copyright pedro julián. dispositivos semiconductores - diec/uns 2008 dispositivos semiconductores

Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008

Dispositivos Semiconductores

Capacitores

Modelo idealdv

i CdtA

Electrical Parameters (V)

Rated Voltage (UR) Direct voltage for which the C has been

designed Operating Voltage (UOP)

Range (between 0V and Ur) typ. 60% Surge Voltage (US)

For short periods of time Superimposed AC, ripple voltage Reverse voltage

Electrical Parameters (C)

AC/DC capacitance

AC value is measured at 20oC / 100Hz-120Hz Rated capacitance

Nominal value Tolerance

Described by a code

Electrical Parameters (C)

Temperature dependence

Frequency dependence

Charge-discharge proof Frequent

charging/discharging cycles may lead to capacitance variation

Electrical Parameters (tan δ)

Dissipation factor tan δ

1/ j C tan R C

Electrical Parameters (tan δ)

Tan δ variation with temperature and frequency

As freq. increases the capacitive impedance reduces and the dissipation factor gets worse

Increasing the temperature results in better dissipation factor

Electrical parameters (Z)

R = dielectric losses, series resistance

L = winding and terminals (only depends on f )

C and R depend on temp. and f

Fig. Temperature behaviour is for an Al electrolytic capacitor

Electrical Parameters (I) Leakage current: depends on time, temperature

and applied voltage

Electrical Parameters (I)

Ripple current: rms value of circulating current

Depends on temp. and frequency Useful life: life achieve without

exceeding a specified failure rate. Depends on: Temperature Ripple current Voltage

Electrical Parameters (I)

Useful life: Calculation

Climatic conditions

UCT: Upper category temperature LCT: Lower category temperature Limits within cap. Can be continuously

operated Storage temperature

There are also restrictions on mechanical stress

Capacitor Types

Electrolíticos Al Ta

Cerámicos G1 G2

Film Polietileno (polyester) Polipropileno Metalizados

Capacitor Types: Values

Cerámicos G1 G2

0.47µF-10.000µF / 5V-500V 220nF-100µF / 1V – 50V

0.5pF – 560pF / 63V – 500V 100pF – 470nF / 53V – 500V

1nF - 1µF / 100V – 1000V

10nF - 10µF / 63V – 1000V

2pF – 22nF / 250V – 4000V

Capacitor Types: Tolerances

Cerámicos G1 G2

-10% / +100 % +- 20%

2%, 5%, 10% +- 20%

2%, 5%, 10%

0.5% - 20%

AL Electrolytic

Electrolytic (Al) Capacitors

Polar elements. Only block current in one direction

Anode is Al of great purity. Cathode is electrolyte (liquid) and paper

Electrolytic (Al) Capacitors

Anode is etched to provide more surface

Dielectric is obtained by oxidation of Al (<1um thickness)

Big values of capacitance

V-I curve

After the forming voltage (Uf) current increases

Safe operation is ensured below Ur

Temperature effects

With decreasing temperature, the viscosity of the electrolyte increases, thus reducing its conductivity.

Datasheet

Tantalium-Niobium Caps.

Electrolytic (Ta-Nb) Capacitors εr is 27 for Ta, 41 for Nb Polar elements. Only

block current in one direction

Frequency dependence

Z and ESR

Low ESR series

Ultra-low ESR

Maximum V,I vs T and I vs. f

Dissipation factor (vs. f, T)

Leakage

Ceramic

Ceramic capacitors

they all have the oxide ceramic dielectric in common.

Ceramic generally means that an inorganic polycrystalline body is formed by sintering at high temperatures.

By means of special production methods, extremely thin layers of ceramic materials can be obtained.

Classification

Class 1 capacitors The dielectric (200) primarily consists of a

mixture of metal oxides and titanates. Defined linear temperature coefficient with

reversible temperature dependence Capacitance does not vary with voltage. Low losses at frequencies up to the UHF range High insulation resistance Applications: resonant circuits, filters, timing

elements

Classification Class 2 capacitors

The dielectric ( 200 to 10000) primarily consists of titanates (barium, calcium, strontium) and zirconates.

Non-linear dependence of capacitance on temperature and voltage

Somewhat higher losses and lower insulation resistance than class 1 capacitors

Capacitance decreases according to a logarithmic function (ageing).

High capacitance values even with small-size capacitors are possible

Applications: coupling, blocking, filtering.

Class 1: Temperature dependence

Class 2: Temperature dependence

Termal characteristics

Change more (class 2) or less (class 1) with temperature.

Change in crystalline structure capacitance value of high K

materials (with a high dielectric constant, e.g. X7R, Z5U) class 2 drastically decreases above the Curie point

materials with a low dielectric constant (C0G) class 1, dissipation factor increases considerably at high temperatures.

high ambient temperature and high electrical energy exchange contributes to heating the capacitor.

Datasheets (C0G)

Datasheets (X7R)

Frequency response

Film Capacitors

Classification

T ˆ= Polyethylene terephthalate (PET) P ˆ = Polypropylene (PP) N ˆ= Polyethylene naphthalate (PEN) An M (ˆ = Metallization) is prefixed to the short identification code of capacitors with

metallized films.

Winding method

Stacked method

The “master capacitors” are produced under well-defined and constant conditions.

Since each individual layer acts as a separate capacitor element, any damage to the contacts due to overloading is restricted to the respective capacitor element and does not affect the entire capacitor

Film vs. Foil

Self-healing property

Capacitors with metallized plastic film have a decisive advantage over capacitors with metal foil electrodes: they have self-healing properties. Self-healing properties permit utilization of full

dielectric strength of dielectric materials of metallized film capacitors

metal-foil electrode capacitors must always be designed with a safety margin to allow for any possible faults in the dielectric.

Metallized types thus have a distinct size advantage, which is particularly apparent with the larger capacitance ratings.

Self-healing property

Temperature

Polypropylene capacitors have negative temperature coefficient Polyester capacitors have positive temperature coefficient

Humidity

the dielectric and the effective air gap between the films will react to changes in the ambient humidity

Frequency

MKT , MFT and MKN

MKP and MFP capacitors: Up to a frequency of 1 MHz, the capacitance remains virtually unaffected by the frequency.

Maximum voltage (T)

V/I limitations

A) corona discharge B) Thermal

dissipation C) Leads resistance

Tan δ

Polypropelene capacitors

Tan δ

The dielectric of MKT capacitors contributes a considerably greater dielectric component tan δD

MKT capacitors display a noticeably higher overall dissipation factor, especially at lower frequencies than MKP and MKN capacitors

Datasheets

Polyester

Metallized Polyester Capacitors (Mylar) With tolerance of 10% Temperature range -40oC to +85oC. Non inductive. Dielectric strength of 150% of rated

voltage for less than 5 sec

Polyester

Metallized Polyester Film Capacitors With tolerance of 10%. Operating temperature -40oC to +85oC. Non Inductive Design Compact Size Available in rolls of 100 or 1,000 at special

prices.

Advantages: dielectric material (mica) is inert. Does NOT change physically or chemically with age Good temperature stability. Very resistant to corona damage Unless properly sealed, susceptible to moisture pick-

up (increases the power factor and decrease insulation resistance).

Higher cost (scarcity of high grade dielectric material) and manually-intensive assembly.

Silver mica capacitors have the above mentioned advantages. In addition, they have much reduced moisture infiltration.

Summary

Summary Ceramics: low stability and precision. Electrolytic - Same as ceramics except they have much

smaller physical size for a given value. Usually polarized. Large tolerances

Tantalum - Better characteristics than electrolytic but still small for high capacity values. Polarized. Smaller tolerance than electrolytic

Poly film – (polyester or polypropylene) --mostly replaced paper capacitors-- Slightly better characteristics than common ceramics. Usually very low leakage currents.

Mica/Silver Mica - Temperature stable, low dissipation factor. Usually large physically.

Polystyrene, Teflon - Very temperature stable. Polystyrene breaks down, however, at high temps (say >80C)

Glass, Air, Oil – Not Common(HV work, big motors)

Electrolytic Capacitors Tantalum

Small size Large values Medium inductance Quite high leakage Usually polarized Expensive Poor stability Poor accuracy

Aluminum Large values High currents High voltages Small size High leakage Usually polarized Poor stability Poor accuracy Inductive

Widely used in low and medium power RF equipment

Low loss at HF Low inductance Very stable Available in 1% values or better Quite large Low values (<10 nF) Expensive

Polyester 0.3% to 0.5% Moderate stability Low cost Wide temperature

range Low inductance

(stacked film) Large size High inductance

Polypropylene 0.001% to 0.02% Inexpensive Wide range of values Large case size High inductance

Appendix

Surface mount formats capacitors 1. A-case (Tantalum

cap) 2. D-Case (Tantalum

cap) 3-4 Electrolytic cap 5. 0805 Ceramic 6. 1206 Ceramic 7. 1210 Ceramic 8 . High Q Porcelan

RF 9. Variable Trimmer

copyright pedro julián. dispositivos semiconductores - diec/uns 2008 dispositivos semiconductores

copyright pedro julin

electrical parameters

calculation slide

code slide

capacitores slide

applied voltage slide

capacitance variation

modelo ideal slide

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