dual output with lnk625
Goodmorning, I'm testing a flyback design with lnk625 for a dual output: +5V and +12V. I followed a design by your PIexpert, but i need a suggestion: how can I improve the +5V regulation? I measure a bad regulation (5,1V down to 4,5V) with light load (near 20-30mA on 5V line). Note that i didn't use R3,R4,C5,C6,C7. I choose D6,D7 as STTH102 and i used a larger value on C8 (1000uF+2*100nF). Thank you. Regards. Nicola.
Comments
Hi, I tested the application with only D6 and it functions well. Also, tests with only D7 get good regulation. In both tests the voltage regulation is approx 100mV. I need a good regulation in 5V line (<±4%) and a discrete regulation in +12V line. What other test can I do? Thank you. Regards. Nicola
measure the phase of each winding of your transformer.
Use a scope probe (let say CH1) and connect it to pin 2 of the transformer. Then connect a second probe (Let say CH2 of the oscilloscope) and measure pin 7 waveform. Both waveforms should be in phase. Do the same at pin 6 and pin 4 of the transformer.
all your measurements should be with respect to pin 2 of the transformer.
the phases of the windings are ok. Adding an RC in FB pin the regulation is better. Other suggestions? Thank you.
How big is the ringing at your DRAIN node? If possible, try to reduce the ringing as shown in figure 10 of data sheets.
http://www.powerint.com/sites/default/files/product-docs/linkcv_family_datasheet.pdf
Your schematic looks ok
what I would do is to remove D7 from the circuit( you do not have R4 and C7 in the circuit)
So now you have a single output power supply. test regulation and see how bad it is. Then connect D7 and disconnect D6.
See if in both conditions the power supply has very poor regulation