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1、RT7304_PFC功能的LED 驱动IC 立奇LED 驱动方案 Preliminary R7304 1 Primary-Side Regulation PWM Controller for PFC LED Driver General Description RT7304 is an active power factor controller specifically designed for use as a constant current LED driver. It embeds a Critical Conduction Mode (CRM) control that suppo
2、rts high power factor across a wide range of line voltages. By using Primary Side Regulation (PSR), RT7304 controls the output current accurately without a shunt regulator and a photo coupler on the secondary side, reducing the external component count, the cost, and the volume of the driver board.
3、RT7304 embeds comprehensive protection functions for robust designs, including LED open circuit protection, LED short circuit protection, output diode short circuit protection , VDD Under Voltage Lockout (UVLO), VDD Over Voltage Protection (OVP), Over Temperature Protection (OTP), and cycle-by-cycle
4、 current limitation. Ordering Information Application AC/DC LED Lighting driver Features Primary Side Regulation (PSR) Power Factor Correction (PFC) Tight LED Current Regulation ( 5%) Critical Conduction Mode (CRM) Maximum/Minimum Switching Frequency Clamping Maximum/Minimum on Time Limitation Wide
5、VDD Range (up to 25V) Multiple Protection Features: LED Open-Circuit Protection LED Short-Circuit Protection Output Diode Short-Circuit Protection VDD Under V oltage Lockout VDD Over V oltage Protection Over T emperature Protection Cycle-by-Cycle Current Limitation Marking Information 立奇LED 驱动方案 Pre
6、liminary RT7304 2 Simplified Application Circuit 立奇LED 驱动方案 Preliminary RT7304 3 Functional Pin Description Pin No. Pin Name Pin Function 1 GND Ground of the controller. 2 VDD Supply voltage input. The controller will be enabled when VDD exceeds V ON_TH and disabled when VDD is lower than V OFF_TH .
7、 3 GD Gate driver output for external power MOSFET. 4 CS Current sense input. 5 ZCD Zero current detection input. Sense the auxiliary winding of the transformer for detecting demagnetization time of the magnetizing inductance. 6 COMP Output of the internal transconductor. Function Block Diagram 立奇LE
8、D 驱动方案 Preliminary RT7304 4 Operation Constant on-Time Voltage Mode Control Figure 1 shows a typical Flyback converter. When man switch Q 1 is turned on with a fixed on-time T ON , inductor current I L can be calculated by the following equation: ON m in L T L V I = 立奇LED 驱动方案 Preliminary RT7304 5 C
9、lamping Circuit RT7304 provides a clamping circuit at ZCD pin since the voltage on the auxiliary winding is negative when the main switch is turned on. As shown in Figure 4, the lowest voltage on ZCD is clamped at zero. In addition, RT7304 embeds propagating delay compensation through CS pin. A sour
10、cing current I CS (equal to gm_L*I CLAMP ) applies an offset which is proportional to line voltage on CS to compensate the propagating effect. Thus, the total power limit or output current can be equal at high and low line. Figure 5. VDD and UVLO When VDD exceeds 27V (typ.), the PWM output of RT7304
11、 is shut down. In addition, an internal 29V zener diode is used to avoid over voltage stress for the internal circuits. 立奇LED 驱动方案 Preliminary RT7304 6 Over Temperature Protection Internal OTP function will protect the controller itself from suffering thermal stress and permanent damage. When the ju
12、nction temperature exceeds 150C (typ.), the built-in OTP is activated to turn off the main switch. Once the junction temperature drops below 120C (typ.), OTP is deactivated and RT7304 resumes normal operation. 立奇LED 驱动方案 Preliminary RT7304 7 Absolute Maximum Ratings (Note 1) Supply Voltage, VDD - ?0.3V to 30V Gate Driver Output, GD - ?0.3V to 20V Other Pins - ?0.3V to 6V Power Dissipation, P D T A = 25C SOP-8 - 0.625W Package Thermal Resistance (Note 2) SOP-8, JA
