Hey guys,
I am wanting to create cleaner DC power rails for some circuits I have been developing, and I wanted to run it by you guys to see if this is a good method or not. I understand that generally you design some of this based off the maximum allowable ripple required, however I do not have those values, so I am trying to make it as clean as reasonably possible.
Basically I need a clean 5V rail (600mA peak tops -> 1 amp will do), and a clean 3.3V rail (80mA peak tops -> 200mA will do). Power input is a 12VDC power adapter. I am using various microcontrollers, sensors, RF, and other breakout boards. Some are susceptible to noise and others are not.
My idea was to have the 12VDC power input come into the circuit, then immediately go through a pi filter (how do I determine appropriate values for this?). I was then thinking of using a adjustable LM2575 switcher and set its voltage output to 7.5 volts, then use a 7805 style linear regulator to get a nice 5V off that. (such as the MC7805AB).
Are these good parts to accomplish this? I was a little uncertain about the 7805 and the heat it may generate (I really do not want to have to use a heatsink if I don't have to), this is why I was trying to get the switcher to output just above the 7805 threshold input voltage.
I had another for instead of using a 7805 style part, to instead use a 5V LDO that has a high PSRR rating - however there are so many parts I didn't really know what I was looking for). This would also allow for me to bring the LM2575 switcher voltage down closer to the 5V rail. I don't know...
I also searched around on the net for a while of possible pi filters that people use for dc power adapter inputs, but couldn't really find much info. I am inclined to use 2x 10uF ceramic capacitors, and 1x 30uH inductor (amperage rating equaling the max power input amperage).
What are your thoughts on this?
I am wanting to create cleaner DC power rails for some circuits I have been developing, and I wanted to run it by you guys to see if this is a good method or not. I understand that generally you design some of this based off the maximum allowable ripple required, however I do not have those values, so I am trying to make it as clean as reasonably possible.
Basically I need a clean 5V rail (600mA peak tops -> 1 amp will do), and a clean 3.3V rail (80mA peak tops -> 200mA will do). Power input is a 12VDC power adapter. I am using various microcontrollers, sensors, RF, and other breakout boards. Some are susceptible to noise and others are not.
My idea was to have the 12VDC power input come into the circuit, then immediately go through a pi filter (how do I determine appropriate values for this?). I was then thinking of using a adjustable LM2575 switcher and set its voltage output to 7.5 volts, then use a 7805 style linear regulator to get a nice 5V off that. (such as the MC7805AB).
Are these good parts to accomplish this? I was a little uncertain about the 7805 and the heat it may generate (I really do not want to have to use a heatsink if I don't have to), this is why I was trying to get the switcher to output just above the 7805 threshold input voltage.
I had another for instead of using a 7805 style part, to instead use a 5V LDO that has a high PSRR rating - however there are so many parts I didn't really know what I was looking for). This would also allow for me to bring the LM2575 switcher voltage down closer to the 5V rail. I don't know...
I also searched around on the net for a while of possible pi filters that people use for dc power adapter inputs, but couldn't really find much info. I am inclined to use 2x 10uF ceramic capacitors, and 1x 30uH inductor (amperage rating equaling the max power input amperage).
What are your thoughts on this?