OK for the power supply design I will be using a dc dc boost converter to crank up 3 volts from two AA batteries to 5 Volt which will be the system VCC.
We also need a -5 volt negative supply and for that we will be using another dc dc converter using the flying capacitor configuration. Luckily the IC we will be using MCP34063 is a multi purpose converter chip capable of step up, step down, and inversion.
So using the fist converter we convert 3 volts to 5 volt system VCC. Then +5 volts from system VCC to -5 volts for the negative supply. Although as the negative supply will be used only for biasing the opamp its current requirement will be much lower.
Let us discuss some feature for the MCP34063 converter:
Just filling in the equations we can calculate the values of the various other passive components components.
For our requirement we need 3 to 5 volt boost.
Turns out I had already designed a power supply which uses this kind of approach i.e. using two AA batteries to generate 5 volt supply. I actually designed a board with it as well which I will share here.
First the circuit diagram
We also need a -5 volt negative supply and for that we will be using another dc dc converter using the flying capacitor configuration. Luckily the IC we will be using MCP34063 is a multi purpose converter chip capable of step up, step down, and inversion.
So using the fist converter we convert 3 volts to 5 volt system VCC. Then +5 volts from system VCC to -5 volts for the negative supply. Although as the negative supply will be used only for biasing the opamp its current requirement will be much lower.
Let us discuss some feature for the MCP34063 converter:
For calculating the values of the other passive elements we follow the tabular approach.
For our requirement we need 3 to 5 volt boost.
Turns out I had already designed a power supply which uses this kind of approach i.e. using two AA batteries to generate 5 volt supply. I actually designed a board with it as well which I will share here.
First the circuit diagram
The final value of the output voltage is set by the ratio of two resistor R4 and R5 here so I have chosen accurate 1% tolerance E96 values. Yes these resistors are costly but to maintain the accuracy of the output voltage it is necessary.
Actually this project I did for the open source hardware community. One of the forums I saw some students wondering how to power the common rail of their breadboard from battery they were using an entire 12 volts 8*AA batteries and then converting then using a linear regulator 7085 to 5 volts. This was cumbersome 8 battery pack plus wastage of power due to linear regulator. So I decide to use this scheme to design a board which has output pins which directly clamp on the breadboard powering the VCC and the ground rails respectively and just using 2*AA rather than 8.
PCB design
The above circuit on a double layer board. XCON1 and XCO2 are the power and Ground pins which directly clamp on with the bread board.
Let us look at the finished PCB design
The complete populated board with onboard battery holder installed
So far for the power supply design in the future I am sure to make modifications to it but for now this will do.
In the next blog we will start working with our software.
To be continued...
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