need help understanding voltage regulator schematic (using CCS) from Raleigh Audio

[jarthel]

Here's the schematic: http://www.raleighaudio.com/ccs.htm

I'm somewhat confused on how to compute the output voltage since R1 and R2 is limited to combinations that produces 2.5V across R2. Is there a formula?

also what kind of triode can I use? can I use 6as7 (the only non-matched tube that I got and I have 2 of them)?

thank you.

[Wavebourn]

Originally posted by jarthel
Here's the schematic: http://www.raleighaudio.com/ccs.htm

I'm somewhat confused on how to compute the output voltage since R1 and R2 is limited to combinations that produces 2.5V across R2. Is there a formula?

Use Ohm's law. Also, a datasheet on the IC may help, to determine range of resistors depending on currents the IC draws.

also what kind of triode can I use? can I use 6as7 (the only non-matched tube that I got and I have 2 of them)?

thank you.

It depends on the current and voltage you need to stabilize.

[jarthel]

Originally posted by Wavebourn


Use Ohm's law. Also, a datasheet on the IC may help, to determine range of resistors depending on currents the IC draws.

it's easy to say ohm's law. but should I use R1 or R2? maybe both? I honestly do not know.

[Wavebourn]

Originally posted by jarthel



it's easy to say ohm's law. but should I use R1 or R2? maybe both? I honestly do not know.

Ok, suppose the IC does not draw a current through the gate;
now let's the current across resistors will be 1 miliamper, so R2 will be 2.5 KOhm. So, to regulate 150V you'll need (150-2.5)=125.5 KOhm, for 250V you will need 225.5 KOhm, and so on...

But I still don't understand why do you want to vaste a tube if you can use one zener diode, or a zener with a transistor if you don't have powerful enough zener?

Suppose, the tube's filament opens up, then unregulated high voltage goes to where lower regulated should go... Also, it is high and unregulated while the tube is cold...

[poobah]

Jarthel,

The equation for the voltage at the input to the TL431 is:

Vin = Vshunt * [ R2 / (R1 +R2)]

Now... declare Vin to be 2.495 Volts.

Put these into the equation and solve for R1:

R1 = (R2 * ( Vsh - 2.495 )) / 2.495

How to choose R2? I just happen to know that 24.9kOhms is a good value for R2. Here's why: R2 should always have 2.5 Volts across it... so we know the current flowing through it. The input to the TL431 steals a little current from the divider, but we don't want this "theft" to cause an error. Furthermore, the amount of current it steals changes all over with temperature.

So we want the current flowing through R1 & R2 to look huge in comparison to little current being stolen... thats where the 24.9k comes in. So look up the "input bias current" for the TL431... then calculate the current in R2... and you can figure out the "swamping factor".

[jarthel]

the raleight audio website also said to play around with R1 and R2 to get the desired output B+ voltage.

I can understand the functions of R1 and R2 to get the 2.5V requirement for the TL431.

but what is R1 and R2's relationship to the output B+ voltage?

thank you very much

[jarthel]

Originally posted by Wavebourn


So, to regulate 150V you'll need (150-2.5)=125.5 KOhm, for 250V you will need 225.5 KOhm, and so on...

how did you come up with 125.5Kohm?

I was thinking along the lines of

150V - 2.5V = 147.5V / 1mA = 147.5Kohm?

say the unregulated voltage across from across R1 and R2 combined is 300V. (not sure if this info is even important)

thank you.

[poobah]

The voltage I called Vshunt, or Vsh, is the same as B+. Sorry, I think in terms of the circuit.

Does that clear things up?

'ang on mite... If B+ (Vsh) goes up, then the 2.5 V goes up too. Then the TL431 starts sinking more current to ground through itself and the tube... and it keeps doing this until its input comes back to 2.5 Volts. You see the TL431 is actually a clever little gizmo... it is an op-amp with a "current" output, and a voltage reference all wrapped in one neat little package.

Now... this is a shunt regulator... you do want a shunt right???

[poobah]

Jarthel,

What exactly are you trying to regulate? I ask because shunt regs have to be applied rather carefully...

The is a bit abstract but, shunts are to used to regulate a current. That is not to say it is a "current regulator"... it's not. A shunt regulator needs to have a current source for a supply... not a voltage.

Just one resistor solves all this basically...

[jarthel]

hope this text schematic comes out clearly

230VAC transformer secondary -> tube rectifier -> choke (10H 90ohm) -> 100uF -> CCS circuit (70ma? - not sure yet) (as found in Bas Horneman's website) -> the voltage regulator as found in the raleigh audio website.

using PSUD2, the voltage across the 100uF is 170VDC. I need 150VDC at the output of the raleigh audio circuit.

I'm just confused on how to calculate the R1 and R2 values to get the 2.5V for the TL431 and at the same time, the resistor values will determine the B+