Hi there,
[Please see attached circuit diagram]
As many of you know, the LM317 is a simple voltage regulator that can be used in a very simple circuit in order to provide for a continuously variable power supply with reasonable temperature compensation. That circuit is shown in the diagram. The intended application is a very low cost variable power supply for general purpose testing so it doesnt have to be super perfect, but it does have to have reasonable temperature behavior like the LM317 already has.
There is a slight problem with the circuit however. Potentiometers are not perfect devices in that sometimes when they fail their 'arm' opens up either permanently or sporadically causing a change of resistance from some low value to some very high unpredictable value (same effect causes static in audio amplifier volume controls). This change in resistance could easily cause the output to jump from an adjusted point of say +5v up to as high as +22v in the circuit shown, and this would quickly blow out a device that was being tested at it's rated 5v. This is where the challenge comes in...
The challenge is to redesign the circuit as simple as possible so that this can not happen, or alternately so that if it does happen (the pot arm opens up) the voltage drops to 0v instead of jumping way up to some high value. The external circuit under test will be ok in that case.
Bear in mind now that this isnt exceptionally hard to achieve if it were not for one other little catch: the circuit can not use any op amps. Transistors would be ok i guess, but limited to 3 small transistors and a few resistors BUT the temperature behavior can not be allowed to get worse than it is with only an LM317 device.
This kind of improvement would be a very nice thing to have for the LM317 when used as a supply for testing other things (LED's, etc.) so i hope you guys/gals can come up with some new ideas.
[Please see attached circuit diagram]
As many of you know, the LM317 is a simple voltage regulator that can be used in a very simple circuit in order to provide for a continuously variable power supply with reasonable temperature compensation. That circuit is shown in the diagram. The intended application is a very low cost variable power supply for general purpose testing so it doesnt have to be super perfect, but it does have to have reasonable temperature behavior like the LM317 already has.
There is a slight problem with the circuit however. Potentiometers are not perfect devices in that sometimes when they fail their 'arm' opens up either permanently or sporadically causing a change of resistance from some low value to some very high unpredictable value (same effect causes static in audio amplifier volume controls). This change in resistance could easily cause the output to jump from an adjusted point of say +5v up to as high as +22v in the circuit shown, and this would quickly blow out a device that was being tested at it's rated 5v. This is where the challenge comes in...
The challenge is to redesign the circuit as simple as possible so that this can not happen, or alternately so that if it does happen (the pot arm opens up) the voltage drops to 0v instead of jumping way up to some high value. The external circuit under test will be ok in that case.
Bear in mind now that this isnt exceptionally hard to achieve if it were not for one other little catch: the circuit can not use any op amps. Transistors would be ok i guess, but limited to 3 small transistors and a few resistors BUT the temperature behavior can not be allowed to get worse than it is with only an LM317 device.
This kind of improvement would be a very nice thing to have for the LM317 when used as a supply for testing other things (LED's, etc.) so i hope you guys/gals can come up with some new ideas.
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