8451	2013-04-02 02:26:01	Stephen Farthing	Measuring power supply noise.
Message	Date	From	Subject
Greetings from England!, Is there a simple way of measuring the noise output from a power supply? I have a Hantek DSO512B digital scope 2 channel 100 MHz scope. Having read a bit of theory it would seem that using normal scope probes will affect the readings because there will be a ground return. I don't have any other relevant test equipment (or knowledge for that matter). But I am able to build simple circuits. The power supply I wish to measure is a switching unit based on an LM2956 set to 6.2 volts followed by a LDO 5 volt regulator to clean up any noise. The application is to power a Raspberry Pi (a single board Linux computer) for transmitting purposes. I am very much a beginner at all this so please keep things simple :-) Thanks in advance 73 Steve G0XAR [Non-text portions of this message have been removed]
8452	2013-04-02 05:43:12	Dino Papas	Re: Measuring power supply noise.
Steve - coincidentally I saw this just yesterday; some good ideas to at least understand the process: http://www.youtube.com/watch?v=pKXPqApOYfk&feature=youtu.be 73 - Dino KL0S On Apr022013, at 0526 AM, Stephen Farthing <squirrox@gmail.com> wrote: > Greetings from England!, > > Is there a simple way of measuring the noise output from a power supply? > > I have a Hantek DSO512B digital scope 2 channel 100 MHz scope. Having read > a bit of theory it would seem that using normal scope probes will affect > the readings because there will be a ground return. I don't have any other > relevant test equipment (or knowledge for that matter). But I am able to > build simple circuits. > > The power supply I wish to measure is a switching unit based on an LM2956 > set to 6.2 volts followed by a LDO 5 volt regulator to clean up any noise. > The application is to power a Raspberry Pi (a single board Linux computer) > for transmitting purposes. > > I am very much a beginner at all this so please keep things simple :-) > > Thanks in advance > > 73 Steve G0XAR [Non-text portions of this message have been removed]
8453	2013-04-03 12:03:51	Gary, WB9JPS	Re: Measuring power supply noise.
The TI video that Dino pointed to is very good. I can't emphasize enough how important probe technique is. My favorite way to observe output noise is to make a direct connection to the 'scope with miniature coax; I use RG-316 or RG-174 but good old RG-58 is fine. Strip the end of the coax and make the connections absolutely as short as possible. Solder them right to the power supply board output, if you can. This will reduce the possible magnetic-pickup loop to a minimum. I also like to wrap the coax several turns thru a toroid to act as a common-mode choke. This reduces interaction between the 'scope ground and the device under test. AC-couple the scope and see what you see. A spectrum analyzer is also very useful here. If you can upload data from your 'scope to a computer, you can do a power spectrum using one of may free applications. That way, you identify the characteristic frequencies associated with switching noise. If you want to filter the output or add more shielding, you will need to know something about the frequency content. Don't forget to hook up some long wires to the power supply output and listen with your receiver (put some kind of load
8455	2013-04-03 14:39:59	NeilDouglas	Re: Measuring power supply noise.
All, Be careful if you use a 1:1 probe or coax connection that you do not inadvertently switch your scope to 50ohm input when selecting the input coupling. My scope is only rated to 5V on the 50ohm input. If your scope is capable I have used the Quasi Differential method by subtracting one input from another to remove some of the common mode effect. Regards NeilD G4SHJ _____