voltage regulator

[dimoune]

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.

 

[MikeMl]

Which capacitor? Input filter? Input bypass? Output bypass?

 

[dimoune]

Sorry I don't quite know the name of the capacitors but I find each circuit diagram uses different capacitor value. For example:

**broken link removed**

https://www.circuitstoday.com/wp-content/uploads/2011/04/LM317-typical-adjustable-regulator-ckt.png

For my purpose, which capacitor I should use please?

Thanks.

 

[tronitech]

Have a look at the datasheet for your particular device and use whatever they specify?

 

[audioguru]

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.

 

[highvoltpower]

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.

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.

 

[dimoune]

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

 

[MikeMl]

...But I'm still not sure what capacitor value and type I must use for the capacitor in and out....

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.

 

[audioguru]

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.

 

[dimoune]

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.

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?

 

[MikeMl]

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.

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???

 

[MikeMl]

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?

The values in Fig 13 will work for your application.

 

[dimoune]

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???

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?

 

[bountyhunter]

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.

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.

 

[audioguru]

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???

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.