Universal to +/-12 volt. Variable load concerns.
I need a universal AC input power supply that will give me a pretty tight bipolar 12-14 volt supply. One of the two legs (I guess I could even balance them) needs to drive a relay that consumes approx 75 mA. There are two relays. So I suppose I could put both of them on the +12 supply for 150 mA.
This will also drive an opamp with fairly low output. But the output needs to be very close to 12 volts. I can use a zener to limit it and design the rail to be +15/-12 volts.
And it will have to drive a microprocessor and some LEDS.
When it boots up, the microprocessor and one LED will be the load. When active, both relays and another LED will come on line. So, I am guessing I will be going from 100mW to about 3W. Reading the AN-37, some of the design considerations and formulas are based on Po.
I am afraid I will end up with a circuit that is unhappy when lightly loaded. I was planning to use the LNK 304/5/6 line of product. I would rather not have a transformer.
Is this possible with that family of chips?
Comments
Heat
Input Voltage Extremes
Load Extremes
It will take a bit of testing to verify proper operation with all these variables. Which end of the variables do I need to be most concerned about? For example, is low load with low temperature an area of concern? Or are there no areas of concern? Do I need to do temperature chamber work? Just want to make sure the device works in all corners of the envelope.
Before you deliever the power suppy/system to your customer, you have to spend a lot of time to verify all the possible conditions, including hot and cold test at thermal chamber. But the biggest concern for me is low line full load at cold and hot temperature, since the part may not have enough capabilty to source the load.
but if you really want to save some effort, you can start from DER186, which is a 12V4.2w design used LNK-II and can be found via the following link: http://www.powerint.com/sites/default/files/PDFFiles/der186.pdf.
Thanks, that is exactly what I need to know.
I will read the DER186 document. Hopefully it does not use a transformer.
The output voltage at 100mw will be a little bit higher for sure, but i do not think it will cause any problems because of the zenner circuit for the micro. I believe DER 47 can give you some idea about the load regulation. DER 47 can be found via the following link: http://www.powerint.com/sites/default/files/PDFFiles/der47.pdf.
if you really concern about the load regulation problem, TNY switch is a very good choice. Optocoupler will be used to handle the regulation problem.
Thanks for using PI part.