Simple Guide to DIY Electronics #1: Passive Components August 16, 2011 16:31
Electronic components are called 'passive' when they don't produce gain or require a power supply to function. While there are numerous components that meet this definition, when we refer to 'passive components' we usually mean the following three types: resistors, diodes, and capacitors.
- Resistance: The amount of resistance, measured in in Ohms (Ω). This is usually indicated on the surface of the resistor with color-coded stripes.
- Tolerance: The degree of precision to which the resistor was manufactured. For example, a 1k resistor manufactured to ±1% tolerance may have an actual value between 990 and 1.1k ohms. This is also typically indicated with a color-coded stripe.
- Power: The maximum power (heat) a resistor can dissipate without being damaged. This is not specified on the body of most resistors, but can often be guessed from the resistor's physical size with a little experience. Most resistors in audio circuits dissipate less than 1/2 Watt of power.
- Resistive Material: Resistors are made from a wide range of materials, but the most common in audio circuits are:
- Metal Film: By far the most common in modern equipment. They are nearly transparent in audio circuits and can be made cheaply to very strict tolerances.
- Carbon Composition: Long since surpassed by film resistors in terms of noise and precision, carbon comps are nonetheless still used, especially in circuits that attempt to clone a vintage unit. Many vintage guitar pedal enthusiasts, for example, use exclusively carbon comps.
- Carbon Film: Precise and low-noise enough for most audio applications. Often used when a certain value or power rating is not available in metal film.
- Capactiance: The amount of capacitance, measured in farads. Common subdivisions of the farad are micro-farads (uF) nano-farads (nF) and pico-farads (pF).
- Voltage: The maximum operating voltage.
- Polarity: Some capacitors are polarized and must be installed a certain way in order to remain in their "unexploded" state :O If a capacitor is polarized, its polarity will be marked on the body of the capacitor and accordingly on the schematic or PCB in which it is used.
- Ceramic: Small, non-polarized, usually used as bypass caps.
- Electrolytic: Capable of high capacitance per volume, usually polarized.
- Silver Mica: Linear and stable, but relatively large and expensive.
- Polyester: Low tolerance and low voltage, often seen in audio circuits.
- Polystyrene: High stability, low distortion.
- Light Emitting Diode: Emits light when current passes through it. The anode is indicated by having a longer lead than the cathode.
- Schottky Diode: Designed to cause as little voltage drop as possible. The cathode is usually marked with a silver stripe on the diode's body.
- Zener Diode: Operates like a standard diode until a certain voltage is reached, when it allows current to flow both ways. The cathode is usually marked with a stripe.