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Old 22nd August 2010, 05:52 PM   #1
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Default Discrete Regulator for VAS and Input Stage

Hi, I thinking to build a discrete regulator for VAS and input stage.
The amplifier not use negative feedback, so I need a very low noise PSU.

I use a doubler voltage + capacitance multiplier + discrete regulator (I donīt want use another transformer), so with Vac=20Vpp, Vout=27.9V(zener).
Rippley = 5.72uV with Rload = 220ohms (this is 126.81mA)

The components are standard, BC547, BD139(MJE340), BC337, BF245.

A appreciate any feedback about this circuit.
Attached Images
File Type: gif Reg PowerSupply.GIF (16.5 KB, 374 views)
File Type: gif Vout.GIF (9.0 KB, 355 views)
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Old 22nd August 2010, 06:17 PM   #2
AndrewT is offline AndrewT  Scotland
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I don't follow the voltages.
The transformer is 20Vpp but after the first regulator/multiplier you have over 32Vdc.

Is the transformer 6Vac or 12Vac? or something else?

R13 is passing ~2.7mA. R11 is passing ~0.26mA.
Is the rest of the current, ~2.4mA, passing R18?

For a balanced LTP you need Q4 & Q5 to pass the same Id +-1%

Does C7 attenuate the ripple reaching the LTP and thus prevent the LTP passing a ripple correction signal to the Vreg transistors
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Last edited by AndrewT; 22nd August 2010 at 06:26 PM.
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Old 22nd August 2010, 08:07 PM   #3
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Hi Andrew.

After the voltage doubler, I donīt have 40V or a near value , I donīt know why. The voltages are in the first picture.

For balanced Iq maybe I can use current mirror with the LPT, as show in the next picture. R11 = R18 = 1k, is too high?
In the new schematic, Vout=27.794V and Vrippley=378uV (after 0.6sec).
BUT Icīs are differents:
Ic(Q4) = 527uA and Ic(Q5) = 2.607mA ...

Maybe change Q17 for darlington transistor, like BC337+BD139.

I use C7 to reduce the ripple present in the base of Q5. I will try without this capacitor.

Cheers

Edit1
With R11=R18=100 and Darlington output transistor, Ic(Q4) = 1.5785mA and Ic(Q5) = 1.5638mA, this is Iunbalance = 14.667uA.
Attached Images
File Type: gif Outs.GIF (19.5 KB, 317 views)
File Type: gif Iq (with Current Mirror).GIF (5.9 KB, 297 views)
File Type: gif Rev Version 1.1.GIF (15.6 KB, 306 views)
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Last edited by Havenwood; 22nd August 2010 at 08:16 PM.
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Old 23rd August 2010, 02:28 AM   #4
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I'm not sure I understand how Q1-Q3 are supposed to "regulate". It just looks an RC filter on the base, not really a regulator. Is this all that is intended?

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Kevin
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Old 23rd August 2010, 04:30 AM   #5
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Hi Kevin. Q1-Q3 they arenīt to regulate. This transistors and C3-C4 are the capacitance multiplier.
Capacitance Multiplier Power Supply Filter

The discrete regulator consist in voltage doubler + cap multiplier + regulator.

The regulator is the LPT and Q25/Q17.

Here, is the version 2 of the regulator, ando some pictures under differents loads. In the next day I hope build the regulator on protoboard and take some photos.
Attached Images
File Type: gif Circuit v2.GIF (14.4 KB, 145 views)
File Type: gif Vout1.GIF (9.9 KB, 111 views)
File Type: gif Vout2.GIF (9.4 KB, 40 views)
File Type: gif Vout3.GIF (5.7 KB, 31 views)
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Old 23rd August 2010, 08:10 AM   #6
Mooly is online now Mooly  United Kingdom
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1n4148's ???????????
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Installing and using LTspice. From beginner to advanced.
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Old 23rd August 2010, 10:23 AM   #7
AndrewT is offline AndrewT  Scotland
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post3
The plot of 20vpp looks like 20Vpk (=40Vpp) to me.
That is ~12Vac, not ~6Vac that equates to 20Vpp.
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Old 23rd August 2010, 01:57 PM   #8
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Quote:
Originally Posted by Mooly View Post
1n4148's ???????????
No, I forget write that.

Pspice donīt have 1N400X series.
Diodes arenīt 1N4148 and Q17 is a BD140.
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Old 27th August 2010, 01:34 PM   #9
sajti is offline sajti  Hungary
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I think, that Your solution is overcomplicated. I want to use something similar. Attached the schematic.
The regulated +/-42V feeding the Vbe multiplier, the first EF stage in my hybrid amplifier, the +/-35V used by the output stage, and the +240V is for the tube VAS.

Sajti
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Old 28th August 2010, 03:20 AM   #10
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Sajti

I am curious about the role of T1 and T2. They create a current source that will stabalize the zener voltage with respect to input voltage changes?

Also, I know that the use of feedback in the audio path is frowned on by many, but need this also apply to power supplies? One more transistor and the circuit could supply a stable voltage with respect to output loading as well as input line changes.

Why not use a TL431 and have a band gap referenced voltage that would be stable with respect to changes in line, load and thermal conditions?

Cheers,
Kevin
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