Switching Regulator Step-up DC-DC Converters problem
I have been working on a PIC18F microcontroller project for a long time now and Im at the point where I have to get a working (efficient) power supply for it. This is a hand held testing device used for the industry I work in. I started off using a 9v battery with a L7805 voltage regulator. Real quick I learned how inefficient this combination is. The microcontroller never turns off just goes into sleep/doormat state when its not being used.
I decided to go with a pair of AA batteries and a MAX756 for its vastly superior efficiency. I built the circuit using the Typical Operating Circuit from the data sheet. The fist time I used a solderless bread board just to see how it worked and it worked great for the most part. The efficiency was well within my designee envelope.
The problem that Im having now it with a .1v ripple in both the output from the battery and the supply to the system. This is causing erratic readings in my analog to digital converters in the IC.
I then transitioned to a SMD board to try to solve the problem and no luck. I have tried larger and larger filtering capacitors to solve it and found no help until I got in the 2000uf range. This is a bit on the large side for the hand held project Im working on. With a very light load the problem goes away.
Im sure that my lack of understanding switching power is biting me.
Any help or suggestions would be greatly appreciated.
Input is 2xAA batteries
Output is 5v
Max current draw is 120mA
Parts for power supply
MAX756
Inductor 22μH (PO770.223T)
Capacitors 2x 100μF (595D107x9016D2T)
Diode Schottky (1N5817)
I have been working on a PIC18F microcontroller project for a long time now and Im at the point where I have to get a working (efficient) power supply for it. This is a hand held testing device used for the industry I work in. I started off using a 9v battery with a L7805 voltage regulator. Real quick I learned how inefficient this combination is. The microcontroller never turns off just goes into sleep/doormat state when its not being used.
I decided to go with a pair of AA batteries and a MAX756 for its vastly superior efficiency. I built the circuit using the Typical Operating Circuit from the data sheet. The fist time I used a solderless bread board just to see how it worked and it worked great for the most part. The efficiency was well within my designee envelope.
The problem that Im having now it with a .1v ripple in both the output from the battery and the supply to the system. This is causing erratic readings in my analog to digital converters in the IC.
I then transitioned to a SMD board to try to solve the problem and no luck. I have tried larger and larger filtering capacitors to solve it and found no help until I got in the 2000uf range. This is a bit on the large side for the hand held project Im working on. With a very light load the problem goes away.
Im sure that my lack of understanding switching power is biting me.
Any help or suggestions would be greatly appreciated.
Input is 2xAA batteries
Output is 5v
Max current draw is 120mA
Parts for power supply
MAX756
Inductor 22μH (PO770.223T)
Capacitors 2x 100μF (595D107x9016D2T)
Diode Schottky (1N5817)