Circlotron

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 150°C, then the heatsink temperature must be 150°C - 295.8K = -145.8°C :cool:

Anyone here has liquid nitrogen? I don´t think so.
I just wonder why they write such things in the datasheet...
 

flg

Member
2005-07-06 1:13 am
North East
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. :cool: :smash: :hot:
You might try imersing the devices in chiled flourenert. Like the early Cray Supercomputors:D :D :D
 

flg

Member
2005-07-06 1:13 am
North East
I did a quick sim of a similar circuit and yes it works:bigeyes: 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...
 
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:D :D :D
 

Babowana

Formerly "jh6you". R.I.P.
2006-07-13 4:23 pm
www.aheadamp.com
I do not know Japanese well, but tried to read the circuit test note.

It says:

"There were noise from the transfomer, but a good thing was there was no power on/off pop noise . . . Output impedence was abt 0.4ohms . . . In the middle of test, over-current happened so that 2 sets of 2SK1529 were broken . . . "

Thermal runaway?
 

flg

Member
2005-07-06 1:13 am
North East
Wow, Does that feedback form a type of X circuit:confused: :confused: :confused:
The circuit would work without overtemping as long as you (not You JH) don't try to run continuos sine waves or something at full power. The voltages are high enough for good headroom though;)
It is Class AB though, and the real beauty of the Circlotron is not being taken full advantage of:whazzat: