SEI General Resistor Training

Ohm: The Unit of Resistance

How much a resistor restricts the flow of current is termed its resistance. This is usually referred to simply as the resistor’s value.

The value of a resistor is expressed in the unit of Ohms, and is symbolized by the Greek letter Omega ()

One ohm (1) of resistance exists when one ampere (1A) of current flows in a material when one volt (1V) is applied across the material.

Ohm: The Unit of Resistance

How much a resistor restricts the flow of current is termed its resistance. This is usually referred to simply as the resistor’s value.

The value of a resistor is expressed in the unit of Ohms, and is symbolized by the Greek letter Omega ()

One ohm (1) of resistance exists when one ampere (1A) of current flows in a material when one volt (1V) is applied across the material.

Ohm’s Law

V = IxR or R = VI or I = VR

Where: V = Voltage in Volts I = Current in AmpsR = Resistance in Ohms

Ohm’s Law

V = IxR or R = VI or I = VR

Where: V = Voltage in Volts I = Current in AmpsR = Resistance in Ohms

Resistor Properties - Resistance Value

The basic defining property of a resistor is its resistance value

Definition: The number of Volts needed to push one Amp of current through the resistor.

Units: Ohms () (milliohms, Kilohms, Megohms are commonly used)

SEI products range in value from milliohms (E.g. current sense parts like MR and CSR) through the “normal” range of 1 Ohm to 1 Megohm to special high value parts at 4.7 Gigaohms.

A data sheet states the maximum and minimum value available. Any value within this range can be made, but we prefer to stick to a limited number of standard values.

Resistor Properties - Resistance Value

The basic defining property of a resistor is its resistance value

Definition: The number of Volts needed to push one Amp of current through the resistor.

Units: Ohms () (milliohms, Kilohms, Megohms are commonly used)

SEI products range in value from milliohms (E.g. current sense parts like MR and CSR) through the “normal” range of 1 Ohm to 1 Megohm to special high value parts at 4.7 Gigaohms.

A data sheet states the maximum and minimum value available. Any value within this range can be made, but we prefer to stick to a limited number of standard values.

Resistance Values

The value of a resistor is measured in Ohms (). Resistance values on circuit diagrams, legend marked resistors and BOMS are usually written in accordance with the IEC specifications as shown below:

100 = 10 ohms (5%)10R0 = 10 ohms (1%)101 = 100 ohms (5%)1000 = 100 ohms (1%)102 = 1000 ohms (5%) = 1K1001 = 1000 ohms (1%) = 1K

and so on. Metric abbreviations are used for values not between 1 and 999. The next slide will summarize.

E24 values, usually used for 5% and higher tolerance parts, only need two digits and a multiplier to accurately state their values; examples 33 ohms, 47K, 6.8M.

E96 values (at least the ones not shared with the E24 values), which are usually used for 1% tolerance product, require 3 digits and a multiplier to accurately state their value; examples 33.2 ohms, 47.5K, 6.81M.

Resistance Values

The value of a resistor is measured in Ohms (). Resistance values on circuit diagrams, legend marked resistors and BOMS are usually written in accordance with the IEC specifications as shown below:

100 = 10 ohms (5%)10R0 = 10 ohms (1%)101 = 100 ohms (5%)1000 = 100 ohms (1%)102 = 1000 ohms (5%) = 1K1001 = 1000 ohms (1%) = 1K

and so on. Metric abbreviations are used for values not between 1 and 999. The next slide will summarize.

E24 values, usually used for 5% and higher tolerance parts, only need two digits and a multiplier to accurately state their values; examples 33 ohms, 47K, 6.8M.

E96 values (at least the ones not shared with the E24 values), which are usually used for 1% tolerance product, require 3 digits and a multiplier to accurately state their value; examples 33.2 ohms, 47.5K, 6.81M.

Commonly used metric prefixes and their symbols

PREFIX+ UNIT METRIC SYMBOL MULTIPLIER LETTER

Teraohms T 1012 TGigohms G 109 GMegohms M 1,000,000 MKilohms k 1000 KOhms 1 RMilliohms m 0.001 R

1.5 is written 1.50.01 is written .01 10,500 (10.5k) is written 10.5K1,800,000 (1.8M) is written 1.8M0.005 (5m) is written .005 (for some manufacturers is written or marked as R005)

Commonly used metric prefixes and their symbols

PREFIX+ UNIT METRIC SYMBOL MULTIPLIER LETTER

Teraohms T 1012 TGigohms G 109 GMegohms M 1,000,000 MKilohms k 1000 KOhms 1 RMilliohms m 0.001 R

1.5 is written 1.50.01 is written .01 10,500 (10.5k) is written 10.5K1,800,000 (1.8M) is written 1.8M0.005 (5m) is written .005 (for some manufacturers is written or marked as R005)

Standard Resistance Values:

E-24 = 5%.

24 values in every decade

E-96 = 1%

96 values in every decade

E-192 = .5% & .1%.

Some values are not possible in certain products.

Resistor Properties - Tolerance

This always follows the value when describing a resistor

Definition: The maximum error in resistance value at room temperature

Units: Percent (%)

All processes have some degree of variation and there is a limit to how accurately resistance measurements can be made. This means the actual value may differ from the nominal value, and tolerance is a way of stating the limit on this.

In general, tighter tolerances (= lower % figures!) mean higher costs / prices. If the requested tolerance is unavailable, a tighter tolerance alternative can be used.

Resistor Properties - Tolerance

This always follows the value when describing a resistor

Definition: The maximum error in resistance value at room temperature

Units: Percent (%)

All processes have some degree of variation and there is a limit to how accurately resistance measurements can be made. This means the actual value may differ from the nominal value, and tolerance is a way of stating the limit on this.

In general, tighter tolerances (= lower % figures!) mean higher costs / prices. If the requested tolerance is unavailable, a tighter tolerance alternative can be used.

20% M Rare 0.5% D Semi-precision10% K Rare 0.25% C Semi-precision5% J Common 0.1% B Precision2% G Common 0.05% W Precision1% F Common 0.02% P Precision

20% M Rare 0.5% D Semi-precision10% K Rare 0.25% C Semi-precision5% J Common 0.1% B Precision2% G Common 0.05% W Precision1% F Common 0.02% P Precision

Standard Tolerances include:Standard Tolerances include:

Resistor Properties - TCR

TCR stands for Temperature Coefficient of Resistance

Definition: How much the resistance changes with temperature across a given temperature range

Units: Parts per million per degree C (ppm / °C) (1ppm = 0.0001% over a 100 °C change)

The resistive properties of all materials vary with temperature. Careful material selection and processing can minimize this.

This is generally more of an issue for precision resistors. These are often available in a range of TCR values - the lower the TCR, the higher the cost / price.

Resistor Properties - TCR

TCR stands for Temperature Coefficient of Resistance

Definition: How much the resistance changes with temperature across a given temperature range

Units: Parts per million per degree C (ppm / °C) (1ppm = 0.0001% over a 100 °C change)

The resistive properties of all materials vary with temperature. Careful material selection and processing can minimize this.

This is generally more of an issue for precision resistors. These are often available in a range of TCR values - the lower the TCR, the higher the cost / price.

Resistor Properties - Power Rating

Any resistor functions such that it limits current flow while dropping voltage. It does this by changing some electrical energy into heat. The amount of energy the resistor is capable of safely changing into heat is called its power rating.

Definition: The maximum power which can be dissipated in the resistor at a certain ambient temperature is the resistor’s power rating.

Units: Watt (W) = 1 Joule / 1 second

If a resistor gets too hot it can a) change value, b) become unreliable or c) burn or damage the circuit board and surrounding product.

This sets a limit on how much electrical power can be allowed to turn into thermal energy in a given time.

The power rating relates to continuous dissipation for an indefinite time. Resistors can dissipate more power if the time is limited to a fraction of a second or a few seconds, known as pulse power.

Resistor Properties - Power Rating

Any resistor functions such that it limits current flow while dropping voltage. It does this by changing some electrical energy into heat. The amount of energy the resistor is capable of safely changing into heat is called its power rating.

Definition: The maximum power which can be dissipated in the resistor at a certain ambient temperature is the resistor’s power rating.

Units: Watt (W) = 1 Joule / 1 second

If a resistor gets too hot it can a) change value, b) become unreliable or c) burn or damage the circuit board and surrounding product.

This sets a limit on how much electrical power can be allowed to turn into thermal energy in a given time.

The power rating relates to continuous dissipation for an indefinite time. Resistors can dissipate more power if the time is limited to a fraction of a second or a few seconds, known as pulse power.

Resistor Properties - Overload

A duration from a fraction of a second to several seconds

Definition: The standard overload test is usually 6.25 times the rated power or 2.5 times the maximum allowable voltage, whichever is the lesser, for 5 seconds

Units: Percent (%)

The standard overload test subjects the resistors to a power greater than their maximum continuous power rating. This can be used to remove faulty components during manufacture, and helps provide an indication of the ‘Pulse Withstand Capability’.

The overload performance is given as a change in resistance between the value before and after the test.

Overload powers and times do vary depending upon the component type or on customer request.

Resistor Properties - Overload

A duration from a fraction of a second to several seconds

Definition: The standard overload test is usually 6.25 times the rated power or 2.5 times the maximum allowable voltage, whichever is the lesser, for 5 seconds

Units: Percent (%)

The standard overload test subjects the resistors to a power greater than their maximum continuous power rating. This can be used to remove faulty components during manufacture, and helps provide an indication of the ‘Pulse Withstand Capability’.

The overload performance is given as a change in resistance between the value before and after the test.

Overload powers and times do vary depending upon the component type or on customer request.

Resistor Properties - Fusibility

Sometimes a resistor needs to fuse, safely switching off a faulty circuit

Fusible resistors are designed to fail permanently open circuit when excessive power is dissipated in them. Many products will fail in this manner – what makes a resistor “fusible” is that the conditions of safe and certain fusing are specified and controlled.

Resistor Properties - Fusibility

Sometimes a resistor needs to fuse, safely switching off a faulty circuit

Fusible resistors are designed to fail permanently open circuit when excessive power is dissipated in them. Many products will fail in this manner – what makes a resistor “fusible” is that the conditions of safe and certain fusing are specified and controlled.

Tmax

Pr Pmin Pmax

Tmin

TIME

POWER

Pr Rated powerPmin Minimum power for guaranteed fusingPmax Maximum safe

fusing powerTmin Minimum fuse timeTmax Maximum fuse time

Notes:Multiple curves may be shown for different value ranges – lower values have higher Pmin.On some data sheets the POWER and TIME axes are transposed. Sometimes only the Tmax curve is shown.

SEI Part Number Construction:

Series Name – Ohmic Value Tolerance Spare

Generic Examples : CSR1 .003 1% RWW3 10K 1% R

Exception : Some resistors also have a ‘TCR’ code inserted after the ‘Series

Name’

Example: RN1/4 T9 10 .1% R

Key Questions to Ask Customers

•What type of resistor?Mounting - Through-hole / Surface Mount / Non-PCBTechnology - Metal Film / Metal Oxide / Wirewound / Thick Film

•What value + tolerance?

•What TCR?

•What rating?Power ratingMaximum working voltage (applies to higher values only)

•What physical size?

•What competitor’s product is it to replace, if any? (Get manufacturer + type)

•What volume of product is required? EAU

•Do any special requirements apply? (High Voltage, Moisture Sensitivity, low noise, pulse power)

Key Questions to Ask Customers

•What type of resistor?Mounting - Through-hole / Surface Mount / Non-PCBTechnology - Metal Film / Metal Oxide / Wirewound / Thick Film

•What value + tolerance?

•What TCR?

•What rating?Power ratingMaximum working voltage (applies to higher values only)

•What physical size?

•What competitor’s product is it to replace, if any? (Get manufacturer + type)

•What volume of product is required? EAU

•Do any special requirements apply? (High Voltage, Moisture Sensitivity, low noise, pulse power)

Types of Resistor

There are TWO main types of resistors;

* FixedThese resistors have their value set during manufacture and it cannot be changed.

All of SEI’s resistors are Fixed Resistors.

* VariableThese resistors are designed so that their resistance values can be changed easily, such as potentiometers. SEI does not manufacture this type of resistor.

Types of Resistor

There are TWO main types of resistors;

* FixedThese resistors have their value set during manufacture and it cannot be changed.

All of SEI’s resistors are Fixed Resistors.

* VariableThese resistors are designed so that their resistance values can be changed easily, such as potentiometers. SEI does not manufacture this type of resistor.

SEI Resistor Termination Technologies

These are divided into three main types;

* Through Hole (or “leaded” or “axial”)

* Surface Mount (or “SMD”, or “SMT”)

* Non-PCB (Specials and high power resistors)

SEI Resistor Termination Technologies

These are divided into three main types;

* Through Hole (or “leaded” or “axial”)

* Surface Mount (or “SMD”, or “SMT”)

* Non-PCB (Specials and high power resistors)

Through HoleThrough Hole Surface MountSurface Mount

Circuit boardCircuit board

SEI Resistor Technologies

Through Hole

SEI Resistor Technologies

Through HoleResistance wireResistance wire

WirewoundWirewound

Resistive film with spiral cutResistive film with spiral cut

Ceramic core + caps + leadsCeramic core + caps + leads

Film (Metal/Metal Oxide/Carbon/Thick Film)Film (Metal/Metal Oxide/Carbon/Thick Film)

SEI Resistor Technologies

Surface Mount

SEI Resistor Technologies

Surface Mount

InsulationInsulation

Resistance filmResistance film

Ceramic chipCeramic chip

Chip ( Thin Film )Chip ( Thin Film )

Formed LeadsFormed Leads

InsulationInsulation

Resistance filmResistance film

Ceramic chipCeramic chip

Chip ( Thick Film )Chip ( Thick Film )

SEI Resistor Technologies

Non-PCB (Specials and high power)

Thick Film on Steel:

Chassis Mounted:

SEI Resistor Technologies

Non-PCB (Specials and high power)

Thick Film on Steel:

Chassis Mounted:

Applications for Resistors

CIRCUIT FUNCTION APPLICATION EXAMPLE

To limit current in a circuit LED illuminated main switchTo measure current in a circuit Car window motor controlTo generate heat Hair dryer, air freshenerTo remove electrical energy High voltage capacitor discharge in TVTo divide a voltage High voltage supply in X-ray equipmentTo set the gain of an amplifier Car audio amplifierTo set a time delay Test equipment - pulse generatorTo set frequency of an oscillator Test equipment - signal generatorTo protect against surges Electronic electricity meterTo absorb unwanted signals High speed computer systemTo measure temperatures Thermal trip in motor controller

Applications for Resistors

CIRCUIT FUNCTION APPLICATION EXAMPLE

To limit current in a circuit LED illuminated main switchTo measure current in a circuit Car window motor controlTo generate heat Hair dryer, air freshenerTo remove electrical energy High voltage capacitor discharge in TVTo divide a voltage High voltage supply in X-ray equipmentTo set the gain of an amplifier Car audio amplifierTo set a time delay Test equipment - pulse generatorTo set frequency of an oscillator Test equipment - signal generatorTo protect against surges Electronic electricity meterTo absorb unwanted signals High speed computer systemTo measure temperatures Thermal trip in motor controller

SEI Major Product Series - Surface Mount

SERIES TYPE DESCRIPTION

RMC Thick Film General Purpose Chip ResistorRGC Thick Film Semi Precision Thick FilmHMC Thick Film High value chip - to 50GHVC Thick Film High voltage chip - to 3.5kV (NEW)FCR Thick Film Trimmable Chip

RNC Thin Film Precision Chip ResistorTTF Tan Film Moisture Sensitive Precision Chip Resistor

CSR Thick Film Low value current sense resistorCSRL Metal Foil Lowest value current sense (.001 and .002)CSRF Foil on Ceramic Low value current sense (.003 to .010)CSRN Thick Film Low value current sense, narrow termination

RAV/RAF Thick Film Convex / Flat termination chip arrayRAC Thick film Concave termination chip array

SM Wirewound Surface mount wirewound - to 3W

SEI Major Product Series - Surface Mount

SERIES TYPE DESCRIPTION

RMC Thick Film General Purpose Chip ResistorRGC Thick Film Semi Precision Thick FilmHMC Thick Film High value chip - to 50GHVC Thick Film High voltage chip - to 3.5kV (NEW)FCR Thick Film Trimmable Chip

RNC Thin Film Precision Chip ResistorTTF Tan Film Moisture Sensitive Precision Chip Resistor

CSR Thick Film Low value current sense resistorCSRL Metal Foil Lowest value current sense (.001 and .002)CSRF Foil on Ceramic Low value current sense (.003 to .010)CSRN Thick Film Low value current sense, narrow termination

RAV/RAF Thick Film Convex / Flat termination chip arrayRAC Thick film Concave termination chip array

SM Wirewound Surface mount wirewound - to 3W

SEI Major Product Series - Through Hole (Film types)

SERIES TYPE DESCRIPTIONRN Metal Film General purpose / Semi-precisionUP Metal Film Ultra precisionRS Metal Oxide General purposeASR/SPR Metal Oxide Anti Surge / Discharge PathRSPF/RSPL Metal Oxide Flameproof powerFRN Metal Film FusibleJW Metal Jumper wireCD Metal Film Zero Ohm Jumper

RC Carbon Comp General purposeCF Carbon Film General purpose

WRF Wirewound Consumer grade, conformal coatedGP Wirewound Commercial grade, conformal coatedWW Wirewound General purpose / precisionMR/TMR Wirewound Low value, current sense, and four wireNSP Wirewound Ceramic housed, consumer gradeCB Wirewound Ceramic housed, general purpose, and other versionsVM Wirewound Ceramic housed, vertical mount, and other versionsVER Wirewound Vitreous Enamel conformal coatedEL/CEL Wirewound Commercial powerKAL Wirewound Aluminum housed

SEI Major Product Series - Through Hole (Film types)

SERIES TYPE DESCRIPTIONRN Metal Film General purpose / Semi-precisionUP Metal Film Ultra precisionRS Metal Oxide General purposeASR/SPR Metal Oxide Anti Surge / Discharge PathRSPF/RSPL Metal Oxide Flameproof powerFRN Metal Film FusibleJW Metal Jumper wireCD Metal Film Zero Ohm Jumper

RC Carbon Comp General purposeCF Carbon Film General purpose

WRF Wirewound Consumer grade, conformal coatedGP Wirewound Commercial grade, conformal coatedWW Wirewound General purpose / precisionMR/TMR Wirewound Low value, current sense, and four wireNSP Wirewound Ceramic housed, consumer gradeCB Wirewound Ceramic housed, general purpose, and other versionsVM Wirewound Ceramic housed, vertical mount, and other versionsVER Wirewound Vitreous Enamel conformal coatedEL/CEL Wirewound Commercial powerKAL Wirewound Aluminum housed

Applications - Industrial

RCD (RCCB / GFCI) Test resistor RS / WW / RNVoltage dropper

MOTOR DRIVE Braking NSP / CB / VMCurrent Sense

CSR /CSRN /CSRL /CSRFInrush limit

WELDING PSU

Output stage ASR / SPR / RSPFLIGHTING BALLAST

Input stage WRF / GP / WW

PROCESS CONTROL Precision RN / UP / RNC/TTF/WW

Applications - Industrial

RCD (RCCB / GFCI) Test resistor RS / WW / RNVoltage dropper

MOTOR DRIVE Braking NSP / CB / VMCurrent Sense

CSR /CSRN /CSRL /CSRFInrush limit

WELDING PSU

Output stage ASR / SPR / RSPFLIGHTING BALLAST

Input stage WRF / GP / WW

PROCESS CONTROL Precision RN / UP / RNC/TTF/WW

Applications - Medical

DEFIBRILLATOR Pulse protection RSC / ASR / RSPF

MONITOR High sensitivity HMC / RNC / TTFamplification

X-RAY High voltage control ASR / SPR / RSPF

DEFIB, MONITOR, X-RAY Power supply regulation CSR / MR / LCB / LVM

Applications - Medical

DEFIBRILLATOR Pulse protection RSC / ASR / RSPF

MONITOR High sensitivity HMC / RNC / TTFamplification

X-RAY High voltage control ASR / SPR / RSPF

DEFIB, MONITOR, X-RAY Power supply regulation CSR / MR / LCB / LVM

Applications - Automotive

IGNITION Pulse suppression RC / WW / ASR / SPR

WINDOW LIFT

SEAT / STEERING / MIRROR POSITION Current sense CSR / MR / LCB / LVMWIPERS

POWER DISTRIBUTION(DC/DC CONVERTORS)

HID LIGHTS Output stage ASR / SPR / RSPF

Applications - Automotive

IGNITION Pulse suppression RC / WW / ASR / SPR

WINDOW LIFT

SEAT / STEERING / MIRROR POSITION Current sense CSR / MR / LCB / LVMWIPERS

POWER DISTRIBUTION(DC/DC CONVERTORS)

HID LIGHTS Output stage ASR / SPR / RSPF