Suntan Blog

The most common type of varistor is the metal oxide varistor, or MOV. This contains a mass of zinc oxide grains, in a matrix of other metal oxides, sandwiched between two metal plates (the electrodes). The boundary between each grain and its neighbour forms a diode junction, which allows current to flow in only one direction. The mass of randomly oriented grains is electrically equivalent to a network of back-to-back diode pairs, each pair in parallel with many other pairs. When a small or moderate voltage is applied across the electrodes, only a tiny current flows, causes by reverse leakage through the diode junctions. When a large voltage is applied, the diode junctions break down because of the avalanche effect, and a large current flows. The result of this behaviour is a highly nonlinear current-voltage characteristic, in which the MOV has a high resistance at low voltages and a low resistance at high voltages.

If the size of the transient pulse (often measured in joules) is too high, the device may melt, or otherwise be damaged. For example, a nearby lightning strike may permanently damage a varistor.

Important parameters for varistors are response time (how long it takes the varistor to break down), maximum current and a well-defined breakdown voltage. When used in communications lines (such as phone lines used for modems), high capacitance is undesirable since it absorbs high frequency signals, thereby reducing the available bandwidth of the line being protected.

The electronics circuits and modules section of this website aims to provide a pot-pourri of electronics design ideas and circuits that can be used within electronics hardware designs. It focuses on providing easy to use designs that can be implemented into electronic product designs, using easy to use formulae and design ideas.

Resistors and capacitors can be considered as the staple components used in electronic circuits. While resistors and capacitors are most commonly used with other active devices, they may also be used on their own in resistor or capacitor circuits, or circuits using combinations of the two.

Tantalum capacitors are manufactured from a powder of pure tantalum metal pressed to form a slug around a tantalum wire and subsequently vacuum sintered at high temperature. The resulting slug, although of high mechanical strength and density, is also highly porous giving a large internal surface area. This forms the positive "plate" of the capacitor. A dielectric layer of tantalum pentoxide is anodized on the surface of the tantalum anode, the cathode is formed by layers of manganese dioxide. Electrical contact is established by the deposition of carbon onto the surface of the "slug". The cathode connection is then made by means of conductive contact to a lead frame. Packaging is carried out to meet individual specification and customer requirements.

There is a great number of different types of circuit that can be used for crystal oscillators, each one having its own advantages and disadvantages. One of the most common circuits used for crystal oscillators is the Colpitts configuration as shown below.

In this configuration, the crystal operates in a parallel mode. When running in this mode, the crystal should be presented with a load capacitance to operate on its correct frequency. This load capacitance is specified with the crystal and is typically 20 or 30 pF. The crystal oscillator circuit will be designed to present this capacitance to the crystal. Most of this will be made up by the two capacitors C1 and C2, although the remaining elements of the circuit will provide some capacitance.

Mica capacitors are typically found in very small capacitance values (less than 100 nF). They will hold a very high voltage static charge, but only a tiny fraction of a joule, and if you handed it to someone they may not even feel the shock from it. If you really want to give someone a good jolt, you should use an electrolytic cap charged up to about 100V. Get one about 10,000 uF. Be careful, because most caps of this size will not be rated for high voltage; they'll explode if you try to charge them much above their rated working voltage.

Don't get too big a cap, or charge it to too high a voltage, because this sort of prank can cause serious burn injury if you take it too far.

Mounting

(1) Do not apply excessive force (preferably 5.0 N max.), when the trimmer capacitor  is mounted on the PCB.
(2) Do not warp and/or bend PCB to prevent trimmer capacitor from breaking.
(3) Use the suitable dimension of the pick-up nozzle (1.1-1.2mm external diameter and 0.8-0.9mm bore diameter).

Cleaning

Cannot be cleaned because of open construction.

Other

Note the polarity of the trimmer capacitor to minimize influence by stray capacitance.
(Refer to the dimensions concerning the polarity.)

Tantalum electrolytic capacitors exploit the tendency of tantalum to form a protective oxide surface layer, using tantalum powder, pressed into a pellet shape, as one "plate" of the capacitor, the oxide as the dielectric, and an electrolytic solution or conductive solid as the other "plate". Because the dielectric layer can be very thin (thinner than the similar layer in, for instance, an aluminium electrolytic capacitor), a high capacitance can be achieved in a small volume. Because of the size and weight advantages, tantalum capacitors are attractive for portable telephones, personal computers, and automotive electronics.

Very low losses, low dielectric absorption, high dielectric strength, very high insulation resistance, and negative temperature coefficient.

Typical applications: Stable oscillators and flters. Sample & hold circuits, pulse handling circuits, AC applications and mains fltering.

Aluminum electrolytic capacitors are made by layering the electrolytic paper between the anode and cathode foils, and then coiling the result. The process of preparing an electrode facing the etched anode foil surface is extremely difficult. Therefore, the opposing electrode is created by filling the structure with an electrolyte. Due to this process, the electrolyte essentially functions as the cathode. The basic functional requirements for the electrolyte are as follows:

(1) Chemically stable when it comes in contact with materials used in the anode, cathode, and electrolytic paper.
(2) Easily wets the surfaces of the electrode.
(3) Electrically conductive.
(4) Has the chemical ability to protect the anode oxide thin film and compensate for any weaknesses therein. 
(5) Low volatility even at high temperatures
(6) Long-term stability and characteristics that take into consideration such things as toxicity.