Passive components and circuits - CCP Lecture 8

Content Passive electronic components – role Passive electronic components – resistors Electrical properties Clasification Parameters Marking Codification

Passive electronic components - role

Passive components - dynamics

Passive components/Active components

Resistor – history and tendencies 1827 first resistor 1976 first integrated resistors General tendencies of evolution: Performances increases Dimensions decreases Costs decreases

Resistor – electrical properties The basic relation for resistance calculus is: Write the values of the resistivities for the main materials used in electronics. http://www.8886.co.uk/ref/resistivity_values.htm http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/rstiv.html#c1 http://www.istonline.org.uk/Handbook/40.pdf

Resistor – equivalent electric scheme Due to the constructive particularities, each resistor has a parasitic inductance and a parasitic capacitance besides the useful resistance. Parasitic parameters must be taken into consideration at high frequencies.

Problems For the resistive voltage divider, determine the dividing factor if: R1=1 K; R2=100  R1=100 K; R2=10 K  R1=100 K; R2=1 K  How is the dividing factor modified with the frequency, if each resistor has a parasitic capacitance equal with 2 pF?

Clasifications – constructiv criterion Discrete Fixed Variable Integrated Resistors arrays Resistor networks Embedded (included in the structure) In the PCB level In the ceramic sublayer (multicip modules – MCM) In silicium with thin film technology In the integrated circuits

Discrete resistors Fixed Variable

Integrated resistors Networks Areas

Embedded resistors Decrease of the total cost of manufacturing Thermodynamic reliability Decrease of the dimensions Compatibility between different materials Values between 10 and 200K with tolerances under 10%.

Clasification – liniarity criterion Linear Non-linear Thermistors Varistors Fotoresistors

Clasification – technological criterion Pelicular resistors – are obtained by depositing a resistiv material (aglomerated charbon, christalin charbon,metalic alloys, metalic oxids) into a thin layer (under 10m) on an isolator support. Reeled (wired) resistors – are obtained wiring a metalic conductor on an isolator support. The technology is used for obtaining either precision resistors or high-power resistors. Volume resistors – the resistiv element represents the whole body of the resistor.

Clasification – geometric criterion It concernes, in general, the way in which terminals are connected to the body of the resistor: With surface mounted terminals (SMD); With axial terminals; With radial terminals;

Parameters of fixed resistors Parameters that must be written on the body of the resistor The nominal resistance Nominal tolerance value Parameters written only on certain resistors The nominal dissipated power The temperature coeficient The superior limit voltage Parameters that are not written (the nominal values’ domain, the nominal domain of temperature, the noise factor)

Series of normalised values In practice, resistors are not manufactured with nominal resistances in a continuous range of values. The solution used is that of a serie of normalised values. Each serie is characterised by a certain tolerance. The nominal values of resistances are obtained from the values of the normalised serie by multiplication with powers of 10. A certain serie covers almost all the domain of possible values for resistances, taking into account that between two succesiv values of the serie the following relation holds :

Series of normalised values The number of values in a series results, depending on tolerance, solving the equation on the right and taking the first superior integer for n. The nominal values of a series are in a geometrical progression given by the following relation:

Series of normalized values The main normalized series are the following: E6(20%); E12(10%); E24(5%); E48(2%); E96(1%); E192(0,5%); Values of the first three normalized series:

Choosing resistors depending on the tolerance In choosing resistors for an application an important factor is their tolerance. The variation of functions of a circuit with respect to the tolerances of the components is called sensitivity.

Nominal power, Pn Represents the maximum power that can be dissipated on a resistor in a regime of prolonged functioning at a temperature equal to the nominal temperature Tn, without it modifying its parameters. This parameter is written only for resistors with nominal power higher than 2W. For this parameter there are 24 standardized values: 0,05W; 0,1W; 0,125W; 0,25W; 0,5W; 1W; 2W; 3W; 4W; .... 10W; 16W; ... 500W

Low power resistors For low power resistors (under 2W) the nominal power can be deducted from the dimensions of the resistor.

Temperature coefficient Apeares written on the body of the resistor only in case of precision resistors. The parameter is defined as follows: For most resistors this parameter can be considered constant.

The superior limit voltage, Vn Apares written in the case of resistors designed for functioning at very high voltages . For a usual resistor it can be deduced as follows: For high value resistors, Vn can be limited under the previous value by reasons concerning the dielectrics breakdown.

The noise factor, F Represents the value of the noise voltage that appears on the resistor when applying a 1V continuous voltage. The noise voltage appears due to the disordered movement of the charge carriers in the conductor.

Marking the resistors Marking refers to the way in which the information written on the resistors is codified. Marking in the code of letters and figures Marking in the colors’ code

Marking with the code of letters and figures Marking the nominal value is made using figures and letters as multipiliers. The letter marks the presence of the decimal dot in the nominal value. Multipliers: R=1; K=1.000 (kilo); M=1.000.000 (mega); G=1.000.000.000 (giga) For tolerance marking one can use either the marking in clear (5%, 1%, etc.) or the letter codified one. B0,1%; C0,25%; D0,5%; F1%; G2%; H2,5%; J5%; K10%; M20%

Marking with the code of letters and numbers To avoid confusions between letters which have the significance of both separator and tolerance, the ones that signify tolerance are written separately from the nominal value code (possibly on another line). Value 2700, tolerance 5% Value 330K, tolerance 20% Value 0,33, tolerance 10% The marking of the power and the temperature coefficient is made in clear for resistors for which is required to display these parameters.

Marking with the code of letters and numbers for SMD resistors For SMD resistors, with very low dimensions, the following code is used.(cod EIA-96).

Marking with the code of colors This type of codified marking, although more difficult to read, has the advantage that the writing is visible on the body of the resistor regardless of its position on the board. The reading of the code is made starting with the colored ring that is the closest to a terminal or with the group of colored rings. For resistors with nominal values from the series E6, E12, E24 and E48 the code has only four colored rings. For resistors with nominal values from the series E96, E192 and with smaller tolerance, the code has five colored rings.

Marking resistors – colors’ code

Remarks Some colors have no significance for tolerance (orange, yellow and white). In the case of the code with four rings, the only possible colors for tolerance are red (2%), gold (5%) or silver (10%). The lack of the colored ring for tolerance means the tolerance is 20%. Therefore, in this case the code will have only three colored rings. Brown, black, red +gold =10•100 5%=1K 5%

Codification of resistors Gives the information by which the resistors are described in catalogs and therefore, also, in the lists of materials that are made. For resistors produced in Romania, the code has the following structure: Field I – contains three letters indicating the technological type; Field II – contains a figure with significance concerning the type of capsule (the way the terminals are connected to the body); Field III – contains three figures indicating the nominal power; Field IV – contains a letter signifying the constructive variant; In the material lists these codes are completed with the information written on the resistor (nominal value and tolerance).

Codification of resistors – examples General usage resistor with carbon film (coat) (RCG), with axial terminals (1), nominal power of 1W (100), reliable variant (L), 5,1K, tolerance 5% (J). Resistor with metallic film (coat) (RPM), with radial terminals (3), nominal power 0,5W (050), reliable variant (L), 1K, tolerance 1%.

Codification of resistors – examples for SMD resistors

Codification of resistors In general, in the electric schemes, next to the symbol of a resistor appears only its reference (R1, R205, etc.) and its nominal value (1K, 3K3, etc.). The power and the tolerance are mentioned only for components that have values different from the others. This information regarding the codification appears on the equipment schemes as well (assembling plans).

Problems For a 100  resistor, the tolerance is t=±0,1% at a reference temperature T0=20 oC. The resistor has a temperature coefficient T=±20ppm/oC. The environmental temperature is between [-30 oC; +90 oC]. Considering that, due to the dissipated power, the resistor body is heated with 50 oC, which is the global tolerance of the resistor?

Problems The resistor body temperature is modified based on the following relation: where TA is environment temperature, and P is the dissipated power. On the resistor is applied a voltage with the waveform presented in the figure bellow. How can be the maximum amplitude of the pulses in order to have the global tolerance lower than tG=±0,3%?

Problems How is the maximum temperature of environment if the voltage applied on the resistor is sinusoidal with 7V amplitude, and the global tolerance is lower than tG=±0,3%?

Dividing factor for R1=1 K şi R2=100 

Dividing factor for R1=100 K şi R2=10 K

Dividing factor for R1=100 K şi R2=1 K