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LD7576JPN 数据表(PDF) 10 Page - Leadtrend Technology |
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LD7576JPN 数据表(HTML) 10 Page - Leadtrend Technology |
10 / 22 page LD7576/76H/76J/76K 10 Leadtrend Technology Corporation www.leadtrend.com.tw LD7576-DS-04a December 2009 Application Information Operation Overview As long as the green power requirement becomes a trend and the power saving is getting more and more important for switching power supplies and switching adaptors, the traditional PWM controllers are not able to support such new requirements. Furthermore, the cost and size limitation forces the PWM controllers to powerfully integrate more functions, thereby reducing the external part count. The LD7576X series is ideal for these applications to provide an easy and cost effective solution; and its detailed features are described as below. Internal High-Voltage Startup Circuit and Under Voltage Lockout (UVLO) R1 OUT CS VCC GND LD7576X C1 Cbulk D1 Rs COMP Vin HV Fig. 13 Traditional circuits provide the startup current through a startup resistor to power up the PWM controller. Nevertheless, it consumes too significant power to meet the current power saving requirement. In most cases, startup resistors carry large resistance, which causes longer startup time. To achieve the optimized topology, as shown in figure 13, LD7576X series is implemented with a high-voltage startup circuit for such requirement. During startup, a high-voltage current source sinks current from the bulk capacitor to provide the startup current as well as to charge the Vcc capacitor C1. During the startup transient when the Vcc is lower than the UVLO threshold, the high-voltage current source is enabled to supply 1mA current. Meanwhile, the Vcc supply current is as low as 100 μA such that most of the HV current is adopted to charge the Vcc capacitor. By using such configuration, the turn-on delay time will be almost the same no matter under low-line or high-line condition. As the Vcc voltage rises higher than UVLO(on) to power on the LD7576X series and further to deliver the gate drive signal, the high-voltage current source is disabled and the supply current is solely provided from the auxiliary winding of the transformer. Therefore, it eliminates the power loss on the startup circuit and performs highly power saving. An UVLO comparator is embedded to detect the voltage on the Vcc pin and to ensure the supply voltage high enough to power on the LD7576X series PWM controller and to drive the power MOSFET. As shown in Fig. 14, a hysteresis is provided to prevent undesired shutdown from the voltage dip during startup. The turn-on and turn-off threshold levels are set at 16V and 10.0V, respectively. Vcc UVLO(on) UVLO(off) t t HV Current 1mA Startup Current (<100uA) Vcc current ~ 0mA (off) Operating Current (Supply from Auxiliary Winding) Fig. 14 |
类似零件编号 - LD7576JPN |
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类似说明 - LD7576JPN |
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