APPENDIX A ■ APPENDIX AAs you move forward in electronics, you’ll run across other terms for voltages. It’s worth knowing these
modern labels, as you’re going to encounter them on datasheets, schematics, books, and articles.
Ground, Not Negative Voltage
Figure A-7 shows one of the most prevalent symbols in a schematic. Recall that this indicates the
conventional return path for all power in a circuit. On a battery-operated circuit, the path indeed leads back
to the negative terminal of the battery. However, this symbol is actually referred to as “ground” or “common.”
Figure A-7. Schematic symbol for ground, usually abbreviated GND
You can think of this as the lowest voltage possible in the circuit; 0 V; the power has reached the ground.
You connect your black multimeter test probe to this location in the circuit and measure all positive voltages
as being “above ground.”
Nowadays, negative voltage suggests three power-supply voltage levels: a positive voltage, a ground,
and a truly negative voltage that ground power can flow to. When speaking informally, there’s nothing wrong
with saying, “Hook one end of the motor to positive and the other end to negative.” However, when there are
really only two connections from the power supply, you should formally refer to negative voltage as ground,
to prevent confusion.
V Double Letter
With few exceptions, all integrated-circuit (IC) chips contain transistors. There are two kinds of transistors,
bipolar and field effect. From an earlier chapter, you know that bipolar transistor leads are labeled collector,
base, and emitter. Field effect transistors happen to be labeled drain, gate, and source.
When IC chips became popular in the 1970s, chip pin voltages were specified based on the internal part
of the transistor to which they were connected. For example, the positive power supply pin would be labeled
VCC. The C stands for collector, and is repeated (VCC) to indicate that it represents the voltage that the power
supply for the collector should create. That’s not necessarily the voltage at the collector (which would be VC).
The transistor pin labeling conventions continue today. No doubt you’ll see them on everything from
discrete transistor circuits, logic chips, all the way up to microcontrollers.
You may consider the following voltage terms positive voltage: +, V+, VBB, VCC, VDD, and VGG.
You may consider the following voltage terms ground (formerly “negative”) voltage: -, V-, GND,
common, VEE, and VSS.