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Old 26th September 2006, 07:07 AM   #11
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Quote:
Originally posted by 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+
Resistors represent a negative feedback. The IC compares the voltage on input against internal 2.5V it has "in mind", and if the voltage is higher it draws more current that causes the tube to draw more current until the IC sees 2.5V on the input, and vice versa.

You defenitely are asking wrong people why that particular guys put such strange schematics on their website. Ask them.
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Old 26th September 2006, 09:17 AM   #12
jarthel is offline jarthel  Australia
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Quote:
Originally posted by Wavebourn


You defenitely are asking wrong people why that particular guys put such strange schematics on their website. Ask them.
this website is called a "discussion forum" for a reason wouldn't you think?
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Old 26th September 2006, 02:06 PM   #13
jarthel is offline jarthel  Australia
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Quote:
Originally posted by 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...

the examples in onsemi's tl431 datasheet uses Vin so maybe it also uses voltage?
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Old 29th September 2006, 01:05 AM   #14
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Hi jarthel,

poobah provided a correct formula in post #5 above. So, if you pick R2 to be 24.9K and want your B+ to be 150V,

R1 = (24.9k * (150 - 2.495)) / 2.495 = 1.47M

Now, it turns out that 1.47M is a standard value so you are done.

However, often it doesn't turn out that close and you will have to play around with the values of R1 and R2 to get the value for B+ that you want.

Dave
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Old 29th September 2006, 01:12 AM   #15
jarthel is offline jarthel  Australia
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Quote:
Originally posted by David Davenport
Hi jarthel,

poobah provided a correct formula in post #5 above. So, if you pick R2 to be 24.9K and want your B+ to be 150V,

R1 = (24.9k * (150 - 2.495)) / 2.495 = 1.47M

Now, it turns out that 1.47M is a standard value so you are done.

However, often it doesn't turn out that close and you will have to play around with the values of R1 and R2 to get the value for B+ that you want.

Dave
some question on the circuit: does the tube protect the tl431 from over-voltage or "over-current" or both?
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Old 29th September 2006, 02:08 AM   #16
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Hi,

The tube provides isolation from the high voltage. The tube is in series with the TL431 so the same current goes through both.

The tube should be chosen by its max plate voltage and max plate current plus a bit for good measure. For plate voltage I usually pick the value of the regulated voltage as a limit. So in your case any tube that can have 150V or more on it. You don't need much current, just the expected variation in the load current plus a few, say five, milliampers.

Dave
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Old 29th September 2006, 02:15 AM   #17
jarthel is offline jarthel  Australia
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Quote:
Originally posted by David Davenport
Hi,

The tube provides isolation from the high voltage. The tube is in series with the TL431 so the same current goes through both.

The tube should be chosen by its max plate voltage and max plate current plus a bit for good measure. For plate voltage I usually pick the value of the regulated voltage as a limit. So in your case any tube that can have 150V or more on it. You don't need much current, just the expected variation in the load current plus a few, say five, milliampers.

Dave
thank you for the help
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Old 29th September 2006, 02:33 AM   #18
poobah is offline poobah  United States
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Jarthel,

What are you going to regulate with this? A voltage source?

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Old 29th September 2006, 02:47 AM   #19
jarthel is offline jarthel  Australia
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Quote:
Originally posted by poobah
Jarthel,

What are you going to regulate with this? A voltage source?


my mistake on that

I didn't realize that on the onsemi datasheet, there is a resistor before R1/R2 (which means it's a current input)
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Old 29th September 2006, 03:02 AM   #20
poobah is offline poobah  United States
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Right... the "new" resistor is what drops the voltage down to your desired regulated voltage.

In order to calculate the 3rd resistor, you need to know your max and min load current... and the raw voltage, and the regulated voltage.


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