Wiki

Differences

This shows you the differences between two versions of the page.

Link to this comparison view

Next revision
Previous revision
Next revision Both sides next revision
university:courses:alm1k:alm-lab-4 [13 Apr 2015 17:27]
Doug Mercer created
university:courses:alm1k:alm-lab-4 [08 Jan 2018 15:18]
Doug Mercer [Questions:]
Line 13: Line 13:
 =====Background:​===== =====Background:​=====
  
-The variable analog outputs supplied by the ALM1000 hardware are voltages but can also measure current at same time. The BJT collector current, I<​sub>​C</​sub>,​ is controlled by the very small base current, I<​sub>​B</​sub>​. The generator output voltage must be converted into a suitable small current to drive the base terminal of the device under investigation. A simple high value resistor can be used to convert this voltage into a current, as shown in figure 1. However, only if the voltage across the resistor is known or controlled in some way. In this simple circuit, the base current I<​sub>​B</​sub>​ = (CB-V - V<​sub>​BE</​sub>​)/​10KΩ. We can set CB-V to known values but we don't know the exact value of V<​sub>​BE</​sub>​. We can of course remove an estimate of the V<​sub>​BE</​sub>​ mathematically. This is still only an estimate but close enough for our purposes here.+The variable analog outputs supplied by the ALM1000 hardware are voltages but can also measure current at same time. The Bipolar Junction Transistor can be modeled as a current controlled current source. The BJT collector current, I<​sub>​C</​sub>,​ is controlled by the much smaller ​base current, I<​sub>​B</​sub>​. The generator output voltage must be converted into a suitable small current to drive the base terminal of the device under investigation. A simple high value resistor can be used to convert this voltage into a current, as shown in figure 1. However, only if the voltage across the resistor is known or controlled in some way. In this simple circuit, the base current I<​sub>​B</​sub>​ = (CB-V - V<​sub>​BE</​sub>​)/​10KΩ. We can set CB-V to known values but we don't know the exact value of V<​sub>​BE</​sub>​. We can of course remove an estimate of the V<​sub>​BE</​sub>​ mathematically. This is still only an estimate but close enough for our purposes here.
  
 {{ :​university:​courses:​alm1k:​alm_lab4_f1.png?​600 |}} {{ :​university:​courses:​alm1k:​alm_lab4_f1.png?​600 |}}
  
-<WRAP centeralign>​Figure 1 NPN I<​sub>​C</​sub>​ vs. V<​sub>​CE</​sub>​ characteristic curve measurments</​WRAP>​+<WRAP centeralign>​Figure 1 NPN I<​sub>​C</​sub>​ vs. V<​sub>​CE</​sub>​ characteristic curve measurements</​WRAP>​ 
 + 
 +If we sweep the voltage on the collector, V<​sub>​CE</​sub>,​ while changing the voltage on the resistor in a step wise fashion for each sweep cycle of the collector voltage, we can generate a set of characteristic curves of the collector current vs collector emitter voltage for a set of base currents. ​
  
 ====Materials:​==== ====Materials:​====
Line 28: Line 30:
 ====NPN device Directions:​==== ====NPN device Directions:​====
  
-Build the simple characteristic curve measurement circuit shown in figure 1 on your solder-less breadboard. The green boxes indicate where to connect the M1000+Build the simple characteristic curve measurement circuit shown in figure 1 on your solder-less breadboard. The green boxes indicate where to connect the ALM1000
  
 ====Hardware Setup:==== ====Hardware Setup:====
Line 54: Line 56:
  
 <WRAP centeralign>​Figure 2 PNP I<​sub>​C</​sub>​ vs. V<​sub>​CE</​sub>​ characteristic curve measurments</​WRAP>​ <WRAP centeralign>​Figure 2 PNP I<​sub>​C</​sub>​ vs. V<​sub>​CE</​sub>​ characteristic curve measurments</​WRAP>​
 +
 +====NPN Beta vs V<​sub>​CE</​sub>​ Directions:​====
 +
 +Beta (β) is defined as the ratio of the collector current, I<​sub>​C</​sub>,​ to the base current, I<​sub>​B</​sub>​. Beta is not constant and varies as the operating conditions of the transistor changes. In this experiment we will be plotting β vs V<​sub>​CE</​sub>​.
 +
 +Change the 10 KΩ resistor in figure 1 to 1 KΩ. 
  
 ====Questions:​==== ====Questions:​====
university/courses/alm1k/alm-lab-4.txt · Last modified: 03 Nov 2021 20:31 by Doug Mercer