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Which is faster,IGBT or vacuum tube?And I also need suggestions for my school project

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hsieh

Mon Mar 19 2012, 01:39PM

Registered Member #1412 Joined: Thu Mar 27 2008, 04:07PM
Location: Taipei Taiwan
Posts: 278

My friend and I is now working on a school project.At the end of the semester,we will demonstrate what we build in front of the class.We want to build something impressive. We decide to build a 3KW induction heater that can melt AND LEVITATE small lightweight metal objects.

He planned to get the power we need from 3 different circuit breakers,each capable of supplying 1KW.And using 3 different PFC circuits to boost the voltage to 380V to power our IGBT bridge.He will possibly use PLL to achieve resonance.

Now he is simulating different topologies on computer.But we soon found that in order to keep frequency low enough for our IGBT bridge,the resonant capacitors will be too expensive for us.

I remembered that I once seen some websites that said that vacuum tube induction heater can work at much higher frequency than IGBT induction heater.And I can find cheap high power vacuum tubes.So I suggested that maybe we can build a vacuum tube induction heater that worked at higher frequency.But he said that vacuum tubes are much slower than MOSFET or IGBT component.IS THIS TRUE?

My friend knows a lot about power electronics and other electronics related things.BUT IS OUR PROJECT POSSIBLE?

I suggest that maybe we should build something simpler and both of us can understand such as the airband receiver or vacuum tube audio amp I am currently working on but he said that they are not impressive at all.

I am also thinking about building a wireless power transmitter that can transmit at least 100W through 10cm spacing at a reasonable efficiency.Is this possible?

Thanks

Steve Conner

Mon Mar 19 2012, 01:54PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

No, it is not true. Like MOSFETs, vacuum tubes have no minority carriers to slow them down. Pretty much any high power tube will give full output up to 30MHz.

Inducktion

Mon Mar 19 2012, 03:44PM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

Yeah, Vacuum tubes are a lot faster than basically any semiconducting device... That's partially the reason a lot of radio transmitting towers still use large tubes to transmit!

I think with certain tubes you can get up to the microwave frequency region...

Mattski

Mon Mar 19 2012, 05:21PM

Registered Member #1792 Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527

Tubes can be pretty competitive compared to solid state devices in terms of maximum frequency, though it all depends on which tube you're comparing to which transistor. What really makes tubes still useful today is that their higher breakdown voltages and high current densities allow creation of a much higher power source or amplifier which would require the output of many transistor amplifiers to be combined.

But is a tube right for you? Tubes are a much more niche technology at this point and I think it will require a lot more effort to find the tubes you want. They are more physically delicate and require more love and care. MOSFETs are much more common and what you learn with them will be more applicable to other power electronics applications. At the frequencies you are likely interested in, MOSFETs should still be available with plenty large breakdown voltages, not like a 100+GHz transistor with a ~1V breakdown.

Electra

Mon Mar 19 2012, 10:21PM

Registered Member #816 Joined: Sun Jun 03 2007, 07:29PM
Location:
Posts: 156

Vacuum tubes are higher impedance devices than mosfets/igbets. So you have to consider the need for a HV power supply too, which may also be big and expensive.

Semiconductors used a switching devices, can be reasonably efficient, how will you be operating your tube and how does this compare ? Iâ€™m afraid I know little about how you would drive a tube for something like this, most applications seem to use them as amplifiers.

There are a lot of things in favour of tubes, and against them frequency is only one of them.

hsieh

Tue Mar 20 2012, 01:11AM

Registered Member #1412 Joined: Thu Mar 27 2008, 04:07PM
Location: Taipei Taiwan
Posts: 278

I found someone selling this

vacuum tube for approximately 40USD in a local auction website.Is this worth buying?

Steve Conner

Tue Mar 20 2012, 07:02AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Looks pretty good, but you'll need a hefty high voltage power supply to make full use of it. The datasheet says 7.5kV and 0.9A.

I guess you would still get some useful output using the power supply from a microwave oven.

teravolt

Tue Mar 20 2012, 01:27PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

are you able to ask what sort of use it has seen? I like this one

using tubes like this can be a major project if you use a 833A it is a kilowatt and you may be able to downsize yet still be impresive.

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