Howto: TeddyReg

[teddy_pardo]

Here is an attempt to summarize the original long (and maybe confusing) TeddyReg thread. My preferred implementation is with a Fetlington (thanks to pigletsdad for the idea, and to agent_cooper79 for taking the initiative and providing the transistors).


I'll start with the diagram for the positive circuit:



Resistors R1 and R2 are used to set the voltage at the output of the linear regulator LR1.

The output is

Vlr1 = 1.25 x (1 + R1/R2)

R2 is anything between 100R and 1000R

The dropout on the gyrator is determined by the ratio of R3 and R4 plus the dropout on T1 and T2. The resistor dropout is a percentage of Vlr1 and is equal to Vlr1 x R3 / (R3+R4). The dropout on T1 and T2 is constant and equal to around 1V on load.

The list of components for a positive 25V regulator is:

R1 = 3.4K
R2 = 150R
R3 = 150K
R4 = 1M
R5 = 100K
R6 = 100-250R

C1 = 0.1uF X7R Ceramic
C2 = 10-20uF Tantalum
C3 = 10-20uF Tantalum
C4 = 20-33uF Tantalum
C5 = 0.1-0.3uF X7R Ceramic
C6 = 10-20uF Tantalum/Oscon or 100uF Silmic, or even better 1-10uF film capacitor (MMK/MKS)

T1 = 2SK117 - GR
T2 = D44H11
LR1 = LM317/LT1086

For the negative version

T1 = 2N5460 (note that the pin layout is different)
T2 = D45H11
LR1 = LM337 (note that the pin layout is different)
Obviously the capacitor polarity should be inverted.

I would recommend to divide the dropout between LR1 and the gyrator evenly. As an example, if the input voltage is 33V and you want the output to be 25V, set LR1 to 29V.

Notes:

1. The no-load voltage is around 0.5-1V higher than the on-load voltage. It is due to the fact that when no current passes through the transistors there is no dropout on them. It can be avoided by adding a 1K - 3K resistor at the output of the regulator, but it's usually not needed.

2. With high values of R3 (50K and above), it takes several seconds until the output voltage rise to the desired value. If you need faster settling use smaller resistors, but the results will not be as good.

3. If you don't want to bother with FETs which are sometimes hard to find, low noise bipolar transistors BC550C/BC560C provide very good results as well.

4. C1 is optional and required only if the regulator is far from the power supply.



Here are some pictures of a positive and negative regulators, mounted on a strip board. The board needs to be cut in one single place only, below the FET.









Hope that helps.

Enjoy, Teddy

[bivalve]

Teddy,

Very useful. I think you probably mean R2 is anything between 100R and 1000R.

Us battery powered types like to save juice, so 1000R when we can be sure that the following circuit will draw 10mA or more, and 100R when we can't, because LT1086/LM317 only operate correctly when supplying 10mA+. 100R will cause 12mA+ to flow out of the reg and down R2/R1.

Nice board you are using.

David

[teddy_pardo]

Thanks David, I've fixed it on the original message to avoid confusion

BTW, this board will soon become a three way active crossover...

[hacker]

Hi Teddy, are you no longer using the Sziklai pair configuration?

[teddy_pardo]

I use it in combination with a FET in the PowerReg

[Pulse Studio]

Hi Teddy, so is this the follow on from " The best Reg I've ever built " thread, if so thankyou for the neg supply.
Teddy I have some very nice axial Solid Tants akin to the Vishay types, these are made by Siemens & ITT, would these be a good replacement for the Tant Beads??
Thankyou for your help
Paul

[p.st]

Thanks Teddy, now I understand everything.

Peter

[teddy_pardo]

Originally Posted by Pulse Studio

I have some very nice axial Solid Tants akin to the Vishay types, these are made by Siemens & ITT, would these be a good replacement for the Tant Beads??

Do you mean wet or solid Tants? Axial are usually wet tantatlum and they work very well. I don't know about axial solid, but I guess that any tantalum will work well here.

[Pulse Studio]

Thanks Teddy, I believe they are solid types, they are damn heavy for the physical size, I have up to 180uF but only 6.3V, but I do have a couple of 33uF 25V and 47uF 25V, and some 100uF 20V, I also have some others 3.3uF 63V that are Filmcap TFI BD35A, they were all ex millitary caps.
Cheers
Paul

[teddy_pardo]

It sounds like you have wet tantalum caps. Yes, they are very good, you can also use them for coupling and feedback.

[Ruach]

Hi Teddy, what is the maximum current output for the TeddyReg?

Cheers

[teddy_pardo]

Depending on the dropout and the heat-sink, it can withstand 1.5A or even more. However, due to it's output impedance I wouldn't take it that far, especially if you have non-constant current loads. It is best used for preamplifiers, CD player analogue stages, DACs, crossovers, etc. that is several hundrads of mA, with constant current. For higher currents look at the PowerReg

[Ruach]

Some questions on the choices for the JFETs.

The higher the transconductance of the JFET, the lower the output impedance of the TeddyReg - am I right?

A 2SK117-BL will have a higher transductance than a 2SK117-GR, assuming the same gate pinch off voltage, and thus be a better choice - am I right?

[teddy_pardo]

The difference between the BL and GR is their Idss. This IMO will mainly have an impact on the initial no-load dropout, but I don't think that it will affect the output impedance. I have some GR and BL types, so I'll try to do some measurements and report.

[slawney]

Teddy,
what motivated you to choose 20-33uF Tant and 0.1-0.3uF X7R for C4 and C5? Did they measure better, sound better, or are they in fact better adapted to the circuit (for RF filtering)? Have you tried these same value/type caps in an ALWSR-based VBE, and were these caps suitable there as well? I tried modest-cost X2 caps you suggested in ALWSR-based VBE and they work very well...