The simplistic Salas low voltage shunt regulator
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 30th September 2012, 12:42 PM #5411 Dr.H diyAudio Member   Join Date: Apr 2002 Thx Salas, Idss of 7.5mA on the K170's on the Zobel R, could that be 0.8 as 2x 0.4R? And the 560R on the current mirror. Would 470R suffice? Last edited by Dr.H; 30th September 2012 at 12:53 PM.
 30th September 2012, 03:55 PM #5412 Dr.H diyAudio Member   Join Date: Apr 2002 I'll get the required components tomorrow, LOL. What determines the range of the reg? I have built the 5V version, using 1K pot in series with a green LED. I have 18V input and yet my output range is just between 5V and 6V...
 30th September 2012, 08:04 PM #5413 Salas   diyAudio Chief Moderator     Join Date: Oct 2002 Location: Athens-Greece See #5395
 1st October 2012, 07:55 AM #5414 Phisci   diyAudio Member   Join Date: Aug 2012 Thx Salas, saw that. Still not sure why the 1k pot would only give me a range from 5 to 6V. Even the formula would suggest a broader range.
 1st October 2012, 08:37 AM #5415 Salas   diyAudio Chief Moderator     Join Date: Oct 2002 Location: Athens-Greece The setting resistor should not be allowed to fall bellow 1/3 of its opposite 1K resistor, the one between the Mosfet's gate stopper and ground. Thus 330R run by about 4Vgs/1K=4mA mirrored, gives 1.32V. Add 2V from the LED and two 0.7Vbe from the right branch mirror BJTs. That gives you the near 5V base. I would expect 4.7-7.4V with 1K VR. Tolerances or some problem may have squeezed that to 5-6V? We should know the practical Vgs, LedVf and Vbe in a build to see if it computes.
see2
diyAudio Member

Join Date: May 2010
Hello,

If placing V1.2R LV sensing part near load circuit, big in size C1 (4.7uf) becomes an issue.
Can it value be greatly lowered, to 10n, and for low output impedance R10 also lowered, from 27k to 2k, and R9 adjusted? See attachment for 5v output. It simulates ok, near DC impedance only about 1.5-2 times bigger than with big C1. Does it has negative effects?
Also, what limiting use of 2sk170 as q8 and q3? (For output 5-15v, input 12-23 v)
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 1st October 2012, 12:02 PM #5417 Salas   diyAudio Chief Moderator     Join Date: Oct 2002 Location: Athens-Greece On which schematic the designations you talk refer to? If you will run a noise simulation you will see the problem with 10n. Its not only about impedance. Use a compact electrolytic 16V with very low ESR & HF impedance 1000uF if you plan for digital. That can filter deeply and have good impedance on low VrefR also. You can find a multitude of computer motherboard capacitors offered cheaply with those characteristics. For J3 in the schematic you show here K170BL can do because in low voltage its high idss will not overheat Q18. Although I would prefer you cut its idss down to 2mA with a resistor for Q18 to work in a less noisy manner. If the other position you refer to is some common gate top half of a cascode CCS to another K170 , forget it, you need double the Vgs and up, for top half. So to have some Vds for bottom. Try a J310 or BF245C.
roender
diyAudio Member

Join Date: Sep 2006
Quote:
 Originally Posted by Salas Although I would prefer you cut its idss down to 2mA with a resistor for Q18 to work in a less noisy manner.
Any degeneration resistor will increase noise not vice versa. Moreover, jfets are less noisier at higher currents

 1st October 2012, 01:20 PM #5419 Salas   diyAudio Chief Moderator     Join Date: Oct 2002 Location: Athens-Greece If he will use 100 Ohm between g&s on an average BL to go ~2-3mA, the contribution is going to be 0.18uV for 20kHz BW.The original calls for a low noise VHF 2-3mA Idss Jfet for Q18's load anyway. No resistors, low capacitance semi. Q18 is a bjt. Current noise also.
 1st October 2012, 01:27 PM #5420 Dr.H diyAudio Member   Join Date: Apr 2002 Thanks Salas, will measure Vgs, LED Vf and Vbe and see

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