Lab 9 - Driving Motors and other Output Devices

1/22/19

Controlling loads....hmmmm... how to do it with power....
A microcontroller is limited to 10mA per channel, and the whole chip  capacity is 50mA. That is not much for larger output devices. An idea is for the microcontroller to control a transistor (a power gate) to allow more current to flow to the output; rather than the power coming all form the microcontroller, the controller will control a transistor, in which power will come from the source through the transistor to the output. The transistor also has a limit, but it is much greater than 50mA. Trasnitir is rated to 200mA, that is 4 times more power than the microcontroller!

Microcontroller controlling a transistor to power a Xmas light bulb

Next step, More Power! Lets pile onto that concept. Lets have the 50mA limit microcontroller output to operate a 200mA transistor, in which that will operate a 0.6A medium power transistor....Yes! Great idea, and the microcontroller only needs about 10mA to operate such a chain, called Darlington Pairs. With this setup, we get more light out of this tiny Xmas light bulb. We will later see that all these transistors can be combined in a single package called the TO-92 package with 5A continuous max limit.

Xmas bulb with Darlington Pair

Xmas bulb with TO-92 package

PWM-Pulse Width Modulation
Control a motor with timed ON and OFF square wave pulses rather than varying the voltage. Basic attempt, and it worked! Controlled not with pure voltage, but controlled with the output of timed voltage pulses. 

PWM Controlled Motor