122-28176 Parallax Inc, 122-28176 Datasheet - Page 181

• 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

"Current sink" means that the output controls the ground, or negative supply, to power a
device, as demonstrated in Figure 5-23. The BASIC Stamp controls the ULN2003,
which energizes a 12 V, 100 mA relay coil. The relay coil is closing contacts to drive a
115 VAC fan. The electromagnetic relay draws considerable power. Frequent cycling
causes chatter and wears out the moving contacts. An alternative is a solid-state relay
discussed shortly.
Current source is where the output is the positive supply. A helpful phrase to remember
is – "Current sinks to ground." By using a Darlington-pair, a very small base current can
saturate the drive stage. Figure 5-24 is a schematic for one driver. Note that it contains
an internal clamping diode for surges from inductive loads such as coils and motors.
Figure 5-24
Example of
ULN2003A Single
Stage Darlington-
Pair Configuration
Figure 5-23
Example of
Driving an
Electromagnetic
Relay for 115 VAC
Control