122-28176 Parallax Inc, 122-28176 Datasheet - Page 68

• Manufacturer Part Number: 122-28176
• Description: GUIDE STUDENT PROCESS CONTROL
• Manufacturer: Parallax Inc

Specifications of 122-28176

• Accessory Type: Manual
• Product: Microcontroller Accessories
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With/related Products: Propeller Education (PE) Kit
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Contains lead / RoHS non-compliant

millions, of transistors working together as an Integrated Circuit (IC) to perform
sophisticated operations.
As a switch, the transistor may be driven to a condition where it drops virtually no
voltage and allows full current flow in a load. In this condition, it acts similar to a closed
switch. No drive control applied to the transistor causes it to behave like an open switch.
The transistor is semi-conductor configured to control current flow, allowing it to be fully
on, fully off, or anywhere in between.
Figure 3-10 represents a typical discrete transistor. A BJT has 3 leads: Base (B), Emitter
(E) and Collector (C). This transistor symbol tells us that it is an NPN.
The BJT is a current-controlled device. A small base-current (I
much larger collector-current (I
The transistor has 3 operating regions and can be thought of as a water valve. When the
valve (the base) is off, there will be no water flow in the pipe (collector-emitter). As you
begin opening the valve, the amount of water flowing in the pipe is proportional to how
far the valve is opened. At a certain point, opening the valve any further may not
produce any appreciable change in water flow. Restrictions in the pipe and supply water
pressure limit the flow rate.
There are three operating regions of the transistor as shown in Figure 3-11.
•
•
Cutoff Region: Insufficient voltage on the base to produce appreciable current
flow in the base and, therefore, no collector current. As an electronic switch, the
collector to emitter is "open" and collector-current (I
Active Region: The amount of current flow in the collector is directly
proportional to the current flow in the base. The BJT is somewhere between
fully-off and fully-on, controlling current flow. I
C
). I
B
controls I
C
.
Figure 3-10
2N3904 NPN Transistor
C
C
is equal to the base-current
) is essentially zero.
B
) is used to control a