In electrical and radio engineering, you cannot do without the use of capacitors. If in the first case the main requirement is reliability and durability, then in the second case, special attention is also paid to dimensions. The miniaturization of radio and electronic devices became possible with the invention of tantalum and niobium capacitors, which are only a few millimeters in size.
Content
- Tantalum promoted progress
- Design features of the device
- Advantages and disadvantages
- Diagnostics of possible malfunctions
Tantalum promoted progress
From the very inception of radio electronics, research was conducted that was aimed at reducing the size of structural elements. The main direction in this matter is to increase the operating frequency of the signal. If we compare two power transformers with operating frequencies of 50 and 400 Hz, then the second is about 8 times smaller in size than the first.
Obsolete capacitor designs are rolled rolls of thin aluminum foil that are placed in an electrolyte. Achieving high capacity was only possible by increasing the size of the element itself. Another drawback of this design is the large parasitic inductance when operating at frequencies of 100 kHz and higher.
A breakthrough in the manufacture of capacitors of large capacity and small size has been achieved with the use of tantalum. This rare earth metal is more expensive than gold and its production is quite difficult, but it takes very little to make one element - no more than a few micrograms. Gradually, tantalum electrolytic capacitors replaced the obsolete ones based on aluminum foil, as their production improved and the cost became quite low.
And this is not the limit for progress and improvements in capacitor design. The receivers of tantalum are niobium capacitors, which are identical in design and production technology to their predecessors, but surpass them in performance.
Design features of the device
The physicochemical properties of tantalum and niobium make it possible to create from them an anode of a special porous structure. Such structures have an inner surface several tens of times larger than the outer one. And this makes it possible to accumulate a significant electrical charge.
Any modern electrolytic capacitor consists of three structural elements:
- cathode and anode;
- dielectric layer;
- one of the types of electrolyte (alkali, acid, water, solid or soft substance).
The role of a dielectric is thinnest oxide film. It is obtained by the method of electrochemical corrosion by passing an electric current through the anode at the production stage.
The electrolyte is a solid substance - manganese dioxide. It has a low coefficient of linear expansion, does not leak or dry out like liquid electrolytes. The inner part of the cathode is made of silver to increase conductivity.
The entire inner filling is filled with a plastic-like substance with dielectric properties - a compound.
Advantages and disadvantages
Both tantalum and niobium capacitors have their own positive and negative qualities. Their main advantage is their small size with a relatively large capacity. And the disadvantage that significantly limits the scope of their application is their low electrical strength. The most powerful samples are able to operate stably and reliably at voltages up to 35 V.
The accepted standard marking for tantalum capacitors consists of an indication of the positive contact and a numerical value. And the color of the case indicates the operating voltage. For example:
- pink color - voltage up to 35 V;
- white color - up to 30 V;
- gray color - up to 35 V;
- blue color - up to 20 V;
- green color - up to 16 V;
- black color - up to 10 V;
- yellow color - up to 6.3 V.
The old marking system is more complicated and inconvenient, so it was abandoned. It consisted of three stripes and dots of different colors. The color of the stripes corresponded to the numerical value, and the color of the dot indicated the multiplier by which the numerical value was multiplied. Such a system often misled radio technicians and required increased attention when working with capacitors, so they abandoned it and developed a new marking.
Diagnostics of possible malfunctions
The most common malfunction is the breakdown of the dielectric film at the anode. Its thickness is only a few thousand angstroms, which is about 500 times thinner than a human hair.
Minor voltage surge can lead to breakdown, in which the dielectric film acquires a crystalline structure and becomes a conductor of electricity. In this case, the capacitor becomes a conductor and the resistance between the anode and cathode approaches zero. Darkening and sometimes carbonization of the protective paint coating are often visually noticeable on the case during breakdown.
Loss of nominal capacitance is more difficult to diagnose. It is impossible to identify such a malfunction at home, for this specialized diagnostic equipment required.
The cost of tantalum and niobium capacitors is so low that it makes no sense to carry out complex measuring work. The suspicious element is simply replaced with a new or known good one.
