STMicroelectronics STEVAL-IHT008V1 User manual

March 2016
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www.st.com
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User manual
Inrush current limitation when charging a DC bus capacitor for
IEC 61000-3-3 compliance
Introduction
The STEVAL-IHT008V1 evaluation board limits the inrush current charging a DC bus capacitor so that it
is compliant with the IEC 61000-3-3 standard. This inrush current is based on a soft-start procedure for
the rectifier bridge achieved with a Triac added in series with the mains line, which is controlled through
progressive phase-control during the startup phase.
This solution drastically reduces standby losses as the DC bus can be totally disconnected from the AC
mains when it is not required. The DC bus is easily turned off by turning off the series Triac, without
needing an additional relay to open the circuit in standby.
Steady-state losses are also reduced because NTC resistors, traditionally used to limit inrush current,
are not required; nor are the corresponding relays to bypass them.
This board also demonstrates that AC loads can be driven with an isolated easy-to-design solution by
using the same power supply as the whole system and some opto-transistors which control the AC
switches.
Figure 1: STEVAL-IHT008V1 evaluation board (top view)

Contents
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Contents
1Evaluation board objectives..........................................................3
1.1 What does this evaluation board aim to demonstrate? ....................3
1.2 Principal board blocks......................................................................3
1.3 Targeted applications.......................................................................4
1.4 Main part numbers...........................................................................4
1.5 Operating range and performances .................................................5
1.6 Stand-by consumption .....................................................................7
2Getting started................................................................................9
2.1 Safety instruction..............................................................................9
2.2 Board connection and start-up.........................................................9
2.3 DC bus capacitor discharge for demonstration purpose ................10
2.4 LED indications..............................................................................10
2.5 Possible board adaptations............................................................11
2.5.1 ACST use and MOV removal..........................................................11
2.5.2EMI filter and DC bus capacitors change........................................11
2.5.3 Power factor circuit connection .......................................................12
2.5.4 Motor Inverter connection................................................................12
2.5.5 Control with an external microcontroller..........................................12
3Conclusion....................................................................................13
4STEVAL-IHT008V1 circuit schematics........................................14
5STEVAL-IHT008V1 power supplies and typical consumption...17
6Inrush-current limitation..............................................................19
7Mains voltage dips and interruptions .........................................23
8AC voltage monitoring and zero-voltage synchronisation........26
9Triacs and AC switches insulated control..................................29
10 EN55014 test results ....................................................................31
11 STEVAL-IHT008V1 silk-screen ....................................................32
12 Test points....................................................................................35
13 Revision history ...........................................................................36

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1 Evaluation board objectives
1.1 What does this evaluation board aim to demonstrate?
This board offers an efficient solution, balancing the following requirements:
Inrush current limitation without inrush current resistor
Standby losses in line with ECO European directive
Low cost and reliable solution to drive AC loads using a single MCU and referenced to
the DC bus ground
The STEVAL-IHT008V1 board is designed to demonstrate these criteria independently;
you only need to connect the AC loads to check this part.
The STEVAL-IHT008V1 board is also intended as a development tool for designers who
want to design a whole system (appliance, air conditioning system, telecom power supply,
etc.).
For this purpose, connectors are available to add an external Power Factor Corrector, an
Intelligent Power Module (IPM) or to use an external microcontroller (see Section 2.5:
"Possible board adaptations").
1.2 Principal board blocks
Section 5: "STEVAL-IHT008V1 power supplies and typical consumption" details the
STEVAL-IHT008V1 schematics.
Figure 2: "Board synopsis" summarizes the STEVAL-IHT008V1 board with the following
main components:
The Triac (T_ICL) in series with the diode bridge
The AC switches (T1 to T5) connected on AC side to control AC loads. It should be
noted that their drive reference (A1) is also connected to the A1 terminal of T_ICL. All
A1 terminals are connected to the VCC_AC terminal, allowing this power supply to
provide a trigger current to all AC switches gates.
The MCU, which drives all the AC switches (through opto-transistors, refer to ) and
can also control any supply or motor inverter referenced to the DC bus ground
(GND_DC) in a final application.
The flyback power converter providing:
VCC_AC: 5 V output connected to the Line L1 to implement a negative power
supply. This supply is used for the Triac and AC switches control. Maximum
output current: 200 mA.
5V_DC: 5 V positive output, referenced to the DC bus Ground (GND_DC). This
output supplies the MCU and all the control circuit. Maximum output current: 90
mA.
15V_DC: 15 V positive output, referenced to the DC bus Ground (GND_DC). This
output can be used to supply an IPM to control a three-phase motor in a final
application. Maximum output current: 500 mA (together with 5V_DC
consumption).
VCC_INS: 5 V insulated output. This supply can be used if certain components,
like sensors, must be insulated from the mains voltage. This output is not used in
the demo board. Maximum output current: 90 mA.
For further information on the SMPS outputs, please refer to Section 5: "STEVAL-
IHT008V1 power supplies and typical consumption".

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Figure 2: Board synopsis
1.3 Targeted applications
Target applications include all applications using a diode-bridge to rectify the line AC
voltage and require the removal of the NTC (or PTC) resistor and the limitation of standby
losses. Such applications include:
telecom power supplies
televisions, DVD and CD players, set-top boxes, etc.
computers
lighting equipment
This demo board is also particularly interesting for applications where AC loads have to be
controlled, such as for valves, fans, pumps, heating resistors, etc. Such applications
include:
wet appliances (washing machines; dish machines; laundry dryers)
cold appliances (fridges, freezers)
air conditioning units
1.4 Main part numbers
The main part number references used in this demo board are:
Microcontroller Unit (MCU): STM8S103K3
Flyback IC: VIPER26LD
Inrush current limiter Triac: T1635T-8FP or ACST1635-8FP (pin-to-pin compatible with
T1635T-8FP, SIOV1 can be removed)
AC loads AC switches:
T1: ACST210-8FP (TO-220FPAB package)
T2 and T3: ACS108-8SN (SOT223 package)

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T4 and T5: Z0109MUF (SMD package)
1.5 Operating range and performances
The STEVAL-IHT008V1 board is designed to operate inside the following operating ranges:
Line voltage, 2 ranges are possible:
198-264 V RMS, 50 or 60 Hz
90-132 V RMS, 50 or 60 Hz. For this voltage range, operation both in rectifier
mode (DC peak voltage = peak line voltage) or in doubler mode are possible (see
Section 2.2: "Board connection and start-up").
Ambient temperature: 0°C to 60°C
Maximum DC load power:
DC load (connected between HVDC and GND-DC): 1000 W or 500 W
respectively for operation on 230 V or 120 V mains.
Maximum AC load power:
T1: maximum load RMS current has to be lower than 1.1 A, this allows 250 VA or
130 VA power for operation on 230 V or 120 V mains, respectively. This Triac
can be used to control a heating resistor or a pump.
T2 to T5: the footprint for each of these devices allow either a SMBflat-3L or a
SOT-223 package to be soldered. By default, two ACS108-8SN (SOT-223) are
used for T2 and T3, with a 5.5 mm² copper area under the tab. These devices
can control an RMS load current up to 0.6 A. This allows a 100 VA or 50 VA
power load to be controlled on 230 V or 120 V mains, respectively. By default,
two Z0109MUF (SMBflat-3L) are used for T4 and T5, with a 33.6 mm² copper
area under the tab. These devices can control an RMS load current up to 0.44 A.
This allows a 140 VA or 70 VA power load to be controlled on 230 V or 120 V
mains, respectively. These four Triacs can be used to control a pump, a fan or
any electromagnet (valve, damper, door-lock, etc.).
Allowed DC output capacitor (or DC bus capacitor) range: 50 µF to 500 µF (in rectifier
mode) or to 1000 µF (in doubler mode).
This DC output capacitor value is the equivalent value of all capacitors placed in
parallel at the bridge output, like C1, C9, C3, and CPFC at PFC output (refer to
Figure 3: "Connection of a PFC at the HVDC output"). If an interleaved PFC is
used, all the output capacitors of each PFC must be added.
If the J7 connector is closed (doubler mode), no PFC should be used. C3 is also
not added. In this case, the equivalent capacitor is only C1 (or C9 as they both
have the same value).

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Figure 3: Connection of a PFC at the HVDC output
The main STEVAL-IHT008V1 board performance characteristics are:
Efficiency at 230 V 50 Hz 1000 W (only DC resistive load) = 97%
Efficiency at 120 V 60 Hz 500 W (only resistive DC load, rectifier or double modes) =
96%
Standby losses < 150 mW (refer also to section 2.6)
Compliance with IEC 61000-3-3 (with potentiometer "MAX_INRUSH CURRENT" set
to default position; refer to Section 6: "Inrush-current limitation")
Compliance with EN55014 (CIPSPR 22 method B; refer to Section 10: "EN55014 test
results")
IEC 61000-4-4: 2 kV criteria A, T_ICL Triac withstands a 5 kV level without triggering.
This is to avoid undesirable triggering and uncontrolled inrush current due to EMI
noise.
IEC 61000-4-5: 2 kV criteria A
IEC61000-4-11: criteria A for dips down to 100% of the line voltage during 1 cycle;
criteria B for interrupts up to 300 cycles or more (refer to Section 7: "Mains voltage
dips and interruptions").
Figure 4: "Inrush current at STEVAL-IHT008V1 startup on 230 V line (500 µF output DC
capacitor)" shows an example of the progressive DC capacitor charge ensured by the
T_ICL Triac. The test is performed at startup when the STEVAL-IHT008V1 board is
connected to a 230 V 50 Hz grid, while the output DC capacitor is completely uncharged
(initial voltage is zero). The output DC capacitor is implemented in this case via the series
association of C1 and C9, hence the equivalent capacitance is 500 µF.
The output capacitor is charged in 550 ms with the input RMS current remaining far below
the 16.1 A limit. IEC 61000-3-3 compliance is therefore easily achieved.

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Figure 4: Inrush current at STEVAL-IHT008V1 startup on 230 V line (500 µF output DC
capacitor)
1.6 Stand-by consumption
One of the main advantages of using the T_ICL Triac in front of the rectifier bridge is that it
allows full bridge disconnection during standby to suppress losses. This can also be
achieved by adding a front-end relay (like S2 in Figure 5: "Solution using relays to limit
inrush current and standby losses"). But, thanks to the T_ICL Triac, this function is already
available by simply turning off this Triac.
Figure 5: Solution using relays to limit inrush current and standby losses
To give an idea of the benefits of such bridge disconnection, we measured the typical
losses of the STEVAL-IHT008V1 board in standby mode. Three cases are tested:
Case 1: STEVAL-IHT008V1 board (unmodified) with T_ICL in OFF state ("HVDC"
switch in OFF position).
Case 2: as above, but with a PTC (EPCOS B59107J0130A020) plugged in place of
the T_ICL Triac to simulate the losses for a classic solution using only one PTC and

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one bypass relay (refer to RLIM and S1 on Figure 5: "Solution using relays to limit
inrush current and standby losses").
Case 3: as above, but circuits used solely for demonstration purposes and which
consume undesired power at standby are disconnected. These circuits are the "HV
Capacitor Discharge" circuit (where R7 and R10 are connected to the DC bus) and the
"HVDC" LED (D2) indicating presence of high voltage (where D1, R12, and R13 are
connected to the DC bus).
Table 1: "Comparison of standby losses" gives the experimental results for the three cases
in the three different modes of operation (230 V, 110 V line voltage in rectifier and doubler
mode). The tests results clearly show that the Triac solution is the only one to achieve a
power consumption level lower than 0.5 W, as currently required by European directive
2005/32/EC.
The losses measured for case 3 are mainly due to the resistor divider circuit (R9, R11,
R14, R16) used to balance the voltage across the 2 series capacitors (C1 and C9) and the
other resistor divider circuit (R30, R31) used to sense the HVDC voltage. On our board, the
HVDC voltage is monitored to check proper soft-start operation and to avoid that the DC
capacitor charge duration is too long (if, for example, a load remains connected to the DC
bus before start-up). In standard circuits, however, such a voltage sensor is often required
(to start the PFC or the DC-DC supplies, for example).
The losses for a 230 V rectified voltage equal 520 mW for the 200 kΩ R9, R11, R14 and
R16 equivalent resistor, and 52 mW for the 2 MΩ R30 and R31 equivalent resistor.
Table 1: Comparison of standby losses
Mode of
operation
Case 1
T_ICL OFF
Case 2
PTC instead of Triac
Case 3
PTC discharge and D2 LED
circuits removed
230 V
125 mW
1.7 W
950 mW
110 V / rectifier
mode
70 mW
0.6 W
280 mW
110 V / doubler
mode
70 mW
1.5 W
860 mW

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2 Getting started
2.1 Safety instruction
The high voltage levels used to operate the STEVAL-IHT008V1 evaluation board
can represent a serious electrical shock hazard. This evaluation board must be
used in a suitable laboratory only by qualified personnel who are familiar with the
installation, use, and maintenance of power electrical systems.
The STEVAL-IHT008V1 evaluation board is designed for demonstration purposes only,
and must never be used for either domestic or industrial installations.
2.2 Board connection and start-up
Please follow this procedure to use the STEVAL-IHT008V1 board:
1. If you want to operate the board on a 98-132 V line voltage and have a DC bus
voltage two times higher than the peak line voltage, plug the jumper (see Figure 6: "(a)
J7 jumper plugged on board (doubler mode)") to the position indicated by the silk-
screen (refer to Figure 7: "(b) Jumper position left free (rectifier mode)"). If you want
the rectifier to operate in a classic rectifier circuit, do not plug the J7 jumper.
2. Connect the AC load terminals (if used) to the associated headers (e.g., for AC switch
T1, refer to the "N1-OUT1" label in Figure 23: "STEVAL-IHT008V1 silk-screen (Top
side)").
3. Connect the L, N and PE (if required) of J9 header to an unpowered mains plug.
4. Apply the mains voltage. From this moment on, avoid any contact with live parts
subject to line voltage.
5. Switch the "HVDC ON" toggle button to the "ON" position" to start charging the DC
capacitors.
6. The AC loads are switched on and off each time the associated push-buttons (T1 to
T5) are pressed. These loads are controlled even if the "HVDC ON" button is kept in
the OFF position.
7. The rate of DC capacitor charging can be increased if the allowed peak current is
increased. To do this, turn the "MAX-INRUSH CURRENT" potentiometer clockwise.
compliance with the IEC 61000-3-3 standard is only guaranteed when th
potentiometer is set to the default position (between 0 and 1 mark) and with
original values of the EMI filter and output DC capacitors.
The following figures show the J7 jumper connection for doubler mode (a) or rectifier mode
(b).

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Figure 6: (a) J7 jumper plugged on board
(doubler mode)
Figure 7: (b) Jumper position left free
(rectifier mode)
2.3 DC bus capacitor discharge for demonstration purpose
With default STEVAL-IHT008V1 1000 µF output capacitors (C1, C5) and associated 50 kΩ
resistors (R9, R11, R14, R16) used in parallel to balance the voltage across the two series
capacitor, the DC bus discharging time takes a few minutes if no load is connected.
A circuit is included to accelerate this discharging time, especially if several startups need
to be performed inside a short time interval for test or demonstration purposes. This circuit
is made with the Q2 MOSFET and R8 Resistor. Q2 remains on for as long as the SW7
SPDT toggle (refer to the "HV CAPACITOR DISCHARGE" label in Figure 23: "STEVAL-
IHT008V1 silk-screen (Top side)") is switched to the momentary ON position.
The two 1000 µF capacitors are then discharged within two seconds, approximately. The
SW2 switch must at least be kept in the momentary ON position during these two seconds.
The D2 LED (refer to the "HVDC" label in Figure 23: "STEVAL-IHT008V1 silk-screen (Top
side)") remains lit while the HVDC voltage is above 50 V, so the SW2 switch can be
released and a new startup can begin as soon as this LED turns off.
2.4 LED indications
Several LEDs are available to signal useful information:
ICL-STATUS" (LED D18): indicates several things according to its color:
When the board is powered, the LED passes from red, to orange, to green, which
indicates that the microcontroller has finished startup (correct mains connection
and line frequency measurement, power supply available, etc.) and the board is
ready. The green LED then switches off to reduce the board consumption in
standby. From this moment, the DC output capacitor can be charged when the
"HVDC" switch (SW6) is set to the "ON" position.
Green flashing indicates the DC bus capacitors are charging (flashing starts after
setting the "HVDC" button to the ON position and ends when the DC bus
capacitors are fully charged). This flashing mode can last less than 1 second and
may therefore go undetected by the end-user.
Green constant indicates the DC bus is charged to the correct voltage.
Orange flashing indicates the DC bus capacitors are charging but the output DC
voltage rate of increase is too low. This may occur if a power load is connected to

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the HVDC bus during charging and sinks a current which is too high, preventing
the DC capacitor from being charged efficiently.
Orange constant indicates the output DC capacitor is not charged to the peak line
voltage. This may occur when the bridge is started, but a power load is already
connected to the HVDC bus and sinks a current which is too high, preventing the
DC capacitor from being fully charged.
Red constant indicates the board is connected to a 198-264 V line while the
doubler jumper is connected.
Red flashing indicates the MCU detected an error (e:g., the line voltage is outside
the two correct operating ranges: 90-132 V and 198-264 V; the line frequency is
not detected as stable for 50 or 60 Hz).
"HVDC" (LED2): this LED lights red when a voltage higher than 50 V is present
between HVDC and GND_DC terminals (refer to Section 2.3: "DC bus capacitor
discharge for demonstration purpose" for further information).
"OUT1" to "OUT5" (LED6 to LED10) are ON when the corresponding AC switch (T1 to
T5) is turned on.
2.5 Possible board adaptations
The STEVAL-IHT008V1 board allows certain external components to be added to the front-
end circuit, so designers can validate an entire system. The main possible modifications
are listed below.
2.5.1 ACST use and MOV removal
The T1635T-8FP Triac used for T_ICL can be replaced by an ACST1635-8FP. Both
devices are indeed pin-to-pin compatible. The MOV used to protect the T1635T-8FP
(SIOV1) can be removed as the ACST1635T is an overvoltage protected device.
if the ACST1635-8FP is triggered in breakover mode, the applied current and its
rate of increase (di/dt) must remain below the values specified in the datasheet:
290 A peak current (8/20 µs waveform) and 150 A/µs, respectively.
For a high output DC capacitor value, the current may exceed this datasheet limit.
On our board, the input varistor (SIOV2) clamps the voltage applied to the ACST1635-8FP
below the typical clamping voltage of the device (VCL) for surges up to 2 kV. This prevents
ACST1635-8FP turn-on in breakover.
2.5.2 EMI filter and DC bus capacitors change
The EMI filter and DC capacitors only use through-hole devices to facilitate unsoldering
them to replacing them with ones used in the target application. This allows a designer to
adapt the EMI filter and HVDC voltage ripple to specific application requirements (such as
the power rating).
Obviously, as soon as these component values are modified, the control law of the T_ICL
Triac has to be updated to ensure ongoing compliance with the IEC 61000-3-3 limits. For
this purpose, the maximum peak current during startup can be adjusted with the "MAX-
INRUSH CURRENT" potentiometer. When this potentiometer is turned clockwise, the Triac
is turned sooner at each half-cycle, leading to a higher peak current.
The maximum RMS current or voltage fluctuation (when a normalized line impedance is
used) must then be measured according to the potentiometer position to check compliance
with IEC 61000-3-3.

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if the EMI filter capacitors (C3, C4, C44 to C47) values are increased, the values
of R9, R11, R14 and R16 may be decreased so the capacitors can still discharge
to below a safe voltage level (120 V for a DC voltage) in less than one or two
seconds. Indeed the EMI filter capacitors voltage is applied to the power plug
when the board is unplugged, so power terminals with accessible live parts
represent an electric shock hazard.
2.5.3 Power factor circuit connection
A PFC can be connected on the HVDC bus through the HVDC and GND_DC connections
(J12 header). To ensure the correct operation of this PFC circuit, capacitors C1 and C9
must be unsoldered. C3 (no capacitor is soldered here by default) may be used to add a
630 V DC film capacitor.
As the T_ICL Triac is controlled by a DC gate current when the HVDC voltage has reached
its steady-state value, either a discontinuous mode or a continuous mode PFC can be
used.
For correct operation of the STEVAL-IHT008V1 front-end circuit with a PFC, the PFC must
be activated after the "PFC_START" signal has been set to a 5 V high level. This signal is
referenced to the GND_DC terminal. It is available through the J20 header.
the PFC DC storage capacitor (ref. CPFC in Figure 3: "Connection of a PFC at
the HVDC output") has to within the value range defined in Section 1.5:
"Operating range and performances".
2.5.4 Motor Inverter connection
An inverter or any other DC-DC power converter can be added after the PFC or directly
behind the HVDC bus output.
A 15 V positive output referenced to the DC Bus Ground (GND_DC) is available through
header J10 to supply an IPM module if needed. Ensure that the maximum current which is
sunk from this supply is well below the limit given in Figure 12: "Typical output
characteristics of the 5 V and 15 V positive supplies (5V_DC / 15V_DC)".
2.5.5 Control with an external microcontroller
It is possible to control the STEVAL-IHT008V1 front-end circuit with an external MCU,
instead of using the embedded STM8S103K3. This allows the end-user to directly check
the compliance of his or her own firmware with this kind of circuit.
For this purpose, all control signals required to drive the different AC switches are available
on the J16 header. EC1 to EC5 are the external control signals of AC switches T1 to T5;
T_ICL is the connection to externally drive the T_ICL Triac. The GND_DC and ZVS signals
are also available on this header to synchronize the control signals of the external MCU.
For correct operation with external signals, jumpers J1 to J6 (refer to the
"INT/EXT_CONTROL" label Figure 23: "STEVAL-IHT008V1 silk-screen (Top side)") must
be removed. The removal of these jumpers indeed allows the disconnection of the opto-
transistor input LEDs from the U9 microcontroller outputs (Figure 8: "STEVAL-IHT008V1
power side and insulated control schematic").

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3 Conclusion
This evaluation provides an innovative front-end circuit to allow both inrush current
limitation and power loss reduction. Above and beyond the simple demonstration of the
efficiency and the robustness of this solution by STMicroelectronics, this front-end circuit
also represents the starting point for building entire system and accelerating the time-to-
market of new application designs.

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4 STEVAL-IHT008V1 circuit schematics
Figure 8: STEVAL-IHT008V1 power side and insulated control schematic

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Figure 9: STEVAL-IHT008V1 control circuit schematic (1 of 3)

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Figure 10: STEVAL-IHT008V1 control circuit schematic (2 of 3)
Figure 11: STEVAL-IHT008V1 control circuit schematic (3 of 3)

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5 STEVAL-IHT008V1 power supplies and typical
consumption
Table 2: "Typical STEVAL-IHT008V1 control-circuit consumption" gives the typical current
consumed from the 5V_DC output for the different operating modes of the STEVAL-
IHT008V1 board.
Table 2: Typical STEVAL-IHT008V1 control-circuit consumption
Operating mode
Current sunk from 5V_DC (mA)
MCU in standby mode
2
MCU running with 1 ACS switch ON (T2 to T5)
14
MCU running with T_ICL ON
17
MCU running with T_ICL and 1 ACS switch ON
24
MCU running with T_ICL and 4 ACS switches ON
45
As listed in Section 1.2: "Principal board blocks", the Flyback implements four output
supplies. The non-regulated 5 V VCC_AC negative supply is used for the Triac and ACS
control. The 15 V and 5 V positive supplies (15V_DC and 5V_DC outputs) are used to
supply circuits referenced to the DC bus Ground (MCU, IPM if one is added).
The 5 V insulated supply (VCC_INS / GND_INS) can be used for sensors if needed. On
original STEVAL-IHT008V1 manufactured boards, this insulated supply is not used.
Only the 15 V positive output is regulated by the VIPer26LD circuit as this supply is always
loaded when the other outputs are loaded. The two 5 V positive supplies (5V_DC,
VCC_INS) are also regulated thanks to two LM2931 positive voltage regulators.
The VCC_AC level is not regulated. Its voltage level will be higher if it is not loaded and if
the 15 V positive supply is loaded with its highest maximum current.
The current capabilities of the different outputs are (for the whole operating range):
for 5V_DC: 90 mA
for VCC_AC (non-regulated 5 V negative output): 200 mA
for 15V_DC: 500 mA (with 5V_DC consumption included)
for VCC_INS (optional 5 V regulated output): 90 mA
Figure 13: "Typical output characteristics of the 5 V negative supply (VCC_AC) and 5 V
insulated supply (VCC_INS)" and Figure 14: "Inrush current during STEVAL-IHT008V1
startup on 230 V line (500 µF output DC capacitor)" give the typical output voltage for the
current which is sunk from each output. These measurements are performed with the
STEVAL-IHT008V1 connected to either a 230 V or 120 V line, with the bridge operating in
rectifier mode (not doubler) and across the entire operating temperature range (0-60 °C).
The 15 V_DC, and the 5 V outputs (5V_DC and VCC_INS) are well regulated thanks to the
VIPer26LD and the LM2931 devices, respectively.
For the VCC_AC, two curves are given to give the minimum and maximum values of this
output. The minimum voltage is reached when the SMPS is delivering the minimum output
current (no current sunk from the 15V_DC and the VCC_INS outputs; the 5V_DC is only
loaded by the MCU, which is controlling one ACS ON).
The VCC_AC measurement is also performed when only one ACS switch is ON as
VCC_AC is dedicated to the Triac and ACS switches driving. So the minimum available
voltage (to define the gate resistor value to apply enough gate current) is an important
value, at least when one AC switch is on.

STEVAL-IHT008V1 power supplies and typical
consumption
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For Figure 14: "Inrush current during STEVAL-IHT008V1 startup on 230 V line
(500 µF output DC capacitor)", the output current of the horizontal axis gives the
extra current sunk from the output voltage when one ACS switch is ON. This
means that for a zero current, a current close to 20 mA is already sunk from the
VCC_AC supply. This is not the case for the VCC_INS output.
The maximum VCC_AC voltage is reached when the SMPS 15V_DC output is loaded to
the maximum output current (500 mA), while only one AC switch is ON. Indeed if more
ACS switch gate currents are sunk from VCC_AC, this level decreases.
Figure 12: Typical output characteristics of the 5 V and 15 V positive supplies (5V_DC /
15V_DC)
Figure 13: Typical output characteristics of the 5 V negative supply (VCC_AC) and 5 V
insulated supply (VCC_INS)

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6 Inrush-current limitation
IEC 61000-3-3 standard reminder
The IEC 61000-3-3 standard gives the limitation of voltage changes and fluctuations for
equipment with rated RMS current lower than 16 A connected to a public low-voltage grid.
These voltage fluctuations are indeed caused by the equipment if too high a current is sunk
from the grid. A voltage drop is then caused due to the line impedance.
The mains voltage fluctuation causes an undesirable variation in the brightness of lamps
and displays; namely, the flicker phenomenon. This is why designers must keep the inrush
current sunk by their equipment to below specific limits.
The following equation explains the link between the line current variation Iinput (due to the
equipment operation) and the relative mains voltage variation (U), which must be lower
than the maximum allowed value (dmax given in %).
U = Iinput x Zref / U x 100 < dmax
where Zref is the normalized line impedance (0.6 with 796 µH in series for a single-phase
grid) and U is the nominal RMS line voltage.
The dmax level should not exceed 4%. A 6% or 7% limit is also allowed according to the way
the equipment is switched (manually or automatically, delayed or not, etc.) or for specific
appliances.
If the U variation exceeds 3.3% during a single voltage change, this should not last more
than 500 ms.
Table 3: "Maximum input RMS current variation for 230 V single-phase grid according to
IEC 61000-3-3" gives the associated maximum input current variation related to these
different dmax levels. To simplify the analysis, it could be said that an appliance will fulfill
with the IEC 61000-3-3 limit at startup if its RMS current remains below 16.1 A. The relative
variation is thus lower than 3.3% and compliance is ensured even if startup lasts more than
500 ms. It is clear that this is a restricted case for simplification purposes, higher current
variations may also still allow compliance with this standard.
Table 3: Maximum input RMS current variation for 230 V single-phase grid according to IEC
61000-3-3
dmax (%)
DU (V)
DIinput (A)
3.3
7.6
16.1
4
9.2
19.5
6
13.8
29.3
7
16.1
34.1
STEVAL-IHT008V1 compliance with the IEC 61000-3-3 limit
Currently, one of the most used solutions to limit inrush current consists of adding a resistor
(refer to RLIM in Figure 5: "Solution using relays to limit inrush current and standby losses")
in series with the DC capacitor (refer to C). This resistor must then be bypassed to limit
power losses during steady-state operation. Usually, a relay or a Triac (S1) is used for this
purpose. To disconnect the DC bus during standby mode, a second switch (S2) is required.
To avoid the use of the RLIM resistor, a different startup procedure can be implemented.
With the Triac T_ICL placed in series with the diode bridge, the capacitor can be charged
smoothly through progressive phase control. As long as the Triac is not triggered, the
bridge does not conduct any current, and the DC bus capacitor is not charged. To start

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charging the DC capacitor, the Triac must be turned on. To reduce the inrush current, the
Triac is first triggered at the end of the line voltage cycle, just a few hundred microseconds
before the line zero voltage. This allows the output capacitor (refer to C in Figure 5:
"Solution using relays to limit inrush current and standby losses") to be charged to a low
level (around 10 to 30 V) and not directly to the peak line voltage. The current driven from
the line is then much lower than in case of directly charging the DC capacitor completely.
This soft-start solution can only work when an inductor is present on the line side as the
current increase rate must also be limited to avoid Triac damage. Such an inductor is
already present for most applications where the EMI filter usually embeds a common-mode
choke which has a differential-mode parasitic inductor due to the copper turns of the
windings.
In our STEVAL-IHT008V1, the EMI filter is implemented by C6-C7 X2 capacitors, C2-C4-
C5-C8 Y2 capacitors, and the L1 common-mode inductor. This inductor features a 12 mH
value in common-mode but also a 10 µH inductor in differential mode. This is the
differential-mode value which allows the reduction of the rate of increase of the line current
each time Triac T_ICL is turned on.
To allow a complete charge of this capacitor to the peak line voltage, the Triac must be
triggered on the following cycle with a shorter turn-on delay than the first one used to start
the charge. In this way, by reducing the Triac turn-on delay by a few tens or hundreds of
microseconds from half-cycle to half-cycle, the output capacitor is progressively charged
while the line current is kept low.
In the STEVAL_IHT008V1 MCU firmware, the Triac turn-on delay reduction step is
constant from one half-cycle to the following one. This step is called
Step_Phase_Control in the firmware. It is set by the Max_Inrush_Current_Order
routine which reads the voltages set by the "MAX_INRUSH CURRENT" potentiometer.
When the T_ICL Triac turn-on delay is lower than 3 ms, the gate pulse is directly set to a
continuous DC pulse (starting typically 70 µs after VAC zero voltage). Indeed, below a
delay of approximately 5 ms or 4.2 ms (for 50 and 60 Hz line frequencies, respectively), the
output DC capacitor is fully charged. Therefore, it is not necessary to ensure a soft start for
turn-on delays much lower than a fourth cycle.
the max T_ICL turn-on delay is defined by the ICL_CTRL_Delay in the
firmware. The minimum value of 3 ms is defined by the
Phase_Control_ON_Max which sets the maximum T_ICL ON time (7 ms, refer
to directive definitions in the firmware).
Figure 14: "Inrush current during STEVAL-IHT008V1 startup on 230 V line (500 µF output
DC capacitor)" (same as Figure 4: "Inrush current at STEVAL-IHT008V1 startup on 230 V
line (500 µF output DC capacitor)") shows an example of such progressive DC capacitor
charging. The test is performed at startup when the STEVAL-IHT008V1 board is connected
to a 230 V 50 Hz grid, while the output DC capacitor is completely uncharged (i.e., its initial
voltage is null). The output DC capacitor is implemented in this case by the series
association of C1 and C9 for an equivalent capacitance of 500 µF.
the electric parameters of Figure 15: "Triac current zoom for the highest peak
current during start-up" are defined in Figure 3: "Connection of a PFC at the
HVDC output" (arrow head gives the hot-point of the voltage). In Figure 3:
"Connection of a PFC at the HVDC output", VDC is actually the voltage across
capacitor C3 as no PFC is used.