal with gate capacitance:

-- 2uC @ 24

-- 2uC/24V = 8.333e-8F = 83.33nF

-- P = C*V^2*f = .00000008333*24^2*200000 = 9.59962W/gate

-- 9.59962*2 ~= 20W per half bridge

you need a pretty chunky transformer to supply your "logic" now. almost an amp per half bridge at 24v.

Wards universal driver will have no problem delivering this drive current, with a standard GDT it can still deliver double rms current than what you require.

When calculating maximum swithcing speeds, there is two max frequencies to find, one looking at switching times, using the overall switching times multiplied by 10-20 and the junction temperature rise limit. Where the last always overrides the first.

One thing that really should jump at your eyes in a datasheet is the Zrjc vs. pulsewidth graph. For a 60N60 TO247 IGBT, you can read out that the normal 0,5K/W thermal resistance can be derated as low as 0,01K/W at the low pulse widths we use in a DRSSTC.

I can not find the thread, I think it is about a year back that someone experimented with resonant switching times, where he proved that bricks could be run way out of specs when in a resonant circuit.

I hope some of this makes sense and it all relates to the linked article above.

ben123324 wrote ...

another thing is why use a brick for a 500W coil? to247's can handle this power no problem. i wouldn't use bricks until you get into the kw range.

With a full bridge IXGN60N60 (isotop) I have pushed 2500W through, so Ben is absolutely right about a CM300 being overkill for a 500W coil.

Dr. ISOTOP

Tue Aug 07 2012, 08:01PM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

Dr. Dark Current wrote ...

Dr. ISOTOP: Nope. The delay times are for the current waveform. During the "turn off delay time", the drain (collector) voltage actually starts rising and reaches supply voltage, but the current still stays at its maximum. During the "fall time" the voltage has already reached full supply voltage, but the current falls to zero. For the turning on this is similar.

Aren't the times you're talking about listed under "rise time/fall time" on datasheets? I'm referring to the turn-on delays and turn-off delays.

Dr. Dark Current

Tue Aug 07 2012, 11:04PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

I'm talking about the switching times manufacturers usually state in the datasheet. They are the turn on delay time (Tdon), rise time (Tr), turn off delay time (Tdoff) and fall time (Tf). These are (should be) related to the current, not voltage waveform. Sometimes there is an example of current and voltage waveforms with the switching times marked in them in the datasheet.

zzz_julian_zzz

Wed Aug 08 2012, 12:45AM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

I was able to run this coil & the output were more than 3x the length of its secondary with just irg4pc50ud (fullbridge) ,. I am just wondering if brick can still drive it because in my country, re-con bricks are far more cheaper than the brand new parts such as irg4 hehe.

Thanks for your inputs, ow. my country is in great disaster right now(if you heard on the news) no power since yesterday (i only used my laptop) =/

What if my coil were submerged in water? specially the secondary, what would happened if turned on?

Dr. ISOTOP

Wed Aug 08 2012, 01:25AM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

zzz_julian_zzz wrote ...

I was able to run this coil & the output were more than 3x the length of its secondary with just irg4pc50ud (fullbridge) ,. I am just wondering if brick can still drive it because in my country, re-con bricks are far more cheaper than the brand new parts such as irg4 hehe.

Thanks for your inputs, ow. my country is in great disaster right now(if you heard on the news) no power since yesterday (i only used my laptop) =/

What if my coil were submerged in water? specially the secondary, what would happened if turned on?

The secondary would probably flash over from being in water.

Goodchild

Wed Aug 08 2012, 01:30AM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

Dr. ISOTOP wrote ...

The secondary would probably flash over from being in water.

I'm not so sure about that, if it was distilled water for instance it may be one hell of a good insulator at ~18.5MÎ© per cm.

brandon3055

Wed Aug 08 2012, 02:52AM

Registered Member #4548 Joined: Mon Apr 23 2012, 03:52AM
Location: tasmania
Posts: 271

The warter would probably detune the coil (unless your driver can compensate)

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