For this particular question, I am wondering if Q1 must be in saturation mode or active? I am aware Q2 must be in saturation but upon trying to solve this circuit I feel as if I have more unknowns than equations. I would show my work but it does not make sense because I cannot straighten out my thought process. anything help would be appreciated as I feel I am missing a key fact. thanks!
Electrical – Transistor and Microcontroller switch
microcontrollerswitchestransistors
Related Solutions
You don't know VDS or ID. But your task is to obtain a resistance of 200 to 1000 Ohms.
That means, depending on how your "variable resistor" will be used, in your final solution you need to have either
\$200 < \dfrac{V_{DS}}{I_D} < 1000\$
or
\$ 200 < \dfrac{\mathrm{d}V_{DS}}{\mathrm{d}I_D} < 1000\$
To get the I/V-Curve of the solar panel (and therefore the Maximum Power Point), I would suggest you use a circuit with feedback to change the current sourced from the solar panel. This is possible with a variable current source like this:
simulate this circuit – Schematic created using CircuitLab
Vref determines the current sinked from the solar panel. The current is calculated as follows:
\$I=\frac{V_{ref}}{R_2}\$
Therefore, from the knowledge of the Vref and the measurement of the solar panel voltage, you can easily determine the maximum power of your panels
For reference: The circuit is from "A collection of Amp Application by James Wong (Analog Devices): http://www.analog.com/media/en/technical-documentation/application-notes/28080533AN106.pdf
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Best Answer
It is easiest to pull the most current from Q2b if Q1 is in saturation. Additionally, the lowest voltage drop across Q2 is when it is in saturation. Therefore you should solve this question with each transistor in saturation during the appropriate time.