Hi!
I am very much a novice with electronic circuitry. I have ben studying on & off for years, but at warp speed the last 3 or 4 months. I finally decided to actually build something, so I chose to make a simple voltage regulator based on the LM317T IC.
I designed it by primarily copying (stealing?) from datasheets. I added a rectifier for AC input if desired & used separate input terminals so a DC source would not have to pass through the bridge. I also put in some protection diodes, per Texas Instrument's sheet.
I also thought I was smart & installed a switch for the fixed resistor. My thought was to have two different (selectable) fixed resistances, thus making the 360 degrees of turn on the variable either coarse or fine. I calculated the two ranges to be:
High Range 1.2 to 27.85 using the 470 ohm resistor with the 10k variable
Low Range 1.2 to 9.58 using a 1.5k ohm resistor with the 10k variable
But, when I tested it things didn't go as planned:
Source was a 12 volt 'regulated' power supply with no load output measured at 13.87 vdc
With no load on the new project, both ranges give me 7.78 volts to 13.68 volts, measured at the output terminals. I thought a load might improve the results.
With a 28 volt 1 watt incandescent panel lamp as the load, I read 1.24 to 1.65 volts as I dialed the variable resistor. I got the same results with each switch position.
With a 250 volt 1/4 watt panel lamp or even 2 of them in series or a 500 ohm resistor or a 220k ohm resistor- I get 7.78 to 13.68 volts at the output terminals. I tried several combinations. The results never varied.
I checked the wiring against my drawing & tested each component, except the LM317T, because I don't know how. I isolated the switch & checked it. A-OK. I even swapped the LM317T for a new one. No change. I have not tested with AC input yet.
My only guess it that I should connect the un-used terminal of the variable resistor to negative. I did not try this, fearing destroying the IC.
I am not sure if I designed the circuit wrong or am testing improperly. If any of you don't mind taking a look at my (rough) sketch of the circuit & commenting, I would be very appreciative of your thoughts & lessons.
Thanks Very Much!
"Paul The Novice"
PS: Note about the drawing- C-1 is 0.1uf Ceramic C-3 is 25uf 50 volt Electrolytic C-4 is 100uf 50 volt Electrolytic The bridge rectifier is taken from an old typewriter, but bench tests OK.
I am very much a novice with electronic circuitry. I have ben studying on & off for years, but at warp speed the last 3 or 4 months. I finally decided to actually build something, so I chose to make a simple voltage regulator based on the LM317T IC.
I designed it by primarily copying (stealing?) from datasheets. I added a rectifier for AC input if desired & used separate input terminals so a DC source would not have to pass through the bridge. I also put in some protection diodes, per Texas Instrument's sheet.
I also thought I was smart & installed a switch for the fixed resistor. My thought was to have two different (selectable) fixed resistances, thus making the 360 degrees of turn on the variable either coarse or fine. I calculated the two ranges to be:
High Range 1.2 to 27.85 using the 470 ohm resistor with the 10k variable
Low Range 1.2 to 9.58 using a 1.5k ohm resistor with the 10k variable
But, when I tested it things didn't go as planned:
Source was a 12 volt 'regulated' power supply with no load output measured at 13.87 vdc
With no load on the new project, both ranges give me 7.78 volts to 13.68 volts, measured at the output terminals. I thought a load might improve the results.
With a 28 volt 1 watt incandescent panel lamp as the load, I read 1.24 to 1.65 volts as I dialed the variable resistor. I got the same results with each switch position.
With a 250 volt 1/4 watt panel lamp or even 2 of them in series or a 500 ohm resistor or a 220k ohm resistor- I get 7.78 to 13.68 volts at the output terminals. I tried several combinations. The results never varied.
I checked the wiring against my drawing & tested each component, except the LM317T, because I don't know how. I isolated the switch & checked it. A-OK. I even swapped the LM317T for a new one. No change. I have not tested with AC input yet.
My only guess it that I should connect the un-used terminal of the variable resistor to negative. I did not try this, fearing destroying the IC.
I am not sure if I designed the circuit wrong or am testing improperly. If any of you don't mind taking a look at my (rough) sketch of the circuit & commenting, I would be very appreciative of your thoughts & lessons.
Thanks Very Much!
"Paul The Novice"
PS: Note about the drawing- C-1 is 0.1uf Ceramic C-3 is 25uf 50 volt Electrolytic C-4 is 100uf 50 volt Electrolytic The bridge rectifier is taken from an old typewriter, but bench tests OK.
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