AN2242
APPLICATION NOTE
Reference design: high performance, L6668-based flyback
converter for Set-Top boxes and PVRs
Introduction
This document describes a reference design of a 40W Switch Mode Power Supply dedicated to
Set-Top box application. The board accepts wide range input voltage (90 to 265Vrms) and
delivers 4 outputs. It is based on the new controller L6668, working in PWM fixed frequency
current mode. High efficiency and low standby consumption are the main characteristics of this
board. Such features, coupled with the minimal part count required and the global solution low
cost approach, makes it an ideal solution for powering digital consumer equipment, meeting
worldwide standby rules.
Figure 1.
AN2242/1205
EVAL6668-STB Demo Board, Described In This Application Note
Rev 1.0
1/31
www.st.com
31
AN2242
Contents
1
Main Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2
Circuit Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3
Cross Regulation and Standby . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4
Functional Checking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.1
Start-up Behaviour at Full Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.2
Wake-up Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.3
Power-down . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.4
Short-Circuit Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
4.5
Over Voltage Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
5
Conducted Noise Measurements (Pre-Compliance Test) . . . . . . . . . . . . 21
6
Thermal Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
7
Part List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
8
PCB Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
9
Transformer Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
10
2/31
9.1
Electrical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
9.2
Mechanical Aspect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
9.3
Manufacturer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Revision History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
AN2242
Figures
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure 8.
Figure 9.
Figure 10.
Figure 11.
Figure 12.
Figure 13.
Figure 14.
Figure 15.
Figure 16.
Figure 17.
Figure 18.
Figure 19.
Figure 20.
Figure 21.
Figure 22.
Figure 23.
Figure 24.
Figure 25.
Figure 26.
Figure 27.
Figure 28.
Figure 29.
Figure 30.
Figure 31.
Figure 32.
Figure 33.
EVAL6668-STB Demo Board, Described In This Application Note. . . . . . . 1
Electrical Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Vin = 115 Vrms - 60Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Vin = 230 Vrms - 50Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Vin = 265 Vrms - 50Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Vin = 115 Vrms - 60Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Vin = 220 Vrms - 50Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Vin = 230 Vrms - 50Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Input Power vs. Mains Voltage During Standby . . . . . . . . . . . . . . . . . . . . 13
Pin at 230vac vs. Iout 5V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Vin = 230 Vrms - 50Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Vin = 90 VAC - 60Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Vin = 265 VAC - 50Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
at 115 VAC - 60Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
at 230 VAC - 50Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
at 115 VAC - 60Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
at 230 VAC - 50Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
12V OUTPUT SHORT at 90 VAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.3V OUTPUT SHORT at 265 VAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.3V OUTPUT SHORT at 265 VAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5V OUTPUT SHORT at 265 VAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
1.8V OUTPUT SHORT at 90 VAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
1.8V OUTPUT SHORT at 265 VAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
OVP at 115 VAC - 60Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Conducted Noise Measurements - Phase A . . . . . . . . . . . . . . . . . . . . . . . 21
Concucted Noise Measurements - Phase B . . . . . . . . . . . . . . . . . . . . . . . 21
115Vac-Max Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
230Vac-Max Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Silk Screen -Top Side . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Silk Screen -Bottom Side . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Copper Tracks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Transformer Electrical Diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Winding Position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3/31
AN2242
Tables
Table 1.
Table 2.
Table 3.
Table 4.
Table 5.
Table 6.
Table 7.
Table 8.
4/31
Output Voltages. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Output Voltage Measurement at Full Load . . . . . . . . . . . . . . . . . . . . . . . . 11
Output Voltage Measurement at HDD SPIN-UP . . . . . . . . . . . . . . . . . . . 11
Output Voltage Measurement at Reduced, W/O HDD . . . . . . . . . . . . . . . 12
Output Voltage Measurement at Minimum Load. . . . . . . . . . . . . . . . . . . . 12
Output Voltage Measurement at Standby Load . . . . . . . . . . . . . . . . . . . . 13
Part List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Winding Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
AN2242
1
1 Main Characteristics
Main Characteristics
The main characteristics of the SMPS are listed here below:
●
INPUT VOLTAGE:
- Vin: 90 - 264 Vrms
- f: 45-66Hz
●
OUTPUT VOLTAGES:
Table 1.
Vout
Output Voltages
IoutMAX IoutMIN
PMAX
STABILITY
NOTES
1.8V
1.73A
0.20A
3.1W
±7%
Dedicated to digital circuitry and to 1.2V local
post regulators
3.3V
0.5A
0.03A
1.65W
±5%
Dedicated to analog peripherals and 2.5V
regulators
5V
2.4A
0.3A
12W
±10%
Dedicated to HDD and 5V circuitry
12V
1.9Avg
2.9Apk
±8%
Dedicated to HDD, SCART, LNBP21 for satellite
STB.
Average load is 1.9A, 2.9A is dedicated to HDD
spin-up
0.05A
34.8W
POUT(W)=40WAVG / 51Wpk
●
STANDBY: Below 1W with 5V at 50mA residual load
●
SHORT CIRCUIT PROTECTION: On all outputs, with auto-restart at short removal
●
PCB TYPE & SIZE: Single Side 70um (2-Oz), CEM-1, 150 x 75mm
●
SAFETY: Acc. to EN60065, creepage and clearance minimum distance 6.4mm
●
EMI: Acc. to with EN50022-Class B
5/31
C30
2N2
R12
10K
C16
100N
90-264Vrms
2
1
R14
30K
R13
36K
C31
100N
11
6
9
16
R15
6K2
13
8
R1
NTC_10R S236
C18
220N-X2
14
R21
3K9
SS
N.C.
SKIPADJ
RCT
ST-BY
VREF
4
1
2
HVS(nc)
3
2
C36
470P
15
3
12
4
C34
220P
R27
5K6
R22
27K
L6668
U2
C33
10N
S_COMP
GND
ISEN
OUT
VCC
5
L1
HF2430-203Y1R0-T01 TDK
1
HV
COMP
PFC_STOP
DIS
OVP
7
g
10
F1
FUSE 2A
2
4
D16
LL4148
3
C40
10uF-50V
R36
3K3
R16
1K0
R17
82R
C19
47uF-50V
1
D1
2W06G
Q5
BC847B
R6
330K
R5
470K
R18
0R47
R19
0R47
D6
BAV103
Q4
BC857B
Q1
STP4NK60ZFP
HS1
R8
33R
C21
10N-400V
D5
BAV103
C20
82uF-400V
R7
33K-2W
U3
SFH617A-4
C5
2N2 - Y1
6
5
3
D7
STTH1L06U
C412
1
T1
SRW28LEC-E01
D10
R2
3R9
7
8
9
C32
100N
C37
3N3
Q2
BC847B
U4
TS2431ILT
L285
R35
1K0
R20
1K8
C35
2200uF-16V YXF
D12
1N5821
R23
1K0
L5
2.7uH
C41
10uF-50V
R29
10K
R10
10K
C23
1000uF-16V YXF
R28
1K
D13
LL4148
R24
1K0
C38
100N
Q3
BC847B
C10
470uF-25V YXF
L2
2.7uH
L3
2.7uH
C39
100N
R34
1K0
L4
22uH
C22
1000uF-16V YXF
C9
470uF-25V YXF
C7
1N0
C24
220uF-16V YXF
D9
STPS1L60A
HS3
10 STPS10L60FP
11
12
4
3
J1
INPUT CONN.
1
R25
3K3
R26
1K0
R4
4K7
R30
270R
R32
1K0
C29
100uF-25V
C28
100uF-25V
R33
1K0
+3V3
+5V
+1V8
+12V
C27
100uF-25V
C11
100uF-25V YXF
C17
100N
+5V
@0.5A
+3V3
@2.4A
8
7
6
5
4
3
2
1
J2
O/P CONN
@1.7A
+1V8
C14
100N
C15
100N
C12
100N
+12V
@1.9A-2.9Apk
Figure 2.
2
6/31
D2
STPS8H100FP
HS2
1 Main Characteristics
AN2242
Electrical Diagram
AN2242
2
2 Circuit Description
Circuit Description
The topology used in this schematic is a classical flyback, working in continuous and
discontinuous conduction mode with fixed frequency, achieves the best tradeoff between peak/
rms current ratio and the output capacitors' size. The nominal switching frequency, 65kHz, has
been chosen to get a compromise between the transformer size and the harmonics of the
switching frequency, optimizing the input filter size and its cost. 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 MOSFET is a standard and cheap 600V-2Ω
max, TO-220FP, needing a small heat sink. The transformer is a layer type, using a standard
ferrite type EER28L. The transformer, designed according to the EN60065, is manufactured by
TDK. The reflected voltage is 70V, providing enough room for the leakage inductance voltage
spike with still margin for reliability of the MOSFET. The network D7, R7, C21 clamps the peak
of the leakage inductance voltage spike. The controller is the new L6668, integrating all the
functionalities needed to control an SMPS with high performance and minimum component
count, offering the maximum flexibility. A new functionality embedded in the device is a highvoltage current source used at start-up that draws current from the DC bus and charges the
capacitor C19. After the voltage on C19 has reached the L6668 turn-on threshold and the
circuit starts to operate, the controller is powered by the transformer via the diode D5. After the
start-up, the HV current source is deactivated, saving power during normal operation and
allowing very good circuit efficiency during standby. The control system is Current Mode, so the
current flowing in the primary is sensed by R18 and R19 and is then fed into pin #12 (Isen). R5
and R6 are also connected to pin #12 (Isen). Their purpose is to compensate the power
capability change vs. the input voltage. The resistor R27 connected between pin #12 (Isen) and
pin #15 (S_Comp) provides the correct slope compensation to the current signal, necessary for
the correct loop stability. The circuit connected to pin #7 (DIS) provides over voltage protection
in case of feedback network failures and open loop operation. An internal comparator senses
this pin voltage and in case its threshold is exceeded the L6668 stops operating and reduces its
consumption. To definitely latch this state an internal circuitry of the L6668 monitors the Vcc
periodically reactivates the HV current source to supply the IC. After OVP detection and
Disable intervention the controller operation can be resumed only after disconnecting the mains
plug. The switching frequency is programmed by the RC connected to pin #16 (RCT) and in
case of reduced load operation the controller can decrease the operating frequency via the pin
#13 (ST-BY) and resistor R15, proportionally to the load consumption. The resistor dividers
R13 and R14 connected to pin #9 (SKIPADJ) allow to set the initial L6668 threshold to burst
mode functionality when the power supply is lightly loaded. Additional functions embedded in
the L6668 are the programmable soft-start and a 5V reference available externally. The output
rectifiers have been selected according to the calculated maximum reverse voltage, forward
voltage drop and power dissipation. The rectifiers for 5V and 12V outputs are Schottky, low
forward voltage drop type, hence they dissipate less power with respect to standard types. A
small heat sink for both devices is required, as indicated on the BOM. The other two output
rectifiers are Schottky too but with a smaller package. The snubber made up of R2 and C7
damps the oscillation produced by the diode D2 at MOSFET turn-on. The output voltage
regulation is performed by secondary feedback on the 12V, 5V and 3.3V output, while for the
1.8V output the regulation is achieved by the transformer coupling. The feedback network uses
a TS2431 driving an optocoupler, in this case a SFH617A-4, ensuring the required insulation
between primary and secondary. The opto-transistor drives directly the COMP pin of the
L6668. A small LC filter has been added on all outputs in order to filter the high frequency ripple
without increasing the output capacitors and a 100nF capacitor has been placed on each
output, very close to the output connector solder points, to limit the spike amplitude.
7/31
AN2242
2 Circuit Description
Here follow some waveforms during normal operation at full load:
Figure 3.
Vin = 115 Vrms - 60Hz
CH1: DRAIN VOLTAGE
CH2: DRAIN CURRENT - VPIN12 (Isen)
Figure 4.
Vin = 230 Vrms - 50Hz
CH1: DRAIN VOLTAGE
CH2: DRAIN CURRENT - VPIN12 (Isen)
The pictures above show the drain voltage and current signal on pin #12 at the nominal input
mains voltage during normal operation at full load. The Envelope acquisition of the scope
provides for the possibility to observe the modulation of the two waveforms, due to the mains
input voltage ripple at twice the line frequency.
Figure 5. The drain voltage waveforms and the measurement of the peak voltage at full load
and maximum input mains voltage are shown. The maximum voltage peak in this condition is
524V, which ensures a reliable operation of the power MOSFET with a good margin against the
maximum BVDSS. The operation during the hard-disk spin-up when the SMPS delivers the
peak power to the loads, brings the drain voltage peak at 540Vpk.
Figure 5.
Vin = 265 Vrms - 50Hz
CH1: DRAIN VOLTAGE
CH2: DRAIN CURRENT - VPIN12 (Isen)
Figure 5. and Figure 6. depict the most salient controller IC signals. In all pictures it is possible
to distinguish clean waveforms free of hard spikes or noise that could affect the controller
8/31
AN2242
2 Circuit Description
correct operation. More precisely, in Figure 5. and Figure 6. the waveforms during normal
operation at max load and both nominal input mains voltage measured on current sense pin,
gate drive, comp and oscillator pin have been captured. It is possible to notice that the circuit
works in continuous over the entire input mains range.. Besides, the signal on pin #12 (Isen),
has a different offset and similar peak for the effect of R5 and R6. Their purpose is in fact to
compensate the over current set point variation with the input voltage, which instead has to be
almost constantover the entire input voltage mains range. Of course, the oscillator waveform
does not change in the two pictures.
Figure 6.
Vin = 115 Vrms - 60Hz
CH1: VPIN12 - ISEN
CH2: VPIN4 - OUT
CH3: VPIN16 - RCT
CH4: VPIN10 - COMP
Figure 7.
Vin = 220 Vrms - 50Hz
CH1: VPIN12 - ISEN
CH2: VPIN4 - OUT
CH3: VPIN16 - RCT
CH4: VPIN10 - COMP
In Figure 8. channel 4 shows the slope compensation signal, coming from pin #15. This pin
provides a voltage ramp during the MOSFET's ON-time, which is a repetition of the oscillator
saw tooth and is dedicated to implementing additive slope compensation on current sense.
This is needed to avoid the sub-harmonic oscillation that arises in all peak-current-modecontrolled converters working in continuous conduction mode with a duty cycle close to or
exceeding 50%, as in this circuit. Besides, only a resistor is needed to implement slope
compensation, and since the voltage ramp is delivered during the ON-time only, the correct
operation of the control circuit is ensured even at light load. The slope compensation signal
delivered only during ON-time in fact prevents perturbations on the current sense due to the
injection of the residual part of the oscillator saw tooth that could affect the control circuit, as it
happens using the oscillator total saw tooth for slope compensation.
9/31
AN2242
2 Circuit Description
Figure 8.
Vin = 230 Vrms - 50Hz
CH1: VPIN12 - ISEN
CH2: VPIN4 - OUT
CH3: VPIN16 - RCT
CH4: VPIN15 - S_COMP
10/31
AN2242
3
3 Cross Regulation and Standby
Cross Regulation and Standby
The following tables show the output voltage measurements and the overall efficiency of the
converter measured at different input voltages. All the output voltages have been measured on
the output connector.
Table 2.
Output Voltage Measurement at Full Load
at 115Vac - 60Hz
Voltage [V] Current [A]
at 230Vac - 50Hz
Deviation
Voltage [V] Current [A]
Deviation
11.70
1.9
-2.50%
OK
11.6
1.9
-3.33%
OK
1.81
1.7
0.56
OK
1.82
1.7
1.11%
OK
4.82
2.4
-3.60%
OK
4.82
2.4
-3.60%
OK
3.28
0.5
-0.61%
OK
3.28
0.5
-0.61%
OK
Pout=38.52W
Vin= 115Vac
Pout=38.34W
Vin= 230Vac
lin= 0.75Arms
lin= 0.44Arms
Pin= 49W
Pin= 47.6W
EFF.= 80.6%
EFF.= 78.6%
Table 2. lists the output voltage measurements at both nominal mains range: all voltages are
within the tolerance given in the specification. The efficiency measured is very good for this
kind of SMPS, thanks to the absence of post regulators.
Table 3. shows the same measurement done during the HDD spin-up, which means higher
current from the 12V output, while the other output currents are not changed.
Table 3.
Output Voltage Measurement at HDD SPIN-UP
at 115Vac - 60Hz
Voltage [V] Current [A]
at 230Vac - 50Hz
Deviation
Voltage [V] Current [A]
Deviation
11.51
2.9
-4.08%
OK
11.46
2.9
-4.50%
OK
1.81
1.7
0.56%
OK
1.82
1.7
1.11%
OK
4.77
2.4
-4.60%
OK
4.80
2.4
-4.00%
OK
3.3
0.5
-0.00%
OK
3.29
0.5
-0.30%
OK
Pout=49.55W
Vin= 115Vac
lin= 0.93Arms
Pin= 64.5W
EFF.= 76.8%
Pout=49.49W
Vin= 230Vac
lin= 0.55Arms
Pin= 61.2W
EFF.= 80.9%
As clearly visible in this table, the output voltages are still within the given tolerance. The
heavier load does not affect efficiency. Please note that that the total output power of Table 3. is
the so-called "electrical power", not the "thermal power". Therefore, the circuit has been
designed to deliver the "electrical power" for a short time only - typically the HDD spin-up has
11/31
AN2242
3 Cross Regulation and Standby
duration of 1 second - but it cannot be delivered significantly longer because, from the thermal
point of view, the circuit can manage the full load only with the required reliability. The board
has been designed to power a digital decoder equipped with a hard disk drive but it can be
used even for powering a Set-Top box without the Hard disk drive. The measurements shown
in Table 4. are relevant to a load condition typical of a satellite Set-Top box. The 12V and 5V
loads have been reduced with respect to the previous measurements.
Table 4.
Output Voltage Measurement at Reduced, W/O HDD
at 115Vac - 60Hz
at 230Vac - 50Hz
Voltage [V]
Current [A]
Deviation
Voltage [V] Current [A]
Deviation
11.86
1.1
-1.17%
OK
11.76
1.1
-2.00%
OK
1.79
1.7
-0.56%
OK
1.81
1.7
0.56%
OK
4.85
1.8
-3.00%
OK
4.9
1.8
-2.00%
OK
3.27
0.5
-0.91%
OK
3.26
0.5
-1.21%
OK
Pout=
26.45
W
Pout=
26.46
W
Pout=26.45W
Pout=26.45W
Vin= 115Vac
lin= 0.48Arms
Pin= 33.1W
EFF.= 79.9%
Vin= 230Vac
lin= 0.29Arms
Pin= 33.4W
EFF.= 79.2%
At minimum load the power supply is still capable of keeping the output voltages regulated
within the specification, as indicated by the measurements in Table 5. Additionally, the auxiliary
voltage has been measured too: note that the voltage powering the IC has a good margin with
respect to the L6668 turn-off voltage.
Table 5.
Output Voltage Measurement at Minimum Load
at 115Vac - 60Hz
Voltage [V] Current [A]
12/31
at 230Vac - 50Hz
Deviation
Voltage [V] Current [A]
Deviation
11.72
0.05
-2.33%
OK
11.65
0.05
-2.92%
OK
1.80
0.2
0.00%
OK
1.80
0.2
0.00%
OK
4.77
0.3
-4.600%
OK
4.78
0.3
-4.40%
OK
3.35
0.03
1.52%
OK
3.34
0.03
1.21%
OK
Pout=2.48W
Vin= 115Vac
Pout=2.48W
Vin= 230Vac
lin= 0.082Arms
lin= 0.05Arms
Pin= 3.6W
Pin= 4.2W
Vaux=1.5V
Vaux=11.4V
EFF.= 68.8%
EFF.= 59.0%
AN2242
3 Cross Regulation and Standby
Table 6.
Output Voltage Measurement at Standby Load
at 115Vac - 60Hz
Voltage [V] Current [A]
at 230Vac
Deviation
Voltage [V]
Current [A]
Deviation
11.80
0
-1.67%
OK
11.70
0
-2.50%
OK
1.92
0
6.67%
OK
1.92
0
6.67%
OK
4.71
0.047
-5.80%
OK
4.73
0.047
-5.40%
OK
3.36
0
1.82%
OK
3.36
0
1.82%
OK
Pout=0.22W
Pout=0.22W
Vin= 230Vac
Vin= 115Vac
lin= 0.0217Arms
lin= 0.017Arms
Pin=0.75W
Pin=0.51W
Vaux=10V
Vaux=9.68V
EFF.= 43.5%
EFF.= 29.8%
In Table 6. the output voltage measurements during standby operation are shown. Even in this
load condition the circuit is able to regulate the output voltages within the required tolerance.
Input Power vs. Mains Voltage During Standby
Input power
Figure 9.
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
90Vac
115Vac
230Vac
265Vac
Pin= [W]
0.49
0.51
0.75
0.88
Vaux= [V]
9.67
9.68
10
10.04
Mains voltage
It is clearly visible that, while delivering the required standby load, (5V at 50mA, 1.8V, 3.3V and
12V at 0mA) the input power consumption is below 800mW at both the nominal input
voltage ranges and remains below 900mW at 265Vac. Figure 10. represents the input power
variation as a function of the 5V current.
During the standby operation the circuit works in burst mode, thus the number of switching
cycles decreases and, therefore it brings to an equivalent continuous switching frequency
reduction. This minimizes all frequency-related losses and maximizes the efficiency with
respect to other controllers without this feature. The L6668 enters automatically in burst mode
when its internal circuitry detects a light load by monitoring the voltage on pin #10 (Comp).
When it falls by 50mV below the threshold programmed via the divider connected at to pin #9
(SKIPADJ), the IC is disabled and its consumption is reduced to minimize the Vcc capacitor
discharge. The soft-start capacitor is not discharged. The control voltage now will increase as a
result of the feedback reaction to the energy delivery stop, the threshold will be exceeded and
the IC will restart switching again. In this way the converter works in burst-mode with a constant
13/31
AN2242
3 Cross Regulation and Standby
peak current defined by the disable level applied at to pin #9. This functionality is well visible in
Figure 11., where the most significant waveforms are depicted during the standby operation. It
is possible to check that the circuit stops switching as soon as the COMP pin voltage is equal to
the SKIPADJ voltage and restarts to operate as soon as the threshold returns at the same level
with the mentioned voltage histeresys. In the above table also the auxiliary voltage
measurement is shown. At minimum load the value is still enough to ensure correct operation
of the L6668 with margin. During standby operation the output voltages are only affected by a
slight ripple at burst frequency, due to the operation of the internal control comparator. The
ripple peak to peak measured in worst case at 265Vac on the 5V output was 68mV.
Figure 10. Pin at 230vac vs. Iout 5V
Pin @230vac vs. Iout 5V
1.4
1.2
Pin @230vac [W]
1
0.8
0.6
0.4
0.2
0
20
30
40
50
Iout 5V [mA]
60
70
80
Figure 11. Vin = 230 Vrms - 50Hz
CH1: VDRAIN
CH2: VPIN10- COMP
14/31
CH3: VPIN16 - RCT
CH4: VPIN9 - SKIP_ADJ
AN2242
4 Functional Checking
4
Functional Checking
4.1
Start-up Behaviour at Full Load
Figure 12. Vin = 90 VAC - 60Hz
CH1: +12 Vout
CH2: +5 Vout
Figure 13. Vin = 265 VAC - 50Hz
CH3: +3.3 Vout
CH4: +1.8 Vout
Figure 12. and Figure 13. capture the rising slopes at full load of output voltages at minimum
and maximum input mains voltage. As shown in the pictures, the rising times are constant and
there is no difference between the rise time of the output voltages. To avoid problems at startup, this characteristic is quite important when the loads are a microprocessor and its
peripherals, as in our case. Just a negligible overshoot is present at both mains voltages,
without consequences for the supplied circuitry. The soft start time can be programmed via the
soft-start capacitor connected to pin #11 of the L6668.
4.2
Wake-up Time
The wake-up time is the time needed for the power supply to deliver the nominal output
voltages once it has been plugged-in or, if there is any, the mains switch has been closed.
Generally, with wide mains power supplies using passive solutions for start-up like the largest
part on the market, it is difficult to find a good compromise between the wake-up time at low
mains, the dissipation at high mains and the circuit complexity. The following figures show the
waveforms with the wake-up time measurements at both nominal input mains. The measured
wake-up time at 115Vac and 230Vac is 750millisecond, which is a common value for this kind of
power supplies. Thus, thanks to high voltage circuitry integrated in the L6668, the wake-up
time is perfectly constant vs. the input voltage, which can be achieved without any external
component or special circuitry. Moreover, as soon as the IC has started, the HV current source
is switched off, saving power that would affect the efficiency and the standby performance of
the SMPS otherwise.
15/31
AN2242
4 Functional Checking
Figure 14. at 115 VAC - 60Hz
CH1: VDD
CH2: VC19 (Vaux)
Figure 15. at 230 VAC - 50Hz
CH3: +12 Vout
CH4: +1.8 Vout
To avoid spurious start-up attempts when power supply is plugged in with abnormal, lower
voltage mains, the HV current source has a turn-on threshold so that it is not activated if the
input voltage is lower than the Start voltage (typ. value is 80V).
As visible in Figure 14. and Figure 15. captured at the nominal mains voltages there is not any
overshoot, undershoot, dip or abnormal behaviour during the power supply start-up phase.
The power supply has been checked over the entire input voltage range with same positive
results as in the above figures.
4.3
Power-down
Even at turn off the transition is clean, without any abnormal behaviour like restart or glitches on
both the auxiliary and the output voltages. This is still provided by the HV start-up circuitry that
controls the power down sequence: at converter power-down the system loses regulation, then
Vcc drops and IC activity is stopped as it falls below the UVLO threshold (8.7V typ.). To prevent
restart attempts of the converter and to ensure monotonic output voltage decay at power-down
an internal logic re-enables the HV current source only if the Vcc voltage goes below the
threshold Vccrest located at about 5V. Thus, the HV generator can restart but, if Vin is lower
than Vinstart, the HV generator is disabled.
Figure 16. and Figure 17. also the hold-up time at both nominal mains voltages is measured
115 Vac the input Elcap stores enough energy to keep the regulation for 20mS at full load. After
that the converter loses regulation and the output voltages drop. The measured time is enough
to provide the required immunity of the Set-Top box against standard mains dip or short
interruptions tests, required by the standard rules such as the IEC1000 and protecting the unit
16/31
AN2242
4 Functional Checking
against lost of channel tuning or video disturbances while the end user is watching TV or
recording programs.
Figure 16. at 115 VAC - 60Hz
CH1: VDD
CH2: VC19 (Vaux)
4.4
Figure 17. at 230 VAC - 50Hz
CH3: +12 Vout
CH4: +1.8 Vout
Short-Circuit Tests
An important functionality of any power supply is the capability to survive in case of load short
circuit and to avoid any consequent failure. Additionally, the power supply must be compliant
with safety rules, which require that, in case of fault, no component will melt or burn-out. The
SMPS protection is another issue of power supplies. Sometimes it is easy to find circuits with
good protection capability against shorts of the load but which are not able to survive in case of
a very hard short like that of an output electrolytic capacitor or of a rectifier or transformer
saturation. Besides, in case of a shorted rectifier the equivalent circuit changes and the energy
is delivered even during the on time, as in forward mode. In case of a short, the voltage at pin
Isen exceeds the VISENdis threshold (Hiccup-mode OCP level) and 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. It
will then try to restart without success until the secondary short is removed. This provides a low
frequency hic-cup working mode, preventing the power supply from being destroyed.
The board has been tested over the entire input voltage mains range. Two critical circuit
parameters, the Vds and the output current have been checked during short circuit tests. In all
conditions the measured drain voltage is always below the BVDSS, while the mean value of the
output current has a value lower or close to the nominal one, therefore preventing the
component damage. As indicated by the waveforms in Figure 18. and Figure 19., once an
output is shorted, the circuit begins to work in hic-cup mode, keeping the mean value of the
current at levels sustainable by the component rating. Because the working time and the dead
time are imposed by the charging and discharging time of the auxiliary capacitor C19, thanks to
the L6668 current source and related circuitry, the on-off periods are independent from the
input mains voltage, contrary to controller using a passive start-up circuitry where the on time
17/31
AN2242
4 Functional Checking
duration increases significantly with the mains voltage. The auto-restart at short removal is
correct in all conditions.
Figure 18. 12V OUTPUT SHORT at 90 VAC
CH1: DRAIN VOLTAGE
CH2: VPIN12(Vcc)
CH3: 12 Vout
CH4: ISHORT CIRCUIT
Figure 20. 3.3V OUTPUT SHORT at 265 VAC
CH1: DRAIN VOLTAGE
CH2: VPIN12(Vcc)
Figure 19. 3.3V OUTPUT SHORT at 265 VAC
CH3: 3.3 Vout
CH4: ISHORT CIRCUIT
Figure 21. 5V OUTPUT SHORT at 265 VAC
CH1: DRAIN VOLTAGE
CH2: VPIN12(Vcc)
CH3: 5 Vout
CH4: ISHORT CIRCUIT
Figure 20. and Figure 21. show the short circuit waveforms shorting the 3.3V and the 5V
output. Like the 12V output voltage the controller keeps under control the circuit preventing in
all conditions the power supply from catastrophic failures. Even the 1.8V output is well
protected against shorts, in fact figures Figure 22. and Figure 23. are relevant to a short at
minimum and maximum mains voltage. Because the coupling between the 1.8V and the
auxiliary windings is poor, to help the circuit enter in burst mode the circuitry based on Q2 and
18/31
AN2242
4 Functional Checking
Q3 has been added. This circuit senses the output voltage and drive the circuit to work in hiccup mode if the 1.8V output voltage disappears
Figure 22. 1.8V OUTPUT SHORT at 90 VAC
CH1: DRAIN VOLTAGE
CH2: VPIN12(Vcc)
4.5
Figure 23. 1.8V OUTPUT SHORT at 265 VAC
CH3: 1.8 Vout
CH4: ISHORT CIRCUIT
Over Voltage Protection
A protection that all power supplies must have is that against the failure of the feedback
circuitry. If this occurs, the SMPS output voltages can get high values, depending on the load
on each output and the transformer coupling between the windings. Consequently, the
rectifiers and the output capacitors are overstressed and they can be destroyed. To avoid this
SMPS failure, a dedicated low-cost circuit has been added that senses the auxiliary voltage,
thus providing a protection threshold not as dependent on the mains voltage or the load. This
signal is connected to the L6668, pin 7 (DIS), dedicated to a latched protection of the circuit, as
needed to properly protect the power supply from OVP or OTP. The IC pin #7 is the noninverting input of a comparator having the inverting input internally referenced to 2.2V (typ.). As
the voltage on the pin exceeds the threshold, the L6668 stops the operation and its
consumption is reduced to a low value. The status is latched until the Vcc goes below the
UVLO threshold. To remain in the latch status, the L6668 internal HV generator is activated
periodically so that the Vcc oscillates between the start-up threshold VccON and VccON - 0.5V.
The SMPS can restart after the disconnection of the converter from the mains and the Vcc pin
decreases below the UVLO threshold. Figure 24. depicts the circuit behaviour described
above. During a feedback loop failure, the board OVP circuitry voltage intervention threshold
allows the 12V output to rise up to 16.8V at 115Vac, and doesn't change significantly with the
input voltage or the load.
19/31
AN2242
4 Functional Checking
Figure 24. OVP at 115 VAC - 60Hz
CH1: VPIN7 (OVP)
CH2: VC19(Vaux)
CH3: +12 Vout
20/31
AN2242
5
5 Conducted Noise Measurements (Pre-Compliance Test)
Conducted Noise Measurements (Pre-Compliance
Test)
The following pictures are the conducted noise measurements at full load and 230Vac mains
voltage, made on phase and neutral line with Peak detection. The limits shown in the diagrams
are the EN55022 CLASS B ones, which is the most common rule for video domestic
equipments, such as Set-Top boxes. As clearly visible in the diagrams there is a good margin
of the measures with respect to the limits.
Figure 25. Conducted Noise Measurements - Phase A
Figure 26. Concucted Noise Measurements - Phase B
21/31
AN2242
6 Thermal Measures
6
Thermal Measures
In order to check the design reliability, a thermal mapping by means of an IR Camera was
done. Here below the thermal measures of the component board side at nominal input voltage
are shown. Some pointers visible on the pictures have been placed across key components or
components showing high temperature. The correlation between measurement points and
components is indicated on the right of both figures.
TAMB = 28 degC for all measures
Figure 27. 115Vac-Max Load
A
B
C
D
E
F
G
H
83.70°C E= 0.95
58.29°C E= 0.95
116.60°C E= 0.95
75.67°C E= 0.95
73.64°C E= 0.95
98.34°C E= 0.95
73.85°C E= 0.95
69.91°C E= 0.95
R1 (NTC)
D1 (BRIDGE)
R7 (CLAMP)
T1 (WINDING)
T1 (FERRITE)
D2
D10
D12
Figure 28. 230Vac-Max Load
A
B
C
D
E
F
94.63°C E= 0.95
69.85°C E= 0.95
67.62°C E= 0.95
97.50°C E= 0.95
76.15°C E= 0.95
69.29°C E= 0.95
R7 (CLAMP)
T1 (WINDING)
T1 (FERRITE)
D2
D10
D12
The thermistor, bridge and output diodes temperature rise are compatible with the reliable
operation of the components. Resistor R7 may need a bigger package to decrease its thermal
resistance. All other components of the board are working within the temperature limits
assuring a reliable long term operation of the power supply.
22/31
AN2242
7
7 Part List
Part List
Table 7.
Des
Part List
Part Type/
Part Value
Description
Supplier
C10 470uF-25V YXF ALUMINIUM ELCAP - YXF SERIES - 105°C
RUBYCON
C11
RUBYCON
100uF-25V YXF ALUMINIUM ELCAP - YXF SERIES - 105°C
C12 100N - 50V
CERCAP - GENERAL PURPOSE
AVX
C14 100N - 50V
CERCAP - GENERAL PURPOSE
AVX
C15 100N - 50V
CERCAP - GENERAL PURPOSE
AVX
C16 100N - 50V
CERCAP - GENERAL PURPOSE
AVX
C17 100N - 50V
CERCAP - GENERAL PURPOSE
AVX
C18 220N-X2
X2 FILM CAPACITOR - R46-KI 3220 00 L2M
ARCOTRONICS
C19 47uF-50V YXF
ALUMINIUM ELCAP - YXF SERIES - 105°C
RUBYCON
C20 82uF-400V
SMH400VN82xx22A - ALUMINIUM ELCAP - SMH
SERIES - 85°C
NIPPON CHEMICON
C21 10N-400V
R66MD2100AA6-K - METALLIZED POLYESTER FILM
CAP.
ARCOTRONICS
C22 1000uF-16V
YXF
ALUMINIUM ELCAP - YXF SERIES - 105°C
RUBYCON
C23 1000uF-16V
YXF
ALUMINIUM ELCAP - YXF SERIES - 105°C
RUBYCON
C24 220uF-16V YXF ALUMINIUM ELCAP - YXF SERIES - 105°C
RUBYCON
C27 100uF-25V YXF ALUMINIUM ELCAP - YXF SERIES - 105°C
RUBYCON
C28 100uF-25V YXF ALUMINIUM ELCAP - YXF SERIES - 105°C
RUBYCON
C29 100uF-25V YXF ALUMINIUM ELCAP - YXF SERIES - 105°C
RUBYCON
C30 2N2 - 50V
CERCAP - GENERAL PURPOSE
AVX
C31 100N - 50V
CERCAP - GENERAL PURPOSE
AVX
C32 100N - 50V
CERCAP - GENERAL PURPOSE
AVX
C33 10N - 50V
CERCAP - GENERAL PURPOSE
AVX
C34 220P - 50V
CERCAP - GENERAL PURPOSE
AVX
C35 2200uF-16V
YXF
ALUMINIUM ELCAP - YXF SERIES - 105°C
RUBYCON
C36 470P - 50V
CERCAP - GENERAL PURPOSE
AVX
C37 3N3 - 50V
CERCAP - GENERAL PURPOSE
AVX
C38 100N - 50V
CERCAP - GENERAL PURPOSE
AVX
C39 100N - 50V
CERCAP - GENERAL PURPOSE
AVX
C40 10uF-50V YXF
ALUMINIUM ELCAP - YXF SERIES - 105°C
RUBYCON
23/31
AN2242
7 Part List
Table 7.
Des
Part List
Part Type/
C41 10uF-50V YXF
24/31
Description
Part Value
ALUMINIUM ELCAP - YXF SERIES - 105°C
Supplier
RUBYCON
C5
DE1E3KX222M 2N2 - Y1 SAFETY CAP.
MURATA
C7
1N0 - 200V
KEMET
C9
470uF-25V YXF ALUMINIUM ELCAP - YXF SERIES - 105°C
RUBYCON
D1
2W06G
SINGLE PHASE BRIDGE RECTIFIER
VISHAY
D10 STPS10L60FP
POWER SCHOTTKY RECTIFIER
STMicroelectronics
D12 1N5821
LOW DROP POWER SCHOTTKY RECTIFIER
STMicroelectronics
D13 LL4148
FAST SWITCHING DIODE
VISHAY
D16 LL4148
FAST SWITCHING DIODE
VISHAY
D2
STPS8H100FP
HIGH VOLTAGE POWER SCHOTTKY RECTIFIER
STMicroelectronics
D5
BAV103
FAST SWITCHING DIODE
VISHAY
D6
BAV103
FAST SWITCHING DIODE
VISHAY
D7
STTH1L06U
ULTRAFAST HIGH VOLTAGE RECTIFIER
STMicroelectronics
D9
STPS1L60A
LOW DROP POWER SCHOTTKY RECTIFIER
STMicroelectronics
F1
FUSE T2A
FUSE 2 AMP. TIME DELAY
WICKMANN
J1
MKDS 1,5/ 25,08
PCB TERM. BLOCK, SCREW CONN., PITCH 5MM - 2
WAYS
PHOENIX CONTACT
J2
MPT 0,5/ 8-2,54 PCB TERM. BLOCK, SCREW CONN., PITCH 5MM - 8
WAYS
PHOENIX CONTACT
L1
HF2430203Y1R0-T01
COMMON MODE CHOKE COIL
TDK
L2
2u7-ELC08D
POWER INDUCTOR
PANASONIC
L3
2u7-ELC08D
POWER INDUCTOR
PANASONIC
L4
22uH-RCH654
POWER INDUCTOR
SUMIDA
L5
2u7-ELC08D
POWER INDUCTOR
PANASONIC
Q1
STP4NK60ZFP N-CHANNEL POWER MOSFET
STMicroelectronics
Q2
BC847B
SMALL SIGNAL NPN TRANSISTORS
STMicroelectronics
Q3
BC847B
SMALL SIGNAL NPN TRANSISTORS
STMicroelectronics
Q4
BC847B
SMALL SIGNAL NPN TRANSISTORS
STMicroelectronics
Q5
BC847B
SMALL SIGNAL NPN TRANSISTORS
STMicroelectronics
R1
NTC_10R S236 NTC RESISTOR P/N B57236S0100M000
200V CERCAP - GENERAL PURPOSE
EPCOS
R10 10K
SMD STANDARD FILM RES - 1/8W - 1% - 100ppm/°C
BC COMPONENTS
R12 10K
SMD STANDARD FILM RES - 1/8W - 1% - 100ppm/°C
BC COMPONENTS
R13 36K
SMD STANDARD FILM RES - 1/8W - 5% - 250ppm/°C
BC COMPONENTS
R14 30K
SMD STANDARD FILM RES - 1/4W - 5% - 250ppm/°C
BC COMPONENTS
AN2242
7 Part List
Table 7.
Des
Part List
Part Type/
Part Value
Description
Supplier
R15 6K2
SMD STANDARD FILM RES - 1/4W - 5% - 250ppm/°C
BC COMPONENTS
R16 1K0
SMD STANDARD FILM RES - 1/8W - 5% - 250ppm/°C
BC COMPONENTS
R17 82R
SMD STANDARD FILM RES - 1/8W - 5% - 250ppm/°C
BC COMPONENTS
R18 0R47
SFR25 AXIAL STANDARD FILM RES - 0.4W - 5% 250ppm/°C
BC COMPONENTS
R19 0R47
SFR25 AXIAL STANDARD FILM RES - 0.4W - 5% 250ppm/°C
BC COMPONENTS
R2
PR01 AXIAL STANDARD FILM RES - 1W - 5% 250ppm/°C
BC COMPONENTS
R20 1K8
SMD STANDARD FILM RES - 1/4W - 1% - 100ppm/°C
BC COMPONENTS
R21 3K9
SMD STANDARD FILM RES - 1/8W - 5% - 250ppm/°C
BC COMPONENTS
R22 27K
SMD STANDARD FILM RES - 1/8W - 5% - 250ppm/°C
BC COMPONENTS
R23 1K0
SMD STANDARD FILM RES - 1/8W - 5% - 250ppm/°C
BC COMPONENTS
R24 1K0
SMD STANDARD FILM RES - 1/4W - 1% - 100ppm/°C
BC COMPONENTS
R25 3K3
SMD STANDARD FILM RES - 1/8W - 1% - 100ppm/°C
BC COMPONENTS
R26 1K0
SMD STANDARD FILM RES - 1/8W - 1% - 100ppm/°C
BC COMPONENTS
R27 5K6
SMD STANDARD FILM RES - 1/8W - 5% - 250ppm/°C
BC COMPONENTS
R28 1K0
SMD STANDARD FILM RES - 1/8W - 5% - 250ppm/°C
BC COMPONENTS
R29 10K
SMD STANDARD FILM RES - 1/8W - 5% - 250ppm/°C
BC COMPONENTS
R30 270R
SMD STANDARD FILM RES - 1/8W - 5% - 250ppm/°C
BC COMPONENTS
R32 1K0
SMD STANDARD FILM RES - 1/4W - 5% - 250ppm/°C
BC COMPONENTS
R33 1K0
SMD STANDARD FILM RES - 1/4W - 5% - 250ppm/°C
BC COMPONENTS
R34 1K0
SMD STANDARD FILM RES - 1/4W - 5% - 250ppm/°C
BC COMPONENTS
R35 1K0
SMD STANDARD FILM RES - 1/8W - 5% - 250ppm/°C
BC COMPONENTS
R36 3K3
SMD STANDARD FILM RES - 1/8W - 5% - 250ppm/°C
BC COMPONENTS
R4
4K7
SFR25 AXIAL STANDARD FILM RES - 0.4W - 5% 250ppm/°C
BC COMPONENTS
R5
470K
SMD STANDARD FILM RES - 1/4W - 5% - 250ppm/°C
BC COMPONENTS
R6
330K
SMD STANDARD FILM RES - 1/4W - 5% - 250ppm/°C
BC COMPONENTS
R7
33K-2W
PR02 AXIAL STANDARD FILM RES - 2W - 5% 250ppm/°C
BC COMPONENTS
R8
33R
PR02 AXIAL STANDARD FILM RES - 2W - 5% 250ppm/°C
BC COMPONENTS
T1
SRW28LECE01 H117
POWER TRANSFORMER
TDK
U2
L6668
PRIMARY CONTROLLER
STMicroelectronics
3R9
25/31
AN2242
7 Part List
Table 7.
Des
26/31
Part List
Part Type/
Description
Part Value
Supplier
U3
SFH617A-4
OPTOCOUPLER
INFINEON
U4
TS2431ILT
PROGRAMMABLE SHUNT VOLTAGE REFERENCE
STMicroelectronics
HS1 LS220
Q1 HEAT SINK
ABL ALUMINIUM
COMP.
HS2 507302
D2 HEAT SINK
AAVID
THERMALLOY
HS3 507302
D10 HEAT SINK
AAVID
THERMALLOY
AN2242
8
8 PCB Layout
PCB Layout
Figure 29. Silk Screen -Top Side
Figure 30. Silk Screen -Bottom Side
Figure 31. Copper Tracks
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AN2242
9 Transformer Specification
9
9.1
Transformer Specification
●
APPLICATION TYPE: Consumer, Home Appliance
●
TRANSFORMER TYPE: Open
●
WINDING TYPE: Layer
●
COIL FORMER: Horizontal type, 6+6 pins
●
MAX. TEMP. RISE: 45°C
●
MAX. OPERATING AMBIENT TEMP.: 60°C
●
MAINS INSULATION: ACC. WITH EN60065
Electrical Characteristics
●
CONVERTER TOPOLOGY: Flyback, CCM/DCM Mode
●
CORE TYPE: EER28L - PC40 or equivalent
●
TYPICAL OPERATING FREQ.: 65kHz
●
PRIMARY INDUCTANCE: 910 µH ±10% at 1kHz - 0.25V (1)
●
LEAKAGE INDUCTANCE: 15 µH MAX at 100kHz - 0.25V (2)
●
MAX. PEAK PRIMARY CURRENT: 1.65 Apk
●
RMS PRIMARY CURRENT: 0.65 ARMS
Note: 1 Measured between pins 1-3
2 Measured between pins 1-3 with all secondary windings shorted
Figure 32. "Transformer Electrical Diagram
12
+12V
11
+5V
10
1
PRIM
9
3
+1.8
5
AUX
6
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8
+3.3
7
AN2242
9 Transformer Specification
Table 8.
Winding Characteristics
PINS
O/P RMS
CURRENT
WINDING
NUMBER OF
TURNS
WIRE TYPE
3-1
PRIMARY - A
0.32 ARMS
95
G2 - 2X Φ 0.23mm
12-11
12V
2.3 ARMS
9
G2 - 3X Φ 0.45mm
11-10
5V
3 ARMS
7 SPACED
G2 - 3X Φ 0.45mm
9-8
3.3V
0.6 ARMS
2
G2 - 3X Φ 0.45mm
8-7
1.8V
2.1 ARMS
3
G2 - 3X Φ 0.45mm
3-1
PRIMARY
0.32 ARMS
95
G2 - 2X Φ 0.23mm
5-6
AUX
0.05 ARMS
17 SPACED
G2 - Φ 0.23mm
Figure 33. Winding Position
4
4
AUX
COIL FORMER
Note:
Primaries A & B are in parallel
9.2
Mechanical Aspect
9.3
PRIMARY - B
1.8V – 3.3V
5V
12V
PRIMARY - A
INSULATING
TAPE
●
MAXIMUM HEIGHT FROM PCB: 30mm
●
COIL FORMER TYPE:HORIZONTAL, 6+6 PINS (PINS #2 and #4 ARE REMOVED)
●
PIN DISTANCE: 5mm
●
ROW DISTANCE: 30 mm
●
PINS #3 and #4 ARE REMOVED
●
EXTERNAL COPPER SHIELD: 12mm WIDTH
Manufacturer
TDK Electronics Europe - Germany
Transformer P/N: SRW28LEC-E01H117
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AN2242
10 Revision History
10
30/31
Revision History
Date
Revision
05-Dec-2005
1.0
Changes
First edition
AN2242
10 Revision History
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