VISHAY
Document Number: 80065
Rev. 1.5, 13-Nov-03
Vishay Semiconductors
www.vishay.com
1
Optocouplers in Switching Power Supplies
The following provide information on how to use opto-
couplers in designs to protect against electric shock.
Safety standards for optocouplers are intended to
prevent injury or damage due to electric shock Two
levels of electrical interface are normally used:
• Reinforced, or safe insulation is required in an
optocoupler interface between a hazardous volt-
age circuit (like an ac line) and a touchable Safety
Extra Low Voltage (SELV) circuit.
• Basic insulation is required in an optocoupler inter-
face between a hazardous voltage circuit and a
non-touchable Extra Low Voltage (ELV) circuit.
The most widely used insulation for optocouplers in
switch-mode power supply is reinforced insulation
(class II). The following information enables the
designer to understand the safety aspects, the basic
concept of the DIN EN 60747-5-2(VDE0884)/ DIN EN
60747-5-5 pending and the design requirements for
applications.
Facts and Information*)
Optocouplers for line-voltage separation must have
several national standards. The most accepted stan-
dards are:
• UL for America
• UL/ CSA for Canada
• CQC for China
• BSI for Great Britain
• FIMKO, SEMKO, NEMKO, DEMKO for Nordic
countries (Europe)
• VDE for Germany
Today, most manufacturers operate on a global
scale. Therefore, it is important to understand and
meet those requirements.
The DIN EN 60747-5-2(VDE0884)/ DIN EN 60747-5-
5 pending is a major safety standard in the world.
The DIN EN 60747-5-2(VDE0884)/ DIN EN 60747-5-
5 pending standard and IEC 60047C/199/CD stan-
dards may become part of IEC 60747-5.
If design engineers work with VISHAY optocouplers,
they will find some terms and definitions in the data
sheets which relate to DIN EN 60747-5-2(VDE0884)/
DIN EN 60747-5-5 pending.
Rated isolation voltages:
VISO is the voltage between the input terminals and
the output terminals.
Note: All voltages are peak voltages!
•V
IOWM is a maximum rms. voltage value of the
optocouplers assigned by VISHAY. This charac-
terizes the long term withstand capability of its
insulation.
•V
IORM is a maximum recurring peak (repetitive)
voltage value of the optocoupler assigned by
VISHAY. This characterizes the long-term with-
stand capability against recurring peak voltages.
•V
IOTM is an impulse voltage value of the optocou-
pler assigned by VISHAY. This characterizes the
long-term withstand capability against transient
over voltages.
Isolation test voltage for routine tests is at factor 1.875
higher than the specified VIOWM/ VIORM (peak).
A partial discharge test is a different test method to
the normal isolation voltage test. This method is more
sensitive and will not damage the isolation behavior of
the optocoupler like other test methods probably do.
The DIN EN 60747-5-2(VDE0884)/ DIN EN 60747-5-
5 pending therefore does not require a minimum
thickness through insulation. The philosophy is that a
mechanical distance only does not give you an indica
tion of the safety reliability of the coupler. It is recom-
mended that construction together with the assem-
bling performance. The partial discharge test
method can monitor this more reliably.
The following tests must be done to guarantee this
safety requirement.
100 % test (piece by piece) for one second at a volt-
age level of specified VIOWM/VIORM (peak) multiplied
by 1.875*) test criteria is partial discharge less than
5 pico coulomb.
A lotwise test at VIOTM for 10 seconds and at a volt-
age level of specified VIOWM/ VIORM (peak) multiplied
by 1.5 for 1 minute*) test criteria is partial discharge
less than 5 pico coulomb.
Design example:
The line ac voltage is 380 VRMS. Your application
class is III (DIN/VDE 0110 Part 1/1.89). According to
table 1, you must calculate with a maximum line volt-
age of 600 V and a transient over voltage of 6000 V.
*)See Safety Agency Applications Note for more information.
www.vishay.com
2
Document Number: 80065
Rev. 1.5, 13-Nov-03
VISHAY
Vishay Semiconductors
Now select the TCDT1100 from our VISHAY coupler
program. The next voltage step of 380 V is 600 V
(VIOWM).The test voltages are 1600 V for the
TCDT1100 for the routine test and 6000 V/ 1300 V for
the sample test.
The DIN EN 60747-5-2(VDE0884)/ DIN EN 60747-5-
5 pending together with the isolation test voltages
also require very high isolation resistance, tested at
an ambient temperature of 100 °C.
Apart from these tests for the running production, the
VDE Testing and Approvals Institute also investigates
the total construction of the optocoupler.
The DIN EN 60747-5-2(VDE0884)/ DIN EN 60747-5-
5 pending requires life tests in a very special
sequence; 5 lots for 5 different subgroups are tested.
The sequence for the main group is as follows:
• Cycle test
• Vibration
• Shock
• Dry heat
• Accelerated damp heat
• Low temperature storage (normally – 55 °C)
• Damp heat steady state
• Final measurements.
Finally there is another chapter concerning the safety
ratings. This is described in DIN EN 60747-5-
2(VDE0884)/ DIN EN 60747-5-5 pending.
The maximum safety ratings are the electrical, ther-
mal and mechanical conditions that exceed the abso-
lute maximum ratings for normal operations. The
philosophy is that optocouplers must withstand a cer-
tain exceeding of the input current, output power dis-
sipation, and temperature for at least 72 hours. This
is a simulated space of time where failures may occur.
It is the designer's task to create his design inside of
the maximum safety ratings.
Optocouplers – approved to the DIN EN 60747-5-
2(VDE0884)/ DIN EN 60747-5-5 pending – must con-
sequently pass all tests undertaken. This enables
you to go ahead and start your design.
Layout Design Rules
The previous chapter described the important safety
requirements for the optocoupler itself; but the knowl-
edge of the creepage distance and clearance path is
also important for the design engineer if the coupler is
to be mounted onto the circuit board. Although sev-
eral different creepage distances refer to different
safety standards, e.g. IEC 60065 for TV or the IEC
60950 for office equipment, computer, data equip-
ment etc. there is one distance which dominates
switching power supplies: This is the 8 mm spacing
requirement between the two circuits: The hazardous
input voltage (ac 240 power-line voltage) and the
safety low voltage.
This 8 mm spacing is related to the 250 V power line
and defines the shortest distance between the con-
ductive parts (either from the input to the output leads)
along the case of the optocoupler, or across the sur-
face of the print board between the solder eyes of the
optocoupler input/ output leads, as shown in figure 1.
The normal distance input to output leads of an opto-
coupler is 0.3". This is too tight for the 8 mm require-
ment. The designer now has two options: He can
provide a slit in the board, but then the airgap is still
low or .
Depending on the product, option 1 or the "G" version
can be used e.g. SFH619-X001 or TCDT1100G.
"G" stands for a wide-spaced lead form of 0.4" and
meets the 8 mm spacing.
The spacing requirements of the 8 mm must also be
taken into consideration for the layout of the board.
Figures 2 and 3 provide examples for your layout.
The creepage distance is also related to the resis
ance of the tracking creepage current stability. The
plastic material of the optocoupler itself and the mate-
VIOWM/VIORM
up to
Appl. Class I Appl. Class II Appl. Class III Appl. Class IV
50 V 350 V 500 V 800 V 1500 V
100 V 500.V 800 V 1500 V 2500 V
150 V 800 V 1500 V 2500 V 4000 V
300 V 1500 V 2500 V 4000 V 6000 V
600 V 2500 V 4000 V 6000 V 8000 V
1000 V 4000 V 6000 V 8000 V 12000 V
Table 1: Reccomended transient overvoltages related to ac/dc line voltage (peak values)
VISHAY
Document Number: 80065
Rev. 1.5, 13-Nov-03
Vishay Semiconductors
www.vishay.com
3
rial of the board must provide a specified creepage-
current resistance.
The behavior of this resistance is tested with special
test methods described in the IEC 112. The term is
CTI (Comparative Tracking Index).
The DIN EN 60747-5-2(VDE0884)/ DIN EN 60747-5-
5 pending requires a minimum of a CTI of 175.
(The creepage path is the shortest distance between
conductive parts along the surface of the isolation
material.
The clearance path is the shortest distance between
conductive parts.)
Not only the solder eyes of the coupler itself on the
board must have the 8 mm distance, but also all lay-
ers located between the SELV areas and the power
interface areas.
Figure 1. Isolation creepage/clearance path along the body
Figure 2. Isolation creepage/clearance path after mounting on a
board (side view)
Creepage
path
Clearance path
18181
0.4 "/ 10.16 mm
0.332 " / 8.2 mm
18182
Figure 3. "Top view of optocoupler mounting on a board"
(clearance on PC board: 0.322 / 8.2 mm, creepage path on PC
board is 0.322 / 8.2 mm)
G
G
GG
SELV control circuit area
SELV control circuit area
G = 0.322 " / 8.2 mm
Power interface area
Power interface area
Layer
18183
