122-28176 Parallax Inc, 122-28176 Datasheet - Page 182

• 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

H-Bridges
Using PWM control, it was seen that the speed of a DC motor might be controlled. How
about direction? This can be performed using the H-Bridge as shown in Figure 5-25.
If P2 applies PWM (unfiltered) to the bridge (with P1 low), which transistors will be
cycled? Q
motor will be + and the right −. The motor will rotate in one direction at a speed based
on the duty cycle applied.
What occurs when P2 is low and P1 applies the PWM? Q
current flow such that the right motor terminal is + and the left -. By reversing polarity to
a standard DC motor, the direction of rotation is reversed. While Figure 5-25 uses BJT
transistors, a better choice would be MOSFETs since the devices are being switched on
and off and are not controlling an analog level. NOTE: The brushless DC fan in the
Process Control Parts Kit is not a standard DC motor and will not operate with reversed
polarity.
4
and Q
1
. Following current flow from +12 to ground, the left terminal of the
2
and Q
3
Figure 5-25
Example H-Bridge
Drive of DC Motor
are cycled applying