Electronic Components Datasheet Search |
|
AN-9752 Datasheet(PDF) 2 Page - Fairchild Semiconductor |
|
AN-9752 Datasheet(HTML) 2 Page - Fairchild Semiconductor |
2 / 6 page AN-9752 APPLICATION NOTE © 2011 Fairchild Semiconductor Corporation www.fairchildsemi.com Rev. 1.0.1 • 1/23/13 2 2. AX-CAP® Technology The AX-CAP® discharge function is one of Fairchild Semiconductor’s mWSaver™ technologies offering best-in- class minimum power consumption in no-load and light- load conditions to meet the latest ENERGY STAR specifications and 2013 ErP Standby Power Regulation (less than 0.5 W consumption with 0.25 W load for ATX power and LCD TV power). The EMI filter in the front end of the Switched-Mode Power Supply (SMPS) typically includes a capacitor across the AC line connector, as shown in Figure 2. Most of the safety regulations, such as UL 1950 and IEC61010-1, require the capacitor to be discharged to a safe level within a given time after the power supply is unplugged from the power outlet. Figure 2. Typical Circuit of Line EMI Filter UL1950: voltage across a capacitance greater than 0.1 µF must decay to 37% of the AC input peak voltage in one second for type-A equipment and 10 seconds for type-B equipment. IEC61010-1: The pins must not be hazardous (live) at five seconds after disconnection from the supply. The discharge resistor must comply with Equation (1) to meet the discharge time of less than one second. The power loss of discharge resistor paralleled with X-cap is shown in Equation (2): s R C DIS X DIS 1 ≤ × = τ (1) DIS AC Loss R V P 2 (RMS) = (2) Table 1 shows the relationship between rated output power, typical effective X capacitor value, and power dissipation of the discharge resistor. As the power level increases, the EMI filter capacitor tends to increase and, therefore, requires a smaller discharge resistor to maintain the same discharge time. This typically results in more power dissipation in high-power applications. Power dissipation in the discharge resistor is a major cause of standby power consumption in high-power applications. Table 1. Power Dissipation in Discharge Resistor for Different Rated Power System Effective X-CAP Typical Rated Output Power Discharge Resistor Power Dissipation in Discharge Resistor at 240 VAC for tDIS=1 s 250 nF 20~50 W 4 MΩ 14.4 mW 500 nF 50~100 W 2 MΩ 28.8 mW 1 µF 100~200 W 1 MΩ 57.6 mW 2 µF 200~400 W 500 kΩ 115.2 mW 4 µF 400~800 W 250 kΩ 230.4 mW 8 µF 800~1,600 W 125 kΩ 460.8 mW The innovative AX-CAP® discharge method, a proprietary mWSaver™ technology of Fairchild Semiconductor, was developed to eliminate X-cap discharge resistors while meeting safety requirements. 2.1 Proposed Solution Figure 3 shows the typical application circuit and internal blocks for AX-CAP® technology. It intelligently discharges the filter capacitor only when the power supply is unplugged from the power outlet. Since the AX-CAP discharge circuit is disabled in normal operation, the power loss in the EMI filter can be virtually removed. In normal operation, the line voltage is detected by sensing X capacitor voltage with a switched voltage divider composed of external high-voltage resistor (RHV) and internal resistor (RLS). The switched voltage divider is driven with a very narrow pulse such that the power consumption of the voltage divider can be minimized. Figure 3. AX-CAP ® Circuit Connection of FSB-Series AX-CAP® detects the line disconnection by checking the zero crossing of X capacitor voltage. In normal operation, X capacitor voltage drops down to zero repetitively as long as it is connected to the line. Once the power supply is disconnected from power outlet, the bridge rectifier is reverse biased and the only discharge path for the X capacitor is through the switched voltage divider. Then, the |
Similar Part No. - AN-9752 |
|
Similar Description - AN-9752 |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.COM |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |