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Power Supply Ripple Measurement

Started by Unknown August 9, 2015
Hi, 

1. I am trying to measure the output voltage ripple of a 5 Volt , 1A power supply. The input to the power supply is 120V, 60Hz. 


Can someone please suggest an appropiate Differential probe to do this measurement?

Plus I am expecting the ripple to be 2mV peak to peak. If I do not get 2mV peak to peak then what should I do to reduce it. I can not use Voltage regulator at the output. 


2. I am also looking at the following part 

http://media.digikey.com/pdf/Data%20Sheets/Fairchild%20PDFs/FAN301.pdf

It's a PWM ocntroller for power charger. I am trying to understand the Figure2 on page 2 and trying to determine the output ripple on paper. 

I do not have the chip yet. Can someone advise how can I calculate the ripple by the data given in the data sheet?

I am sorry if I have asked a stupid question.

melissa
walrave...@gmail.com wrote:
> > > 1. I am trying to measure the output voltage ripple of a 5 Volt, > 1A power supply. The input to the power supply is 120V, 60Hz. > > Can someone please suggest an appropiate Differential probe to > do this measurement?
** You do not need one.
> Plus I am expecting the ripple to be 2mV peak to peak.
** So it's a switching supply. Hook you scope ( with AC coupling) across the output with a load attached an see what you get.
> If I do not get 2mV peak to peak then what should I do to reduce it.
** If you have such a problem, come back then and describe it.
> 2. I am also looking at the following part > > http://media.digikey.com/pdf/Data%20Sheets/Fairchild%20PDFs/FAN301.pdf > > It's a PWM ocntroller for power charger. I am trying to understand the Figure2 on page 2 and trying to determine the output ripple on paper. > > I do not have the chip yet. Can someone advise how can I calculate the ripple by the data given in the data sheet? > > I am sorry if I have asked a stupid question.
** Not stupid, but outside the realm of "basic" electronics. The actual p-p ripple voltage seen will depend on load current, circuit layout, stray inductances in PCB tracks plus the actual ESR the electros in the filter. .... Phil
Hi, 

What is the purpose of the transformer TX1 in Figure 1 of the schematic?

http://media.digikey.com/pdf/Data%20Sheets/Fairchild%20PDFs/FAN301.pdf 


melissa
 walrave...@gmail.com wrote:

> > What is the purpose of the transformer TX1 in Figure 1 of the schematic? > > http://media.digikey.com/pdf/Data%20Sheets/Fairchild%20PDFs/FAN301.pdf > >
** O - M - G . . . . . :-0 I suppose this new Q is at least "on topic " for SEB. ... Phil
It is to isolate the load from the AC line.  Also I would assume that it is 
to cut the voltage from the AC line down to a voltage more compatiable with 
the battery it is charging.

Notice the ground sysmbles on the left side is not the same as the chassies 
ground onthe right.


<walravenmelissa@gmail.com> wrote in message 
news:b50ee986-6cab-4c21-93f0-6f408f47fddb@googlegroups.com...
> Hi, > > What is the purpose of the transformer TX1 in Figure 1 of the schematic? > > http://media.digikey.com/pdf/Data%20Sheets/Fairchild%20PDFs/FAN301.pdf > > > melissa
On Mon, 10 Aug 2015 04:09:55 -0700, walravenmelissa wrote:

> Hi, > > What is the purpose of the transformer TX1 in Figure 1 of the schematic? > > http://media.digikey.com/pdf/Data%20Sheets/Fairchild%20PDFs/FAN301.pdf
That question, coupled with the lethal voltages on the left of the schematic, is rather alarming. What Ralph said: it isolates the output from the line (because you can't trust either pin of the line to be "safe"), and it probably has a many:1 turns ratio to help cut the voltage while keeping the power supply efficient. Have fun. Learn. Don't electrocute yourself or burn your house down. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
On Sun, 09 Aug 2015 19:33:37 -0700, walravenmelissa wrote:

> Hi, > > 1. I am trying to measure the output voltage ripple of a 5 Volt , 1A > power supply. The input to the power supply is 120V, 60Hz. > > > Can someone please suggest an appropiate Differential probe to do this > measurement? > > Plus I am expecting the ripple to be 2mV peak to peak. If I do not get > 2mV peak to peak then what should I do to reduce it. I can not use > Voltage regulator at the output. > > > 2. I am also looking at the following part > > http://media.digikey.com/pdf/Data%20Sheets/Fairchild%20PDFs/FAN301.pdf > > It's a PWM ocntroller for power charger. I am trying to understand the > Figure2 on page 2 and trying to determine the output ripple on paper. > > I do not have the chip yet. Can someone advise how can I calculate the > ripple by the data given in the data sheet? > > I am sorry if I have asked a stupid question.
The output ripple is the amount of voltage that the output capacitors (Co1 and Co2) sag when D6 is not conducting. To a first approximation, this is close to the output current divided by the switching frequency times the total output capacitance. But there's a hell of a lot going on in that circuit, and first approximations may not work. If you can find an example circuit that's already laid out and has all the part numbers called out for it you'll get a huge boost in having a successful outcome. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
<walravenmelissa@gmail.com> wrote:

> Hi, > > What is the purpose of the transformer TX1 in Figure 1 of the schematic? > > http://media.digikey.com/pdf/Data%20Sheets/Fairchild%20PDFs/FAN301.pdf > > > melissa
careful that the drawing of the chip in figure 2 is mirrored respect of reality (figure 5). Bye Jack -- Yoda of Borg am I! Assimilated shall you be! Futile resistance is, hmm?
On 2015-08-10, Ralph Mowery <rmowery28146@earthlink.net> wrote:
> It is to isolate the load from the AC line. Also I would assume that it is > to cut the voltage from the AC line down to a voltage more compatiable with > the battery it is charging. > > Notice the ground sysmbles on the left side is not the same as the chassies > ground onthe right.
infact the ground symbols on the left don't mean ground at all. they'll be over 100V different from protective earth -- \_(&atilde;&fnof;&bdquo;)_
Tim Wescott wrote:

> > The output ripple is the amount of voltage that the output capacitors (Co1 > and Co2) sag when D6 is not conducting. To a first approximation, this > is close to the output current divided by the switching frequency times > the total output capacitance. > >
** The FAN301 switches at 45kHz, a frequency where the ESR of typical electros dominates the impedance ( ESR meters test electros at this kind of frequency ) plus the overall impedance is rising with frequency due to stray inductance in the leads and body of the cap. To a first approximation, the ripple voltage is the *ESR* times the load current.
> But there's a hell of a lot going on in that circuit, and first > approximations may not work. >
** For sure.
> If you can find an example circuit that's > already laid out and has all the part numbers called out for it you'll > get a huge boost in having a successful outcome.
** See p32, further down the same pdf. ... Phil