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AN1376 APPLICATION NOTE
25W QUASI-RESONANT FLYBACK CONVERTER FOR SET-TOP BOX APPLICATION USING THE L6565
by Claudio Spini
This document describes a reference design of a 25W Switch Mode Power Supply dedicated to Set-Top Box application. The board accepts full range input voltage (90 to 265Vrms) and delivers 5 outputs. It is based on the new controller L6565, working in variable frequency mode.
1
INTRODUCTION
Set-Top Boxes are growing very fast and they are becoming very popular in all Countries either for satellite or cable decoding. Hence the market is asking for solutions having high cost effectiveness, providing for good performances, low noise, small volumes at low cost. The Quasi-resonant operation and the high flexibility of the L6565 make it a very suitable device, able to satisfy all the requirements with only few external components. The board has been designed with mixed technology components, both PTH and SMT. For this reason some components are doubled, in accordance with their ratings.
November 2001
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AN1376 APPLICATION NOTE
2 MAIN CHARACTERISTICS
The main characteristics of the SMPS are listed here below: s INPUT VOLTAGE: Vin: 90 - 264 Vrms f: 45-66 Hz s OUTPUT VOLTAGES:
Vout (V):
Iout (A):
Pout (W):
STABILITY
NOTES
3.3 5 12 7 30
2.00 1.1 0.7 0.5 0.015
6.6 5.5 8.4 3.5 0.45
+/- 2% +/- 2% +/- 5% +/- 8% +/- 2% (A) (B) (C) (D)
POUT (W) =
24.45
NOTES: (A) (B) (C) (D) Dedicated to 5V digital circuitry and to 3.3v local post regulators Dedicated to SCART, LNBP21 for satellite STB. For other applications the current is 0.4A Dedicated to 5V local post regulators Dedicated to tuner
s s s s s
STAND-BY No stand-by mode is foreseen by equipment OVERCURRENT PROTECTION On all outputs, with auto-restart at short protection PCB TYPE & SIZE: Cu Single Side 35 um, FR-4, 122.5 x 75 mm SAFETY: In acc. with EN60950, creepage and clearance minimum distance 6.4mm EMI: In acc. with EN50022 Class B
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3
1
3
D7 STPS10L60CF
GND
5
VCC 7 R3 33R-0805 C17 220PF-1KV HRR R13 NOT MOUNTED D8 STPS10L60CF
ZCD
4
1
3
2
3/33
C8 2N2-2KV (Y1) R24 180R 1/2W PTH T1 2414.0011 rev. C1 R16 470R - 1/2W PTH C30 220PF-1KV HRR
14 2
D1 SMBYT01-400 C20 22uF-50V YXF C18 22uF-50V YXF D11 BZV55-C15 D6 STPS2H100U R12 470K-1206 R1 270K-1206 D10 BZV55-C15 C27 100N - 0805 D2 2W08G-GS D9 SMCJ130CA GBI D9A NOT MOUNTED PTH 4 R20 10K - 1206
JP1
F1
L1 39mH - EPCOS
2
ON 6mm
FUSE 2A
2
3
13
C10 47uF-400V C28 100N - 0805 D3 STTA106U 10u ELC06D R19 1K0 - 1/2W PTH
L2
Figure 1. Electrical Diagram
ELECTRICAL DIAGRAM
C9 100N
1
4
JP1A
C16 100N
C12 1N0-1KV
C13 1N0-1KV
4
R15 470K-1206 R14 270K-1206
AN1376 APPLICATION NOTE
ON 6mm
R2 NTC_16R S236
12
C19 2200uF-16V - YXF
C6 100uF-16V - YXF
8 12V @0.7
VIN R17 1R0 - 2W - PTH C29 100N - 0805 IC3 LD1086V50 C25 100N - 0805 C5 100uF-16V - YXF
VOUT
30V @0.0 GND 7V @0.5A
R4 100K - 0805
TO-220 HEAT SINK ABL LS220
IC1 L6565 - DIP8 Q1 STP4NC60FP
11
P8 JUMPER D4 LL4148 C3 2200uF-16V YXF R21 470R - 1206 L3 10u ELC06D C7 100uF-16V - YXF C26 100N - 0805
5V @1.1A GND GND
C23 1N0-0805
TO-220 HEAT SINK ABL LS220 10
8
R11 4K7 - 0805
OUT
3 4 R22 0R0 - 0805 Q2 BC856 C31 220P - 0805 6 C21 0805 - NOT MOUNTED R6 0R47 - 1/2W PTH R27 120K - 0805 C11 22uF-25V YXF
VFF
6 8 TO-220 HEAT SINK
L4 2u7 ELC08D
ISEN
3.3V @2A
R18 47R - 1/2W PTH C24 100N - 0805 C4 100uF-16V - YXF
1
FB
1
JP2 MKS 1858-6-0-808
R28 24K - 0805
2
2 2 - 0805 D5 LL4148 C33 100N - 0805 R5 3K3 - 0805 2200uF-16V YXF 2200uF-16V YXF
COMP
GND
7
C1 C2
9
C22 220PF-0805
R7 2K7 - 0805 R23 NOT MOUNTED R9 82R - 0805
C15 NOT MOUNTED
OPT1 SFH617A-4 R8 560R-0805 C14 330N - 1206 IC2 TL431ACD - SO-8 R10 220R - 0805 D12 LL4148
R25 1K8 - 0806 Q4 BC848 Q3 BC848 R26 1K0 - 0806
AN1376 APPLICATION NOTE
The switching frequency (minimum is ~30 kHz @Vin = 80 VDC) has been chosen to get a compromise between the transformer size and the harmonics of the switching frequency, in order to optimise the input filter size and its cost. The MOSFET is a standard and cheap 600V-2.2, TO-220FP. It needs a small heat sink. The transformer reflected voltage is 90V, providing enough room for the leakage inductance voltage spike with still margin for reliability. The network D9+D3 clamps the peak of the leakage inductance voltage spike. These two components are SMT, allowing cost saving of the manual labour with respect to a passive solution, needing manual insertion on the PCB. A 220pF HV capacitor has been added across the drain to optimise MOSFET losses by a small snubbing effect on the drain voltage rate of rise. The controller L6565 is activated by a couple of dropping resistors (R1+R14, for voltage and power rating reasons) that draws current from the DC bus and charges the capacitor C11. This circuit dissipates only about 240mW @ 264 Vac, thanks to the extremely low start-up current. During the normal operation the controller is powered by the transformer via the diode D4. The network Q101, C102, R104 acts as a spike killer, improving the auxiliary voltage fluctuations and the performance in short circuit. R12+R15 and R11 compensate for the power capability change vs. the input voltage (Voltage Feed-forward). A 1nF ceramic capacitor bypasses any noise on pin #3 to ground (C23). The current flowing in the transformer primary is sensed by the resistor R6. The circuit connected to pin1 (FB) provides for the over voltage protection in case of feedback network failures and open loop operation. The output rectifiers have been chosen in accordance with the maximum reverse voltage and power dissipation. The rectifiers for 3.3V and 7V outputs are Schottky, type STPS10L60CF. These diodes are low forward voltage drop, hence dissipating less power with respect to standard types. Both are the same to decrease the component diversity, as well as for the capacitors C1 to C3 and C19. The diode D8 needs a small heat sink, as indicated on the BOM. The other two output rectifiers are SMT, fast recovery. The snubber R102 and C101 damps the oscillation produced by the diode D1 at MOSFET turn-on. The output voltage regulation is performed by secondary feedback on the 3.3V output, while for other voltages the regulation is achieved by the transformer coupling. The feedback network is the classical TL431 driving an optocoupler, in this case an SFH617A-4, insuring the required insulation between primary and secondary. The opto-transistor drives directly the COMP pin of the controller. The 5V output is linearly post-regulated from the 7V output to get a very stable voltage. A zener regulator assures the 30V stability at low cost. The 5V regulator needs to be dissipated. A small LC filter has been added on the +12V, +7V, +3.3V in order to filter the high frequency ripple without increasing the output capacitors. A 100nF capacitor has been connected on each output, very close to the output connector soldering points to limit the spike amplitude. The input EMI filter is a classical Pi-filter, 1-cell for differential and common mode noise. A NTC limits the inrush current produced by the capacitor charging at plug-in. The transformer is slot type, manufactured by Eldor Corporation, in accordance with the EN60950. Here following some waveforms during the normal operation at full load:
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AN1376 APPLICATION NOTE
Figure 2. Vds & Id @ Full Load
Vin = 115 Vrms - 50 Hz Vin = 220 Vrms - 50 Hz
CH1: DRAIN VOLTAGE; CH2: RAIN CURRENT - VR.SENSE (R6)
The pictures above show the drain voltage and current at the nominal input mains voltage during normal operation at full load. The Envelope acquisition of the scope provides for the possibility to see the modulation of the two waveforms due to the input voltage ripple. Figure 3. Vds & Id @ Full Load (Vin = 265 Vrms - 50 Hz) This picture gives the measurement of the drain peak voltage at full load and maximum input mains voltage. The voltage peak, which is 548V, assures a reliable operation of the PowerMOS with a good margin against the maximum BVDSS.
CH1: DRAIN VOLTAGE; CH2: RAIN CURRENT - VR.SENSE (R6)
Figure 4. Vin = 265 Vrms - 50 Hz, @FULL LOAD: DIODE PIV
CH3: +35V DIODE: ANODE VOLTAGE; CH4: +12V DIODE: ANODE VOLTAGE
CH3: +7V DIODE: ANODE VOLTAGE; CH4: +3V3 DIODE: ANODE VOLTAGE
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AN1376 APPLICATION NOTE
The maximum PIV of the diodes has been measured during the worst operating condition and it is indicated on the right of each picture. The margin, with respect to the maximum voltage sustained by the diodes, assures a safe operating condition for the devices. Here following the most salient controller IC signals are depicted. In both the pictures is possible to distinguish clean waveforms free of hard spikes or noise that could affect the controller correct operation. Figure 5. Vin = 115 Vrms - 50 Hz Vin = 220 Vrms - 50 Hz
CH1: CH2: CH3: CH4:
VPIN5 - ZCD VPIN4 - ISENSE VPIN7 - OUT VPIN2 - COMP
4
CROSS REGULATION
In the following tables the output voltage cross regulation is measured with static and dynamic loads and the overall efficiency of the converter measured at different input voltages. All the output voltages have been measured after the load connector soldering point of the STB motherboard. The length of the connection cable is 100 mm. s FULL LOAD
Vout [V} = Iout [A] =
30.06 0.015
7.23 0.500
12.297 0.702
3.278 2.073
4.492 1.103
Vin [Vrms]= Iin [Arms] =
115 0.51
Pout [W] =
0.451
3.615
8.632
6.795
4.955
Pin [W] =
36.0
VUNREG = VC11 =
37.2 11.88
PoutTOT [W] = 24.448 EFF. = 67.91% ALL VOLTAGES ARE WITHIN TOLERANCE
fS = 41/51 kHz
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AN1376 APPLICATION NOTE
Vout [V} = Iout [A] = 30.5 0.015 7.197 0.5 12.19 0.702 3.279 2.073 4.94 1.103 Vin [Vrms]= Iin [Arms] = 220 0.31
Pout [W] =
0.458
3.599
8.557
6.797
5.449
Pin [W] =
35.1
VUNREG = VC11 =
37.2 12.04
PoutTOT [W] = 24.860 EFF. = 70.82% ALL VOLTAGES ARE WITHIN TOLERANCE
fS = 66/68 kHz
The efficiency of the converter is not very high but it is heavily affected by 5V the linear regulator delivering 1.1 A. Delivering 1.6A on the 7V output but removing the 5V regulator the efficiency measured is 75.6% @220Vac and 76.9% at 115Vac.
s
Reduced Load - for Cable STB, without the LNB
Vout [V} = Iout [A] =
31.4 0
7.18 0.25
12.11 0.3
3.359 1.008
4.965 0.55
Vin [Vrms]= Iin [Arms] =
115 0.26
Pout [W] =
0.000
1.795
3.633
3.386
2.731
Pin [W] =
16.8
VUNREG = VC11 =
35.5 11.39
PoutTOT [W] = 11.545 EFF. = 68.72% ALL VOLTAGES ARE WITHIN TOLERANCE
fS = 83/89 kHz
Vout [V} = Iout [A] =
31.4 0
7.16 0.25
12.08 0.3
3.36 1.008
4.975 0.55
Vin [Vrms]= Iin [Arms] =
220 0.17
Pout [W] =
0.000
1.790
3.624
3.387
2.736
Pin [W] =
17.6
VUNREG = VC11 = fS = 112 kHz
35.4 11.5
PoutTOT [W] = 11.537 EFF. = 65.55% ALL VOLTAGES ARE WITHIN TOLERANCE
The above tables shown the output voltage measured applying the same loads that we could have in case of a different Set-top Box type is powered (e.g. a terrestrial or cable) without the LNB block of the satellite antenna. Like before all the output voltages are within the tolerances.
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AN1376 APPLICATION NOTE
s
Reduced Load - 9W
31.6 0 7.16 0.300 12.77 0.051 3.36 1.008 4.96 0.6 Vin [Vrms]= Iin [Arms] = 115 0.22
Vout [V} = Iout [A] =
Pout [W] =
0.000
2.148
0.651
3.387
2.976
Pin [W] =
14.2
VUNREG = VC11 =
36 11.48
PoutTOT [W] =
9.162 EFF. = 64.52%
fS = 94/101 kHz
ALL VOLTAGES ARE WITHIN TOLERANCE
Vout [V} = Iout [A] =
31.5 0
7.16 0.300
12.76 0.051
3.36 1.008
4.96 0.602
Vin [Vrms]= Iin [Arms] =
220 0.15
Pout [W] =
0.000
2.148
0.651
3.387
2.986
Pin [W] =
15.2
VUNREG = VC11 =
35.8 11.7
PoutTOT [W] = 9.172 EFF. = 60.34% ALL VOLTAGES ARE WITHIN TOLERANCE
fS = PFM/PWM
Even still reducing the load till 9W, Thanks to the good coupling of the transformer, all the output voltages are still in tolerance. s At No-Load (Output connector unplug)
Vout [V] =
30.4
7.20
12.15
3.39
5.00
Vin [Vrms]= Pin [W] =
220 1.6
Vin [Vrms]= Vout [V] = 30.4 7.20 12.0 3.38 5.00 Pin [W] =
115 1.5
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AN1376 APPLICATION NOTE
Figure 6. Vin = 115 Vrms - 50 Hz Unplugging the output connector the circuit is still able to maintain all the voltages perfectly under control and within the tolerance. Hence a perfect functionality of the circuit is achieved also in this abnormal condition. During the no load operation the circuit works in burst mode and, thanks to the controller functionality, the switching frequency inside the Burst pulses is kept at low. This provides for a low power consumption of the power supply, making it suitable to support stand-by operation with low consumption from the mains. It has to be kept into account that this circuit has not been optimized for the Stand-by operation, hence it could be improved. Vin = 220 Vrms - 50 Hz
CH1: CH2: CH3: CH4:
VPIN5 - ZCD VPIN4 - ISENSE VPIN7 - OUT VPIN2 - COMP
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AN1376 APPLICATION NOTE
5 OUTPUT VOLTAGE RIPPLE @FULL LOAD
In the following picture all the output voltage ripple at switching and mains frequency are measured. As per the previous measures, the probes have been connected on test points after the output flat cable. As shown in the pictures, the ripple and the spikes are very low. Figure 7. @115 VAC - 50Hz
@220 VAC - 50Hz
CH2: CH3: CH4:
+7 Vout +3.3 Vout +12 Vout
CH2: CH3:
+30 Vout +5 Vout
10/33
AN1376 APPLICATION NOTE
Figure 8. @115 VAC - 50Hz - LINE FREQUENCY RIPPLE
CH1: CH2: CH3: CH4:
VC10 +7 Vout +3.3 Vout +12 Vout
CH2: CH3:
+30 Vout +5 Vout
The low frequency residual ripple compared with the ripple across C10 (input Elcap) shows an excellent rejection of the circuit (>80 dB).
6
MEASUREMENT OF THE RMS CAPACITOR CURRENTS
The tables show the rms currents flowing in the output capacitors at 115Vac and 220Vac, full load. All the rms currents are within the rating of the capacitor type indicated (Rubycon, YXF series). This avoids the component overstress that should affect the reliability and/or the expected lifetime of the SMPS .
@ 115Vac: ICAP C1 = 1.02 ARMS @ 115Vac: ICAP C19 = 1.15 A RMS @ 115Vac: ICAP C3 = 1.78 ARMS @ 115Vac: ICAP C18 = 140 mA RMS
@ 220Vac: ICAP C1 = 0.7 ARMS @ 220Vac: ICAP C19 = 0.92 A RMS
@ 220Vac: ICAP C1 = 1.4 A RMS @ 220Vac: ICAP C18 = 130 mA RMS
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AN1376 APPLICATION NOTE
7 DYNAMIC LOAD TESTS
Regulated Output
Load condition: +5V, +7V, +12V, +30V: +3,3V: FULL LOAD LOAD 50 %/100%, 70Hz
Figure 9. @115 VAC - 50Hz
@220 VAC - 50Hz
CH3: CH4: R1:
+3V3 Vout at test points +3V3 Iout +3V3 Vout before L4
CH1: CH2: CH3: CH4:
+30 Vout +12 Vout +7 Vout +3V3 Iout
The pictures show the output voltage regulation against a dynamic load variation of the feed backed voltage, at the nominal input voltage values. As shown in the left pictures the response after the connector is not very good from the peak point of view, even if the response is quite fast. Making the same measure before the filter inductor (L4), at the feed back divider connection points, the response is much better (2.2 %). This means that the filter inductor heavily affect the response. To avoid any expensive solution to improve it the better way is to
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AN1376 APPLICATION NOTE
measure the voltage regulation during the normal operation, powering the real load circuitry. This, because there are some local capacitors or filters helping a lot the regulation. Moreover, normally the dynamic load changes are less than the testing value indicated. The regulation for all the other output voltage is good, remaining well within tolerances.
s
Unregulated Outputs
The following tests show the response of the output voltages varying the load for each unregulated output. The load conditions are specified at the right of each picture. The regulation has been tested at both the nominal mains voltages. Figure 10. @115 VAC - 50Hz
CH1: CH2: CH3: CH4:
+12 Vout +7 Vout +3V3 Vout +12V Iout
CH1: CH2: CH3: CH4:
+12 Vout +7 Vout +3V3 Vout +5V Iout
+3,3V +5V, +7V, +30V: FULL LOAD +12V: DYNAMIC LOAD 0.1 to 0.7A, 70Hz
+3,3V +5V, +7V, +30V: FULL LOAD +5V: DYNAMIC LOAD 0.5 to 1.1A, 70Hz
@ 220Vac the waveforms have the same amplitude.
5V modulation: 20 mVpp @ 220Vac the waveforms have the same amplitude.
ALL THE VOLTAGES ARE WITHIN TOLERANCES, AT BOTH INPUT MAINS VOLTAGES
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AN1376 APPLICATION NOTE
Figure 11. @115 VAC - 50Hz +3,3V +5V, +7V, +30V: FULL LOAD +7V: DYNAMIC LOAD 0.1 to 0.5A, 70Hz
5V modulation: 20 mVpp @ 220Vac the waveforms have the same amplitude.
ALL THE VOLTAGES ARE WITHIN TOLERANCES, AT BOTH INPUT MAINS VOLTAGES
CH1: CH2: +12 Vout +7 Vout CH3: CH4: +3V3 Vout +7V Iout
8
START-UP BEHAVIOUR @FULL LOAD
Figure 12.
@115 VAC - 50Hz @220 VAC - 50Hz
@85 VAC - 50Hz
@265 VAC - 50Hz
CH1: CH2:
+12 Vout +5 Vout
CH3: CH4:
+3.3 Vout +7V Iout
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AN1376 APPLICATION NOTE
In the previous 4 pictures there are the rising slopes at full load of the more significant output voltages at nominal, minimum and maximum input mains voltage. As shown in the pictures, the rising times are constant and there is only a slight difference for the 5V rise time, with respect to the other outputs. This characteristic is quite important when the loads are a P and its peripherals as in our case, to avoid problem at start-up. At minimum voltage a super imposed ripple at line frequency is present, due to the high ripple at the input that is not completely rejected by the loop before reaching the steady state operation. This because while the input voltage is rising, the ripple valley voltage is less than the minimum operating voltage of the circuit, therefore the ripple it is properly rejected only when it reaches that value. 9 WAKE-UP TIME
In the following pictures there are the waveforms with the wake-up time measures at the nominal input mains. Obviously, due to the circuitry characteristics, the wake-up time is not constant but it is dependent on the input voltage. The measured time at 115 and 220 Vac are 1.2 and 0.6 second, which are rather common values for this kind of Power Supplies. The worst condition, of course, is at 85 Vac when the start-up time becomes around 1.7 seconds, which is quite a long time even if still acceptable. This because there is anyway the start-up time of the STB which is longer. Additionally, the 85Vac input mains is a steady state voltage but it is not a very common value. Figure 13.
@115 VAC - 50Hz
@220 VAC - 50Hz
In Figure 14 there are the waveforms at minimum and maximum voltage with a magnification of the time base: on the picture is clearly indicated that no any overshoot, undershoot, dip or lost of control happens during the power supply start-up phase. Obviously also the nominal voltages are been detected without showing any abnormal behaviour.
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AN1376 APPLICATION NOTE
Figure 14.
@85 VAC - 50Hz @265 VAC - 50Hz
CH1: CH2: CH3:
VDD VC11 (Vaux) +3V3 Vout
CH1: CH2: CH3:
VDD VC11 (Vaux) +3V3 Vout
10
TURN-OFF
Even at turn off the transition is clean, without any abnormal behaviour like restart or glitches both on the primary or secondary side. Figure 15.
@85 VAC - 50Hz @265 VAC - 50Hz
CH1: CH2: CH3:
VDD VC11 (Vaux) +3V3 Vout
CH1: CH2: CH3:
VDD VC11 (Vaux) +3V3 Vout
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AN1376 APPLICATION NOTE
11 SHORT-CIRCUIT TESTS @ FULL LOAD
The short circuit tests have been done in two phases, both making the test shorting by a power switch the output electrolytic capacitor or making the short by the active load option. This gives an idea about the circuit behaviour with a hard short (at very low impedance) or with a "soft" short that could happen on the STB main board, having slightly higher impedance. All the tests have been done at maximum and minimum input voltage. For all conditions the drain voltage is always below the BVDSS, while the mean value of the output current has a value close to the nominal one, then preventing component melting for excessive dissipation. The auto-restart is correct at short removal in all conditions. Figure 16. 7V OUTPUT: SHORT C3
@85 VAC @265 VAC
CH1: CH2: CH4:
DRAIN VOLTAGE VC11 (Vaux) ISHORT CIRCUIT
CH1: CH2: CH4:
DRAIN VOLTAGE VC11 (Vaux) ISHORT CIRCUIT
As clearly indicated by the waveforms, the circuit start to work in hic-cup mode, so maintaing the mean value of the current at levels supported by the component rating. Because the working time and the dead time are imposed by the charging and discharging time of the auxiliary capacitor C11, it is proportional to the input mains voltage. Figure 17. 7V OUTPUT: SHORT BY ACTIVE LOAD
@85 VAC @265 VAC
CH1: CH2: CH4:
DRAIN VOLTAGE VC11 (Vaux) ISHORT CIRCUIT
CH1: CH2: CH4:
DRAIN VOLTAGE VC11 (Vaux) ISHORT CIRCUIT
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AN1376 APPLICATION NOTE
As expected the circuit protects itself as well. The secondary peak current is obviously lower, due to the higher circuit impedance. Figure 18. 3V3 OUTPUT: SHORT C1
@85 VAC @265 VAC
CH1: CH2: CH4:
DRAIN VOLTAGE VC11 (Vaux) ISHORT CIRCUIT
CH1: CH2: CH4:
DRAIN VOLTAGE VC11 (Vaux) ISHORT CIRCUIT
Like the previous output voltage the controller keeps under control the circuit preventing in all conditions the circuit from catastrophic failures. This happens even shorting the output by the active load. Figure 19. 12V OUTPUT: SHORT C19
@85 VAC @265 VAC
CH1: CH2: CH4:
DRAIN VOLTAGE VC11 (Vaux) ISHORT CIRCUIT
CH1: CH2: CH4:
DRAIN VOLTAGE VC11 (Vaux) ISHORT CIRCUIT
Even the 12V output is well protected against shorts, either by a power switch or by the active load
18/33
AN1376 APPLICATION NOTE
Figure 20. 35V OUTPUT: SHORT C18
@85 VAC @265 VAC
CH1: CH2: CH4:
DRAIN VOLTAGE VC11 (Vaux) ISHORT CIRCUIT
CH1: CH2: CH4:
DRAIN VOLTAGE VC11 (Vaux) ISHORT CIRCUIT
The above pictures are relevant to a hard short by switch of the output capacitor C11. The short by active load has not been tested because the load is not connected on this point, but after the zener limiting resistors. The short circuit on the +30V has not been tested because the power rating of the limiting resistors in series to the zener diode is not enough to insure a reliable protection against long-term short circuits. A solution could be to PUT a PTC resistor or similar component, or changethe present resistor with a fusible resistor. Figure 21. 5V OUTPUT: SHORT BY ACTIVE LOAD
@115 VAC
A short circuit made on the flat cable soldering points with a power switch provides for the current limiting intervention of the regulator at 2A (LD1086V50) Then, due to the internal over temperature protection the regulator starts to switch on and off itself, always keeping the output current under control. Hence, with this transformer and this regulator, an overcurrent on the 5V is not able to provide for the hic-cup working mode the previous tests but anyway all the most important circuit parameters are below any dangerous overstress point.
CH1: CH2: CH4: DRAIN VOLTAGE VC11 (Vaux) ISHORT CIRCUIT
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AN1376 APPLICATION NOTE
12 SHORT CIRCUIT PROTECTION @ LOW LOAD
After the full load tests some checks on the short circuit protection with reduced loads have been done. @Half Load
35V 15mA PoutTOT = 12.6W 12V 0.25 A 7V 0.35A 5V 0.55A 3.3V 1A
At Vin = 115Vac: shorting each output by the active load the over current protection works correctly, providing for the hic-cup working mode, except for the 5V which is protected by the current limiting of the linear regulator. At Vin = 220Vac: the circuit behaves like at 115V.
@Reduced Load - 1
35V 15mA PoutTOT = 9.5W 12V 0.5 A 7V 0A 5V 0A 3.3V 1A
At Vin = 115Vac: shorting the 3.3V, 7V, 12V and 35V it provides for the hic-cup working mode of the circuit. At Vin = 220Vac: the behaviour is the same.
@Reduced Load - 2
35V 15mA 12V 0.4 A 7V 0A 5V 0A 3.3V 0A
Both at 115V and 220V the circuit is still protected against short circuits on all the outputs 13 AT NO LOAD
Even in this abnormal condition, with the output connector unplugged, a short on the outputs provides for the same results of the previous tests, both at 115Vac or at 220 Vac. Figure 22. 3.3V OUTPUT: SHORT @NO LOAD
@115 VAC @220 VAC
CH1: CH2: CH3:
DRAIN VOLTAGE VC11 (Vaux) 3.3V OUTPUT
CH1: CH2: CH4:
DRAIN VOLTAGE VC11 (Vaux) 3.3V OUTPUT
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AN1376 APPLICATION NOTE
14 SHORT CIRCUIT OF THE OUTPUT RECTIFIERS
A frequent problem in a power supply is relevant to the protection of the SMPS itself: thus sometimes it is easy to find circuits with a good protection capability against shorts of the load but which are not able to survive in case of a very hard short like an output electrolytic capacitor or a diode. Besides, in case of a rectifier shorted the equivalent circuit changes and the energy is delivered even during the on time, like in forward mode. To insure reliable operation of the design, even this fault condition has been simulated for each rectifier. Thanks to the controller functionality, the SMPS can withstand this failure, working in burst mode as visible in the pictures, Figure 23. RECTIFIERS SHORT: @FULL LOAD - 220 VAC
3.3V 7V
CH1: CH2:
DRAIN VOLTAGE VPIN4 - ISENSE 12V
CH1: CH2:
DRAIN VOLTAGE VPIN4 - ISENSE 35V
CH1: CH2:
DRAIN VOLTAGE VPIN4 - ISENSE
CH1: CH2:
DRAIN VOLTAGE VPIN4 - ISENSE
In case of an output diode short, the current sensing voltage exceeds a second protection level, then the controller stops the operation, so avoiding the destruction of the components at primary side. The controller remains in off-state until the voltage across the Vcc pin decreases below the UVLO threshold. Then it try to restart and it will switch off again until the secondary short is removed. This provides for the hic-cup working mode, preventing the circuit destruction. The operating frequency inside the burst is the internal timer one (~2.5 Khz).
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AN1376 APPLICATION NOTE
15 SWITCH ON AND TURN OFF IN SHORT CIRCUIT CONDITION s FULL LOAD s SHORT ON 3V3 BY ACTIVE LOAD
The following pictures describe the SMPS behaviour during the start-up phase with an output voltage shorted. As clearly visible the circuit starts correctly then it works in hic-cup mode protecting itself. The start-up phase is clean in all conditions, without showing any dangerous transition for the SMPS circuitry. Figure 24. START
@85 VAC - 50Hz @265 VAC - 50Hz
Figure 25. TURN-OFF
@85 VAC - 50Hz @265 VAC - 50Hz
CH1: CH2: CH3:
VDD VC11 (Vaux) +3V3 Vout
CH1: CH2: CH3:
VDD VC11 (Vaux) +3V3 Vout
Even at turn off in short circuit the SMPS functionalities are good, protecting properly the circuit. No any abnormal transition or level has been observed during the tests.
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AN1376 APPLICATION NOTE
16 OVER VOLTAGE PROTECTION
A dangerous fault that could happen in case is the failure of the feedback circuitry. If this occurs, the SMPS output voltages can get high values, depending on the load by each output and the transformer coupling between the windings. Consequently, the rectifiers and the output capacitors are overstressed and can be destroyed. To avoid the SMPS failure a suitable protection circuit has been added. Then the circuit has been tested opening the loop, giving the following results:
3.3V OUTPUT: @ full load @115V - 50Hz @220V - 50Hz 3.3V OUTPUT: @ No load @115V - 50Hz @220V - 50Hz
V3V3: 4.02 V
V3V3: 4.08 V
V3V3: 4.64 V
V3V3: 4.67 V
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AN1376 APPLICATION NOTE
17 CONDUCTED NOISE MEASUREMENTS (PRE-COMPLIANCE TEST)
The following pictures are the peak and quasi-peak conducted noise measurements at full load and nominal mains voltages. The limits shown on the diagrams are the EN55022 CLASS B ones, which is the most widely rule for domestic equipments like a STB. As visible on the diagrams there is a good margin of the measures with respect to the limits, either in peak or quasi-peak mode.
The detail of the filtering components used is on the right of each diagram. Figure 26.
Vin = 115 Vrms 50 Hz - FULL LOAD
Limits: EN55022 CLASS B
PEAK MEASURE BOARD #2
C9 = 100nF EPCOS L = 39 mH EPCOS C16 = 100nF EPCOS TRAFO 2412.0011 REV. C1
Pout = 25W
QUASI-PEAK MEASURE BOARD #2
C9 = 100nF EPCOS L = 39 mH EPCOS C16 = 100nF EPCOS TRAFO 2412.0011 REV. C1
Pout = 25W
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AN1376 APPLICATION NOTE
Figure 27.
Vin = 220 Vrms 50 Hz - FULL LOAD
Limits: EN55022 CLASS B
PEAK MEASURE BOARD #2
C9 = 100nF EPCOS L = 39 mH EPCOS C16 = 100nF EPCOS TRAFO 2412.0011 REV. C1
Pout = 25W
QUASI-PEAK MEASURE BOARD #2
C9 = 100nF EPCOS L = 39 mH EPCOS C16 = 100nF EPCOS TRAFO 2412.0011 REV. C1
Pout = 25W
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AN1376 APPLICATION NOTE
18 THERMAL MEASURES
In order to check the reliability of the design a thermal mapping by means of an IR Camera was done. Here below the thermal measures on the board, at both nominal input voltages at ambient temperature (24 C) are shown. The pointers AE have been placed across some key components, affecting the reliability of the circuit. The points correspond to the following components:
component side A B C D E Input coil - L1 PowerMOS - Q1 +7V diode - D7 +3.3V diode - D8 +5V regulator - IC3
As shown on the maps, all the other points of the board are within the temperature limits assuring a reliable performance of the devices. Figure 28. @115VAC - FULL LOAD COMPONENT SIDE
A 47.41C B 47.24C C 78.39C D 59.02C E 70.67C
SMD SIDE
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AN1376 APPLICATION NOTE
The highest temperatures are for the NTC thermistor, the filter inductor, the input bridge, the clamp diode (D9), the 5V regulator and the output diodes D7 and D6. The temperature rise of the transformer is around 40 C. Regarding the thermistor, the bridge and the output diodes the temperature rise is compatible with reliable operation of the circuit. Figure 29. @220VAC - FULL LOAD COMPONENT SIDE
A 39.31C B 54.21C C 80.15C D 60.05C E 72.00C
SMD SIDE
At 220Vac the input circuitry is thermally less stressed and generally the component temperature rise is lower. 19 CONCLUSIONS
A SMPS for Set-Top Box has been completely designed, assembled and tested, giving positive results from all the different aspects (Component Stress, Functionalities, Protections, EMI, thermal behaviour). The design meets also the low-cost requirement, a key driver in the Consumer Electronic market. 20 REFERENCES
[1] "L6561-based Fly-back Converters" (AN1060) [2] "L6565 Quasi-Resonant Controller " (AN1326) [3] "How to handle Short Circuit Conditions with ST's Advanced PWM Controllers" (AN1215)
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AN1376 APPLICATION NOTE
21 ANNEX 1
Designator 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 C1 C10 C11 C12 C13 C14 C15 C16 C17 C18 C19 C2 C20 C21 C22 C23 C24 C25 C26 C27 C28 C29 C3 C30 C31 C32 C33 C4 C5 C6 C7 C8 C9 D1 D10 Part Type 2200uF-16V YXF 47uF-400V 22uF-25V YXF 1N0-1KV 30LVD10 1N0-1KV 30LVD10 330N - 1206 0805 - NOT MOUNTED 100N-275Vac - B81133 220PF-1KV HRR 22uF-50V YXF 2200uF-16V - YXF 2200uF-16V YXF 22uF-50V YXF 0805 - NOT MOUNTED 220PF-0805 1N0-0805 100N-0805 100N-0805 100N-0805 100N-0805 100N-0805 100N-0805 2200uF-16V YXF 220PF-1KV HRR 220P - 0806 2N2-0805 100N-0805 100uF-16V - YXF 100uF-16V - YXF 100uF-16V - YXF 100uF-16V - YXF 2N2-4KV (Y1) 44LD22 100N-275Vac - B81133 SMBYT01-400 BZV55-C15 ELCAP ELCAP ELCAP CERCAP HV CERCAP HV CHIP CAPACITOR CHIP CAPACITOR X CAP CERCAP HV ELCAP ELCAP ELCAP ELCAP CHIP CAPACITOR CHIP CAPACITOR CHIP CAPACITOR CHIP CAPACITOR CHIP CAPACITOR CHIP CAPACITOR CHIP CAPACITOR CHIP CAPACITOR CHIP CAPACITOR ELCAP CERCAP HV CHIP CAPACITOR CHIP CAPACITOR CHIP CAPACITOR ELCAP ELCAP ELCAP ELCAP CERCAP-SAFETY X CAP RECTIFIER ZENER DIODE Description Supplier RUBYCON SAMHWA RUBYCON CERA-MITE CERA-MITE AVX AVX EPCOS MURATA RUBYCON RUBYCON RUBYCON RUBYCON AVX AVX AVX AVX AVX AVX AVX AVX AVX RUBYCON MURATA AVX AVX AVX RUBYCON RUBYCON RUBYCON RUBYCON CERA-MITE EPCOS STMICROELECTRONICS PHILIPS SEMICOND.
PART LIST
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AN1376 APPLICATION NOTE
Designator 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 D11 D12 D2 D3 D4 D5 D6 D7 D8 D9 D9A F1 HS1 HS2 HS3 IC1 IC2 IC3 JP1 JP1A JP2 L1 L2 L3 L4 OPT1 P1 P2 P3 P4 P5 P6 P7 L5 PCB Q1 Q2 STP4NC60FP BC856 0R0-1206 0R0-1206 NOT MOUNTED - SHORTED Part Type BZV55-C15 LL4148 2W08G-GS STTA106U LL4148 LL4148 STPS2H100U STPS10L60CF STPS10L60CF SMCJ130CA (GBI) - SMC 1,5KE150A - NOT MOUNTED FUSE 2A ABL LS220 ABL LS220 6073 L6565 - DIP8 TL431ACD LD1086V50 FASTON 6mm FASTON 6mm MKS1858-6-0-808 B82732-R2701-B30 10u ELC06D 10u ELC06D 2u7 ELC06D SFH617A-4 0R0-1206 0R0-1206 0R0-1206 0R0-1206 HEAT SINK FOR Q1 HEAT SINK FOR IC3 HEAT SINK FOR D8 INTEGRATED CIRCUIT INTEGRATED CIRCUIT LIN. REGULATOR CONNECTOR CONNECTOR CONNECTOR - 8 POLES 2*39 mH - FILTER COIL INDUCTOR INDUCTOR INDUCTOR OPTOCOUPLER CHIP RESISTOR CHIP RESISTOR CHIP RESISTOR CHIP RESISTOR JUMPER, WIRE CHIP RESISTOR CHIP RESISTOR JUMPER, WIRE 35u, SINGLE SIDE, FR4 POWER MOSFET SMALL SIGNAL BJT STMICROELECTRONICS ZETEX BEYSCHLAG BEYSCHLAG STOCKO EPCOS PANASONIC PANASONIC PANASONIC INFINEON BEYSCHLAG BEYSCHLAG BEYSCHLAG BEYSCHLAG Description ZENER DIODE GEN. PURPOSE DIODE BRIDGE RECTIFIER RECTIFIER GEN. PURPOSE DIODE GEN. PURPOSE DIODE RECTIFIER RECTIFIER RECTIFIER TRANSIL TRANSIL Supplier PHILIPS SEMICOND. PHILIPS SEMICOND. GEN. SEMICOND. STMICROELECTRONICS PHILIPS SEMICOND. PHILIPS SEMICOND. STMICROELECTRONICS STMICROELECTRONICS STMICROELECTRONICS STMICROELECTRONICS STMICROELECTRONICS WICKMANN ABL ABL THERMALLOY STMICROELECTRONICS STMICROELECTRONICS STMICROELECTRONICS
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AN1376 APPLICATION NOTE
Designator 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 Q3 Q4 R1 R10 R11 R12 R13 R14 R15 R16 R17 R18 R19 R2 R20 R21 R22 R23 R24 R25 R26 R27 R28 R3 R4 R5 R6 R7 R8 R9 T1 BC848 BC848 270K-1206 220R - 0805 4K7 - 0805 470K-1206 0805 - NOT MOUNTED 270K-1206 470K-1206 470R - 1/2W PTH 1R0 - 2W PTH 47R - 1/2W PTH 1K0 - 1/2W PTH NTC_16R S236 10K - 1206 470R - 1206 0R0-0805 0805 - NOT MOUNTED 180R 1/2W PTH 1K8 - 0805 1K0 - 0805 120K - 0805 24K - 0805 33R-0805 100K - 0805 3K3 - 0805 0R47 - 1/2W PTH 2K7 - 0805 560R-0805 82R - 0805 2414.0011 rev. C1 Part Type Description SMALL SIGNAL BJT SMALL SIGNAL BJT CHIP RESISTOR CHIP RESISTOR CHIP RESISTOR CHIP RESISTOR CHIP RESISTOR CHIP RESISTOR CHIP RESISTOR FUSE RESISTOR PTH POWER RESISTOR SFR RESISTOR PTH SFR RESISTOR PTH NTC THERMISTOR CHIP RESISTOR CHIP RESISTOR CHIP RESISTOR CHIP RESISTOR SFR RESISTOR PTH CHIP RESISTOR CHIP RESISTOR CHIP RESISTOR CHIP RESISTOR CHIP RESISTOR CHIP RESISTOR CHIP RESISTOR SFR RESISTOR PTH CHIP RESISTOR CHIP RESISTOR CHIP RESISTOR TRANSFORMER ZETEX ZETEX BEYSCHLAG BEYSCHLAG BEYSCHLAG BEYSCHLAG BEYSCHLAG BEYSCHLAG BEYSCHLAG NEOHM NEOHM BEYSCHLAG BEYSCHLAG EPCOS BEYSCHLAG BEYSCHLAG BEYSCHLAG BEYSCHLAG BEYSCHLAG BEYSCHLAG BEYSCHLAG BEYSCHLAG BEYSCHLAG BEYSCHLAG BEYSCHLAG BEYSCHLAG BEYSCHLAG BEYSCHLAG BEYSCHLAG BEYSCHLAG ELDOR CORPORATION Supplier
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AN1376 APPLICATION NOTE
22 ANNEX 2
Figure 30. SILK SCREEN -TOP SIDE
Figure 31. SILK SCREEN -BOTTOM SIDE
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AN1376 APPLICATION NOTE
Figure 32. COPPER TRACKS
TABLE OF CONTENTS 1. 2. 3. 4. 5. 6. 7. 8. 9. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Main characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Electrical Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Cross Regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Output voltage ripple @full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Measurement Of The RMS Capacitor Currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Dynamic Load Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Start-Up Behaviours @full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Wake-up time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
10. Turn-Off . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 11. Short-Circuit Tests @ Full Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 12. Short Circuit Protection @ Low Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 13. At No Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 14. Start-up Behaviour @ Full Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 15. Switch On And Turn Off In Short Circuit Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 16. Over Voltage Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 17. Conducted Noise Measurements (Pre-Compliance Test) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 18. Thermal measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 19. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 20. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 21. ANNEX1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 22. ANNEX2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
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AN1376 APPLICATION NOTE
Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics. The ST logo is a registered trademark of STMicroelectronics (R) 2001 STMicroelectronics - All Rights Reserved STMicroelectronics GROUP OF COMPANIES Australia - Brazil - Canada - China - Finland - France - Germany - Hong Kong - India - Israel - Italy - Japan -Malaysia - Malta - Morocco Singapore - Spain - Sweden - Switzerland - United Kingdom - United States. http://www.st.com
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