EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: echen1024 on September 01, 2013, 03:51:28 pm
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I currently have a LM317 set up in the method TI has it in the datasheet, with a rectifier, and then 2 1000uf filter caps, then the regulator. I was wondering if there is anyway to, for example, use op-amps, to further reduce the ripple voltage. Any help would be appreciated, and please, put the part numbers in.
Thanks.
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Do you have the bypass cap on the adjust pin? Do you have sufficient load current?
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Measurements are done with 0.5A of load current, and a bypass cap.
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I am assuming you have this set up as in Figure 1 in the datasheet.
How much ripple are you seeing on the output?
What are the input and output voltages? The datasheet specifies a minimum differential of 3 volts between the input and output, and of course, that's going to have to be true under the expected load and the lowest points in the waveform seen on the input filter cap.
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I am assuming you have this set up as in Figure 1 in the datasheet.
How much ripple are you seeing on the output?
What are the input and output voltages? The datasheet specifies a minimum differential of 3 volts between the input and output, and of course, that's going to have to be true under the expected load and the lowest points in the waveform seen on the input filter cap.
Input is around 20 volts, and output is 5. I am seeing around 400mv p-p of ripple, though that could be the scope noise as well.
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Input is around 20 volts, and output is 5. I am seeing around 400mv p-p of ripple, though that could be the scope noise as well.
Wow, that is a lot. You have input and output capacitors, and a capacitor on the adjust pin? What values (besides the 2000 uF you already mentioned on the input)?
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What is the shape of the ripple waveform?
And more importantly, do you have a largish heatsink on the regulator? 7.5W is enough to fry it...
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What is the shape of the ripple waveform?
And more importantly, do you have a largish heatsink on the regulator? 7.5W is enough to fry it...
I have a heatsink used for the Intel 486, with a large, brushless DC fan on the back. And I have a 10uf, 0.1uf, and a 1uf capacitor.
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It's probably time for you to post the actual schematic you built and/or a decent photo, because 400mV of ripple is way more than you should ever get out of an LM317. Maybe the chip is actually not working?
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It's probably time for you to post the actual schematic you built and/or a decent photo, because 400mV of ripple is way more than you should ever get out of an LM317. Maybe the chip is actually not working?
I investigated, and I think that most of the noise is the oscilloscope probe crap.