# Circlotron

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#### djk

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.

#### UltimateX86

HI

you are certain that this diagram functions ?

THX

#### Nelson Pass

Paid Member
UltimateX86 said:
you are certain that this diagram functions ?

Hmmmm. Do you see a reason why not?

#### UltimateX86

Hello Nelson

No protection for the speaker ?

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

thx

#### kubeek

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

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

#### flg

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

#### Samuel Jayaraj

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?

#### flg

Am I seeing that right?

#### flg

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...

#### flg

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

#### Babowana

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

Looking at the Datasheet for the 2SK1529... Especially the SOA curves: I would suggest, testing continuosly, at low frequency, at full power, into 8 ohms. You better have that liquid Nitrogen running, or your output is toast. No running away involved!

#### Babowana

.

I think that the 10K feedback resistors control idling current stable.

#### flg

Wow, Does that feedback form a type of X circuit
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

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