frequency error about top253en

this is the output voltage.

Hi,

It appears from the screen capture that your power supply seems to be operating at very light load. In order to minimize the switching losses and to maximize the efficiency our device will adjust the switching frequency for given output load conditions. There is nothing wrong in that frequency.

For more details Please refer to TOPSwitch-HX control Pin characteristics. You can find the datasheet at following location

http://www.powerint.com/sites/default/files/product-docs/tophx_family_datasheet.pdf

I am not sure about how the output voltage ripple has been measured. From screen capture it appears that it has lot of noise pick-up in the output ripple and not actual ripple.

Please measure the output ripple by using the following method and limit the bandwidth of the probe to 20MHZ in order to avoid the high frequency noise pick up.

Ripple Measurement Technique

For DC output ripple measurements, a modified oscilloscope test probe must be utilized in order to reduce spurious signals due to pick up. Details of the probe modification are provided in the Figures attached.

The 4987BA probe adapter is affixed with two capacitors tied in parallel across the probe tip. The capacitors include one (1) 0.1 uF/50 V ceramic type and one (1) 1.0 uF/50 V aluminum electrolytic. The aluminum electrolytic type capacitor is polarized, so proper polarity across DC outputs must be maintained.

hi,
PI-NANO
I am appreciated for your answer.
I mean the output noise is terrible,I use a scope to measure the noise,the Vp-p is about 1v.
while for other commercial power supply, the noise is almost invisible.
I am confused about my situation and don't know how to fix it.
because I am a newbie about switch power supply, I use PI's expert software to generate a schematic.