IN-PLUG

© Copyright 2005-2007 - ASIC Advantage, Inc. – All rights reserved

- Revision 11 – April 02, 2007

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Application Information

The IPS401 is intended for use as an LED controller in non-isolated applications directly connected to the AC line. It

operates as a boost-converter that controls output current rather than voltage. Constant current ensures controlled

brightness and consistent spectral output from the LEDs.

POWERING THE CHIP (Pin 5 – VCC, Pin 1 – GND)

The VCC pin acts like a 10V zener. The chip requires about 100uA to start and about 660 uA to operate. This does

not include the current used to drive the gate of the FET. The recommended value of startup resistor R6 is 750k

ohms. This will provide the 100uA of startup current when the input is above 750k x 100uA = 75 volts. Using a value

of 47uF for Vcc capacitor C5 should give sufficient holdup time for the chip to begin operating before the bias winding

on the boost inductor begins supplying power. Note that the frequency and duty-cycle on the bias winding will vary as

the driver follows the input voltage. The polarity of the bias winding does not matter if connected as shown in the

application schematic. The suggested values for the bias supply components are C4 = 4.7nF, D7/D8 = 1N4148, and

R4 =100 ohms. The current consumption during normal operation is 660 microamps maximum plus the gate drive

current.

During debug, it can be helpful to do testing with power supplied to the chip from a lab power supply. It is suggested

that PCB designs have a place to connect clips to the VCC and GND traces to facilitate this. It is important that an

external supply connected in this way be set in “constant current” or “current limited” mode. Typical settings are 10

milliamps and 12 volts.

AC LINE SENSE (Pin 4 – VLINE)

The amplitude of the rectified AC input is sensed through dropping resistor R5. The suggested value for R5 is 820k

for wide input range (85-265VAC) applications. The input impedance of the VLINE pin is about 20k ohms (plus two

diode drops) to ground.

GATE DRIVE (Pin 3 – GDRV)

The GDRV pin switches between VCC and GND with about 30 ohms resistance to VCC and about 20 ohms

resistance to GND. A series resistor between this pin and the gate of the FET of about 100 ohms is suggested to

control the turn-on and turn-off speed of the FET and thereby reduce the conducted and radiated EMI. Generally, a

higher resistor value means slower switching of the FET, lower efficiency, lower EMI, and higher FET losses (more

FET cooling needed).

Figure 7: Start-Up Current Drift over Temperature

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Temperature (°C)