TL431 High Voltage Regulator - How to get it thermally stable? - Page 4 - diyAudio
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Old 15th March 2014, 03:48 PM   #31
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Originally Posted by Elvee View Post
You need to fix the transistor's base potential.

Now, it still requires some compensation to work properly
hi Elvee, this is really help. thank you very much. will you be able to simulate the thetmal stability of the circuit? i think the zener can be replaced with a current source. do you think it will make it better?
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Old 15th March 2014, 05:27 PM   #32
dmills is offline dmills  United Kingdom
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A current source would make it worse not better as you want the base at a fixed voltage not one which tracks with the output (which would be positive feedback).

Stop messing about in spice and BUILD the damned thing, while I would add a cap across the zenner to lower the noise and another one to stabilise the loop, the basic idea will work and should be reasonably stable with temperature.

Regards, Dan.
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Old 15th March 2014, 05:28 PM   #33
Elvee is online now Elvee  Belgium
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Originally Posted by jazzclassics View Post
hi Elvee, this is really help. thank you very much. will you be able to simulate the thetmal stability of the circuit?
Here you are, but thermal stability is not exactly a priority if there are dynamic instablities
Quote:
i think the zener can be replaced with a current source. do you think it will make it better?
No
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Old 16th March 2014, 12:13 AM   #34
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Originally Posted by jazzclassics View Post
ilimezn, the question is how to get it thermally stable. the circuit works in simulation as well as in real world experiment. the only problem with it is the drift.

is there anybody who care for the 431 behavior when its working condition is out of the spec?
In your circuit you are just using the base-collector junction of one of the transistors inside the TL431 (as shown in the attachment) in series between your NPN transistor and the feedback divider.

If you want the TL431 to work in the way it is intended to, for starters the feedback polarity is wrong in your circuit even if you were to provide the TL431 with cathode current.
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Old 16th March 2014, 12:24 AM   #35
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Originally Posted by dmills View Post
A current source would make it worse not better as you want the base at a fixed voltage not one which tracks with the output (which would be positive feedback).

Stop messing about in spice and BUILD the damned thing, while I would add a cap across the zenner to lower the noise and another one to stabilise the loop, the basic idea will work and should be reasonably stable with temperature.

Regards, Dan.
hi Dan, i meant voltage souce formed by a current source and a load. thanks for your suggestion.
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