Horizontal deflection (or high voltage type) transistors to directly drive ESLs? - diyAudio
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Old 8th March 2006, 05:45 PM   #1
bigwill is offline bigwill  United Kingdom
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Default Horizontal deflection (or high voltage type) transistors to directly drive ESLs?

Just wondering if you could do this without too much hassle. I don't know what else to ask really
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Old 8th March 2006, 06:39 PM   #2
Bazukaz is offline Bazukaz  Lithuania
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I am currently working on this.
However , the max. voltage of these transistors is about 800-900V , and they are only available as NPN types.By using bridge , it is possible to get around 400-500 Vrms from this... Not so much , but should give some sound.
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Old 10th March 2006, 01:21 AM   #3
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By using big inductors in a brigde amp the power supply voltage can be doubled, it will only work in class A though but class AB with only npn transistors is very hard anyway.
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Old 10th March 2006, 05:51 AM   #4
Bazukaz is offline Bazukaz  Lithuania
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But , for as i understand , you cannot exceed transistors Vce rating , even if choke is used.In this case , only efficiency is incresed... By the way , could somebody explain why using a choke as a collector load does not cause full power bandwidth problems ?
I was thinking about quasi complementary AB output stage , but the PNP transistors , 2SA1968 , seems to be hardly avalable.

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Lukas
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Old 12th March 2006, 12:58 PM   #5
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You still need very high voltage transistors, fets or IGBT's might be even better since high voltage transistors usually have a low hfe.

Maybe current drive will also be better than voltage drive, pherhaps someone could elaborate on that.
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Old 13th March 2006, 03:55 AM   #6
Eva is offline Eva  Spain
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1200V IGBTs are rugged and quite cheap in comparison with MOSFET. Bridge output stages should be also considered, because 600V IGBTs are much more common (check IRG4BCxxx series from International rectifier and SKPxxNxx series from Infineon). For high voltage low-cost (switching) bipolar transistors check MJE1300x and MJE1800x series from On Semiconductor.

Series connecion of two or three lower voltage transistors with active dividers is another alternative, and of course, high efficiency class H is just an improvement over series connection. For example, consider an amplifier having +-1200V supplies tappered at 200V intervals (that may even come from a single pair of 200V rails with capacitor-diode multipliers), each interval having its own diode and output device (the problem here is to design a suitable VAS).
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Old 13th March 2006, 04:55 AM   #7
Bazukaz is offline Bazukaz  Lithuania
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Hi,
Not necessarilry HV transistors have low hFE.Some have 30 or so.But their SOA is greatly decresasing with collector-emitter voltage.Because of this i am watching for fets now...
IRFBG20/30 1000V MOSFETS are cheap and easy to get.I am not sure if they are really suitable for audio , but , using a strong n/f, should work...


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Lukas.
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Old 13th March 2006, 10:29 AM   #8
Calvin is offline Calvin  Germany
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Default How about these?

Hi,

ther are a few High-Voltage-Trannies/-Modules with Uce in the kV-range.
Sensitron SCP-4979 is a module with 4 IGBTs, each 2.500V/1A
The Powerex CM200HG-130H is a single IGBT-Power Module with 6.500V/200A, the CM400HB-90H is a 4.500V/400A module.
Even though these are quite slow devices with high input-/output-capacitances, they should be fast enough for audio frequencies.
I don´t know anything about availibility and cost of these devices, but on the first glance they seem quite interesting fo me to replace the Pentodes in a ´classical´ High-voltage ESL-amp.
With such high Uces there should be no need for cascaded designs with their problems of generating the drive signals for the Bases/Gates.

Any comments?

jauuu
Calvin
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Old 13th March 2006, 10:33 AM   #9
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High voltage of many kilovolts and transistors. Which part of this suicidal comination don't you understand?

Think vacuum tubes here, enjoy reliability and never loose any sleep.
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Old 13th March 2006, 08:26 PM   #10
Bazukaz is offline Bazukaz  Lithuania
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These IGBTs are amazing ... Ive just seen a datasheet of 6.5 kV 400A monster! Not so easy to destroy , even comparing with tubes )).
I wonder about their pricing and availability ...Its probably worse than output transformer ... Isn't it ?

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Lukas.
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