TL783 Regulator voltage at input
- Thread starter pf9000
- Start date
Help Support GroupDIY Audio Forum:
[quote author="pf9000"]TL783 Regulator has 150volt max input limit.[/quote]
No, it doesn't? :? I don't think I've seen the first 3-terminal regulator that has an input voltage limit.
As long as the output is high enough to keep the the input-to-output differential below 125V, 220V at the input will be just fine (until you short the output, of course). :thumb:
Peace,
Al.
No, it doesn't? :? I don't think I've seen the first 3-terminal regulator that has an input voltage limit.
As long as the output is high enough to keep the the input-to-output differential below 125V, 220V at the input will be just fine (until you short the output, of course). :thumb:
Peace,
Al.
jdr
Active member
http://www.gyraf.dk/gy_pd/g9/g9_sch.gif
Check out the rest of Gyraf's DIY too, lots of great information.
:guinness:
Check out the rest of Gyraf's DIY too, lots of great information.
:guinness:
bcarso
Well-known member
[quote author="alk509"][quote author="pf9000"]TL783 Regulator has 150volt max input limit.[/quote]
No, it doesn't? :? I don't think I've seen the first 3-terminal regulator that has an input voltage limit.
As long as the output is high enough to keep the the input-to-output differential below 125V, 220V at the input will be just fine (until you short the output, of course). :thumb:
Peace,
Al.[/quote]
Might want to qualify the statement to "...first 3-terminal adjustable regulator that has an input voltage limit." The fixed output three-term regs definitely have an input-to-common voltage limit. It's true we don't see too many of the fixed regs in here, but they are common elsewhere.
One of the problem with adjustables, besides short circuits, is the dynamics of the system during power-up---if the output has significant capacitive loading, it doesn't come up as fast as the input and you get breakdown as the differential is exceeded. This may not be destructive but it is worrisome. You can put a zener with a suitably lower-than-diff-max voltage across input to output, but it may need to be a pretty hefty one to withstand potentially large transient currents.
Or, you can just make sure the cap on the output is small enough and the downstream loads don't do anything funny at low voltages.
No, it doesn't? :? I don't think I've seen the first 3-terminal regulator that has an input voltage limit.
As long as the output is high enough to keep the the input-to-output differential below 125V, 220V at the input will be just fine (until you short the output, of course). :thumb:
Peace,
Al.[/quote]
Might want to qualify the statement to "...first 3-terminal adjustable regulator that has an input voltage limit." The fixed output three-term regs definitely have an input-to-common voltage limit. It's true we don't see too many of the fixed regs in here, but they are common elsewhere.
One of the problem with adjustables, besides short circuits, is the dynamics of the system during power-up---if the output has significant capacitive loading, it doesn't come up as fast as the input and you get breakdown as the differential is exceeded. This may not be destructive but it is worrisome. You can put a zener with a suitably lower-than-diff-max voltage across input to output, but it may need to be a pretty hefty one to withstand potentially large transient currents.
Or, you can just make sure the cap on the output is small enough and the downstream loads don't do anything funny at low voltages.
[quote author="bcarso"]The fixed output three-term regs definitely have an input-to-common voltage limit.[/quote]
Not really - a 7805 is just an LM317 with 5V between the output and control pin instead of 1.25V. In other words I haven't seen a three-pin regulator that wasn't adjustable...
Best regards,
Mikkel C. Simonsen
Not really - a 7805 is just an LM317 with 5V between the output and control pin instead of 1.25V. In other words I haven't seen a three-pin regulator that wasn't adjustable...
Best regards,
Mikkel C. Simonsen
bcarso
Well-known member
[quote author="mcs"][quote author="bcarso"]The fixed output three-term regs definitely have an input-to-common voltage limit.[/quote]
Not really - a 7805 is just an LM317 with 5V between the output and control pin instead of 1.25V. In other words I haven't seen a three-pin regulator that wasn't adjustable...
Best regards,
Mikkel C. Simonsen[/quote]
Perhaps I should have said "When used as directed..."---i.e., with the common terminal tied to circuit common.
You have a point. Although the structures of the two regulator types are very different, with the fixed regs having the low voltage ref multiplied up by an internal output divider to ground (they aren't different ref voltages from what I can see), you can treat the resulting system as if it were an adjustable reg. with an internal reference equal to the "fixed" output voltage. However, the regulator quiescent current has to be handled by the output divider, and its drift with temperature, input voltage, and load will be error terms, leading to quite a stiff output divider for good results.
For example the 7815 has an Iq out of the common pin of about 4.4mA, but as high as 8mA, and then has a variation of a net 1.5mA over temp and input voltage. So the impedance of the divider had better be awfully low.
Not really - a 7805 is just an LM317 with 5V between the output and control pin instead of 1.25V. In other words I haven't seen a three-pin regulator that wasn't adjustable...
Best regards,
Mikkel C. Simonsen[/quote]
Perhaps I should have said "When used as directed..."---i.e., with the common terminal tied to circuit common.
You have a point. Although the structures of the two regulator types are very different, with the fixed regs having the low voltage ref multiplied up by an internal output divider to ground (they aren't different ref voltages from what I can see), you can treat the resulting system as if it were an adjustable reg. with an internal reference equal to the "fixed" output voltage. However, the regulator quiescent current has to be handled by the output divider, and its drift with temperature, input voltage, and load will be error terms, leading to quite a stiff output divider for good results.
For example the 7815 has an Iq out of the common pin of about 4.4mA, but as high as 8mA, and then has a variation of a net 1.5mA over temp and input voltage. So the impedance of the divider had better be awfully low.
