Power Supply Ripple Measurement

** You do not need one. ** 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 you have such a problem, come back then and describe it.

** 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?

melissa

** 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.

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

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

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?

infact the ground symbols on the left don't mean ground at all. they'll be over 100V different from protective earth

--
  \_(?)_

1

** The FAN301 switches at 45kHz, a frequency where the ESR of typical elect ros dominates the impedance ( ESR meters test electros at this kind of freq uency ) plus the overall impedance is rising with frequency due to stray in ductance in the leads and body of the cap.

To a first approximation, the ripple voltage is the *ESR* times the load cu rrent.

** For sure.

** See p32, further down the same pdf.

... Phil

Thats true. The ground symbles on the left side seem just to indicate a common point more so than a real ground like the chassies ground symble on the right.

Hi,

I have been testing this Switching power supply ( 12V, 1A) to find out that if it is carrying any differential and common mode noise and how much. The block diagram of the circuit is as follows

The block diagram of the way, I am testing it is as follows

The load was picking lots of noise from the supply. I was inserting common mode noise to the power supply.

But when I shorted the neutral of the power supply to the Ground of the DC output of the supply, the noise went really low almost zero.

I was wondering why did that happen.

melissa