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Old 16th August 2012, 04:17 PM   #801
lhquam is offline lhquam  United States
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Quote:
Originally Posted by tadek View Post
Hi,
to avoid capacitors in signal path - that should be possible to use two identical DC current sources.
Drop voltage on each of secondary winding ( Resistance part ) will serve as necessary bias, and final magnetic flux remain 0.
Hopefully Mr.Pass will forgive me that "reuse" of his drawing.

I ran a Spice simulation of your idea and it looks good. The LT3092 regulator looks like it would do the job for the current sources.
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Old 16th August 2012, 04:43 PM   #802
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what about tl431. Not as simple but has some history.
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Old 16th August 2012, 06:04 PM   #803
lhquam is offline lhquam  United States
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Quote:
Originally Posted by buzzforb View Post
what about tl431. Not as simple but has some history.
Yeah, there are probably many other regulators that will work. The LT3092 just happened to be one that I found an application note for and a Spice model.
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Old 16th August 2012, 06:16 PM   #804
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Quote:
Originally Posted by buzzforb View Post
what about tl431. Not as simple but has some history.
buzzforb: I recall TL431 to be a low power regulator. May/will not handle the 43 mA demand multiplied by the rail voltage.
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Old 16th August 2012, 06:19 PM   #805
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100mA continuous.
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Old 16th August 2012, 06:21 PM   #806
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Old 16th August 2012, 06:29 PM   #807
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There is also max Pd to consider. In a typical BA-2/BA-3 style bias maybe 45mA with 4.4V for Tosh and 8.2V for Fairchild. Any of the pkg styles offered should do that
You should also consider the Pd with signal applied..
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Old 16th August 2012, 07:08 PM   #808
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Dear DIYers. I stand [and sit] corrected about power dissipation. But; TL431 is a shunt regulator; a zener with a dynamic resistance of 0.2 Ohms between its anode and cathode. Thus, it is an AC short between the positive rail and the transformer winding of the upper JFET. The second TL431 is also an AC short between the output and the secondary winding of the lower JFET.

The original suggestor may have envisioned an LM317 positive voltage regulator connected as a constant current source. The Vo output port of LM317 is connected to one end of an 28 Ohm resistor, and the adjustment pin of LM317 is connected to the other end of this resistor. The output current is 1.25 V/28 Ohm = 0.045 A.

Last edited by Antoinel; 16th August 2012 at 07:10 PM.
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Old 16th August 2012, 07:10 PM   #809
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The TL431 can be run as a current source. Not saying it will work, just not limited to shunt operation.
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Old 16th August 2012, 07:55 PM   #810
lhquam is offline lhquam  United States
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I found a problem with the LT3092, TL431, and LM134 regulators. The maximum voltage across the devices is 40V, which is not enough for an amplifier with 24 volt rails. Back to the drawing board.

Edit: I might have to backtrack on that observation. Figure 22 in http://www.onsemi.com/pub/Collateral/TL431-D.PDF show the use of an NPN transistor with the TL431 to create a constant current source. The voltage across the TL431 is limited to the voltage across Rcl Plus Vbs of the NPN transistor. The Vce of the NPN transistor must be high enough for rail voltages, in this case, at least 50 volts.

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