Capacitors: types, dielectrics and what the datasheet hides
Capacitor types explained: MLCC ceramic dielectrics (C0G, X7R, X5R, Y5V), DC bias derating, aluminium electrolytic, polymer, tantalum and film capacitors, ESR and voltage ratings.
What a capacitor does
A capacitor stores charge between two plates. It blocks steady DC current, lets changing signals through, and delivers current quickly when the voltage around it dips. Capacity is in farads; real parts go from pF to thousands of µF.
The main families
| Type | Range | Strengths | Watch out |
|---|---|---|---|
| Ceramic MLCC | 1 pF – 100 µF | Tiny, cheap, very low ESR | Class 2 loses capacitance with voltage and temperature |
| Aluminium electrolytic | 1 µF – 10 000 µF+ | Large values, cheap | Polarised, high ESR, lifetime shortens with heat |
| Polymer (aluminium or tantalum) | 10 µF – 1 000 µF | Low ESR, stable | Price, voltage limits |
| Tantalum (MnO₂) | 0.1 µF – 1 000 µF | Stable, compact | Can fail short and burn; derate voltage 50 % |
| Film | 1 nF – 100 µF | Stable, high voltage, self-healing | Large; X/Y types used across mains |
Ceramic dielectrics
The three-character code tells you how stable the part is. C0G / NP0 (class 1): capacitance does not change with voltage or temperature; used for timing, filters and oscillators. X7R: ±15 % from −55 to 125 °C. X5R: ±15 % from −55 to 85 °C. Y5V: +22/−82 %; avoid it.
The DC-bias trap
Class 2 ceramics (X5R, X7R) lose capacitance as DC voltage is applied, and the smaller the package the worse it gets. A 10 µF 6.3 V capacitor in 0603 may give only a third of its value at 3.3 V. This does not appear on the label or in the BOM; it is in the manufacturer's DC-bias curves.
Voltage and temperature ratings
Choose a voltage rating well above the working voltage: at least 1.5 to 2 times for ceramics and electrolytics, 2 times for tantalum. Electrolytic lifetime is specified at the maximum temperature (for example 2 000 hours at 105 °C) and roughly doubles for every 10 °C cooler. In a hot enclosure, electrolytics are the first thing to fail.
Capacitor selection is where many designs fail months later: DC bias that halves the filtering, an electrolytic that dries out in a hot box, a tantalum that shorts on a power surge. We check every capacitor against voltage, temperature and ripple in the schematic phase.
Parts and tools to practise
| Item | What to look for | Buy |
|---|---|---|
| Ceramic capacitor assortment | From 10 pF to 1 µF, 50 V. Through-hole for breadboards. | View on Amazon ↗ |
| Electrolytic capacitor assortment | 1 µF to 1000 µF, 16 to 50 V, 105 °C rated. | View on Amazon ↗ |
| SMD resistor and capacitor sample book | 0603 or 0805 values in a book. Handy for rework once you solder SMD. | View on Amazon ↗ |
| Component tester | Identifies and measures resistors, capacitors, diodes and transistors automatically. | View on Amazon ↗ |
| The Art of Electronics (Horowitz and Hill) | The reference book. Dense, but worth it for anyone serious. | View on Amazon ↗ |
Links go to Amazon. As an Amazon Associate we earn from qualifying purchases, at no extra cost to you. We only list tools of the kind we use on our own bench.
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