This is a task that requires you the learner to take responsibility for your learning. You will be given a problem statement. In this problem statement are some highlighted key terms / jargon.

It is your task to research these terms in order to understand the problem and to attempt to solve it.
Start with the references provided.
Don’t feel bad if you struggle and feel free to work with others to try and tackle this problem.

Intended Learning Outcomes

Calculate the total resistance of two resistors in series
Calculate the total resistance of two resistors in parallel
Calculate the current through two resistors in series
Derive the equation for potential division using two resistors
Use a potential divider to create a voltage reference
Calculate the Thévenin equivalent circuit of a potential divider voltage source.
From (6), describe the trade offs between power consumption, noise and output resistance.

Problem Statement

Real world voltage sources can be modeled as an ideal voltage source V and an internal resistor, as shown below. The power supply on the Nucleo Board is 3.3V, with a small internal resistance. For the purposes of this exercise, we will ignore this internal resistance and assume it to be close to ideal.

Problem A (everyone)

Using the Nucleo Board power supply and two resistors,

design a potential divider circuit to create a $2.2V$ voltage reference using two resistors. The quiescent current should be $\leq 1mA$
calculate the series resistance of the two resistors
calculate the quiescent power consumption of your design (when not under load). Quote your answer in milliwatts (mw).

Problem B (advanced)

NOTE – Only attempt this if you are very confident and/or have plenty of spare time!

Derive the Thévenin equivalent circuit for the voltage source (see over) of this new 2.2V source.

What is the internal resistance $R_{int}$ ?
If this new voltage source were to drive a $1k\Omega$ load, what would be the output voltage Vout?
If this new voltage source were to drive a $1M\Omega$ load, what would be the output voltage $V_{out}$ ?
What changes would you have to make to make this suitable for driving a $1k\Omega$ load? How would this impact on quiescent power consumption?

Comment on the suitability of a voltage divider as a power supply.

The component inside the dashed border represent a real voltage source, with ideal voltage source V and internal resistance Rint. The resister RL represents the **load resistance**. The actual voltage output Vout is calculated using the equation for a **potential divider**.

Thévenin Equivalent Circuit for the 2.2V voltage source

References

[1] Ohms Law, BBC BiteSize, http://www.bbc.co.uk/schools/gcsebitesize/science/edexcel_pre_2011/electricityintheory/voltagecurrentresistancerev3.shtml, accessed 27/09/2018

[2] Voltage divider tutorial., https://www.youtube.com/watch?v=XxLKfAZrhbM, accessed 27/09/2018

[3] Voltage Dividers, https://www.youtube.com/watch?v=AyB2kXThlvE, accessed 27/09/2018

[4] Thévenin’s theorem., https://en.wikipedia.org/wiki/Thévenin%27s_theorem,accessed 27/09/2018

Feedback

If you wish to leave feedback or have a question, please use the form below.

[contact-form][contact-field label=”Name” type=”name” required=”true” /][contact-field label=”Email” type=”email” required=”true” /][contact-field label=”Website” type=”url” /][contact-field label=”Message” type=”textarea” /][/contact-form]