AL1771/1772

Document number: DS41314 Rev. 1 - 2

11 of 24

www.diodes.com

August 2018

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AL1771/1772

Functional Description

The AL1771 and AL1772 are PFC controller +single/dual-channel constant-current regulators optimized for 1-channel Dimmable White and 2-

channel Tunable White Smart Connected Lighting (SCL) applications. AL1771/1772 implements a 2-stage 1-chip topology optimized for Smart

Connected Lighting (SCL) applications. It integrates both Stage 1 (High PFC AC-to-Constant Voltage CV Power Conversion) and Stage 2 (CV-to-

Constant Current CC for Channel Current Mixing) inside a single chip (TSSOP-16EP (Type DX). The PFC Controller provides high Power Factor

Correction (PFC) while consuming low standby current to meet Energy Star low standby power requirement for SCL products. The Linear LED

driver regulates the LED currents and supports high performance PWM dimming.

PFC Controller

The PFC constant voltage controller operates with constant on time to achieve high power factor. It adopts the Quasi-Resonant (QR) mode valley

switching method to reduce switching loss and improve EMI performance.

1.

Start-up

After AC supply is powered on, the capacitor C3 across AVCC and GND pins will be charged up by BUS voltage through a start-up resistor R7.

To accelerate the start-up process, the COMP voltage is internally pulled up and clamped high, leading to large MOSFET duty cycle and fast

turns to be modulated by the external compensation network.

PWM

Internal COMP

External COMP

Figure 5. Start Up Waveform

2.

Constant Voltage Operation

As to constant-voltage (CV) operation mode, the PFC controller detects the auxiliary winding voltage at FB pin to regulate the output voltage. The

auxiliary winding voltage is coupled with secondary side winding voltage, so the auxiliary winding voltage at D3 conduction time is:

Where:

R5 and R6 that is shown as Figure 1 divide reflected voltage.