Gives a high voltage regulation circuit. The first paragraph states that the LM117 can only withstand 40V across it's input and output terminals. Yet surely in the circuit the voltage drop across the LM117 can be at least the approximately the full voltage? The circuit shows
170 input and output min of 8V which is at least 162V being dropped
across the LM317. How does this jive with what they are saying?
Nope, the Darlington pair Q1/Q2 drops almost all the voltage--there's only about 4.7V across the LM317. That's because the Zener D1 forces the base of the Darlington to be 6.2V above the output voltage, which makes the input voltage of the LM317 only about 4.7V above its output.
Cheers
Phil Hobbs
Don't stop there.
0 input and output min of 8V which is at least 162V being droppedThe second paragraph of the datasheet: "Figure 1 shows how it=92s done. Zener diode D1 ensures that the LM317H sees only a 5V input-output differential over the entire range of output voltage from 1.2V to 160V"
That circuit is a mess... it's trying way too hard to use the 117 where it doesn't fit. And its capacitive load stability could keep one up at night.
You can make a nice HV reg from six cheap discretes. Three more to add active current limiting, one more after that for foldback.
John
Well, it _is_ a datasheet circuit. ;0
At least it's better than the PNP wraparound for getting 30A from an LM7805.
Cheers
Phil Hobbs
Have you a circuit fot this Hv reg with 6 discrete?
Thanks "John Larkin" ha scritto nel messaggio news: snipped-for-privacy@4ax.com...
Sorry, no circuits for top posters.
John
At least email it to us bottom-posters!
The darlington Q1-Q2 is an emitter follower that is driven by D1 to produce a voltage input for the LM317 that is only about 5V higher than the output.
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