AN1732 - APPLICATION NOTE
VIPower: 28W LOW COST WIDE RANGE POWER SUPPLY FOR LCD MONITOR OR TV USING VIPer53
C. Spini This paper describes a reference design for a 28W Switch Mode Power Supply dedicated to LCD monitors or TV sets. The board accepts full range input voltage (90 to 265Vrms) and delivers 4 outputs. It is based on the new VIPer53, integrating the controller and the Mosfet in a DIP-8 (VIPer53DIP) or in a PowerSO-10 package (VIPer53SP).
1. INTRODUCTION The LCD monitors and TVs are becoming very popular all over the world thanks to their performances and compactness. Thus, the market asks for cost effectiveness, good performances, low noise and compact power supplies to feed this kind of applications. The VIPer53 is a very suitable device, satisfying all the requirements with just few external components. The proposed reference design can supply an LCD monitor or even an LCD-TV, with 15" or 17" panels and 2 lamps for backlight together with multimedia functions like audio. The SMPS accepts a full range input voltage and it can deliver four output voltages dedicated to the scaler (3.3V), to the P (7V), to the backlight and audio (12V), and to the TV tuner (35V). The stand-by performance is very good, and the power consumption during stand-by is 800mW at 230Vac. The circuit is also full protected against faults like output short circuit or overvoltage. The design has been done with a particular attention to the final cost of the solution, so the PCB has been designed single layer, and the circuit has no any heat sink. The technology used is the standard thru-holes, but it can be changed very easily in SMT because most of the components are available also in this technology. The circuit has been tested deeply in all the most relevant aspects with positive results and it has been integrated with a 15" LCD-TV application without showing any problem. Table 1: Main characteristics Input Voltage
Output Voltages
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Vin:90 - 264Vrms f:45-66 Hz 3.3V2% at 1A - Dedicated to panel and digital circuitry for scaling 7V8% at 0.2A - Dedicated to post-regulator for microprocessor 12V8% at 2A - Dedicated to backlight lamp inverters, audio and SCART 35V10% at 10mA - Dedicated to tuner for TV-LCD Input power less than 1W at 230Vac, delivering 30mA on 7V On all outputs, with auto-restart at short removal Cu Single Side 35 m, CEM-1, 130 x 70 mm According to EN60950, creepage and clearance minimum distance 6.4mm According to EN50022 Class B
Stand-by Overcurrent Protection Pcb Type & Size Safety Emc
September 2003
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C2 1N0-Y1 T1 24140011_D 2 C16 1N0 D7 1.5KE180A 13 D5 STTH106 R11 47R D8 STPS8H100CF 14 4 D4 DF06M 2 2 1
F1 FUSE 2A L2 20mH - SUMIDA 1 C3 220N 4 3 3 CON1 2 1
uc d
CON2
MOLEX 2 R1 NTC_16R S236 C4 68uF-400V 4 12
1 R8 5K6 C11 1000uF-25V YXF C12 1000uF-25V YXF
12V@2A
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90-264Vrms
2
12V@2A
C7 100N
3 D9 BYW100-200 11 R9 RES
GND
4
GND
te le
5 C17 470uF-16V YXF
GND
R12
1R5 D2 1N4148 R13 3K65-1% 7 5 C20 220PF-2KV C15 47uF-25V
C8 100N 6 10 D1 STPS3L60 7 L1 2.7uH ELC08D
6
7V@0.2A
7
3.3V@1A
so Ob -
8 8
3.3V@1A
VDD
DRAIN
CONN 8P C13 2200uF-6.3V YXF C14 100uF-25V YXF 9 R10 180R
C9 100N
SOURCE
SOURCE
2 OSC CO M P TO V L R14 470R C18 10N 4 1 3 4
D6 STTH106
C10 100N U3 VIPER53_DIP C19 15NF
C1 1N0-Y1
R5 1K0
AN1732 - APPLICATION NOTE
U1 SFH617A-2
R6 RES
du o
4 1 C5 RES 3 2 C6 100N 3 U2 TL431 2 R2 33K R4 4K7-1% 1 R15 1K8 Q1 BC547B Q2 BC547B R16 1K0
(s) ct
R3 1K5-1%
Pr e
R7 RES
Electrical Diagram
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D3 1N4148
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AN1732 - APPLICATION NOTE
The converter topology of this SMPS is the very popular fly-back, discontinuous current mode, and core of this design is the primary controller VIPer53DIP, integrating the controller and a POWERMOS in a single, standard MINIDIP package. The device integrates all the functions needed to control and protect a power supply, giving a modern, compact and cheap solution to SMPS designers. In case an SMT mounting is required, a PowerSO-10 version is also available (VIPer53SP). The operating frequency of the circuit (~40 kHz) has been chosen in order to obtain a compromise between the transformer size and the input filter complexity. Thus, the input EMI filter can be a simple LC-filter, 1-cell only, for differential and common mode noise, using a cheap 2-sectors coil filter. An NTC limiting the inrush current at plug-in, and a standard 5*20mm fuse against catastrophic failures are also foreseen in the circuit. The transformer reflected voltage is ~80V providing enough room for the leakage inductance voltage spike leaving margin for reliability. Besides, the reflected voltage, the switching frequency and the primary inductance have been chosen to allow the discontinuous current operation of the transformer overall the input voltage range. This improves the efficiency, because at turn-on the current is zero, so the switching losses are zero too, while the capacitive losses are unchanged; the loop stability becomes easier to achieve. The diode D5 and the Transil D7 clamp the peak of the leakage inductance voltage spike, assuring reliable operation of the Viper53. The transformer is slot type, manufactured by ELDOR Corporation, designed according to the EN60950. It has four secondary windings, providing 3.3V, 7V, 12V and an additional winding providing for 35V. This winding will occur in case the SMPS also needs to deliver the 30V dedicated to the tuner varicap diode. The 30V can be obtained very easily by means of a resistor and a 30V zener diode. The 3.3V is dedicated to the LCD panel Scaler circuitry, while the 12V is dedicated to the panel Backlight. The 7V is dedicated to power the microprocessor via a cheap, 5V linear regulator, thus providing a clean and stable voltage to the P. The output rectifiers have been chosen in accordance with the maximum reverse voltage and their power dissipation. The 3.3V rectifier is a Schottky barrier, type STPS3L60. This rectifier has low forward voltage drop, therefore it improves the efficiency having a lower power dissipation with respect to a standard type. It is assembled in a cheap, axial DO-201 package. A small LC filter has been added on this output in order to filter the high frequency ripple without increasing the output capacitors size or quality. The 12V rectifier is an STPS8H100, still a high voltage Schottky rectifier offering a good trade-off between the forward voltage drop and the maximum operating junction temperature available by STM in 5 different package versions. For this design, the ISOWATT220AC (similar to a standard insulated TO-220) has been used, without any heat sink. The 7V output rectifier is a standard and cheap axial, fast recovery rectifier (BYW100-200). The output voltage regulation is performed by the secondary feedback monitoring the 3.3V output. The feedback network is the classical one, which uses a TL431 driving an optocoupler, in this case an SFH617A-2, assuring the required insulation between primary and secondary. The opto-transistor directly drives the COMP pin of the Viper53, and the capacitor C19 is part of the compensation loop filtering the high frequency noise. The VIPer53 is activated at start-up by an internal current source, charging the capacitor C15 from the DC bus via the Drain pin. Thanks to this circuit, the start-up time is short and independent from the input mains voltage, while during the normal operation the device is powered by the transformer via the diode D2. The switching frequency is selected by R13 and C18 and the capacitor C10 provides for a delay to the current protection intervention, the socalled TOVL function.
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AN1732 - APPLICATION NOTE
Figure 1: Drain voltage and current at Vin=115Vac - 60 Hz and full load Figure 2: Drain voltage and current at Vin=230Vac - 50 Hz and full load
TE K00003 1
CH1: VPIN5 (Drain) CH4: IPIN5 (Drain current)
CH1: VPIN5 (Drain) CH4: IPIN5 (Drain current)
Figure 3: Drain voltage and current at Vin=265Vac - 50 Hz and full load
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T EK00 0032
TEK 000034
CH1: VPIN5 (Drain) CH4: IPIN5 (Drain current)
Figure 1 and 2 show the drain voltage and current at the nominal input mains voltage during normal operation at full load. As visible, the current peak is below the VIPer53 peak current limitation. The drain voltage rise time is around 120ns. Figure 3 shows the measurement of the drain peak voltage at full load and maximum input mains voltage. The measured voltage 564V, assures a reliable operation of the Viper53 MOSFET with a good margin against the maximum BVDSS. The maximum rectifiers PIV have been measured during the worst operating condition and they are indicated in figure 4. The margin, with respect to the maximum voltage sustained by each diode, assures a safe operating condition for these devices.
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AN1732 - APPLICATION NOTE
Figure 4: Maximum rectifiers PIV at Vin = 265 Vac - 50 Hz and full load
TEK 000035
CH2: +7V DIODE: ANODE VOLTAGE CH3: +3.3V DIODE: ANODE VOLTAGE
CH4: +12V DIODE: ANODE VOLTAGE
In figure 5 and 6, the most salient controller IC signals are shown. In both the pictures it is possible to distinguish clean waveforms free of hard spikes or noise that could affect the controller correct operation. Figure 5: Drain-source and Vdd voltage at Vin=115 Vac - 60 Hz
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Figure 6: Oscillation and Compensation pin voltage at Vin = 230 Vac - 50 Hz
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TEK 000036
T EK00 0037
TEK0 00038
CH1: VPIN5 (Drain) CH2: VPIN7 (Vdd)
CH3: VPIN2 (Osc) CH4: VPIN1 (Comp)
2. CROSS REGULATION In tables 2 and 3, the output voltage cross regulation measures with static loads has been reported. Table 2 refers to the Monitor configuration and table 3 to the TV one. The overall efficiency of the converter is
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AN1732 - APPLICATION NOTE
also calculated at the nominal input voltages. All the output voltages have been measured after the load connector soldering points of the mother-board. The length of the connection cable is 100 mm. The circuit has been tested for both the configurations, monitor and TV having different current consumption of the P. Table 2a: Monitor configuration cross regulation at 115Vac
3.3V 2%
Vout [V] 3.27 3.27 3.27 3.27 3.28 3.28 3.28 3.28 @ Iout [A] 1.05 1.05 1.05 1.05 0.5 0.5 0.5 0.5
7V 8%
Vout [V] 7.08 7.1 7.16 7.32 6.81 6.81 6.82 6.87 @ Iout [A] 0.066 0.066 0.066 0.066 0.066 0.066 0.066 0.066
12V 8%
Vout [V] 11.99 12.16 12.42 12.93 11.53 11.65 11.85 12.15 @ Iout [A] 2 1.5 1 0.5 2 1.5 1 0.5
T OLERANCE Po utTOT [W] OK OK OK OK OK OK OK OK 27.88 22.14 16.33 10.38 25.15 19.56 13.94 8.17
115vac
Pin [W] 35.000 27.700 20.500 13.300 31.300 Efficien cy
79.7% 79.9% 79.6% 78.1%
Table 2b: Monitor configuration cross regulation at 220Vac
3.3V 2%
Vout [V] 3.27 3.27 3.27 3.27 3.28 3.28 3.28 3.28 @ Iout [A] 1.05 1.05 1.05 1.05 0.5 0.5 0.5 0.5
7V 8%
Vout [V] 7.06 7.09 7.16 7.31 6.79 6.8 6.82 6.88 @ Iout [A] 0.066 0.066 0.066 0.066 0.066 0.066 0.066
12V 8%
Vout [V] 11.97 12.15 12.41 12.93 11.49 @ Iout [A] 2
T OLERANCE
Table 3a: TV configuration cross regulation at 115Vac
3 .3 V 2%
V o u t [V] 3.27
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3.27 3.27 3.27 3.27 3.27 3.27 3.27
let o
@ I o u t [A] 1.0 5
Pr e
6.71 6.86 6.92 7.06 6.56 6.58 6.60 6.64
7 V 8%
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0.066
0 .2 0 .2 0 .2 0 .2 0 .2 0 .2 0 .2 0 .2
ct
11.65
11.84 12.16
(s)
11.9
Ob 1 0.5 2 1 0.5 1.5
@ I o u t [A] 2 1 .5 1 0 .5 2 1 .5 1 0 .5
1.5
so
OK OK OK OK OK OK OK OK
te le
Po utTOT [W] 27.84 22.13 16.32 10.38 25.07 19.56 13.93 8.17
ro P
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17.200 10.300 Pin [W] 34.200 27.300 20.100 14.000 30.800 24.000 17.400 10.400
24.200
s) t(
80.3% 80.8% 81.0% 79.3%
Efficien cy
220vac
81.4% 81.0% 81.2% 74.1% 81.4% 81.5% 80.1% 78.6%
1 2 V 8%
V o u t [V]
T O L E R AN C E P o u t T O T [W] OK OK OK OK OK OK OK OK 28 .58 23 .05 17 .22 11 .30 26 .01 20 .47 14 .82 9 .05
11 5 va c
P i n [W ] 35 .90 0 28 .80 0 21 .70 0 14 .50 0 32 .40 0 25 .40 0 18 .30 0 11 .30 0 E ffi c i e n c y
V o u t [V]
@ I o u t [A]
1.0 5 1.0 5 1.0 5 0 .5 0 .5 0 .5 0 .5
12.1 6 12.4 12.9 11.5 3 11.6 8 11.8 6 12.1 7
7 9 .6 % 8 0 .0 % 7 9 .3 % 7 7 .9 % 8 0 .3 % 8 0 .6 % 8 1 .0 % 8 0 .1 %
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AN1732 - APPLICATION NOTE
Table 3b: TV configuration cross regulation at 220Vac
3.3V 2%
Vout [V] 3.27 3.27 3.27 3.27 3.28 3.28 3.28 3.28 @Iout [A] 1.05 1.05 1.05 1.05 0 .5 0 .5 0 .5 0 .5
7V 8%
Vout [V] 6.8 6.85 6.91 7.05 6.56 6.58 6.61 6.64 @Iout [A] 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
12V 8%
Vout [V] 11.97 12.15 12.41 12.89 11.52 11.67 11.85 12.16 @Iout [A] 2 1.5 1 0.5 2 1.5 1 0.5
T OL ERANCE Pou tTOT [W] OK OK OK OK OK OK OK OK 28.73 23.03 17.23 11.29 25.99 20.46 14.81 9.05
220vac
Pin [W] 35.400 28.700 21.500 14.600 31.800 25.300 18.300 11.600 Efficien cy
81.2% 80.2% 80.1% 77.3% 81.7% 80.9% 80.9% 78.0%
2.1. Monitor configuration The circuit has been tested keeping the current on the 3.3V constant and varying the 12V load. The 7V has been loaded with 66mA, a typical consumption for a monitor microprocessor during the normal operation. The voltage regulator delivering 5V dedicated to the P (for example an LE50ABZ TO-92 or an LE50ABD SO-8) it is not on the SMPS board because usually it is close to the P itself. 2.2. TV configuration To check the LCD-TV application the circuit has been tested keeping the current on the 3.3V constant and varying the 12V load as the previous measurements, but differently from the monitor configuration, the 7V has been loaded with 200mA, which is typical consumption for a TV microprocessor during the normal operation. The P voltage regulator delivering 5V can be an L4931ABZ50 TO-92 or an L4931ABD50 SO-8. As shown in both tables, the voltages are within their tolerance at any load condition and the circuit efficiency is always good. This point can be very important for this kind of application because sometimes the SMPS are put into the panel pedestal, with poor air flowing. 3. STAND-BY OPERATION The output voltage and the efficiency have been checked, and the input power has been measured. In stand-by condition (7V at 30mA, 3.3V and 12V at 0mA), the input power consumption is 800mW at both the input voltage ranges. Besides, the circuit has been characterised at both the nominal input voltage values for different output load, giving very interesting results: the efficiency is still high and the input power is lower than 1W. In figure 7, the output voltage variation as a function of the 7V current is represented. It is possible to note the 12V variation: it increases due to the coupling between the transformer windings, but this is not a problem because the 12V is disconnected by the circuit by means of a MOSFET switch placed on the motherboard. Table 4 reports the +7V Output voltage and current needed to supply the P.
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Table 4: +7V Output voltage and current at 115Vac and 230Vac
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20 30 40 50
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115 Vac
@Iout [mA] PoutTOT [W]
0.127 0.189 0.248 0.307
7V
Vout [V] @Iout [mA]
20 30 40 50
230Vac
PoutTOT [W]
0.126 0.185 0.243 0.300
Vout [V]
Pin [W] 0.694 0.792 0.869 0.949
Efficiency
Pin [W] 0.682 0.800 0.915 0.998
Efficiency
6.37 6.29 6.21 6.14
18.3% 23.8% 28.6% 32.4%
6.30 6.17 6.08 6.00
18.5% 23.1% 26.6% 30.0%
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AN1732 - APPLICATION NOTE
Figure 7: Output voltages at low load
13.5 13.4 13.3 13.2 +12V @Stand-by 13.1 13 12.9 12.8 12.7 12.6 12.5 20 30 40 Iout +7V [mA] 50 5.8 6 6.1
+12V @115Vac +12V @230Vac +7V@ 115Vac +7V@ 230Vac
6.4
6.3
6.2 +7V @Stand-by
5.9
During the stand-by operation at 230Vac the circuit works in burst mode thus, thanks to this function, the switching frequency decreases. Because in a power switch the switching and the capacitive losses are directly proportional to the working frequency, this allows an input power saving with respect to other devices without this feature. The VIPer53 enters automatically in burst mode when it detects a light load by monitoring the voltage on pin 1 (Comp): if this voltage is lower than 0.5V the device stops the switching cycles, and it recovers the operation as soon as the Pin1 voltage becomes higher than 0.5V. Therefore, the output voltage is always under control and the device is ready to recover the normal operation in case of load increasing, like when the monitor or the TV recovers from stand-by to normal operation. Figure 8 and 9 show the main device voltages in stand-by operation (7V at 30mA). Figure 8: Vin = 115 Vac - 60 Hz
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Figure 9: Vin = 220 Vac - 50 Hz
T EK00 002
TEK0 0003
CH1: VPIN5 (Drain) CH2: VPIN7 (Vdd) CH3: VPIN1 (Comp)
CH1: VPIN5 (Drain) CH2: VPIN7 (Vdd) CH3: VPIN1 (Comp)
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AN1732 - APPLICATION NOTE
4. OUTPUT VOLTAGE RIPPLE AT FULL LOAD Figure 10: Output voltage ripple at Vin=115Vac - 60 Hz
TE K0000 5
CH2: +7 Vout CH3: +3.3 Vout CH4: +12 Vout
In figure 10, the output voltage ripples at switching frequency are measured. As per the previous measures, the probes have been connected on test points after the output cable. As shown, the ripple and the spikes are very low. An additional LC filter has been added on the 3,3V only, while not to the 7V and the 12V for saving costs. This because the 7V will feed a linear regulator and the 12V will feed the backlight inverters, so both don't need a very clean voltage. The residual line frequency modulation is extremely low at any input voltage. This is due to the very high gain of the inherent feed forward input voltage compensation of the current mode control, providing for a superior rejection of the input voltage ripple with respect to the voltage mode control. 5. MEASUREMENT OF THE RMS CAPACITOR CURRENTS Table 5: Rms capacitor currents
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ICAP C13 = 1.16 ARMS ICAP C17 = 0.46 ARMS ICAP C11 = C12 = 1.08 ARMS/each
Table 5 shows the rms currents flowing in the output capacitors at full load. All the rms currents are within the rating of the capacitor type indicated (Rubycon, YXF series) hence the component overstress that should affect the reliability and/or the expected lifetime of the SMPS is avoided.
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AN1732 - APPLICATION NOTE
6. DYNAMIC LOAD TESTS Figure 11: Vin = 115 Vac - 60 Hz; +3.3V dynamic load 0.5÷1A, 70Hz; +7V, +12V: full load
TEK 00006
CH1: +12 Vout CH2: +7 Vout CH3: +3.3 Vout CH4: +3.3 Iout
Figure 11 shows the output voltage regulation against a dynamic load variation of the feed backed voltage, at the nominal input voltage values. The voltage variation and the response time are very good, meaning excellent loop behaviour. In fact, the 3.3V voltage variation is in the range of 20mV (0,6%), and the spikes during the load transition, due to the filter inductor on the output, are only 45mV beyond the steady state (1,3%), with a recovery time of few tens of microseconds. The variations of the unregulated output have also been checked without showing any abnormal variation. Besides, the circuit response has been verified at minimum, nominal and maximum input voltage and it doesn't change at any input voltage. Figure 12 and 13 show the response of the output voltages for a load variation of each unregulated output. The load conditions are specified at the top of each picture. The regulation has been tested at both the nominal mains voltages giving the same results.
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AN1732 - APPLICATION NOTE
Figure 12: Vin = 115 Vac - 60 Hz +12V Dynamic Load 0÷2A, 70Hz +3,3V, +7V: Full Load Figure 13: Vin = 115 Vac - 60 Hz +7V: Dynamic Load 0.033÷0.2A, 70Hz +3,3V, +12V: Full Load
TE K0000 8
CH1: +12 Vout CH2: +7 Vout CH3: +3.3 Vout CH4: +3.3 Iout
CH1: +12 Vout CH2: +7 Vout CH3: +3.3 Vout CH4: +3.3 Iout
In figure 12, the variations of the outputs varying the 12V from minimum to maximum load are shown, simulating the backlight lamps switch off: its variation is within 1.66V and on the other outputs there are no heavy perturbations induced. The same occurs in case of strong variations of the 7V loads, like when the P changes the operating state to/from stand-by. The conclusion is therefore that no abnormal behaviour of the SMPS is generated by a load change and this allows a good confidence about its behaviour when integrated in the equipment. 7. START-UP BEHAVIOURS AT FULL LOAD AND WAKE-UP TIME Figure 14: 85 Vac - 50Hz Figure 15: 265 Vac - 50Hz
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TEK0 0009
TEK 00009
TEK 00009
CH1: +12 Vout CH2: +7 Vout CH3: +3.3 Vout
CH1: +12 Vout CH2: +7 Vout CH3: +3.3 Vout
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AN1732 - APPLICATION NOTE
In figures 14 and 15, the rising slopes at full load of the output voltages at minimum and maximum input mains voltage are captured and the rise time is measured. As shown in the pictures, the rising time is monotonic and it is almost constant overall the input mains range. No overshoot or abnormal behaviour is present overall the input main range. Figure 16: Wake up time at 115 Vac - 50Hz
TE K00015
CH1:VPIN5 (Drain) CH2:VPIN7 (Vdd) CH3:+3V3 Vout
In figure 16, the wake-up time is measured at the lower nominal input mains. Obviously, thanks to the Viper53 characteristics, the wake-up time is constant independently from the input voltage. The measured time at 115Vac is 180ms, which is a very short time for this kind of Power Supplies. It is obtained by a double charge current level of the VDD capacitor: the first part of the capacitor charging is done at 12mA till VDD reaches ~5V, then the current becomes 2mA. This allows to shorten the time between the main-switch is pushed and "something happens" to the equipment but avoids heavy duty cycles during the hiccup mode. Besides, on the picture is clearly visible that no overshoot, undershoot, dip or lost of control happens during the power supply start-up phase.
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8. TURN-OFF AND HOLD-UP TIME Even at turn off the transition is clean, without abnormal behaviours. The Hold-up time, in evidence between the vertical lines in figure 17, is 20ms at 115Vac, full load and becomes around 96ms at 230Vac. It is enough to offer a good immunity against line dips. A very short restarting of the Mosfet happens during the falling of the voltages, due to the drop of the 3.3V output and the lost of polarization of the transistor Q2. So, Q1 forces the switch off before the residual energy of C4 is definitely ended, then when the 7V drops too, the opto and Comp pin are released and the device tries to restart the operation. Anyway, this phenomenon happens only for few cycles and it is not critical for the circuit, neither for the load.
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AN1732 - APPLICATION NOTE
Figure 17: Turn off and Hold-up time at 115 Vac - 50Hz Figure 18: Turn off and Hold-up time at 230 Vac - 50Hz
TEK 00016
CH1: VPIN5 (Drain) CH2: VPIN7 (Vdd) CH3: +3V3 Vout
CH1: VPIN5 (Drain) CH2: VPIN7 (Vdd) CH3: +3V3 Vout
9. SHORT-CIRCUIT TESTS AT FULL LOAD In power supplies, the short circuit protection is a very important function because in any equipment a good short circuit protection avoids that the so-called "fault-chain" gets longer, increasing risks for safety and the equipment repairing cost to the end-user. Besides, the modern safety rules for equipments sold in the Consumer market ask to test many different fault types, checking the equipment behaviour before acquiring their marking. Hence, an effective fault protection is vital for avoiding problems during the equipment qualification phase and for decreasing the MTTR (Mean Time To Repairing). With universal mains input SMPS the behaviour of the protection overall the input voltage range sometimes it is irregular overall the input voltage range and in detail, can be difficult to limit the power involved at same level overall the input voltage range. In fact, we have to protect the shorted output components and the primary side elements from overheating or melting because, during the short, the output current can be very high as well as the power involved at primary side. To limit the power involved in fault condition avoiding any expensive component over sizing, a common solution adopted by the controllers is the so-called hic-cup mode functionality. Therefore, if a short happens, the reflected low impedance provides for the auxiliary voltage disappearing, and consequently the controller is off. Then it restarts with a normal start-up phase and its time constant, and then works until the fault is detected again and a new cycle is triggered. The on-off working ratio provides for the limitation of the average power delivered. However, sometimes, using old concept controllers it may happen that at low mains, a good low frequency hic-cup mode is achieved, but it becomes ineffective at high mains. This happens typically when the start-up capacitor is charged by a simple resistor connected to the DC bus, providing for a charging time proportional to the input mains voltage. The result is a hic-cup with an on-off working ratio not low enough, unable to limit the circuit power dissipation of the shorted output. The consequence in case of long-term shorts is a catastrophic failure of the circuit due to the rectifier or Mosfet overheating. Thanks to the VIPer53 integrated start-up current source, the circuit behaviour is very similar all over the
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TE K0001 7
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AN1732 - APPLICATION NOTE
input voltages range because, like during the start-up phase, the VDD capacitor is charged at constant current. This internal functionality eliminates definitively the problem of a poor short circuit protection bringing a superior safety level of the circuit against shorts. Thus, no circuit over sizing of the power semiconductors or heat sinks are required, so saving from additional costs for protections. Besides, a thermal protection is also integrated, stopping the device operation until the device temperature gets lower. The short circuit trials have been done testing both a short of the output electrolytic capacitor or making the short closer to the loads. 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 another part of the equipment, so having slightly higher impedance due to the connections in between. All tests have been done at maximum, nominal and minimum input voltage but to avoid a large amount of similar pictures, only the most significant have been inserted (figure 19 to 24). The circuit parameters, checked in all conditions, have been the drain voltage and the mean value of the output current. The drain voltage is an important parameter to check during shorts at maximum input voltage to insure the reliability against long term-shorts. For all conditions, the drain voltage is always below the BVDSS, and the mean value of the output current is similar to the nominal one, thus preventing component melting for excessive dissipation. The auto-restart has been also checked and it is correct at short removal in all conditions. Figure 19: Short on 7V output - 115 Vac - 50Hz Figure 20: Short on 7V output - 230 Vac - 50Hz
CH1: VPIN5 (Drain) CH2: VPIN7 (Vdd)
CH4: ISHORT CIRCUIT
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CH4: +3.3 Iout
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TEK 00018
TEK 00019
CH1: VPIN5 (Drain) CH2: VPIN7 (Vdd) CH4: ISHORT CIRCUIT
As clearly indicated by the waveforms, the circuit starts to work in hic-cup mode, so keeping the mean value of the current at levels compatible with the component rating. Because the working time and the dead time are imposed by the charging and discharging time of the auxiliary capacitor on VDD (C15), it is constant overall the input mains voltage range.
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Figure 21: Short on 3.3V output - 85 Vac Figure 22: Short on 3.3V output - 265 Vac
TEK 00021
CH1: VPIN5 (Drain) CH2: VPIN7 (Vdd) CH4: ISHORT CIRCUIT
CH1: VPIN5 (Drain) CH2: VPIN7 (Vdd) CH4: ISHORT CIRCUIT
Like the previous test of the 7V output voltage, the Viper53 keeps well under control the circuit preventing the circuit from catastrophic failures in all conditions. Even the 12V output is well protected against shorts, like the other outputs. Figure 23: Short on 12V output - 85 Vac
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TE K0002 0
Figure 24: Short on 12V output - 265 Vac
TEK 00022
TEK 00023
CH1: VPIN5 (Drain) CH2: VPIN7 (Vdd) CH4: ISHORT CIRCUIT
CH1: VPIN5 (Drain) CH2: VPIN7 (Vdd) CH4: ISHORT CIRCUIT
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10. SHORT CIRCUIT PROTECTION AT REDUCED LOAD After the full load tests, some checks on the short circuit protection with reduced loads have been done as reported here following. The tests have been done even at minimum and maximum input voltage with the same results, as the previous checks. Table 6: Short circuit protection at half load 12V 1A 7V 0.1A PoutTOT=14.3W 3.3V 0.5A
Table 6 reports a fault during normal conditions of the equipment, with a consumption halved with respect to the maximum output power levels. At Vin = 115Vac: shorting each output, the over current protection works correctly, providing for the hiccup working mode. At Vin = 220Vac: the circuit behaves correctly like at 115Vac. Table 7: Short circuit protection at reduced load 12V 0A 7V 30mA PoutTOT=1.86W
Table 7 reports a fault during an operating transition of the equipment, with the backlight off and a reduced consumption of the other outputs. At Vin = 115Vac: shorting each output, the over current protection works correctly, providing for the hiccup working mode. At Vin = 220Vac: the behaviour of the circuit is correct like at 115Vac. Table 8: Short circuit protection at stand-by
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Table 8 reports a fault during the stand-by operation of the equipment, with the backlight and the scaler off, and the mP is working with a reduced consumption. At Vin = 115Vac: shorting each output, the over current protection works correctly, providing for the hiccup working mode. At Vin = 220Vac: the behaviour of the circuit is correct like at 115Vac.
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Figure 25: Short on 3.3V output in stand-by at 265Vac Figure 26: Short on 7V output in stand-by at 265Vac
TEK 00025
Figure 27: Short on 12V output in stand-by at 265 Vac
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The main circuit parameter measurements have been done also during the test at reduced load or standby. In detail, during Stand-by short it is possible to check the perfect functionality of the protection (figures 25 to 27). This load condition in fact, is critical because all the power available from converter can be delivered to one output only, because the others are lightly loaded or unloaded, and this can bring to the destruction of the rectifier of the shorted output. Besides, during stand-by operation, the transformer coupling and the leakage inductance can be able to supply the controller charging the VDD capacitor by spikes generated at Mosfet turn-off preventing the hic-cup mode. This happens typically shorting a low voltage output. To avoid this, the circuit around Q1 and Q2 has been added, constraining the Hic-cup mode anyway. As visible in the pictures, the SMPS is always protected even in this very critical load condition.
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TEK 00027
CH1:VPIN5 (Drain) CH2:VPIN7 (Vdd) CH4:ISHORT CIRCUIT
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10.1. SWITCH-ON AND POWER-OFF IN SHORT CIRCUIT Figure 28 and figure 29 depict the SMPS behaviour during the Start-up and Turn-off phase, with the 12V 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. Even at turn off in short circuit the SMPS functionalities are good, properly protecting the circuit. No abnormal transition or level has been observed during the tests. Figure 28: Start-up at 230 Vac - 50Hz Figure 29: Turn-off at 230 Vac - 50Hz
TEK 00028
CH1: VDD CH2: VC11 (Vaux) CH4: +3V3 Vout
12. OVERVOLTAGE PROTECTION
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The open-loop fault is another very dangerous event that could happen in case of a feedback circuitry failure. 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. Hence, the rectifiers and the output capacitors are overstressed and can be destroyed or even worse, can catch fire. To avoid this, the safety rules ask that the SMPS has a suitable protection against safety risks. The Viper53 connected with a secondary feedback offers a double protection: the first one is represented by the internal error amplifier, monitoring the Vdd voltage. Since for a correct operation of the circuit with the secondary feedback the VDD has to be lower than the VDD regulation point (14.5V min), in case of open loop the Viper53 internal error amplifier will take over the control of the circuit. Besides, in case this error amplifier doesn't work properly, an additional OVP comparator is integrated, stopping the operation if the VDD reaches the VDD-OVP. Of course, in the secondary feedback circuit configuration, this OVP protection will probably never work but it becomes very important in case the primary side feedback configuration is used. Hence, using the Viper53, the solution to this problem is fully integrated in the device and free of charge: in fact, no additional external component is required by the circuit. The circuit has been tested opening the loop, and the following output voltages have been measured:
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CH1: VDD CH2: VC11 (Vaux) CH4: +3V3 Vout
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230Vac - 50Hz at full load 3.3V at 1A 7V at 0.2A 12V at 2A V3V3: 3.65 V V7V: 7.9 V V12V: 13.5 V
230Vac - 50Hz at stand-by 3.3V at 0A 7V at 30mA 12V at 0A V3V3: 4.95 V V7V: 9.73 V V12V: 18.9 V
As shown in the above tables, in both conditions the measured voltages are not critical for the circuitry.
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13. CONDUCTED NOISE MEASUREMENTS (PRE-COMPLIANCE TEST) In figure 30 and figure 31, the Peak conducted noise measurements at full load and nominal mains voltages are shown. The limits shown on the diagrams are that ones specified by the EN55022 CLASSB, which is the most widely used for Information Technology Equipments intended for domestic use, in the bandwidth 150KHz÷30MHz. The filter configuration used is the 2-wires one, without the ground connection at mains plug, suitable for domestic equipments like LCD-TVs. In case we are designing a monitor, the applicable rule is still the same intended for Information Technology Equipments, but CLASS-A, relevant to equipments not intended for domestic use. Usually the mains input plug has the ground connection and this changes a little the input filter configuration, because a couple of Y2 capacitors are added between the live wires and ground. It has to be taken into account that in case of PC monitors the manufacturers applies generally the Class-B because they can be used also in a domestic environment and the limits are more stringent while the Class A is used in the other cases. As visible on the diagrams, there is a good margin between the peak measures respect to the QP limits (lower one) and this assures that the QP and Average measures will be within their limits. Figure 30: Vin = 115 Vac 50 Hz - FULL LOAD Limits: EN55022 CLASS-B PEAK MEASURE
Figure 31: Vin = 220 Vac 50 Hz - FULL LOAD Limits: EN55022 CLASS B PEAK MEASURE
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14. THERMAL MEASURES In order to check the reliability of the design a thermal mapping by means of an IR Camera was done. In the table here below the thermal measures of some components on the board are reported at 115Vac and 230Vac input voltage, at ambient temperature (24C). The key components have been carefully checked, and no further hot spot has been found anywhere on the board. Table 9: Device temperature at 115Vac and 220Vac Reference U3 D7 T1 D8 D9 D1 D4 L1 Description VIPer53DIP TRANSIL CLAMPER POWER TRANSF. +12V RECTIFIER +7V RECTIFIER +3.3V RECTIFIER BRIDGE RECT. MAINS FILTER 115Vac Temperature 78C 90C 58C 91C 61C 66C 73C 54C 220Vac Temperature 86C 85C 59C 94C 63C 69C 58C 38C
15. LAY-OUT HINTS The layout of switching power supplies is very important to achieve a correct functioning of the circuit and minimizing noise and interference. The VIPer53 basically doesn't require any particular treatment, but the typical and common layout rules for SMPS have to be carefully applied, in order to prevent annoying noise problems and undesired malfunctioning. So, the primary side connections between the power components can sometimes be the main cause of noise because high current and voltage switched are involved in the circuit, thus high switching current loop areas have to be kept as small as possible and connections very short as well, also to decrease the layout parasitic. Hence, practically, the input bulk capacitor C4 has to be placed near the VIPer53 and the transformer. The ground connection of C4 has to be directly linked to the Viper53 source pins, while the returns of primary side control circuitry has to be connected to the VIPer53 Source pins too that will be the ground "star point", avoiding any connection of signal component return to tracks where the primary current flows. The Y-caps connections are very important too; they have to be as short as possible, connecting the VIPer53 source pins with the secondary ground and the C4 positive with still the secondary ground. Besides, to avoid possibly that any noisy component or track acts as a "bypass" for the input filter, radiating undesired noise on it. A similar approach can also be followed for the secondary side paths, keeping the ground connection of the feedback components separated by the power ones. The capacitors C7/8/9 have to be placed close to the output connector.
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16. CONCLUSIONS A SMPS for LCD monitors or LCD-TV sets has been completely designed, assembled and tested using the new Viper53. All the different aspects (Component Electrical Stress, Functionalities, Protections, Conducted EMI, Thermal Stress) have been checked, giving positive results. The design also meets the low-cost requirement and low-complexity, key drivers in the Consumer Electronic market. REFERENCES [1]"VIPer53 Data Sheet"
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ANNEX 1: Component list Reference C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15 C16 C17 C18 C19 C20 CON1 CON2 D1 D2 D3 D4 D5 D6 D7 D8 D9 F1 L1 L2 Q1 Q2 R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 Part Type 1N0-Y1 1N0-Y1 220N 275Vac X2 68uF-400V RES 100N - 50V 100N - 50V 100N - 50V 100N - 50V 100N - 50V 1000uF-25V YXF 1000uF-25V YXF 2200uF-6.3V YXF 100uF-25V YXF 47uF-25V YK 1N0 - 50V 470uF-16V YXF 10N - 50V 15N - 50V 220PF-2KV HR STOCKO 2 POLES CONN 8P STPS3L60 1N4148 1N4148 DF06M STTH106 STTH106 1.5KE180A STPS8H100CF BYW100-200 FUSE T2A 2.7uH ELC08D 20mH BC547B BC547B NTC_16R S236 33K 1/4W 5% 1.5K 1/4W 1% 4.7K 1/4W 1% 1K 1/4W 5% RES RES 5.6K 1/4W 5% RES 180 1/4W 5% Description Y1 SAFETY CAP. DE1E3KX102M Y1 SAFETY CAP. DE1E3KX102M R46.KI.3220.DQ.M1.M ALUMINIUM ELCAP B43504A9686M000 NOT USED CERCAP CERCAP CERCAP CERCAP CERCAP ALUMINIUM ELCAP ALUMINIUM ELCAP ALUMINIUM ELCAP ALUMINIUM ELCAP ALUMINIUM ELCAP CERCAP ALUMINIUM ELCAP CERCAP CERCAP HV CERCAP DEHR33A221K INPUT CONNECTOR MKS2822-1-0-202 CABLE WITH CONNECTOR ASSY POWER SCHOTTKY RECT. GEN. PURPOSE DIODE GEN. PURPOSE DIODE GEN. SEMICOND. FAST REC. RECTIFIER FAST REC. RECTIFIER TRANSIL POWER SCHOTTKY RECT. FAST REC. RECTIFIER FUSE 2 AMP. TIME DELAY DRUM INDUCTOR ELC08D 20mH-0.5A FILTER INDUCTOR UU16LF203 SMALL SIGNAL NPN BJT SMALL SIGNAL NPN BJT NTC THERMISTOR STANDARD FILM RESISTOR METAL FILM RESISTOR METAL FILM RESISTOR STANDARD FILM RESISTOR NOT USED NOT USED STANDARD FILM RESISTOR NOT USED STANDARD FILM RESISTOR Supplier MURATA MURATA ARCOTRONICS EPCOS AVX AVX AVX AVX AVX RUBYCON RUBYCON RUBYCON RUBYCON RUBYCON AVX RUBYCON AVX AVX MURATA STOCKO
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STMicroelectronics VISHAY VISHAY BRIDGE RECTIFIER STMicroelectronics STMicroelectronics STMicroelectronics STMicroelectronics STMicroelectronics WICKMANN PANASONIC SUMIDA STMicroelectronics STMicroelectronics EPCOS BEYSCHLAG BEYSCHLAG BEYSCHLAG BEYSCHLAG
BEYSCHLAG BEYSCHLAG
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AN1732 - APPLICATION NOTE
ANNEX 1: Component list (continued) R11 R12 R13 R14 R15 R16 T1 U1 U2 U3 47 1/2W 5% 1.5 1/4W 5% 3.65K 1/4W 1% 470 1W 5% 1.8K 1/4W 5% 1K 1/4W 5% 24140011_D SFH617A-2 TL431 VIPer53DIP STANDARD FILM RESISTOR STANDARD FILM RESISTOR METAL FILM RESISTOR POWER RESISTOR 1W STANDARD FILM RESISTOR STANDARD FILM RESISTOR POWER TRANSFORMER OPTOCOUPLER SHUNT REGULATOR OFF-LINE PRIMARY SWITCH BEYSCHLAG BEYSCHLAG BEYSCHLAG BEYSCHLAG BEYSCHLAG BEYSCHLAG ELDOR CORP. INFINEON STMicroelectronics STMicroelectronics
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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 results 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 trademark of STMicroelectronics 2003 STMicroelectronics - Printed in ITALY- 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 - U.S.A. http://www.st.com
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