Technical Knowledge: Electronics, Instrumentation and Computer Trades
This section spans semiconductor devices, digital electronics, measurement and instrumentation, and computer fundamentals. Expect short numerical items on transistor currents, logic gates and number systems.
Core concepts
- Diode: conducts in forward bias above the barrier voltage, about 0.7 V for silicon.
- Transistor: IE = IB + IC, and IC = beta x IB in the active region.
- Op-amp: very high input impedance, and virtual ground at the inverting input in negative feedback.
- Logic gates: AND, OR, NOT, NAND, NOR, XOR, with NAND and NOR as universal gates.
- Instrumentation: transducers convert physical quantities into electrical signals; the CRO displays waveforms; a multimeter measures V, I and R.
- Computer: binary number system, memory hierarchy, operating system, and basic networking.
Worked example
A transistor has beta = 100 and base current 20 microampere. Then IC = 100 x 20 microampere = 2000 microampere = 2 mA. Emitter current IE = IC + IB = 2 mA + 0.02 mA = 2.02 mA. The result confirms the transistor is in the active region, where the current gain relation holds.
Traps
In an NPN transistor, conventional current flows into the base and collector and out of the emitter; do not reverse it. Virtual ground applies only with negative feedback. Convert binary to decimal by place values, not by reading digits as decimal. Remember that 1 kB is often 1024 bytes in memory contexts.
Key points
- Silicon diode forward drop is about 0.7 V.
- IC = beta x IB, and IE = IC + IB.
- NAND and NOR are universal gates.
- Virtual ground holds only under negative feedback.
- Memory: 1 kB = 1024 bytes in the binary convention.