A BJT characteristic curve, also known as collector curves, is a graph which shows the relationship between the collector-emitter voltage and the collector current for different value of base current. The characteristic curve is used to determine value of collector current for different collector-emitter voltage at a specific base voltage. This graph is useful in determining the operation region of the BJT and set BJT transistor biasing or operating point. Here it is shown how one can plot BJT characteristic curve in Proteus electronics circuit design software.
The following picture shows the connection to be made.
1. Place the BJT like BC547 transistor on the schematic
2. Place and connect a DC current source from the generator palette to the base of the transistor as shown.
Double click on the generator to open its properties. Now, set the name to Ib, make it a DC source and ensure that that current source is checked.
3. Place a DC voltage source from the generator palette and name it Vce as shown below.
4. Place a collector current probe from the probe palette and name it Ic. Ensure that it is directed downwards as shown below.
5. Place a transfer graph from the graph palette onto the schematic. Then drag and drop the Ic current probe into the transfer graph as shown below.
Right click on the graph and click on edit properties. Then in the setting window, set the name of the graph like BJT characteristic curve, in source 1 select ROOT_Vce and set the start value to 0, stop value to 20 and no. of steps t 100, in source 2 select ROOT_Ib, set the start value to 0, stop value to 20m and no. of steps to 10. Then click OK to exit.
6. Then right click the graph and click on Stimulate graph or just press SPACE bar on the keyboard.
This will then plot the characteristic curve for the BJT transistor BC547 as shown below.
This tutorial showed how one can plot a BJT transistor characteristic curve in Proteus. This is useful when, for example, if you don't know the properties of a transistor and you need to build BJT amplifier circuit. For building BJT amplifier, you need to know operating point so that you can calculate the biasing voltages and current. In this situation, it is good to have a collector curves for unknown BJT transistor so that you know what value of collector current and collector-emitter voltage to expect for given base current. Once you know the input and output requirement you can then use the BJT amplifier calculator to calculate the biasing components values.
