| Why batteries
last
long in wrist watches ... It's the electronics, not the batteries |
What is the special property of
batteries in a wrist watch so that they last for many months --- sometimes
years --- at a time?
Nothing. The batteries last so long simply because the watch requires so little power. The transistor circuitry in the watch uses CMOS, Complementary Metal-Oxide Semiconductor technology. Transistors in the circuit act as switches, and there are always two such switches in series between the battery terminals. At no time are both switches conducting. The junction between the switches is either connected to the positive terminal, to the negative terminal, or to nothing. (That's the complementary part.) The transistors are controlled by voltages existing on the gates of the metal-oxide transistors. However, a layer of silicon-dioxide (alias glass) separates the gate from the rest of the transistor. The insulation provided by the glass keeps current from flowing. |
