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AL1665 Datasheet(PDF) 8 Page - Diodes Incorporated |
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AL1665 Datasheet(HTML) 8 Page - Diodes Incorporated |
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8 / 17 page  AL1665 Document number: DS41772 Rev. 3 - 2 8 of 17 www.diodes.com March 2020 © Diodes Incorporated AL1665 Application Information The AL1665 is a constant-current high-PF flyback and buck-boost controller with primary side regulation (PSR), targeting LED lighting applications. The device eliminates the optocouplers or the secondary feedback circuits, which is helpful to minimize the cost of the whole system. High power factor is achieved by constant on-time operation. In order to reduce the switching losses and improve EMI performance, quasi-resonant switching mode is applied. The AL1665 integrates multiple protections including UVLO protection, VCC overvoltage protection, output open-voltage protection, overcurrent protection, thermal foldback protection, and overtemperature protection. The AL1665 can support analog and PWM dimming modes. T1 OUT + VCC OUT CS GND U1 R5 R6 R4 D1 C6 RTH AC Input F1 VR1 DB1 C2 L1 C1 RCS R10 FB COMP D2 C5 R14 C7 D3 Q1 CCOMP Aux NTC/ PWM R9 D4 AL1665 ADIM RCOMP CVCC R11 Figure 1. Flyback Application Circuit T1 OUT VCC OUT CS GND R5 R6 R4 D1 C6 RTH AC Input F1 VR1 DB1 C2 L1 C1 RCS FB COMP Q1 Aux NTC/ PWM R9 D4 AL1665 D3 R11 ADIM CCOMP RCOMP CVCC Figure 2. Buck-Boost Application Circuit Start Up After AC supply is powered on, the capacitor CVCC across VCC and GND pin charges up by BUS voltage through a start-up resistor RTH. Once VCC reaches VCC_TH, the internal blocks start to work. VCC is supplied by VBUS until the auxiliary winding of flyback transformer could supply enough energy to maintain VCC above VOPR_MIN. If VCC voltage is lower than VOPR_MIN, the switch turns off. After VCC exceeds VCC_TH, the drive blocks do not start to switch on/off signals until VCOMP is higher than the initial voltage VCOMP_ST, which can be programmed by RCOMP. The formula is shown below. Such design can program startup on time to reduce the startup time or the output overshoot current. COMP ST COMP R A V V 700 4 . 1 _ Where VCOMP_ST is the pre-charged voltage of COMP pin. Figure 1 shows RCOMP. Generally, a big capacitance of CCOMP is necessary to achieve high power factor and stabilize the system loop (1μF to 2μF is recommended). The pre-charged voltage in start-up procedure can be programmed by RCOMP. |
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