A capacitor stores charge for a moment and then releases it. It smooths ripples in the supply, filters unwanted frequencies out of a signal, and is used to create time in things like the 555 timer. There are many types and some have polarity, so it is easy to get confused at first. This article covers the types of capacitors beginners meet often, their polarity, how to read values, and how to choose.
Units first
The unit of capacitance is the farad (F), but it is so large that smaller units are used in practice.
| Unit | Read as | Size |
|---|---|---|
| µF | microfarad | 10⁻⁶ F |
| nF | nanofarad | 10⁻⁹ F = 0.001 µF |
| pF | picofarad | 10⁻¹² F = 0.001 nF |
1 µF = 1,000 nF = 1,000,000 pF.
Main types
Ceramic capacitors
Small discs or rectangles with no polarity. Capacitance runs from pF to several µF, they are cheap and good at high frequency, so they are used most for decoupling next to IC power pins. Characteristics differ by dielectric type.
- C0G (NP0): stable with temperature and voltage, but no large values. For precision timing and filters.
- X7R, X5R: some variation in capacitance and cheap, widely used for decoupling.
- Y5V, Z5U: capacitance drops a lot with temperature and applied voltage, so they are unsuitable for signal processing.
Film capacitors
Capacitors that use plastic film, with no polarity, small tolerance, and good stability. Used in audio and precision timers, but bulky and expensive.
Aluminum electrolytic capacitors
Large capacitance (several µF to several thousand µF), cheap, and polarized. Cylindrical, with the rated voltage and capacitance printed on the body. Used for stabilizing the supply, but the tolerance is ±20% or more, capacitance falls with age, and high-frequency behavior is poor.
Tantalum capacitors
Polarized parts with relatively large capacitance in a small size. They are weak to reverse voltage and overvoltage and can burst or catch fire, so they are not recommended at the beginner stage.
Polarity and orientation
If you insert an electrolytic or tantalum capacitor backwards, gas builds up inside and it can swell or burst.
- The side of the body with a white (or silver) stripe and a
−mark is the negative terminal. - On a new part, the positive lead is longer (once you cut the leads after soldering you cannot tell, so check first).
- Check the polarity marking on the layout diagram and check again before soldering.
Reading the number code
Small ceramic capacitors have a three-digit number such as 104 printed on them. The first two digits are digits, the last is the multiplier, and the unit is pF.
| Marking | Calculation | Capacitance |
|---|---|---|
| 101 | 10 × 10¹ pF | 100 pF |
| 102 | 10 × 10² pF | 1 nF |
| 103 | 10 × 10³ pF | 10 nF |
| 104 | 10 × 10⁴ pF | 100 nF (0.1 µF) |
| 224 | 22 × 10⁴ pF | 220 nF |
| 473 | 47 × 10³ pF | 47 nF |
| 4n7 | — | 4.7 nF |
A letter after the digits is the tolerance. J is ±5%, K is ±10%, and M is ±20% (for example, 104K).
Rated voltage
A capacitor has a maximum voltage it can withstand (the rated voltage). Choose 1.5 to 2 times the operating voltage or more, such as 16 V or higher for a 5 V circuit and 25 V or higher for a 12 V circuit. Large-value ceramics also have the property that their real capacitance falls as the applied voltage rises.
Choosing by use
| Use | Recommended |
|---|---|
| IC decoupling | 100 nF ceramic (X7R), one per IC |
| Supply stabilization | 47–470 µF electrolytic (at the power entry) |
| Timing and oscillation (555 and so on) | Film or C0G ceramic; electrolytic for large values |
| Signal coupling and filters | Film, ceramic |
Decoupling placement is covered in Power Rails, Grounding, and Decoupling Capacitor Placement, and time calculations in Understanding RC Time Constants and Capacitor Charging and the RC time constant calculator.
Using them on perfboard
- Lead spacing is commonly 2.5 mm (1 hole) or 5.0 mm (2 holes). Choose one that fits the holes.
- Electrolytic capacitors are tall, so solder them last, after checking the orientation is right.
- For decoupling capacitors, cut the leads short and stand them up close to the IC; the wires get shorter and it works better.
Summary
Polarity or not is the first thing to check on a capacitor. Use ceramic (no polarity) for decoupling and small values, and electrolytic (polarized) for stabilizing the supply. The code 104 is 100 nF, and pick a rated voltage at least 1.5 times the operating voltage. In the next article, Blinking an LED with a 555 Timer, you will use a capacitor as a timing part.