voltage regulator

Status
Not open for further replies.
D

dimoune

Member
Hello,

I'm trying to build a reliable voltage regulator to deliver 23vdc. I think LM317 is good for that and I searched the internet for some circuits. Each circuit I found uses different capacitor. I'm confused. what capacitor should I need please? My power supply is 30v. Thanks.
 
The people at Circuits Today did not see the LM117 in the circuit on the datasheet and they think a cheaper LM317 uses the same resistors.
 

Attachments

  • LM317 resistors.png
    17.1 KB · Views: 148


It’s depends on which capacitor u used. LM317 is an adjustable 3terminal positive voltage regulator that is capable of supplying in excess of 1.5 This voltage regulator is remarkably easy to use and requires only 2 external resistors to fixed the output voltage.
 
Thanks everyone for your input. But I'm still not sure what capacitor value and type I must use for the capacitor in and out. I have 30vdc power supply and I want to use the LM317 to regulate voltage to 23vdc. I'm using a first resistor of 220 ohm and second one is 3.9k. The voltage is effectively regulated around 23v but for the capacitor I don't what to use. Thanks.

Ps. I'll be using small current under 50ma
 
Last edited:
Without a load an LM317 with spec's at one end of their range will have its output voltage rise which is why a 120 ohm resistor should be used.
 
MikeMl said:
Then go to the people that really know instead of a bunch of smart ass nerds...

Read paragraph 9.2, figure 9, subparagraph 9.2.1, on page 10.
Click to expand...

Thanks. I went through the document you pointed and I would be grateful if you could help me understand why in figure 9 Cadj is a fixed capacitor when they gave example in figure 13 a polarized capacitor is used instead. Are these capacitor substitute?
 
audioguru said:
Without a load an LM317 with spec's at one end of their range will have its output voltage rise which is why a 120 ohm resistor should be used.
Click to expand...
If the load is always connected and the load current exceeds the minimum current that provides good regulation, then the upper voltage divider resistor can be anything up to ~1KΩ. Why waste power you dont have to???
 
The values in Fig 13 will work for your application.
 
MikeMl said:
If the load is always connected and the load current exceeds the minimum current that provides good regulation, then the upper voltage divider resistor can be anything up to ~1KΩ. Why waste power you dont have to???
Click to expand...

What is the implication if the load is a usb for example and is not always connected? Does it mean the circuit will draw current even when nothing is connected?
 
dimoune said:
Thanks everyone for your input. But I'm still not sure what capacitor value and type I must use for the capacitor in and out.
Click to expand...
You are overthinking this. You can use virtually any capacitor you want whose value is larger than about 5 uF for input and output caps and you don't need the bypass cap on the adj pin. The only caveat would be not to use ceramic caps as they sometimes (rarely) can cause oscillations. Use aluminum electrolytics or tantalums.
 
MikeMl said:
If the load is always connected and the load current exceeds the minimum current that provides good regulation, then the upper voltage divider resistor can be anything up to ~1KΩ. Why waste power you dont have to???
Click to expand...
Many people set the voltage on a power supply before connecting the load. If the current drawn by the programming resistors is too low then the output voltage will rise and not be regulated, then it drops when the load is connected. If you want a 240 ohms resistor then use an LM117 (as shown on all circuits in the National Semi datasheet before TI bought them), not a cheaper LM317.
 
Status
Not open for further replies.

Similar threads

G
  • Question
Voltage regulator
2
Replies
23
Views
2K
tumbleweed
T
A
  • Question
Voltage regulator 230722
Replies
9
Views
2K
AllenPitts
A
V
  • Question
Logging Voltage
2
Replies
22
Views
2K
Voltmanbucks
V
  • Question
No contact AC voltage sensing
Replies
11
Views
921
lilimike
G
  • Question
Voltage follower with feedback resistor?
2
Replies
32
Views
4K
Diver300
D
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…