Quote Originally Posted by mischl
i'm no a step further. the problem seems not to be in PSU... i made a mistake in the software which have updated the outputs too fast and this problem sourced. normally the output at the 7805 is stable at 4.9 V

the 5 V looks at in the attachment...?

thanks for any comments again
The problem is DEFINATELY in your PSU. The attachment shows the voltage dropping towards the end of the mains cycle due to Capacitor C5 in your PSU not being large enough to maintain the voltage above the 7805's minimum input requirement.

The fact that this only becomes apparent as you draw more current confirms this. More current discharges the reservoir more quickly.

Increase C5 to at least 1000uF, more if you have it available. I would probably go for 4700uF.

Regards

Keith