IEC 62024-2:2024

High frequency inductive components - Electrical characteristics and measuring methods - Part 2: Rated current of inductors for DC-to-DC converters

IEC 62024-2:2024 specifies the measuring methods of the rated DC limits for inductors as defined below. Standardized measuring methods for the determination of ratings enable users to accurately compare the current ratings given in various manufacturers' data books. This document is applicable to leaded and surface mount inductors with dimensions according to IEC 62025-1 and generally with rated current less than 125 A, although inductors with rated current greater than 125 A are available that fall within the dimension restrictions of this document (no larger than a 625 mm2 footprint). These inductors are typically used in DC‑to‑DC converters built on printed circuit boards (PCBs), for electronic and telecommunication equipment, and small size switching power supply units. The measuring methods are defined by the saturation and temperature rise limitations induced solely by direct current (DC).
This edition includes the following significant technical changes with respect to the previous edition:
a) extension of scope by increase of range of rated current from 22 A to 125 A;
b) extension of scope by increase of footprint limitation from 12 mm × 12 mm to 625 mm2;
c) addition of upper current limitation for Iclass B, Iclass C and Iclass D board to Table 1;
d) revised application examples for Table 1;
e) addition of wire size references for current ranges between 22 A ≤ I ≤ 125 A to Table 2;
f) addition of crimp terminal references to Table 2;
g) addition of thermal camera method.

Composants inductifs à haute fréquence - Caractéristiques électriques et méthodes de mesure - Part 2: Courant assigné des bobines d'inductance pour les convertisseurs continu-continu

L'IEC 62024-2:2024 spécifie les méthodes de mesure des limites de courant continu assigné pour les bobines d'inductance, définies ci-après. Les méthodes de mesure normalisées pour la détermination des caractéristiques assignées permettent aux utilisateurs de comparer avec exactitude les caractéristiques assignées de courant indiquées dans les fiches de données des différents fabricants. Le présent document s'applique aux bobines d'inductance plombées et à montage en surface dont les dimensions sont conformes à l'IEC 62025-1 et dont le courant assigné est généralement inférieur à 125 A, même si des bobines d'inductance de courant assigné supérieur à 125 A sont disponibles et respectent les limites de dimensions du présent document (empreinte inférieure ou égale à 625 mm2). Ces bobines d'inductance sont habituellement utilisées dans des convertisseurs continu-continu montés sur des cartes à circuit imprimé (PCB, printed circuit boards), pour des équipements électroniques et de télécommunications, ainsi que pour les blocs d'alimentation à découpage de petite taille. Les méthodes de mesure sont définies par les limites de saturation et d'échauffement induites par le courant continu (DC) uniquement.
Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
a) le domaine d'application a été élargi en portant la plage du courant assigné de 22 A à 125 A;
b) le domaine d'application a été élargi en portant les limites de l'empreinte de 12 mm × 12 mm à 625 mm2;
c) une limite haute de courant a été ajoutée pour les cartes Iclasse B, Iclasse C et Iclasse D dans le Tableau 1;
d) les exemples d'application ont été révisés pour le Tableau 1;
e) des tailles de fils de référence ont été ajoutées pour les courants d'intensité 22 A ≤ I ≤ 125 A dans le Tableau 2;
f) des bornes à sertir de référence ont été ajoutées dans le Tableau 2;
g) la méthode par caméra thermique a été ajoutée.

General Information

• Status: Published
• Publication Date: 18-Dec-2024
• ICS: 29.100.10 - Magnetic components
• Technical Committee: TC 51 - Magnetic components, ferrite and magnetic powder materials
• Drafting Committee: WG 9 - TC 51/WG 9
• Current Stage: PPUB - Publication issued
• Start Date: 19-Dec-2024
• Completion Date: 27-Dec-2024

Relations

• Revises: IEC 62024-2:2020 - High frequency inductive components - Electrical characteristics and measuring methods - Part 2: Rated current of inductors for DC-to-DC converters
• Effective Date: 05-Sep-2023

Standards Content (Sample)

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Edition 3.0 2024-12
REDLINE VERSION
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STANDARD
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High frequency inductive components – Electrical characteristics and measuring
methods –
Part 2: Rated current of inductors for DC-to-DC converters

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IEC 62024-2 ®
Edition 3.0 2024-12
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
High frequency inductive components – Electrical characteristics and
measuring methods –
Part 2: Rated current of inductors for DC-to-DC converters
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.100.10 ISBN 978-2-8327-0120-1

– 2 – IEC 62024-2:2024 RLV © IEC 2024
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Standard atmospheric conditions . 7
4.1 Standard atmospheric conditions for testing . 7
4.2 Reference conditions . 7
5 Measuring method of direct saturation limited current (DC) . 7
5.1 General . 7
5.2 Test conditions . 7
5.3 Measuring circuit and calculation . 8
5.3.1 Measuring circuit . 8
5.3.2 Calculation . 9
5.4 Attachment jig of inductor . 9
5.5 Measuring method . 9
5.6 Quality conformance inspection . 10
6 Measuring method of temperature rise limited current. 10
6.1 General . 10
6.2 Test conditions . 10
6.3 Measuring jig . 10
6.3.1 General . 10
6.3.2 Printed-wiring board method . 11
6.3.3 Lead wire method . 21
6.4 Measuring method and calculation . 22
6.4.1 General . 22
6.4.2 Resistance substitution method . 22
6.4.3 Thermocouple method . 23
6.4.4 Thermal camera method . 24
6.5 Quality conformance inspection . 26
7 Determination of rated current . 26
8 Information to be given in the detail specification . 26
8.1 General . 26
8.2 Measuring method of direct saturation limited current (DC) . 26
8.3 Measuring method of temperature rise limited current . 26
Annex A (informative) Example of recommended description on product specification
sheets and catalogues . 27
Bibliography . 28

Figure 1 – Inductance measuring circuit under application of DC saturation condition . 8
Figure 2 – Example of printed-wiring boards . 21
Figure 3 – Temperature rise measuring circuit by resistance substitution method . 22
Figure 4 – Temperature rise measuring circuit by thermocouple method . 23
Figure 5 – Temperature rise measuring circuit by thermal camera method . 25

Table 1 – Width of circuits . 11

Table 2 – Circuit pattern width and thickness .
Table 2 – Wire size of circuits . 21

– 4 – IEC 62024-2:2024 RLV © IEC 2024
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
HIGH FREQUENCY INDUCTIVE COMPONENTS –
ELECTRICAL CHARACTERISTICS AND MEASURING METHODS –

Part 2: Rated current of inductors for DC-to-DC converters

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
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6) All users should ensure that they have the latest edition of this publication.
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent
rights. IEC shall not be held responsible for identifying any or all such patent rights.
This redline version of the official IEC Standard allows the user to identify the changes
made to the previous edition IEC 62024-2:2008. A vertical bar appears in the margin
wherever a change has been made. Additions are in green text, deletions are in
strikethrough red text.
International Standard IEC 62024-2 has been prepared IEC technical committee 51: Magnetic
components, ferrite and magnetic powder materials.
This second edition cancels and replaces the first edition published in 2008. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) addition of Table 2 and Figure 2 b).
The text of this International Standard is based on the following documents:
CDV Report on voting
51/1303/CDV 51/1325/RVC
Full information on the voting for the approval of this International Standard can be found in the
report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of IEC 62024 series, published under the general title High frequency inductive
components – Electrical characteristics and measuring methods can be found on the IEC
website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The "colour inside" logo on the cover page of this document indicates
that it contains colours which are considered to be useful for the correct understanding
of its contents. Users should therefore print this document using a colour printer.

– 6 – IEC 62024-2:2024 RLV © IEC 2024
HIGH FREQUENCY INDUCTIVE COMPONENTS –
ELECTRICAL CHARACTERISTICS AND MEASURING METHODS –

Part 2: Rated current of inductors for DC-to-DC converters

1 Scope
This part of IEC 62024 specifies the measuring methods of the rated DC limits for small
inductors as defined below.
Standardized measuring methods for the determination of ratings enable users to accurately
compare the current ratings given in various manufacturers' data books.
This document is applicable to leaded and surface mount inductors with dimensions according
to IEC 62025-1 and generally with rated current less than 22 125 A, although inductors with
rated current greater than 22 125 A are available that fall within the dimension restrictions of
this document (no larger than a 12 mm × 12 mm 625 mm footprint approximately). These
inductors are typically used in DC-to-DC converters built on printed circuit boards (PCBs), for
electric electronic and telecommunication equipment, and small size switching power supply
units.
The measuring methods are defined by the saturation and temperature rise limitations induced
solely by direct current (DC).
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60068-1:2013, Environmental testing – Part 1: General and guidance
IEC 62025-1, High frequency inductive components – Non-electrical characteristics and
measuring methods – Part 1: Fixed, surface mounted inductors for use in electronic and
telecommunication equipment
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
3.1
direct saturation limited current (DC)
allowable value of direct current (DC) for which the decrease of the inductance is within the
specified value
3.2
temperature rise limited current
allowable value of direct current (DC) for which the self-generation heat of the inductor results
in temperature rise within the specified value
4 Standard atmospheric conditions
4.1 Standard atmospheric conditions for testing
Standard atmospheric conditions for testing shall be as follows (see IEC 60068-1:2013, 4.3):
• temperature: 15 °C to 35 °C;
• relative humidity: 25 % to 75 %;
• air pressure: 86 kPa to 106 kPa.
In the event of dispute or where required, the measurements shall be repeated using the referee
temperatures and such other conditions as given in 4.2.
4.2 Reference conditions
For reference purposes, one of the standard atmospheric conditions for referee tests taken from
IEC 60068-1:2013, 4.2, shall be selected and shall be as follows:
• temperature: 20 °C ± 2 °C;
• relative humidity: 60 % to 70 %;
• air pressure: 86 kPa to 106 kPa.
5 Measuring method of direct saturation limited current (DC)
5.1 General
When alternating current (AC) in which direct current (DC) is superimposed is supplied to an
inductor, the inductance of the inductor decreases according to the DC current value.
In a typical application, the saturation current results from the peak current of the superposition
of alternating current (AC) on direct current (DC). In this document, the saturation current is
measured as direct current (DC) offsetting a small signal alternating current (AC).
NOTE It is not practical to set a standard for alternating saturation limited current (AC), because there is an
unlimited number of different ways to apply alternating current (AC) in an application. Therefore, manufacturers and
users have generally defined direct saturation limited current (DC) as a common point of reference. This document
does the same.
5.2 Test conditions
Unless otherwise specified in the detail specification, the test conditions shall be in accordance
with Clause 4.
NOTE The variation of the value of direct saturation limited current (DC), as a function of temperature, is dependent
on the magnetic material and the structure of the magnetic core of the inductor. However, measurement of direct
saturating currents at elevated temperatures is generally not practical for inspection purposes. Therefore, the
measurement at room temperature as provided by this document is generally applied for specification purposes. De-
rating curves indicating variation of direct saturation limited current (DC) as a function of maximum operating
temperature of the inductor can be generated. These curves can be used to correlate the direct saturation limited
current (DC) at room temperature to the direct saturation limited current (DC) at typical operating temperatures. In
some cases, it will become necessary for the manufacturer and user to will agree on an additional specification at a
high temperature such as 85 °C, 105 °C or 125 °C.

– 8 – IEC 62024-2:2024 RLV © IEC 2024
5.3 Measuring circuit and calculation
5.3.1 Measuring circuit
The measuring circuit is as shown in Figure 1.

Key
Components
R source resistor R = R
s s
R range select resistor R = R
r r
V voltmeter V = E
1 1 1
V voltmeter V = E
2 2 2
E RMS voltage value measured by voltmeter V
1 1
E RMS voltage value measured by voltmeter V
2 2
E RMS voltage value of source
s
C DC current blocking capacitor
Supplies
f frequency of source
s
I supplied current to range select resistor
r
I supplied current to specimen
x
I = I
x r
Figure 1 – Inductance measuring circuit under application of DC saturation condition

5.3.2 Calculation
Voltages E and E shall be measured when frequency f and voltage E of the signal generator
1 2 s s
are supplied in accordance with the detail specification, and an initial value of the inductance
shall be calculated by the following formulae:
EE−
ZR
xr
IE
r2
ZZ cosθ+jZ sinθ
xx x
Z R+jX
xx x
XX
xx
L
x
ω 2πf
s
where
R is the resistance of the specimen;
x
X is the reactance of the specimen;
x
Z is the impedance of the specimen;
x
L is the equivalent series inductance of the specimen;
x
E is the applied voltage to the specimen;
E is the applied voltage to the range select resistor (= I R ) (E can be regarded as current);
2 r r 2
θ is the phase angle difference between E and E of the complex impedance.
1 2
5.4 Attachment jig of inductor
The attachment jig of the specimen shall be specified in a detail specification (see Clause 8).
5.5 Measuring method
a) A short compensation shall be done before measurement.
a) The specimen shall be connected to the circuit shown in Figure 1, by using the attachment
jig specified in 5.4.
b) When the specimen is connected by soldering, it shall be left until it becomes cool enough.
c) Voltages E and E shall be measured when frequency f and voltage E of the signal
1 2 s s
generator are supplied in accordance with the detail specification, and an initial value of the
inductance shall be calculated by the formulae of 5.3.2.
d) The value of the DC current that is superimposed on the specimen shall be modulated and
the inductance value shall be measured.
e) The decrease from the initial value of the inductance shall be calculated. Direct saturation
limited current (DC) shall be determined by measuring the direct current (DC) when the
decrease in inductance matches the specified value in the detail specification.
f) The decrease in inductance that is specified in the detail specification should be 10 % or
30 %.
NOTE 10 % is one of the design points typical for sharp-saturating inductors, and 30 % is one of the design points
typical for soft-saturating inductors. See Annex A.
==
=
=
= =
– 10 – IEC 62024-2:2024 RLV © IEC 2024
5.6 Quality conformance inspection
The direct current (DC) specified in the detail specification shall be supplied to a specimen in
accordance with the methods specified in 5.3 to 5.5, and then inductance shall be measured.
The decrease in inductance shall be within the specified value.
6 Measuring method of temperature rise limited current
6.1 General
When direct current (DC) is supplied to an inductor, the inductor generates heat by itself
according to the supplied DC value because of its DC resistance.
NOTE 1 Temperature rise results from self-heating of the inductor. The sources of heating are DC copper losses,
AC copper losses and AC core losses. This document defines the temperature rise induced only by direct currents
(DC). In actual operating conditions, AC copper losses and AC core losses are considered for the temperature rise
will be considered. AC losses are highly affected by waveform, amplitude and frequency.
NOTE 2 It is not practical to set a standard for alternating temperature rise limited current (AC), because there is
an unlimited number of different ways to apply alternating current (AC) in an application. Therefore, manufacturers
and users have generally defined DC direct temperature rise limited current as a common point of reference. This
document does the same.
6.2 Test conditions
Unless otherwise specified in the detail specification, for example an elevated ambient
temperature, the test conditions shall be in accordance with Clause 4.
Since the value of DC current resistance increases as a function of temperature, some
applications require a high ambient temperature such as 85 °C, 105 °C or 125 °C for the
temperature rise test.
NOTE 1 The overall power loss of an inductor is a combination of DC power loss due to DC current resistance, as
well as AC power loss due to AC current in the windings, and losses due to the corresponding AC flux induced in the
magnetic core. The value of AC and DC current resistance (the conductor resistance) increases with temperature,
thus the power loss associated with conductor resistance increases with temperature. The loss associated with the
magnetic core is all due to AC excitation. The core loss decreases with increasing temperature up to a temperature
typically referred to as the core loss minima temperature, above which point this loss begins to increase. The minima
temperature and magnitude of loss are dependent on the magnetic material type and grade. Some ferrites exhibit
sharp minima temperatures. These considerations are taken into account when applying temperature rise currents
to applications with high operating temperatures and a non-trivial amount of AC power loss in addition to DC power
loss. The overall total loss at any given temperature can be dominated by DC loss or AC loss depending on the power
loss distribution at room temperature as well as the variation of each of these power losses with temperature.
NOTE 1 Power losses are factors that affect the efficiency of the DC-to-DC converter and the temperature rise of
the inductor during actual operation, regardless of the operating temperature. In this document, temperature rise
currents are defined in terms of direct currents (DC), so including alternating currents (AC) would be confusing and
will be removed from the test conditions. The power ferrite core losses decrease with increasing temperature up to
a temperature typically referred to as the core loss minima temperature, above which point this loss begins to
increase. The minima temperature and magnitude of loss are dependent on the material type and grade. Some ferrite
materials components exhibit sharp minima temperature. The temperature variation of the loss of the metal powder
core, depending on the type of material, is considerably smaller than that of the ferrite core and does not tend to
vary with temperature as the ferrite core exhibits.
NOTE 2 Regarding direct temperature rise limited currents (DC) at high temperatures, the variation in direct
temperature rise limited current (DC) with ambient temperature variation can be modelled. Measurement at room
temperature is commonly applied for detail specifications. In any event, the ambient temperature for the test is
specified in the detail specification.
6.3 Measuring jig
6.3.1 General
The measuring jig shall be either the printed-wiring board method given in 6.3.2 or lead wire
method given in 6.3.3, and shall be specified in the detail specification.

6.3.2 Printed-wiring board method
The printed-wiring board shall be made of epoxide woven glass (FR4). Unless otherwise
specified in the detail specification, the dimensions shall be as shown in Table 1, Table 2 and
Figure 2.
Table 1 – Width of circuits
Rated current class Rated current of inductor Pattern width
I W
A mm
I
I ≤ 1 1,0 ± 0,2
class A
1 < I ≤ 2 2,0 ± 0,2
2 < I ≤ 3 3,0 ± 0,3
3 < I ≤ 5 5,0 ± 0,3
5 < I ≤ 7 7,0 ± 0,5
7 < I ≤ 11 11,0 ± 0,5
11 < I ≤ 16 16,0 ± 0,5
16 < I ≤ 22 22,0 ± 0,5
22 < I According to the detail specification
NOTE See Figure 2a).
Rated Pattern Pattern Test board Thermal Example application
Rated
current of width thickness Environment
current
inductor
class
I W t
A mm μm
I ≤ 1 1,0 ± 0,2 35 ± 10 Figure 2a) Low heat Consumer
I
class A
Figure 2g) dissipation
1< I ≤ 2 2,0 ± 0,2
environments
2 < I ≤ 3 3,0 ± 0,3
3 < I ≤ 5 5,0 ± 0,3
5 < I ≤ 7 7,0 ± 0,5
7 < I ≤ 11 11,0 ± 0,5
11 < I ≤ 16 16,0 ± 0,5
16 < I ≤ 22 22,0 ± 0,5
I ≤ 22 40,0 ± 1.0 Figure 2b) Standard heat Consumer/Automotive
I
class B
Figure 2c) dissipation
Figure 2d) environments
Figure 2h) High heat Consumer/Automotive
I ≤ 46 105 ± 10
I
class C
dissipation
environments
Figure 2b) Very high heat Automotive/Large
I ≤ 125 1 000 ± 50
I
class D
Figure 2e) dissipation current power line
Figure 2f) environments (data centers, network
Figure 2i) infrastructure, etc.)
Figure 2j)
NOTE Winding cable to board: See Table 2.

– 12 – IEC 62024-2:2024 RLV © IEC 2024
Table 2 – Circuit pattern width and thickness
Rated current Pattern width Pattern thickness Example application
class W t
mm µm
I (1,0 to 22,0) ± 0,2 35 ± 10 Consumer application (single-sided printed circuit
class A
to 0,5 boards application)
I 40 ± 0,2 35 ± 10 Consumer application (double-sided printed circuit
class B
boards application)
I 40 ± 0,2 105 ± 10 Consumer application (multilayer printed circuit
class C
boards application)
I 40 ± 0,2 1000 ± 50 Automotive or large current power line application
class D
NOTE 1 I : see Figure 2a).
class A
NOTE 2 I I I : see Figure 2b).
class B, class C, class D
Dimensions in millimetres
a) Example of printed-wiring board for SMD type (I class A)

b) Example of printed-wiring board for SMD type (I class B,C,D)

– 14 – IEC 62024-2:2024 RLV © IEC 2024
Dimensions in millimetres
c) Example of printed-wiring board for leaded type
Key
Solderable areas (only the recommended land pattern should be covered by soldering)
Current applying connection areas
Voltage measuring areas
(Voltage should be measured at the product's electrodes in case the DC resistance of the product
is lower than the pattern resistance)
Non-solderable areas (covered with non-solderable lacquer)
Cu areas
NOTE 1 a, b, c, d , d and p: according to the detail specification.
1 2
NOTE 2 Material of substrate: epoxide woven glass (FR4).
NOTE 3 Material of patterned areas: copper.
NOTE 4 Pattern width (W): see Table 1 and Table 2.

NOTE 5 e , e , e , f , f , f , f and f : according to the detail specification

1 2 3 1 2 3 4 5
Dimensions in millimetres
a) Example of printed-wiring board for SMD type (I )
class A
Dimension in millimetres
b) Example of printed-wiring board for SMD type (I , I , I )
class B class C class D
– 16 – IEC 62024-2:2024 RLV © IEC 2024
Dimension in millimetres
c) Example of printed-wiring board for SMD type (I , I )
class B class C
Dimensions in millimetres
NOTE Install crimp terminals suitable for the wire size. (See Table 2.)
d) Example of printed-wiring board for SMD type (I , I )
class B class C
Dimensions in millimetres
NOTE 1 Install crimp terminals suitable for the wire size. (See Table 2.)
NOTE 2 Lead wires can also be fitted near the inductor terminals as a sense trace on a class D board.
e) Example of printed-wiring board for SMD type (I )
class D
– 18 – IEC 62024-2:2024 RLV © IEC 2024
Dimensions in millimetres
NOTE 1 Install crimp terminals suitable for the wire size. (See Table 2.)
NOTE 2 Lead wires can also be fitted near the inductor terminals as a sense trace on a class D board.
f) Example of printed-wiring board for SMD type (I )
class D
Dimensions in millimetres
g) Example of printed-wiring board for lead type (I )
class A
Dimensions in millimetres
NOTE Install crimp terminals suitable for the wire size. (See Table 2.)
h) Example of printed-wiring board for lead type (I , I )
class B class C
– 20 – IEC 62024-2:2024 RLV © IEC 2024
Dimensions in millimetres
NOTE 1 Install crimp terminals suitable for the wire size. (See Table 2.)
NOTE 2 Lead wires can also be fitted near the inductor terminals as a sense trace on a class D board.
i) Example of printed-wiring board for lead type (I )
class D
Dimensions in millimetres
NOTE 1 Install crimp terminals suitable for the wire size. (See Table 2.)
NOTE 2 Lead wires can also be fitted near the inductor terminals as a sense trace on a class D board.
j) Example of printed-wiring board for lead type (I )
class D
Key
Solderable areas (only the recommended surface should be covered by soldering)

Current applying connection areas
Voltage measuring areas
(Voltage should be measured at the product's electrodes in case the DC resistance of the product is
lower than the pattern resistance)
Non-solderable areas (covered with non-solderable lacquer)

Copper areas
NOTE 1 a, b, c, d , d and p: according to the detail specification.
1 2
NOTE 2 Material of substrate: epoxide woven glass (FR4).
NOTE 3 Material of patterned areas: copper.
NOTE 4 Pattern width (W): see Table 1.
NOTE 5 e , e , e and f : according to the detail specification.
1 2 3 1-5
Figure 2 – Example of printed-wiring boards
6.3.3 Lead wire method
Unless otherwise specified in the detail specification, the wire diameter of the lead wire to
connect the inductor and the measuring circuit shall be in accordance with Table 2.
Table 2 – Wire size of circuits
Rated current of inductors Wire size
I
mm AWG (for reference)
A
I ≤ 3 0,50 ± 0,05
3 < I ≤ 5 0,65 ± 0,05
5 < I ≤ 11 0,8 ± 0,1 20
11 < I ≤ 16 1,0 ± 0,1 18
16 < I ≤ 22 1,3 ± 0,1
22 < I According to the detail specification
NOTE 1 The wire size refers to MIL standard (MIL-PRF-15733).
NOTE 2 AWG is a wire diameter number of American Wire Gauge.

Rated current of inductors Wire size To connect to the test board
I
A mm AWG (for reference) Crimp terminals
I ≤ 3 0,65 ± 0,05 22 R1.25-5
3 < I ≤ 5 0,8 ± 0,05 20 R1.25-5
16 R1.25-5
5 < I ≤ 11 1,3 ± 0,1
14 R2-5
11 < I ≤ 16 1,65 ± 0,1
16 < I ≤ 22 2,0 ± 0,1 12 R5.5-5
8 R8-5
22 < I ≤ 35 3,3 ± 0,1
6 R14-5
35 < I ≤ 46 4,1 ± 0,1
46 < I ≤ 55 5,2 ± 0,1 4 R22-8
– 22 – IEC 62024-2:2024 RLV © IEC 2024
55 < I ≤ 90 6,5 ± 0,1 2 R38-8
90 < I ≤ 125 8,3 ± 0,1 0 R60-8
NOTE 1 AWG is a wire diameter number of American Wire Gauge.
NOTE 2 Multiple strands of finer conductor wire gauges can be used in lieu of a single wire gauge if the composite
cross section area of the conductor remains the same.

6.4 Measuring method and calculation
6.4.1 General
The measuring method shall be the resistance substitution method of 6.4.2, the thermocouple
method of 6.4.3, or the thermal camera method of 6.4.4, and shall be specified in the detail
specification.
6.4.2 Resistance substitution method
a) The specimen shall be connected to the circuit shown in Figure 3, by using the measuring
jig specified in 6.3.
Figure 3 – Temperature rise measuring circuit by resistance substitution method
b) When the specimen is connected by soldering, it shall be left until it cools to the test ambient.
c) The specimen should be measured inside a cubic box of roughly 20 cm on each side to
prevent temperature change from air flow. The box may have some vents in the top to
prevent trapping heat inside.
The specimen shall be measured on the condition that it does not contact directly with the
test board any surface. When it is measured by mounting on the printed-wiring board, the
printed-circuit board on which the specimen is mounted shall not contact directly with the
test board any surface.
d) The resistance value of the specimen and ambient temperature t shall be measured before
a1
direct current (DC) is supplied.
e) Direct current (DC) shall be supplied to the specimen from a direct power supply. After the
DC voltage value of the specimen becomes steady, DC current value I and DC voltage
x
value E shall be measured by the ammeter and the voltmeter; ambient temperature t shall
x a2
also be measured. The resistance value R shall then be calculated by the following formula.
x
E
x
R =
x
I
x
where
I is the DC current value;
x
E is the DC voltage;
x
R is the resistance of the specimen.
x
f) The temperature rise value t of the specimen shall be calculated by the following formula,
by using the resistivity coefficient of the metal and the resistance of the specimen.
– t  shall be 5 °C or less.
t
a1 a2

R −R
t=t− t = Ct+ +−t t
( )

2 a2 a1 a1 a2
R
1
where
t is the temperature rise value (°C);
t is the temperature of the specimen when direct current (DC) is supplied (°C);
t is the initial ambient temperature (°C);
a1
t is the ambient temperature when direct current (DC) is supplied (°C);
a2
R is the resistance of winding at temperature t = t (Ω);
1 1 a1
R is the resistance of winding at temperature t (Ω);
2 2
C is a material constant. C for copper = 234,5 related to the thermal coefficient of
resistivity of the winding conductor. For the purposes of this document the value for
copper shall be taken as 234,5.
g) The value of the supplied direct current (DC) shall be modulated and the temperature rise
value shall be measured.
h) Temperature rise limited current shall be determined by measuring direct current (DC) when
the temperature rise value becomes the specified value in the detail specification. Two
consecutive temperature readings made 1 min apart and shown should not to vary by more
than 1 °C.
i) The temperature rise of connecting conductor shall be less than 50 % of the temperature
rise of the specimen.
j) The temperature rise value that is specified in the detail specification should be 20 °C or
40 °C.
6.4.3 Thermocouple method
a) The specimen shall be connected to the circuit shown in Figure 4, by using the measuring
jig specified in 6.3.
Figure 4 – Temperature rise measuring circuit by thermocouple method

– 24 – IEC 62024-2:2024 RLV © IEC 2024
b) When the specimen is connected by soldering, it shall be left until it cools to the test ambient.
c) The specimen should be measured inside a cubic box of roughly 20 cm on each side to
prevent temperature change from air flow. The box may have some vents in the top to
prevent trapping heat inside.
The specimen shall be measured on the condition that it does not contact directly with the
test board. When it is measured by mounting on the printed-wiring board, the printed-wiring
board on which the specimen is mounted shall not contact directly with the test board.
d) Consideration The thermocouple shall be given to in the correct measuring position of the
thermo-couple for the temperature measurement. It should be placed at the location where
the maximum temperature of the inductor will occur. The best location may be direct contact
at the surface of the specimen, or within the coil by placing the thermocouple inside, or
under the coil by positioning it prior to winding.
The measuring position shall be specified in the detail specification.
and ambient temperature t shall be measured before
e) The temperature of the specimen t
1 a1
direct current (DC) is supplied.
f) Direct current (DC) shall be supplied to the specimen from a DC power supply. After the
and
temperature of the specimen becomes steady, the temperature of the specimen t
ambient temperature t shall be measured again.
a2
Criteria of temperature stability: ∆T < 1 (°C /min).
g) The value of the supplied direct current (DC) shall be modulated, and the temperature rise
value shall be calculated by the following formula.
t – t  shall be 5 °C or less
a1 a2
t= (t− t )− (tt− )
2 a2 1 a1
where
t is the temperature rise value (°C);
t is the initial temperature of the specimen (°C);
t is the temperature of the specimen when direct current (DC) is supplied (°C);
t is the initial ambient temperature (°C);
a1
t is the ambient temperature when direct current (DC) is supplied (°C).
a2
h) The temperature rise limited current shall be determined by measuring direct current (DC)
when the temperature rise value becomes the specified value in the detail specification.
Two consecutive temperature readings made 1 min apart and shown should not to vary by
more than 1 °C.
i) The temperature rise of the connecting conductor shall be less than 50 % of the temperature
rise of the specimen.
j) The temperature rise value that is specified in the detail specification should be 20 °C or
40 °C.
6.4.4 Thermal camera method
a) The specimen shall be connected to the circuit shown in Figure 5, by using the measuring
jig specified in 6.3.
Figure 5 – Temperature rise measuring circuit by thermal camera method
b) When the specimen is connected by soldering, it shall be left until it cools to the test ambient.
c) The test piece and the conductor of the test current should be painted black or the emissivity
should be pre-set so that the appropriate temperature can be measured.
d) The specimen should be measured inside a cubic box of roughly 20 cm on each side to
prevent temperature change from air flow. The box may have some vents in the top to
prevent trapping heat inside. The box may have an opening for the thermal camera to have
line of sight access to the top of the test specimen.
The specimen shall be measured on the condition that it does not contact directly with any
surface. When it is measured by mounting on the printed-wiring board, the printed-wiring
board on which the specimen is mounted shall not contact directly with any surface.
The measuring position shall be specified in the detail specification.
e) The temperature of the specimen t and ambient temperature t shall be measured before
1 a1
direct current (DC) is supplied.
f) Direct current (DC) shall be supplied to the specimen from a DC power supply. After the
temperature of the specimen becomes steady, the temperature of the specimen t and
ambient temperature t shall be measured again.
a2
Criteria of temperature stability: ∆T < 1 (°C /min).
g) The value of the supplied direct current (DC) shall be modulated, and the temperature rise
value shall be calculated by the following formula.
t – t  shall be 5 °C or less
a1 a2
t= t− t − tt−
( ) ( )
2 a2 1 a1
where
t is the temperature rise value (°C);
t is the initial temperature of the specimen (°C);
t is the temperature of the specimen when direct current (DC) is supplied (°C);
t is the initial ambient temperature (°C);
a1
t is the ambient temperature when DC current is supplied (°C).
a2
h) The temperature rise limited current shall be determined by measuring direct current (DC)
when the temperature rise value becomes the specified value in the detail specification.
Two consecutive temperature readings made 1 min apart should not vary by more than 1 °C.
i) The temperature rise of the connecting conductor shall be less than 50 % of the temperature
rise of the specimen.
j) The temperature rise value that is specified in the detail specification should be 20 °C or
40 °C.
– 26 – IEC 62024-2:2024 RLV © IEC 2024
6.5 Quality conformance inspection
The direct current (DC) specified in the detail specification shall be supplied to a specimen in
accordance with the methods specified in 6.3 and 6.4, and then the temperature rise value shall
be measured.
The temperature rise value of the specimen shall be within the specified value.
7 Determination of rated current
For any inductor that is given a current rating, a direct saturation limited current (DC) value, or
a temperature rise limited current value, whichever is less, defined and measured as shown in
this document, shall be adopted as the rated current.
8 Information to be given in the detail specification
8.1 General
The following information shall be given in the detail specification.
8.2 Me
...