Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on January 01, 2013, 04:35:45 pm
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I was looking for a substitute for the NTE Mosfet we usually use in the VVR circuits
I asked if a STW11NK100Z (1000v 8.3A) which price is only € 3.80 (instead of near € 20.00 for an NTE)
could be a reasonable substitute, the response was affirmative but was also told me that probably an IGBT can be used for a VVR (there are IGBT that has high current and voltage ratings at low price)
so I give a look and I find the FGA20S120M (1200v 40A) and the price is only € 2.85
http://docs-europe.electrocomponents.com/webdocs/10c9/0900766b810c97d7.pdf (http://docs-europe.electrocomponents.com/webdocs/10c9/0900766b810c97d7.pdf)
Please can someone confirm the usability of this component and also if the normal VVR circuit need to be modified to use an IGBT
Many Thanks in Advance
K
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I don't know of any linear applications using IGBTs.
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Are you saying that usually a pulse circuit must be used to drive the gate of the IGBT ?
Something like an NE555 oscillator ?
K
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Are you saying that usually a pulse circuit must be used to drive the gate of the IGBT ?
Not necessarily. The device is a high current high speed switch device that can be controlled with a low voltage low current gate signal. They are used in motor controllers, PWM controllere, and switching power supplies. And they are used in high power UPS systems.
But I've never seen one in a linear/analog circuit such as a VVR or an audio/video/rf circuit.
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the only use for them i've seen in audio is class D power amps. their high speed switching characteristics can be exploited in that role.
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Many thanks Friends
When there will be an opportunity I think I'll try one IGBT in a VVR
K
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Here's some reading for you K
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Ehi Dave
I've read only the first lines of the text and I must thank you
that is a very interesting text, I'm going to read it with attention
Many Many Thanks
K
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> near € 20.00 for an NTE
NTE is just over-priced.
You do NOT need 8A or 40A rating for a 0.2A load.
You do want a big package and lots of Watts.
There must be 1000V 5A 50+ Watt MOSFETs at your local suppliers. Sorry I can't name a part-number; all my old favorites go out of production.
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I was looking for a substitute for the NTE Mosfet we usually use in the VVR circuits
I think almost all power MOS FETs that fulfill the specs can be used.
I have succesfully used the following ones that cost ~2€ each if you buy a bigger amount e.g. more than 10:
STW11NK100Z
IRFPC50PBF
/Leevi
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http://uk.farnell.com/vishay-formerly-i-r/irfpg40pbf/mosfet-n-1000v-4-3a-to-247ac/dp/8649570 (http://uk.farnell.com/vishay-formerly-i-r/irfpg40pbf/mosfet-n-1000v-4-3a-to-247ac/dp/8649570)
1.74 euros + ship from UK.
surely that won't break the wallet?
--DL
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Many thanks to all for the info and suggestions
I've read the pdf file that SILVERGUN posted and I've find it very interesting
For application under 250v seems that actually the Mosfet is the better component to be used
but for application that are higher than 250v and are at relatively low switch frequency
the IGBT seems a good antagonist of the Mosfet
may be in the future the IGBT will overtake the Mosfet
and will be used in near all applications
At the moment and for our purpose I think that what we can get cheaper is the best
K
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but for application that are higher than 250v and are at relatively low switch frequency
with VVR you're not switching. the MOSFET device is operating in the linear region. IOW, you're using the linear region of a MOSFET to control voltage through the device by varying the bias condition. unless i missed something in your post about a switching power supply?
may be in the future the IGBT will overtake the Mosfet
not when it comes to working in the linear region. bipolars and MOSFETs will still reign in that arena.
that article is dealing with merits of both MOSFET and IGBT in switching applications - not linear. with tube amps we are building linear power supplies - not switching power supplies. VVR for guitar amps is a linear implementation.
--DL
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unless i missed something in your post about a switching power supply?
No you are missing nothing
As my knowledge is very poor on SS
I was assuming that the linear region is comparable with the lower region of switching region
Something as the frequency of switching is so slow that we can't measure it
K
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I'm sorry K....my intention was good
DL is right....that comparison doesn't really relate to your intended application in VVR
If we were still talking welding machines, I might have been some help.......but the application I see them used the most is high speed switching, sometimes "creating" high frequency AC from a DC source....not useful in an amp PS
They sure do take a beating in inverter based power supplies....when they fail,,,they go hard
Usually used in sets of 2,,,,if one is bad----replace both
If I can find a block diagram for one of those inverter units, I'll post it over on that other thread for you
Here's a great article that compares linear to switched mode power supplies:
http://www.kterra.com/kb/Switched_mode_Power_Supply-27.html (http://www.kterra.com/kb/Switched_mode_Power_Supply-27.html)
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Ciao Dave
Your pdf about IGBT & Mosfet is anyway very interesting
In an italian forum (not related to guitar amp, only general purpose electronics) there are some very experienced guys who are saying that the IGBT is usable in a linear application like VVR
only it need a bit more to be drive and it becomes a bit more hot (a low higher level than a Mosfet, not very much)
so, in the schematic of the VVR we usually use, the 10R resistor is to be increased a bit and they say an IGBT can be used
(http://www.electroyou.it/fidocad/cache/1f5b4cebd37973bb393b8bb04120938533b7784a_3_650.png)
I'm going to read with interest also the new link you posted
Thanks again
Franco
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I have used the following circuit when both preamp and power amp are regulated.
In this case I have not used the diodes. I'm not sure why there is the 220k resistor parallel with the 1M pot and 100k resistor
but I have left it there.
http://forum.allaboutcircuits.com/cache.php?url=http://i92.photobucket.com/albums/l9/generalguitar/VVR4.jpg (http://forum.allaboutcircuits.com/cache.php?url=http://i92.photobucket.com/albums/l9/generalguitar/VVR4.jpg)
/Leevi
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Excellent discussion, K, and others, you are thinking outside the amp. This is what I love about this forum.
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> I've never seen one in a linear/analog circuit such as a VVR or an audio/video/rf circuit.
I have. It never caught on.
IMHO, IGBT combines bad features of both FET and BJT technology. Well, good-and-bad features. But in the audio power amp it seemed the less-good features dominated the design.
> experienced guys who are saying that the IGBT is usable in a linear application like VVR
I'm sure it is.
However the MOSFET really should be cheaper. They are simpler. They are MUCH more common. Perhaps the problem is that there are SO many uses that there are too-many part-numbers to look through.
Over 500V (1,000V for monster amps)
BIG case
High dissipation
The current and R(on) numbers are sure to be much better than you need.
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so I give a look and I find the [IGBT] FGA20S120M (1200v 40A) and the price is only € 2.85
I've never seen a 1200v 40A Mosfet at € 2.85 ($ 3.74)
the only my interest was to find something cheaper than the NTE Mosfet
the IGBT FGA20S120M (1200v 40A) seems something to give a try
the Mosfet STW11NK100Z (1000v 8.3A) at € 3.80 ($ 4.98) seems a good candidate to substitute the expensive NTE Mosfet
K