BJT Constant Current Source

For an example of a temperature dependence, we will look at the circuit below  

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There are two ways to look at this circuit One is that this is a self-biasing circuit for a BJT amplifier. If this were an amplifier, the load would most likely be a resistor. (The term self-bias means that the goal of the circuit is to make the collector current independent of device parameters such as Hfe and Vbe.). The second way to look at the circuit is that as far as the load is concerned, Ql, Rl, R2, and R3 form a current source that is, the current through the load is determined by Ql. Rl, R2, and R3. If this circuit were designed as a current source for the load, we could view the circuit as  

No matter what the application, the circuit is designed to make the collector current independent of VBE and Hfe-We will assume that the resistors used have no tolerance and have their exact values specified in the circuit. To see how the tolerance of resistors affects the collector current, see Section 9.C. From previous sections we know that the resistance of a resistor, and Hfe and VBe of a BJT, are affected by temperature. The question is, if the temperature changes, how much does the collector current change  

We will perform two analyses on the circuit. The first will be a plot of collector current versus temperature with ideal resistors. The resistors will have no temperature dependence. The only temperature-dependent device will be the BJT. The second simulation will use temperature dependence for resistors and the BJT. For simulation, we will use the circuit below  

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