ALQ25B50_03 Datasheet, PDF (7/11 Pages) Astec America, Inc – Industry Standard ¼ Brick: 300W DC Transformer

Technical Reference Notes
ALQ25B50 Bus Converter
DC Transformer
Basic Operation and Features
INPUT UNDER VOLTAGE LOCKOUT
To prevent any instability to the converter, which may affect the end system, the ALQ25B50 series have been designed to turn-
on once V_IN is in the voltage range of 41-43 VDC. Likewise, it has also been programmed to turn-off when V_IN drops down to
39-41 VDC.
INPUT OVER VOLTAGE PROTECTION
The ALQ25B50 employs a DC Transformer conversion scheme where the input and output relationship is dictated by the turns
ratio of the windings. The OVP circuit senses the input line and shuts down the entire module once the sensed voltage reaches
the OVP threshold. Restart is possible once the fault is removed and the input power is recycled.
OUTPUT ENABLE
The ALQ25B50 series comes with an Enable pin (PIN 2), which is primarily used to turn ON/OFF the converter. Both a
Positive (no part number suffix required) and a Negative (suffix “N” required) Enable Logic options are being offered. Please
refer to Table 2 for the Part Numbering Scheme.
For Positive Enable, the converter is turned on when the Enable pin is at logic HIGH or left open. The unit turns off when the
Enable pin is at logic LOW or directly connected to -V_IN. On the other hand, the Negative Enable version turns unit on when
the Enable pin is at logic LOW or directly connected to -V_IN. The unit turns off when the Enable pin is at Logic HIGH.
OVER CURRENT PROTECTION (OCP)
The Over Current Protection circuit comes in latching mode. The converter is latched off if the load current on the output
reaches the OCP threshold limit. The OCP latch can be reset either by cycling the input voltage or toggling the Enable signal
for 100ms. Consult factory for Auto-restart option.
OVER TEMPERATURE PROTECTION (OTP)
The Over Temperature Protection circuit will shutdown the converter once the average PCB temperature reaches the OTP
range. This feature prevents the unit from overheating and consequently going into thermal runaway, which may further
damage the converter and the end system. Such overheating may be an effect of operation outside the given power thermal
derating conditions. Restart is possible once the temperature of the sensed location drops to less than 110°C.
MODEL: ALQ25B50 SERIES
SEPTEMBER 11, 2003 - REVISION A (PRELIMINARY)
SHEET 7 OF 11