The electrolytic capacitor is the most popular type for values greater than about 1 microfarad, having the one of the highest levels of capacitance for a given volume. It is constructed using two thin films of Aluminum or Tantalum foil, one layer being covered with an oxide layer as an insulator. An electrolyte-soaked paper sheet is placed between them and then the two plates are wound around on one another and then placed into a can.
These capacitors are polarised, i.e. they can only be placed one way round in the circuit. If they are connected incorrectly they can be damaged, and in some extreme instances they can explode. Care should also be taken not to exceed the rated working voltage. Normally they should be operated well below this value.
These capacitors have a wide tolerance. Typically the value of the component may be stated with a tolerance of -50% +100%. Despite this they are widely used in audio applications as coupling capacitors, and in smoothing applications for power supplies. They do not operate well at high frequencies and are typically not used for frequencies above 50 – 100 kHz.
Aluminum Electrolytic Capacitors
- Aluminum electrolytic capacitors are not damaged by heat when soldering.
- Electrolytic capacitor is used as a ripple filter in a power supply circuit, or as a filter to bypass low frequency signals, etc. Because this type of capacitor is comparatively similar to the nature of a coil in construction, it isn’t possible to use for high-frequency circuits. (It is said that the frequency characteristic is bad.)
- The main advantage of the electrolytic capacitor is the large capacitance-per-size factor.
- Two obvious disadvantages are the polarity, which must be observed, and the higher leakage current feature. Also, in many capacitors of this type, the electrolyte can dry out with age and depreciate the capacitor quality or render it useless.
- Because of the losses of the dielectric at higher frequencies, electrolytic capacitor applications are generally limited to power-supply circuits and audio-frequency applications.
Tantalum Capacitors
- Tantalum capacitors are polarized and have low voltage ratings like electrolytic capacitors. They are expensive but very small, so they are used where a large capacitance is needed in a small size.
- Similar to aluminum electrolytic capacitors, in tantalum capacitors large values of capacitance can be obtained.
- Tantalum capacitors are superior to aluminum electrolytic capacitors in temperature and frequency characteristics. When tantalum powder is baked in order to solidify it, a crack forms inside. An electric charge can be stored on this crack.
- Tantalum capacitors are used for circuits which demand high stability in the large capacitance values and lower leakage current. Also, they do not dry out as fast, thus have a longer shelf life.
- It is said to be common sense to use tantalum capacitors for analog signal systems, because the current-spike noise that occurs with aluminum electrolytic capacitors does not appear.
- Aluminum electrolytic capacitors are fine if you don’t use them for circuits which need the high stability characteristics of tantalum capacitors.
Advantages of Tantalum electrolytics over Aluminum electrolytics
- Small size
- No liquid electrolyte
- Superior temperature stability
- Wider operating temperature range (up to +125OC)
- Long storage (shelf) life
- Larger reverse voltage tolerance
- Low dissipation factor
- Self healing
Advantages of Aluminum Electrolytics over Tantalum Electrolytics
- Lower cost
- Higher availability
- Shorter production lead times
- Low leakage current
- Higher voltage range (up to 400 VDC)
Considerations on substituting an Aluminum Capacitor for a Tantalum Capacitor
- Aluminum electrolytic capacitor’s higher dissipation factors/ESR, which in turn reduces their ripple current capabilities.
- Aluminum electrolytic capacitor’s larger capacitance change over temperature. Electrolytic capacitors can change capacitance up to six times more than tantalums.
- Aluminum electrolytic capacitor’s capacitance change over frequency.
- Aluminum electrolytic capacitor’s capacitance change over time (up 20% change after 2,000 hours for aluminum electrolytic capacitors).
