About the DC/DC Convertor

[kencai]

Hi,

I meet a DC/DC power design and its basic requirement is :input voltage=DC3.0v,Output voltage=DC5.0V,Iout_max≤250mA,isolated by transformer.
And could I use the ADP1621 as my dc/dc switch chip ?If could ,Could i take the flyback voltage from the transformer as my sampling voltage by the feedback circuit?

And thanks your any advice or other good option.
thanks again.

 

[Claude Abraham]

I would use the TL431 shunt regulator with an optocoupler for the feedback loop. The regulation is much better. Most SMPS control IC vendors have app notes covering this method. I am currently using such a method and with great results. The auxiliary winding off the transformer is not a bad way to sense voltage if the line and load regulation needed is not too tight. With winding feedback, 1 or 2 % line and 2 to 3 % load regulation can be expected. With the TL431/optocoupler approach, I get line and load regulation of around 0.2%. Just my thoughts. I don't know how precise your output needs to be, but the TL431 is the tighter of the two regarding regulation.

 

[kencai]

I would use the TL431 shunt regulator with an optocoupler for the feedback loop. The regulation is much better. Most SMPS control IC vendors have app notes covering this method. I am currently using such a method and with great results. The auxiliary winding off the transformer is not a bad way to sense voltage if the line and load regulation needed is not too tight. With winding feedback, 1 or 2 % line and 2 to 3 % load regulation can be expected. With the TL431/optocoupler approach, I get line and load regulation of around 0.2%. Just my thoughts. I don't know how precise your output needs to be, but the TL431 is the tighter of the two regarding regulation.

First,thanks for your advice.
My precise need is around 5% in my output.I had ever used mc33063 (Voltage Inverting Converter) as my transformer-isolated(AC4000V isolated) converters.And in the case,I directly detected the flyback voltage from the primary-side winding(no auxiliary winding) as the feedback sense voltage .But after the rectifier I added a LDO to help arriving 5% output precision.
But now ,I am finding a suitable chip to replace the MC33063 ,Because the MC33063's minimal input voltage is just 3V and I need to improve the efficiency. I don't know if I could use the ADP1621 to replace it,But I know little about the ADP1621 using as transformer-isolated converters.
And if no good idear,I would try to use the resistors dividing the output voltage with an optocoupler as the feedback loop.