Cross regualtion on TOP257YN HX
Our product changed so we have to update the power supply.
We need two outputs 15V 1A regualted and 4 V 1.2A.
I want to regulate the 15 volt because the load variation ranges from maybe 5 mA to 1A depending og the brightnes of TFT backlight and the amount of connected sensors.
From the 4 volt we connect a 3.3 V LDO with a worst case dropout voltage of 0.55 volt. I use the LDO to take care of the cross regulation. The maximum temp on the 4 volt output is 5.3V at that voltage the LDO becomes quit hot.
We use LDO because it is cheap. and atmax load had an efficiency of 94.6% at $ volt input and 3.3 1.14 A output.
The tow power outputs must be isolated so we use the floating option in PI extert.
66µF input cappacitors EEL22 core.
Is this the best way to design my power supply or do you have an other suggestion?
Comments
Can you give a estimation of the minimum power that must be drawn from the 15V to get the 4V within the spec ?
That is not possible to say precisely -- you will have to experiment to find range.
Since I do not know the regulation tolerance on 15 volts output I can only comment on what you have. When 15V is at minimum load you may not have enough headroom for regulator so you may need to preload 15V with resistor to keep 4V up during lightly loaded +15v output condition.