Dispositivos
Semiconductores
Copyright Pedro Julián. Dispositivos
Semiconductores - DIEC/UNS 2008
Capacitores
Copyright Pedro Julián. Dispositivos
Semiconductores - DIEC/UNS 2008
Modelo ideal
dv
iC
dt
A
Ck
d
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
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
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Electrical Parameters (C)
 AC/DC capacitance
AC value is measured at 20oC / 100Hz-120Hz
 Rated capacitance
Nominal value
 Tolerance
Described by a code
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Electrical Parameters (C)
 Temperature dependence
 Frequency dependence
 Charge-discharge proof
 Frequent
charging/discharging cycles
may lead to capacitance
variation
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Electrical Parameters (tan δ)
R
 Dissipation factor tan δ
tan   R  C
1/ jC

Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
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
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
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
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Electrical Parameters (I)
 Leakage current: depends on time, temperature and applied
voltage
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
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
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Electrical Parameters (I)
 Useful life:
Calculation
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
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
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Capacitor Types
 Electrolíticos
 Al
 Ta
 Cerámicos
 G1
 G2
 Film
 Polietileno (polyester)
 Polipropileno
 Metalizados
 Mica
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Capacitor Types: Values
 Electrolíticos
 Al
 Ta
 0.47µF-10.000µF / 5V-500V
 220nF-100µF / 1V – 50V
 Cerámicos
 0.5pF – 560pF / 63V – 500V
 100pF – 470nF / 53V – 500V
 G1
 G2
 Film
 Polietileno (polyester)
 Polipropileno
 Metalizados
 Mica
 1nF - 1µF / 100V – 1000V
 10nF - 10µF / 63V – 1000V
 2pF – 22nF / 250V – 4000V
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Capacitor Types: Tolerances
 Electrolíticos
 Al
 Ta
 -10% / +100 %
 +- 20%
 Cerámicos
 G1
 G2
 Film
 Polietileno (polyester)
 Polipropileno
 Metalizados
 Mica
 2%, 5%, 10%
 +- 20%
 2%, 5%, 10%
 0.5% - 20%
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
AL Electrolytic
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Electrolytic (Al) Capacitors
 Polar elements. Only block current in one direction
 Anode is Al of great purity. Cathode is electrolyte (liquid)
and paper
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Electrolytic (Al) Capacitors
 Anode is etched to provide
more surface
 Dielectric is obtained by
oxidation of Al (<1um
thickness)
 Big values of capacitance
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
V-I curve
 After the forming voltage
(Uf) current increases
 Safe operation is ensured
below Ur
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Temperature effects
 With decreasing temperature, the viscosity of the electrolyte
increases, thus reducing its conductivity.
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Datasheet
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Tantalium-Niobium Caps.
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Electrolytic (Ta-Nb) Capacitors
 εr is 27 for Ta, 41 for Nb
 Polar elements. Only block
current in one direction
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Frequency dependence
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Z and ESR
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Low ESR series
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Ultra-low ESR
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Maximum V,I vs T and I vs. f
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Dissipation factor (vs. f, T)
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Leakage
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Ceramic
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
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.
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
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
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
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.
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Class 1: Temperature dependence
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Class 2: Temperature dependence
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
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.
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Datasheets (C0G)
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Datasheets (X7R)
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Frequency response
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Film Capacitors
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
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.
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Winding method
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
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
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Film vs. Foil
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
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.
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Self-healing property
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Temperature
 Polypropylene capacitors have negative temperature coefficient
 Polyester capacitors have positive temperature coefficient
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Humidity
 the dielectric and the effective air gap between the films
will react to changes in the ambient humidity
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Frequency
 MKT , MFT
and MKN
MKP and MFP capacitors: Up to a frequency of 1 MHz, the
capacitance remains virtually unaffected by the frequency.
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Maximum voltage (T)
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
V/I limitations
 A) corona discharge
 B) Thermal dissipation
 C) Leads resistance
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Tan δ
 Polypropelene
capacitors
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
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
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Datasheets
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
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
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
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.
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Mica
 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.
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Summary
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
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)
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
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
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Mica
 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
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Film
 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
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
Appendix
Copyright Pedro Julián. Dispositivos Semiconductores - DIEC/UNS 2008
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