Go Back   Home > Forums > Blogs > rjm

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Voltage Regulators A series of articles about voltage regulator circuits.
Old

Voltage Regulators for Line Level Audio. Part 10 : Simple Shunts

Posted 11th April 2014 at 06:59 AM by rjm
Updated Yesterday at 11:52 PM by rjm

Part of a series.

I've been meaning to take up shunt regulators for some time. I've never got around to building one myself to try, so I'll have to make do by playing in simulation.

Today's circuit is the shunt analog of the Z-reg series regulator: no feedback, Zener reference, single transistor regulation. The output impedance and ripple rejection-characteristics are similar too, with about 40 dB of RR and an output impedance of just a few ohms. It can be built equivalently from either an pnp or pnp transistor. (See attached LTSpice .asc files.)

The difference between shunt and series regulation can best be explained by considering the upstream power supply: In a series regulator an increase in current demand by the load causes the regulator to increase the current to compensate. In a shunt regulator an increase in current demand by the load causes the regulator to decrease the shunt current to balance, so there is no net change in current flowing...
Attached Thumbnails
Click image for larger version

Name:	voltageregulator8ripple.png
Views:	33
Size:	92.7 KB
ID:	1265   Click image for larger version

Name:	voltageregulator8zout.png
Views:	24
Size:	87.7 KB
ID:	1266  
Attached Files
File Type: asc voltageregulator8-npn.asc (1.5 KB, 12 views)
File Type: asc voltageregulator8-pnp.asc (1.5 KB, 9 views)
rjm's Avatar
rjm
diyAudio Member
Views 67 Comments 0 rjm is offline
Old

Voltage Regulators for Line Level Audio. Part IX : Two Transistor Series Regulator

Posted 20th February 2014 at 11:50 PM by rjm
Updated 4th March 2014 at 01:56 AM by rjm

Part of a series.

So you have a small handful of parts and want to build a (simple) discrete voltage regulator instead of using an IC. What to do?

For line-level audio circuits, especially op amp based (IC or discrete) preamps with high PSRR, something like the Z-reg is generally sufficient. Robust, works well, has enough ripple rejection to cut power line noise from the preamp output.

If you add just a couple more parts, however, you can add feedback to the Z-reg circuit, a simple error amplifier in the form of an additional transistor Q2, with the output-sampling voltage divider R1,R2.

The ripple rejection is not vastly superior to the circuit without the feedback unless some additional bypass capacitors are added as shown in the first version of the circuit below. The output impedance, however, improves from a few ohms to a few tenths of an ohm as a result of the feedback. Which could, in principle, be of use.

...
Attached Thumbnails
Click image for larger version

Name:	voltageregulator7 ripple.png
Views:	181
Size:	88.8 KB
ID:	1244   Click image for larger version

Name:	voltageregulator7s ripple.png
Views:	111
Size:	89.0 KB
ID:	1245  
Attached Files
File Type: asc voltageregulator7.asc (2.3 KB, 53 views)
File Type: asc voltageregulator7s.asc (1.7 KB, 51 views)
rjm's Avatar
rjm
diyAudio Member
Views 424 Comments 2 rjm is offline
Old

Voltage Regulators for Line Level Audio. Part VIII : The Teddyreg

Posted 19th February 2014 at 01:44 AM by rjm
Updated 19th February 2014 at 01:46 AM by rjm

Part of a series.

The circuit is described here.

I'm not going to spend too much time on this one. The idea is to increase the input impedance of the pass transistor by buffering it with a jFET so it will support a high-impedance passive CRCRC filter section that generates a low noise reference voltage. The reference is defined not by a Zener or diode stack, but by a simple voltage divider. There is a LM317 pre-regulator on the front, but it is traditionally configured and works independent of the following circuit so it is omited here together with the additional transistor that speeds up the charging of the reference voltage filter capacitors.

The basic problem is that lowering the noise of the reference cannot lower the output noise indefinitely. After a point the output noise is defined by the performance of the pass transistor instead.

As you can see from the simulation, the circuit has the same ripple rejection as the filtered zener-referenced one-transistor regulator,...
Attached Thumbnails
Click image for larger version

Name:	voltageregulator-treg ripple.png
Views:	95
Size:	98.1 KB
ID:	1241   Click image for larger version

Name:	voltageregulator-treg Zout.png
Views:	71
Size:	93.3 KB
ID:	1242  
Attached Files
File Type: asc voltageregulator-treg.asc (2.4 KB, 47 views)
rjm's Avatar
rjm
diyAudio Member
Views 267 Comments 0 rjm is offline
Old

Voltage Regulators for Line Level Audio. Part VII : The k-multiplier

Posted 17th February 2014 at 11:55 PM by rjm
Updated 18th February 2014 at 12:08 AM by rjm

Part of a series.

This circuit is from this page by Kean Token, also referenced in his recent blog post.

Two versions are presented, one with all the protection diodes and a simplified version with extraneous components removed.

LTSpice simulation shows so-so performance into a light load, with about 70 dB of ripple rejection and a fairly high output impedance, but the drop out voltage is respectably low and we must factor in - coming directly from the Jung Super Regulator - that this is just a two transistor circuit, with no error amplifier to provide feedback.

As a frame of reference, it is quite similar in performance to the Z-reg we looked at back in part III.

The k-multipler is of a class of voltage regulators where the output is referred to the input voltage, rather than to ground. It provides "X volts less than the input", rather than the traditional regulator which provides "X volts above zero"....
Attached Thumbnails
Click image for larger version

Name:	voltageregulator-kmult ripple.png
Views:	81
Size:	97.3 KB
ID:	1235   Click image for larger version

Name:	voltageregulator-kmult Zout.png
Views:	45
Size:	98.9 KB
ID:	1236   Click image for larger version

Name:	voltageregulator-kmult simple ripple.png
Views:	50
Size:	95.3 KB
ID:	1237   Click image for larger version

Name:	voltageregulator-kmult simple Zout.png
Views:	48
Size:	95.7 KB
ID:	1238  
Attached Files
File Type: asc voltageregulator-kmult.asc (2.9 KB, 45 views)
File Type: asc voltageregulator-kmult-simple.asc (2.1 KB, 51 views)
rjm's Avatar
rjm
diyAudio Member
Views 268 Comments 0 rjm is offline
Old

Voltage Regulators for Line Level Audio. Part VI : The Jung Super Regulator

Posted 13th February 2014 at 04:21 AM by rjm
Updated 14th February 2014 at 10:52 AM by rjm (clean up)

In the next part of the series, I'll be presenting various published regulator circuits.

Today we have the "Jung Super Regulator" (2000 version) on deck, thanks to Tangentsoft's excellent write-up.

In translating the circuit to LTSpice, I've made some concessions. While I have kept the protection diodes so as to be consistent with the original - even if they do nothing in this simulation - the op amp, transistors, voltage regulator and reference have been substituted with working equivalents from the LTSpice libraries. I've been approximate in the resistance and capacitance values, and tuned the circuit to output 10 V at 10 mA to keep in line with the previous circuits I've uploaded.

It works though, and, under simulation at least, it works extremely well. Putting it together in LTSpice gave me a new appreciation for just how much work and refinement went into its design. Now, its an open question whether such over-the-top performance...
Attached Thumbnails
Click image for larger version

Name:	voltageregulator-jung.png
Views:	174
Size:	44.8 KB
ID:	1231   Click image for larger version

Name:	voltageregulator-jung ripple.png
Views:	97
Size:	99.0 KB
ID:	1232   Click image for larger version

Name:	voltageregulator-jung Zout.png
Views:	82
Size:	94.8 KB
ID:	1233  
Attached Files
File Type: asc voltageregulator-jung.asc (5.7 KB, 73 views)
rjm's Avatar
rjm
diyAudio Member
Views 410 Comments 0 rjm is offline
Old

Voltage Regulators for Line Level Audio. Part V : Graduation Day

Posted 20th January 2014 at 03:32 AM by rjm
Updated 20th January 2014 at 10:21 PM by rjm

Part five of a series.

Last time, we'd got to a functional voltage regulator, with a pass transistor and op amp error amplifier but I cheated and used ideal voltages for the reference and op amp power supply.

This time I've sketched out a functional circuit using real parts found in the LTSpice library. I've chosen a rail-to-rail op amp to avoid problems with low voltage references. The LT1009 reference puts out 2.5 V, the op amp gain is 4, for an output of 10 V into 1 kohms.

Two versions of the circuit are included below. Voltageregulator5 has some additional RC filter stages to remove noise from the reference and op amp power supply Voltageregulator5b just takes everything straight from the input voltage. As you can see there's a fairly substantial advantage gained from judicial use of RC filtering.

So that's the end of Term 1. The basics have been covered, however briefly. I encourage you to download the LTSpice files and play...
Attached Thumbnails
Click image for larger version

Name:	voltageregulator5.png
Views:	196
Size:	61.6 KB
ID:	1226  
Attached Files
File Type: asc voltageregulator5.asc (2.8 KB, 72 views)
File Type: asc voltageregulator5b.asc (1.9 KB, 56 views)
rjm's Avatar
rjm
diyAudio Member
Views 332 Comments 0 rjm is offline
Old

Voltage Regulators for Line Level Audio. Part IV : The Error Amplifier

Posted 18th January 2014 at 06:05 AM by rjm
Updated 20th January 2014 at 10:21 PM by rjm

Part 4 for a series.

At the end of Part 3 I promised to introduce feedback, and I will, but what we are really talking about here is the addition of the error amplifier, the heart of all modern series pass regulators. The error amplifier is a non-inverting DC signal amplifier, and its function is simple: amplify and buffer the reference voltage. The twist is that the amplifier output is connected to the base of the pass transistor, while the feedback connection is taken from it’s emitter. The pass element is thus placed inside the feedback loop of the error amplifier, improving the ripple rejection and output impedance of the regulator dramatically.

So here we are, the three building blocks of a voltage regulator are in place: the reference voltage, the error amplifier, and the pass device. In the LTSpice circuit I’ve cheated, deliberately, in order to make the operation easier to follow. Instead of building a practical voltage reference I’ve...
Attached Thumbnails
Click image for larger version

Name:	voltageregulator4.png
Views:	123
Size:	43.1 KB
ID:	1223   Click image for larger version

Name:	voltageregulator4b.png
Views:	118
Size:	41.9 KB
ID:	1224  
Attached Files
File Type: asc voltageregulator4.asc (1.9 KB, 53 views)
rjm's Avatar
rjm
diyAudio Member
Views 344 Comments 0 rjm is offline
Old

Voltage Regulators for Line Level Audio. Part III : The Z-reg

Posted 17th January 2014 at 04:35 AM by rjm
Updated 20th January 2014 at 10:21 PM by rjm

Part 3 of a series.

I’m going to have to make a detour to point out what we are doing here is learning how these circuits work, and get a very rough idea of their relative merits. We’re not trying to minimize the output impedance, or maximize the ripple rejection. Three reasons immediately come to mind for why it would be bad practice to try and do that:

1. Any such contest will be easily won by the largest capacitor placed on the regulator output.

2. There are clear limits on these parameters after which further “improvement” is unlikely to serve any useful purpose.

3. There are other considerations such as the output noise of the regulator and the stability under dynamic loads, which are equally if not more important.

Clear? No cookies for the “most bestest” circuit in LTSpice. The great utility of LTSpice is it allows you, the designer, to easily check if you’ve left performance...
Attached Thumbnails
Click image for larger version

Name:	voltageregulator3.png
Views:	147
Size:	95.2 KB
ID:	1220   Click image for larger version

Name:	voltageregulator3b.png
Views:	118
Size:	97.5 KB
ID:	1221   Click image for larger version

Name:	LM317.png
Views:	72
Size:	37.2 KB
ID:	1222  
Attached Files
File Type: asc voltageregulator3 (zreg).asc (1.7 KB, 59 views)
rjm's Avatar
rjm
diyAudio Member
Views 377 Comments 0 rjm is offline
Old

Voltage Regulators for Line Level Audio. Part II : The Pass Transistor

Posted 16th January 2014 at 04:14 AM by rjm
Updated 20th January 2014 at 10:21 PM by rjm

Part 2 of a series.

Instead of pulling the output current through R1, we add an npn pass transistor, Q1. The output current now "passes" through the transistor, while the Zener diode still regulates the output voltage by being connected to the transistor base.

The output impedance falls to a few ohms, but the ripple rejection improves only slightly.

This is a useful basic circuit block for audio, but the ripple rejection can easily improved by the addition of a couple of additional components, as we'll see shortly.
Attached Thumbnails
Click image for larger version

Name:	voltageregulator2.png
Views:	139
Size:	90.6 KB
ID:	1217   Click image for larger version

Name:	voltageregulator2b.png
Views:	87
Size:	92.7 KB
ID:	1218  
Attached Files
File Type: asc voltageregulator2.asc (1.2 KB, 60 views)
rjm's Avatar
rjm
diyAudio Member
Views 277 Comments 0 rjm is offline
Old

Voltage Regulators for Line Level Audio. Part I : Zeners

Posted 15th January 2014 at 11:34 PM by rjm
Updated 16th January 2014 at 04:40 AM by rjm

This is the first of a series, where I will be investigating the output impedance and ripple rejection of various voltage regulator circuits using LTSpice.


Today, for the first "lesson" (I'm teaching myself, as much as anything) we will look at the very simple zener voltage regulator.

The load is 1 kohm, and the Zener breakdown voltage is 12 V. The load current is about 10 mA, and to avoid gross inefficiency we will limit the current flowing through the Zener to about 5 mA, by adjusting R1 accordingly. The input voltage is fixed at 18 V.

To measure the ripple rejection, we perform an AC analysis with the voltage source AC set to 1 and the current source AC set to zero. The ripple rejection is the negative value of the signal at Vout: so -20 dB means 20 dB ripple rejection (1 V ripple at Vin generates 0.1 V ripple at Vout at a given frequency.).

To measure the output impedance, again the AC analysis function is used but...
Attached Thumbnails
Click image for larger version

Name:	voltageregulator1.png
Views:	116
Size:	92.9 KB
ID:	1213   Click image for larger version

Name:	voltageregulator1b.png
Views:	99
Size:	92.6 KB
ID:	1214  
Attached Files
File Type: asc voltageregulator1.asc (1.1 KB, 63 views)
rjm's Avatar
rjm
diyAudio Member
Views 305 Comments 0 rjm is offline
Hide this!Advertise here!

New To Site? Need Help?

All times are GMT. The time now is 11:48 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2