TL783 question
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That 125 volts is the maximum difference between the input voltage and regulated output voltage, not the maximum regulated output voltage. More than 125 volts difference or less than 1.25 between input and output and it can't regulate.
Here is a quote from the TL783 data sheet "Output Adjustable From 1.25 V to 125 V When Used With an External Resistor Divider"
That sure is decieving if what you're saying is true. Also it says maximum voltage in 150volts? And if so then could I use a LM317 as a high voltage regulator too.http://focus.ti.com/docs/prod/folders/print/tl783.html
That sure is decieving if what you're saying is true. Also it says maximum voltage in 150volts? And if so then could I use a LM317 as a high voltage regulator too.http://focus.ti.com/docs/prod/folders/print/tl783.html
Farther down the data sheet it says, under "recommended operating conditions: VI-VO input to output voltage differential 125V max"
Farther down under "typical applications" Fig. 18 shows a schematic with 125-200VDC VI. Other than that I can't decipher anything that says what the maximum VI or VO is.
www.tubecad.com/articles_2001/the_300b_reg/the300breg.pdf is a schematic and article where they're using a TL 783 to produce a 430VDC output
Farther down under "typical applications" Fig. 18 shows a schematic with 125-200VDC VI. Other than that I can't decipher anything that says what the maximum VI or VO is.
www.tubecad.com/articles_2001/the_300b_reg/the300breg.pdf is a schematic and article where they're using a TL 783 to produce a 430VDC output
clintrubber
Well-known member
Have a look at the Gyraf-G9 page, there's a remark about this. I forgot the exact wording, but it was mentioning the three zeners across it.
Bye,
Peter
Bye,
Peter
[quote author="jrmintz"]
Farther down under "typical applications" Fig. 18 shows a schematic with 125-200VDC VI. Other than that I can't decipher anything that says what the maximum VI or VO is.
www.tubecad.com/articles_2001/the_300b_reg/the300breg.pdf is a schematic and article where they're using a TL 783 to produce a 430VDC output[/quote]
If you look at the original link I posted you'll see an input voltage maximum of 150 volts, although it was less clear on the actual data sheet.
Fig.18 in the data sheet shows an input voltage of 200V, but that circuit uses a mosfet to somehow increase the maximum input voltage of the regulator (there's a whole paper on it at TI, it states all IC regulators have a maximum input voltage) The 300B regulator uses a tube to handle the high voltage. I don't think the zener diodes affect the regulators maximum input voltage for the G9, I thought that was for protecting the regulator in a different way. If it works it works, but It might be that the G9's use of that regulator is pushing the limits a bit. Can anyone clarify this?
Thanks
Farther down under "typical applications" Fig. 18 shows a schematic with 125-200VDC VI. Other than that I can't decipher anything that says what the maximum VI or VO is.
www.tubecad.com/articles_2001/the_300b_reg/the300breg.pdf is a schematic and article where they're using a TL 783 to produce a 430VDC output[/quote]
If you look at the original link I posted you'll see an input voltage maximum of 150 volts, although it was less clear on the actual data sheet.
Fig.18 in the data sheet shows an input voltage of 200V, but that circuit uses a mosfet to somehow increase the maximum input voltage of the regulator (there's a whole paper on it at TI, it states all IC regulators have a maximum input voltage) The 300B regulator uses a tube to handle the high voltage. I don't think the zener diodes affect the regulators maximum input voltage for the G9, I thought that was for protecting the regulator in a different way. If it works it works, but It might be that the G9's use of that regulator is pushing the limits a bit. Can anyone clarify this?
Thanks
[quote author="rich"]Can anyone clarify this?[/quote]
Yes. There is NO maximun input voltage on any of the LM317-like regulators (including the TL783). If the voltage the regulator sees is below the limit it couldn't care less what the actual voltages are.
If you have 400V in and 300V out how will the TL783 ever find out that the input voltage is above 125V? It has no ground connection , so it can't "measure" the input or output voltage. If you short circuit the output it will find out however, as you will have 400V accross the input/output. So when using the regulators above the "limits" you will have no short circuit protection.
Best regards,
Mikkel C. Simonsen
Yes. There is NO maximun input voltage on any of the LM317-like regulators (including the TL783). If the voltage the regulator sees is below the limit it couldn't care less what the actual voltages are.
If you have 400V in and 300V out how will the TL783 ever find out that the input voltage is above 125V? It has no ground connection , so it can't "measure" the input or output voltage. If you short circuit the output it will find out however, as you will have 400V accross the input/output. So when using the regulators above the "limits" you will have no short circuit protection.
Best regards,
Mikkel C. Simonsen
[quote author="mcs"][quote author="rich"]Can anyone clarify this?[/quote]
If you have 400V in and 300V out how will the TL783 ever find out that the input voltage is above 125V? It has no ground connection , so it can't "measure" the input or output voltage. If you short circuit the output it will find out however, as you will have 400V accross the input/output. So when using the regulators above the "limits" you will have no short circuit protection.
Best regards,
Mikkel C. Simonsen[/quote]
Just read the LM317 data sheet and it said exactly what you just said, if you exceed the voltage range you loose short circuit protection, so the mosfet before the regulator is just away to keep your short circuit protection and still exceed the voltage range.
Thanks
If you have 400V in and 300V out how will the TL783 ever find out that the input voltage is above 125V? It has no ground connection , so it can't "measure" the input or output voltage. If you short circuit the output it will find out however, as you will have 400V accross the input/output. So when using the regulators above the "limits" you will have no short circuit protection.
Best regards,
Mikkel C. Simonsen[/quote]
Just read the LM317 data sheet and it said exactly what you just said, if you exceed the voltage range you loose short circuit protection, so the mosfet before the regulator is just away to keep your short circuit protection and still exceed the voltage range.
Thanks
Yes.
What we do in the G9 psu-circuit is safe enough - providing that we do not short the output voltage to ground. And "internally" in a box like that, there's little chance of shorting the HT.
What we do is protect the 783 from larger in/out differential voltages than 117V by the three series-coupled 39V zeners.
This means that at power-up - where the in/out voltage difference is momentary large - the zeners conducts from in to out, charging the second reservoir cap till there's lower than 117V difference.
This is why the two 470R series resistors R33/R37 are important - they limit the current through the zeners.
The last protection is D2, the 1N4007 from out to in on the regulator. This protects the regulator in power-down mode, where input voltage otherwise could get momentary lower than output voltage - which would kill the regulator.
In all, this is a quite stable and very good regulating circuit. I have ONLY had trouble with it after shorts at the HT lines.
Jakob E.
What we do in the G9 psu-circuit is safe enough - providing that we do not short the output voltage to ground. And "internally" in a box like that, there's little chance of shorting the HT.
What we do is protect the 783 from larger in/out differential voltages than 117V by the three series-coupled 39V zeners.
This means that at power-up - where the in/out voltage difference is momentary large - the zeners conducts from in to out, charging the second reservoir cap till there's lower than 117V difference.
This is why the two 470R series resistors R33/R37 are important - they limit the current through the zeners.
The last protection is D2, the 1N4007 from out to in on the regulator. This protects the regulator in power-down mode, where input voltage otherwise could get momentary lower than output voltage - which would kill the regulator.
In all, this is a quite stable and very good regulating circuit. I have ONLY had trouble with it after shorts at the HT lines.
Jakob E.
