AL1692 datasheet(8/15 Pages) DIODES

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AL1692

Document number: DS39008 Rev. 2 - 2

8 of 15

www.diodes.com

September 2017

AL1692

Functional Description and Application Information

Operation

The AL1692 is a single stage, single winding, high efficiency, and high power factor dimmable LED driver controller/drivers for triac dimmable LED

lamp applications. The AL1692 controller with an external MOSFET can support larger power application up to 25W. The AL1692 LED drivers:

AL1692-30BA with 400V/3A and AL1692-20C with 600V/2A internal MOSFET options can cover both 120VAC and 230VAC application.

The AL1692 adopts source-driver technique to decrease the system operating current. It uses a novel method to detect the tOFF time which results

in the removal for the need of an auxiliary winding. The AL1692 operates at boundary conduction mode (BCM) which can ease EMI design and

achieve high efficiency. High power factor (HPF) is achieved by using constant on-time mode; coupled with a closed loop of constant current

control, the AL1692 achieves good line and load regulation.

Start-up and Supply Voltage

Before start-up, the VCC capacitor C4 is charged by the startup resistors (R2, R3) from the high voltage mains. When the start-up voltage is

reached, the AL1692 starts switching. During normal operation, the VCC supply is provided by start-up resisters (R2, R3) and the output voltage

(VOUT) rectified by one diode (D2). In this way the system can provide VCC supply at low dimming angle.

The AL1692 has an internal VCC clamp voltage (typical 15.5V), which is limited by one internal active Zener diode.

When V

CC voltage drops to below the VOPR(MIN), switching is stop. So the device can operate normally when the voltage on VCC pin is between

VOPR(MIN) and VCC clamp voltage.

Protections

Under Voltage Lockout (UVLO)

When the voltage on the VCC pin drops to below VOPR(Min), the IC stops switching. The IC can restart when the voltage on VCC exceeds the

startup voltage (VTH(ST)).

Leading-Edge Blanking (LEB)

To prevent false detection of the peak current of the inductor, a blanking time following switch-on is designed. When the internal switch turns on, a

short current spike can occur because of the capacitive discharge of the voltage over the drain and source. It is disregarded during the LEB time

(tON_MIN).

Cycle-by-cycle Over Current Protection (OCP)

The AL1692 has a built-in peak current detector. It triggers when the voltage on CS pin reaches the peak level VCS_CLAMP. The R5 is connected to

the CS pin to sense the current of the inductor. The maximum peak current (IPEAK(MAX))of the inductor can be calculated as below:





CS CLAMP

PEAK MAX



……………………(1)

The detection circuit is activated after the LEB time. When the detection circuit sense the CS voltage is higher than 1V, the IC will turn off the

switching to limit the output current. It automatically provides protection for the maximum LED current during operation. A propagation delay exists

between over current detection and actual source-switch off, so the actual peak current is a little higher than the OCP level set by the R5.

Over-Voltage Protection and Output-Open Protection (OVP)

The output voltage is sensed by the FB pin, which provides an over-voltage protection (OVP) function. When the output is open or large transient

happens, the output voltage will exceed the rated value (R8, R9). When the voltage exceeds VFB, the over-voltage is triggered and the IC will

discharge VCC. When the VCC is below the UVLO threshold voltage, IC will restart and the VCC capacitor is charged again by start-up resistance. If

the over voltage condition still exists, the system will work in hiccup mode.

Output-Short Protection (OSP)

When LED is shorted, the device cannot detect the tOFF time, and the device controls the system operation at 4kHz low frequency.

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