Startup Noise

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I have designed power supply using TOP244, With Three outputs 5V@0.75A,16V@0.5A(post regulated by LM7812 to get 12V) and 19V@.75A(post regulated by LM7815 to get 15V). During Startup of power supply i get audible sound from transformer about 30 seconds however the outputs are OK at startup. If the 12V Output(from 7812) is loaded by 12V,0.45A DC Fan, output shows too many ripple with frequency around 20Hz


This could very well be a power supply stability problem.

If you have not already done so, please use PI Expert to determine the components required for loop compensation.

If the feedback circuit components are correctly selected, please attach a copy of your schematic and provide details of your transformer design and we will help you to resolve this issue.



I have attached Schematic and Layout. I have designed using PI Expert7 and use the components as suggested by software. Only I have doubled the values of all output capacitors. Please reply soon as I have time limitation.
With Changing Optocoupler LED Resistor(R6) to 27E(from 100E) the Peak to Peak ripple is reduced from 6V to 800mV on 12V Output. So is it ok to use R6 as 27E. There is no application notes regarding control loop components, each components should be explained in detail in some appl. notes for new users to troubleshoot power supply.
change d2 to fr107, opto to pc817a, r9 to 10k, r8 to suitable value, thn check if noise is frm transformer? thn let m knw if this ripple is on low line input voltage or at 230V?