Physics 536 - Spring 2008
Electronic Techniques for Research
Still Another Example of Using Berkeley SPICE with nanoHUB
Example of temperature dependence
Consider the circuit shown below:
In which the components have the following values:
The voltage source VC is used to measure the current
into the collector of the transistor. Since it has a voltage of zero
volts, it does not change the behavior of the circuit in any way. It only
provides a way to measure the current in one part of the circuit.
Because the sign of the current is positive when it flows into a
voltage source, the current into VC will be positive
when connected in this way.
| VCC ||10 V |
| VEE ||10 V |
| R1 ||29.6 kΩ|
| R2 ||4.64 kΩ|
| RE ||200 Ω|
| Q1 ||2N3904|
| VC ||0 V|
The SPICE netlist, including the model for the transistor is
The output indicates that the current into the collector is 8.79 mA.
But, by increasing R2 to 5.3 kΩ, the current is increased
to 10.008 mA, without significantly changing the current through the bias
Simulation with different temperatures
The temperature of the circuit can be specified, in degrees Celcius,
using the line
For example, to simulate the circuit at 100 degrees C with the adjusted
value for R2, the netlist would look like this:
and the resulting output would be
demonstrating that the temperature increase from the default of 27 degrees
C to 100 degrees C results in the current decreasing by 1 mA, due to the
temperature dependence of the PN junction in the transistor.