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AN2512 Datasheet(PDF) 5 Page - STMicroelectronics |
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AN2512 Datasheet(HTML) 5 Page - STMicroelectronics |
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5 / 38 page  AN2512 Application description 5/38 Figure 1. Top layer circuit schematic 1.3 Power supply circuit A 3-phase 4-wire bridge is used for mains rectification because the neutral rectification is needed to ensure proper operation in case of missing neutral connection or neutral miss- wiring. A varistor is connected between each line and neutral to guarantee pulse voltage test immunity according to the EN62052-11 standard. The input EMI filter is a simple, undamped LC-filter for both differential and common mode noise suppression. The circuit for input voltage limiting is connected between the input EMI filter and the bulk capacitor C4. Such a circuitry includes a Power MOSFET and a self driven control section. The MOSFET Q1 is a standard N-Channel 500 V 3.3 Ω in D-PAK package, mounted on a small copper area to improve thermal performance. The self driven control section consists of a voltage divider and zener diodes. The resistors R1, R2 and R3 ensure the gate-source charge for the switch, while the zener diodes D3 and D4 set the maximum voltage value (360 V) across the bulk capacitor. An NTC limits the inrush current and ensures Q1 operation inside its safe operating area. The Flyback converter is based on VIPer12A, a product in the VIPerX2A family, which combines a dedicated current mode off-line PWM controller with a high voltage power MOSFET on the same silicon chip. The switching frequency is fixed at 60 kHz by the IC internal oscillator in order to optimize the transformer size and cost. The transformer reflected voltage has been set to 60 V, providing enough margin for the leakage inductance voltage spike and no snubber circuit is needed which allows consequent cost savings. As soon as the voltage is applied on the input of the converter, the high voltage start-up current source connected to the drain pin is activated and starts to charge the Vdd capacitor C8 through a constant current of 1 mA. When the voltage across this capacitor reaches the Vddon threshold (about 14 V), the VIPer12A starts to switch. During normal operation the PHASE_2 PHASE SDA SCS SCL SYN N P GND VDD LED VOTP CLKIN CLKOUT SMPS SMPS P1 P2 N P3 5V GND 3.3V PHASE_3 PHASE SDA SCS SCL SYN N P GND VDD LED VOTP CLKIN CLKOUT PHASE_1 PHASE SDA SCS SCL SYN N P GND VDD LED VOTP CLKIN CLKOUT VDD VDD VDD 5V VDD 5V VDD VDD P3 VOTPL1 SCSL1 SCSL1 P1 P1 N N VOTPL3 LEDL3 SCSL3 LEDL3 P3 SCSL3 LEDL1 LEDL1 N SDA SCL SDA N SCL CLKIN SYN LEDL2 SYN SCL SYN SYN P2 VOTPL2 LEDL2 P2 SCSL2 SDA SDA SCL SCSL2 SCSL1 SCSL2 SCSL3 VOTPL1 VOTPL2 VOTPL3 SCS VOTP SDA SCL SYN J13 SCSJUMPER 1 2 3 4 5 6 J1 1 2 3 4 5 6 7 8 9 10 J14 JUMPER3 1 2 3 4 5 6 U8B 74HC14A/SO J7 1 J11 1 J8 1 C2 15pF C1 15pF J2 CON20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 J12 1 Y1 4.194304MHz R1 1M J9 1 J5 1 J10 1 U8A 74HC14A/SO 1 2 |
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