I have built a regulated supply using a LM317T, adjusted to produce 15 volts. Transformer produces a rectified voltage of 23 volts. The supply is to drive a scanner which requires a current of 1 amp. On bench testing the supply at about 600 milliamp. the 317 (mounted on a heatsink) gets very hot within about 2-3 minutes . The specs says the 317T should handle 1.5 amps!
Is it possible to use two 317's connected in parallel to share the load? I have a bunch of them in my parts bin, any ideas?
DieterD
Is it possible to use two 317's connected in parallel to share the load? I have a bunch of them in my parts bin, any ideas?
DieterD
Um, 23-15=8v dropped across the regulator. Your target current is 1A. P=IV, so you are disapating 8W with your TO-220 device. Assuming 10 C/W with your heatsink (probably overly generous if it is a little flag sink) you are talking an 80 degree rise above ambient.
The rated 1.5 amp assumes two things: adequate heatsinking, and a small enough voltage drop to keep the device in its safe operating area. You probably need to increase your sinking and reduce the input voltage, or consider something other than a series-drop regulator.
The rated 1.5 amp assumes two things: adequate heatsinking, and a small enough voltage drop to keep the device in its safe operating area. You probably need to increase your sinking and reduce the input voltage, or consider something other than a series-drop regulator.
You could put two regulators in series. The first one drops half the voltage, the second sets the final output voltage. That will halve the power dissipated by each regulator.
Oops, just noticed Harry beat me to it. Use bigger heatsinks even if you do change it to use two regulators.
Oops, just noticed Harry beat me to it. Use bigger heatsinks even if you do change it to use two regulators.
Dieter,
You could add several diodes in series with the regulator to get the required voltage drop (0.6v per diode). No additional heatsink required.
Jam
You could add several diodes in series with the regulator to get the required voltage drop (0.6v per diode). No additional heatsink required.
Jam
Additonal Transistor
Just off the top of my head...
Using an appropriately sized NPN power transistor, place the LM 317 in parallel with the base to emitter junction so that the input of the LM 317 is connected to the transistor base and the output of the LM 317 is connected to the transistor emitter. Next connect a resistor with proper value and rating from collector to base. You now have a properly biased emitter follower that is controlled by the voltage that you adjust on the LM 317. Or just chuck the LM 317 all-together and use a zener on the base if you do not need adjustability.
Just off the top of my head...
Using an appropriately sized NPN power transistor, place the LM 317 in parallel with the base to emitter junction so that the input of the LM 317 is connected to the transistor base and the output of the LM 317 is connected to the transistor emitter. Next connect a resistor with proper value and rating from collector to base. You now have a properly biased emitter follower that is controlled by the voltage that you adjust on the LM 317. Or just chuck the LM 317 all-together and use a zener on the base if you do not need adjustability.
Thanks guys,
I tried the heatsink in Harry's picture but it just seemed to make things hotter!
I think I will go for the NPN solution, seems to be the better way out nd retails ajustability etc.
DieterD
I tried the heatsink in Harry's picture but it just seemed to make things hotter!
I think I will go for the NPN solution, seems to be the better way out nd retails ajustability etc.
DieterD
Harry,
nice pix, really nice shape, but does she have enough CPU power to control more than her face musculature? 😀 ..
the pix doesn't look like it 🙂
Jam,
nice idea, those diodes! But don't they disspiate heat, too? They should atleast dissipate 0.6 Watt per Ampere each.
nice pix, really nice shape, but does she have enough CPU power to control more than her face musculature? 😀 ..
the pix doesn't look like it 🙂
Jam,
nice idea, those diodes! But don't they disspiate heat, too? They should atleast dissipate 0.6 Watt per Ampere each.
Bernhard,
If you use large enough diodes you should not have a problem, but let us not go there least we anger Harry(Hoary) Haller who is also the president of the Brittany Spears fan club.
Jam😀
If you use large enough diodes you should not have a problem, but let us not go there least we anger Harry(Hoary) Haller who is also the president of the Brittany Spears fan club.
Jam😀
president of the Brittany Spears fan club
That's a good one....... You mean she recomends heat sinks and fans?
That's a good one....... You mean she recomends heat sinks and fans?
Harry,
i am sure her PR manager recommends heatsinks for her fans 🙂
Look at her waistline, could really excite (provided you avoid to examine the face to closely) 🙂
i am sure her PR manager recommends heatsinks for her fans 🙂
Look at her waistline, could really excite (provided you avoid to examine the face to closely) 🙂
I am sorry
It appears there are many fans of her heatsinks.....
I wish I had never posted that infernal picture! At least we now
know that Bernhard is a belly button fan.
H.H.
It appears there are many fans of her heatsinks.....
I wish I had never posted that infernal picture! At least we now
know that Bernhard is a belly button fan.
H.H.
I always thought the quote was
" a picture paints a thousand words" not "creates" looks like I was wrong.
To get back to the original thread ( boring) I have eventually gone for two 317's in series and it seems to have sorted the problem out.
Now where do I get that heatsink?
DieterD
" a picture paints a thousand words" not "creates" looks like I was wrong.
To get back to the original thread ( boring) I have eventually gone for two 317's in series and it seems to have sorted the problem out.
Now where do I get that heatsink?
DieterD
According to the press, nobody has gotten that heatsink yet !. 🙂
http://www.salon.com/sex/world/2001/05/29/spears/?CP=YAH&DN=110
Eric.
http://www.salon.com/sex/world/2001/05/29/spears/?CP=YAH&DN=110
Eric.
Words of wisdom
I have heard very few words of wisdom from anyone on this thread...... I will never post anything like this again.
H.H.
I have heard very few words of wisdom from anyone on this thread...... I will never post anything like this again.
H.H.
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