I am designing a robot using the PIC16F877A microcontroller that will avoid walls and obstacles. I plan to have it run off of 4 AA batteries. I was wondering how i would convert the 6 volt input voltage to the 5 volts that the pic needs. I need to use 6 volts because the h bridge circuit/the motors that I am using require it. I also need exactly 5 volts, because i need a 5 volt reference voltage for my ADC and to run my sensor off of. Using two batteries is an option, but I would hope to avoid at all costs. Finally SMD products won't work, because I would like to build this on a breadboard. I did ask a similar question here How to get input voltage of 5 and 6 volts but my needs have changed since then and the answers wont fit my problem. How would a normal project overcomethis problem.
Answer
Easy way is to connect a diode in series with your batteries (voltage drop across diode is around 0.7V). If you dont dissipate too much power you should be fine.
For example: if you use a general purpose diode 1n400x (x = 1 to 7) You have to look in datasheet for voltage drop at max. current you want to draw
example datasheet: www.diodes.com/datasheets/ds28002.pdf
it says: Forward Voltage @ If = 1.0A -> 1V
so if you draw 1A out of your battery it will drop the voltage 1V and will dissipate 1V*1A = 1 Watt of power.
Thermal resistance of this diode is 100K/W and maximum operating temperature is 150 degree Celcius.
So if you ambient temperature is 25'Celsius the diode temperature will be 125'Celsius. this is high but within specs. if you want lower diode temperature you should look for diodes with lower thermal resistance (usually diodes with larger package have lower thermal resistance)
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