LM317 Current Limiting problem with switching power supply

[Lyncos]

I didn't try with a 47uF cap.. I tried only with a 2200uF .. and what you mean by "a 47 uf cap designed for switching supplies" Is this a special cap ? or a normal 47uF will work ?

 

[KeepItSimpleStupid]

You need to parallel multiple types of caps. Maybe even three. Electrolytic, metalized polyester and Ceramic. The polester and ceramic caps in the range of 1 to 0.1 uf. Not having a scope, you won't be able to determine the effects.

Yes, there are differences in capacitors used for switchig power supplies. They are designed for high ripple current frequency such as these: **broken link removed** Replaceing caps rated for 120 Hz ripple frequency will sometimes start to bulge prematurely.

 

[Lyncos]

Ok I see, Maybe I should get one of these cheap scope from ebay... What you think ?I know this is cheap .. and I know I only have one channel but it's cheap. Is this will help me ?


V1.5 ARM Pocket-Sized Size Digital Oscilloscope DSO New on eBay.ca (item 200579573196 end time 24-Mar-11 18:04:35 EDT)

Thanks

 

[KeepItSimpleStupid]

Definately low cost. Shipping is just as expensive as the scope.

 

[ronv]

Maybe a schematic just to make sure?

 

[rasterburn]

I have 5 of these chips coming to me in the mail and of course the datasheet on file according to the datasheet, you will need capacitor from Vin to GND rated at 0.1uF (100nF) (required if a filter cap isnt within 6" of the LM317) they also show a 1uF electrolytic cap connecting Vout to GND but state its optional. 1 resistor should be placed across Vout and ADJ and then straight to ground. Normally you would use a second resistor or a potentiometer to set Vout by connecting ADJ to ground through the resistor or potentiometer.