I am designing a circuit for SIM900 and PIC MCU. I am facing few problem on power supply for them. I will be giving 12v to the circuit. Now PIC works on 5volts and SIM900 works on 3.2v - 4.8v. At first I thought of using two different voltage regulators. But Now i am using 7805 to convert 12v to 5v and then using a voltage divider to convert 5v to 4v. Below is the schematic:
Here input voltage is 12v and using 7805 to convert it to 5v which will be given to PIC MCU. This 5v is also used in voltage divider circuit to convert it to 4v for SIM900. I have used R1=100 and R2=400 for voltage divider circuit. Is this circuit safe to use. Does voltage divider circuits are good to use. Please help. Thanks.!
Answer
Don't use voltage divider unless in these situations:
high impedance load
inaccurate voltage
almost fixed current consumption circuits
If you have a digital circuit with different current consumption it means you have a variable load then your output voltage will vary in a wide range. This will affect performance of your circuit.
For better efficiency I suggest use a two stage regulator, first stage is a switching regulator with efficiency up to 85%. This stage will deliver you a 5 volt regulated voltage. In second stage use a linear regulator to produce 3.3 voltage. In this scenario you will have a good efficiency behind a stable circuit for your digital circuits.
Always remember : power supply is the most important thing in a circuit for working stable and desirable.
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