Understanding Common Electronic Parts Physically
Resistors: The main uses of resistors is current limiting and safeguarding the active components from damage. The resistance value selection may broadly depend on the type of active component to which it is connected and the load current. For carbon and metal film resistors, the values may be recognized through their printed color codes; for the wire wound types, the numbers are directly marked. A resistor does not have a polarity and may be connected any way round.
Capacitor: Commonly they may be seen in ceramic disc, polypropylene, tantalum, and electrolytic types. Mostly the electrolytic and tantalum types have polarity and need to be strictly and correctly oriented accordingly to a circuit as per the circuit schematic. Tantalum capacitors are valued for their negligible leakage characteristic and accuracy. In these capacitors the capacitive value is directly shown over their body, whereas for the other two types the value may be coded through special figures.
For example, if a figure 104 is impressed, it indicates 4 zeros to be placed after the initial digit which is 10. So it becomes – 100,000.
The above value will always be in picoFarad or pF. So, a 104 capacitor has a value of 100,000 pF.
Simply dividing it by 1,000 gives 100 nanoFarad or 100 nF, and further dividing it by 1,000 produces 0.1 microFarad or 0.1 µF. It’s simple, isn’t it? What does the figure 103 indicate?
Diode: These active components may be basically categorized as rectifier, zener, and light emitting diodes. The most commonly used 1 amp rated rectifier diode is 1N4007. You can increase this rating by simply wiring many diodes in parallel or using a single higher rated one like 1N 5408 (3 Amps). Zener diodes primarily do the job of restricting the voltage to a particular desired level as per their voltage ratings. LEDs are pretty popular as they have the special quality of emitting light and are available in different colors. However, basically they behave the same way as a rectifier diode (low power).
SCR and TRIACS: These are high voltage switching devices, typically used for mains AC voltage load switching. They are quite comparable to transistors as they too have a separate triggering terminal with respect to ground. Their leads may be identified through their specific datasheets, but most of them have their lead orientations as shown in the diagram. An SCR or called thyristor is able to pass only one half cycle of an AC signal whereas a triac is able to pass both the halves of an AC signal input. These devices are different from transistors due to the following reasons:
- SCRs require critical gate firing angle parameters and are not linear.
- The triggering cannot take place at relatively lower currents, very unlike transistors.
- They work only with alternating currents (ACs) and will latch up if a DC load is involved.
Transistors: These active, and perhaps the most important electronic part ever, devices come in a variety of different shapes, sizes, and internal configurations. A transistor may be normally either a NPN or PNP, which are complementary to each other. It’s very easy to differentiate and recognize them through their external appearances and through datasheets. The following explanation will provide you the necessary general information regarding transistors.
Like every active component, each category of transistors too will have their own specified breakdown thresholds. Typically, you should be careful about their Collector to Emitter and Base to Emitter breakdown voltages and Currents. They are represented as UCEO, UBEO, and IC (maximum) respectively. If you are not sure with the parameters of a particular device, refer the datasheet immediately.
Relays: These are electromagnetic mechanical devices used to toggle loads involving heavy current and voltages. A relay is mostly used in conjunction with a transistor where low power switching from the transistor is used to operate the relay and the subsequent output is a much heavier load. This configuration is called a relay driver circuit.
The next page will further explain how to identify electronic components through their external appearances and lead configurations.