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Old 8th January 2002, 12:06 PM   #1
djk is offline djk
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Default Circlotron

How about this http://www.ne.jp/asahi/evo/amp/J200K1529/exp21.gif with IRFBA22N50A, 357W devices for USD$2.64 or IRFPS37N50A, 446W for USD$5.85 Of course the front end could be MOSFET too.Could be able to get 60~70W in class A with only one pair of devices without matching.
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Old 18th August 2006, 12:39 PM   #2
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HI

you are certain that this diagram functions ?

THX
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Old 18th August 2006, 10:34 PM   #3
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Quote:
Originally posted by UltimateX86
you are certain that this diagram functions ?
Hmmmm. Do you see a reason why not?

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Old 19th August 2006, 11:46 AM   #4
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Hello Nelson

No protection for the speaker ?

How to calculate the power of a transistor / Mosfet Circlotron ?

thx
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Old 19th August 2006, 12:02 PM   #5
kubeek is offline kubeek  Czech Republic
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the datasheet stated 340W dissipation of the IRFBA22N50A seems quite unreal to me, as there is junction-case thermal resistance of 0.37K/W and case-sink of 0.5K/W, which totally makes 0.87K/W with ideal heatsink (thermal resistance of 0K/W).

theraml difference is: 0.87K/W*340W = 295.8K

As the junction max temperature is 150C, then the heatsink temperature must be 150C - 295.8K = -145.8C

Anyone here has liquid nitrogen? I dont think so.
I just wonder why they write such things in the datasheet...
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Old 19th August 2006, 03:39 PM   #6
flg is offline flg  United States
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I believe the 340W number is at 25 degrees C??? This is not meant to be a continuos rating. There is also a derating factor you must subtract from the Pd number. Look at the safe operating area curves (SOA)... They show pulsed operation - continuos operation including package limitations. Very often you can only get up to about 1/3 that max Pd number.
You might try imersing the devices in chiled flourenert. Like the early Cray Supercomputors
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Old 19th August 2006, 05:33 PM   #7
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And looking at the circuit diagram, each half of the output stage draws 300mA; is that Class A Iq? What about thermal runaway because there is no Vgs/Vbe stage?
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Old 19th August 2006, 06:52 PM   #8
flg is offline flg  United States
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Hey, your right Samuel Jayaraj.
Am I seeing that right?
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Old 19th August 2006, 10:35 PM   #9
flg is offline flg  United States
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I did a quick sim of a similar circuit and yes it works I used different devices/resistances etc and only the 2nd and Output stages. You get a little DC at the output (I had about 800mV) due to the 10K bias and 2K refrence resistors but, that's really not a problem...
I'll go play a little more... I'ld like to see just what's really going on here and what the current ballance really looks like. Of coase the class A, AB etc also...
Just as I thought. Although looking at the load voltage, and as I'm using a resistor, the load current, it looks class A. But Looking at the source currents in the output devices you are only seeing 1/2 the signal on each source. Class B...
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Old 19th August 2006, 11:51 PM   #10
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Well, this thing won't let me edit that last post again? Oh well. So, I raised my Output device Iq to about 2A and I'm only using 25V Output supplies. With this configuration we are very close to Class A, when driving Iq or less into the load. Simulated distortion is quite good. As you attempt to drive the load beyond Iq, the current balance shifts. It still maintains the voltage at the load. Both absolute and differential. But the positive going and negative going current waveform of each Output, developes a nonlinear characteristic. More negative in one side while less postive in the other, and the opposite on the other half cycle. This is what I would refer to as going towards Class B or Class AB. I don't beleive this is exactly class AB though because we are talking about 2 amplifiers in series.
My simpler version of Circlotron and I believe Grey's Nu-Tron also, have this function... Distortion tends to worsen somewhat when you try to drive the load beyond Iq.
djk, since you were wondering if it works? I hope this was of interest
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