AMG-LM302 Datasheet, PDF (5/23 Pages) alpha microelectronics gmbh – Ballast Controller for Metal Halide Lamps

AMG-LM302
Ballast Controller for Metal Halide Lamps
5. Block Descriptions
The whole application for a metal halide lamp needs the following major function blocks:
• mains rectification
• PFC
• lamp power regulation
• lamp ignition control
• high voltage bridge
• bridge drivers
The mains rectification and the high voltage bridge are completely built using discrete
components.
There are two basic options to do the bridge drivers, either discrete or integrated. Alpha
recommends the use of a fully integrated full bridge gate driver AMG-DF102.
The AMG-LM302 does have the PFC, lamp power regulation, ignition control and other
subfunctions integrated.
The PFC part of the AMG-LM302 is a standard power factor correction regulator.
The CDM part contains the power and ignition control of the lamp. For power control the lamp
current Iouti and the lamp voltage Vouti get measured and then multiplied to receive the actual
lamp power. The power is then outputed via the CTRLo pin. It can be manipulated and filtered
by external devices and will then get fed (as the actual value) into an error amplifier via the FB
pin. The error amplifier uses an internal 2.5V reference voltage as the set value. The output of
the error amplifier is fed into a current limiter stage and finally outputed via the PWMo pin. The
signal from the PWMo pin eventually drives the buck converter, thus impacting the bridge
voltage and in turn the lamp power.
A capacitor connected to the COP pin sets the frequency of the internal oscillator. The
oscillator frequency eventually determines the switching frequency of the bridge. The oscillator
frequency needs to be double the resonant frequency of the LC low pass filter for the CDM-
lamp. The output BR drives a low and it's corresponding high side transistor. The output nBR
is inverted to BR and drives the other low and high side transistors. A dead time is
automatically inserted before the rising edges of BR and nBR so to avoid shoot through. This
dead time can externally be influenced with a capacitor connected to the CDT pin. The
switching frequency of the oscillator should not be high enough, to avoid audible noise from
the plasma in the lamp. It should not be too high either, cause this will increase power
consumption.
There is a control logic, which senses the state of the lamp. For ignition, it will generate a high
AMG-LM302 Revision: A
29. Jul. 2010 © All rights reserved Page 5 of 23