File:Regulated 6.3V heater DC from two Li-ion cells.png

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Captions

Captions

Schematic for a low-dropout linear voltage regulator, NMOS+TL431

Summary

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Description
English: Low-dropout heater DC regulator for a battery-powered tube preamp. These days, mains power is so dirty, and lithium cells so inexpensive, that all-battery-powered amplification is a viable reality.
  • Two lithium cells in series (7.0 ... 8.5V) -> 6.3V DC.
  • No fine adjustments necessary with 1% resistors.
  • CSS of 1000 uF provides around 10s soft-start ramp. There is no provision for a forced discharge at power-off, not really necessary.
  • There is no buffer capacitance at either input or output, not really necessary. No capacitance - no protection diodes. Likewise, there is no need to protect the MOS gate in a 8V non-inductive environment.
  • Current overhead: 3 mA max to feed the TL431 and its voltage divider
  • Watts dissipated across the MOS (worst-case at 8.5V in): 2.2W per 1A output current
  • Any low-voltage NMOS power transistor will do, provided that (a) it's gate levels are "normal" and not "logic level" (b) Rds is low enough so that Rds*Iout is not more than 0.5V (which is almost always the case), and (c) that it is properly heatsinked for the intended current at the highest Vin-Vout point (around 2.4 V max). I only used normal-level transistors and currents of 0.6 to 2A. With "logic-level" transistor the TL431 may not regulate properly. Never tested it, just a suspicion.
  • The circuit can be grounded at either terminal. Or tied to a raised potential for low noise, or left floating. Just make sure that the heater battery currents don't pass through the audio circuit.
  • There is no undervoltage monitor; the circuit will happily regulate even when the battery is drained to death (below 3.5V per cell). Take care.
Date
Source Own work
Author Retired electrician

Licensing

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I, the copyright holder of this work, hereby publish it under the following license:
Creative Commons CC-Zero This file is made available under the Creative Commons CC0 1.0 Universal Public Domain Dedication.
The person who associated a work with this deed has dedicated the work to the public domain by waiving all of their rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law. You can copy, modify, distribute and perform the work, even for commercial purposes, all without asking permission.

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Date/TimeThumbnailDimensionsUserComment
current15:54, 18 March 2021Thumbnail for version as of 15:54, 18 March 20211,653 × 1,131 (169 KB)Retired electrician (talk | contribs)added Rgate
15:48, 18 March 2021Thumbnail for version as of 15:48, 18 March 20211,653 × 1,148 (169 KB)Retired electrician (talk | contribs)added Rgate
22:53, 11 March 2021Thumbnail for version as of 22:53, 11 March 20211,653 × 1,148 (144 KB)Retired electrician (talk | contribs){{Information |Description={{en|Low-dropout heater DC regulator for a battery-powered tube preamp. These days, mains power is so dirty * Two lithium cells in seriese -> 6.3V DC. * No fine adjustments necessary with 1% resistors. * CSS of 1000 uF provides around 10s soft-start ramp. * Any low-voltage NMOS power transistor will do, provided that (a) it's gate levels are "normal" and not "logic level" (b) Rds is low enough so that Rds*Iout is not more than 0.5V (which is almost always the cas...

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