Specifications

5/2/2013 888-2500-001 4-7
WARNING: Disconnect primary power prior to servicing.
Section 4 Theory of Operation
DAX-1/DAX-3
4.4.1.1 AC Mains Input and Transformer Primary
The AC input of the B+ power supply is configured to be powered from 220, 230, or
240VAC. Three taps on the primary of the input transformer allow the selection of the
correct AC mains voltage input. +/-5% taps are provided on the transformers AC input
in order to accommodate installations with low or high AC line voltages.
4.4.1.2 AC Mains Input Protection
The AC mains input for the DAX-1 is protected from over-current by an 15A circuit
breaker, and the DAX-3 by a 30A circuit breaker. This circuit breaker also acts as the
transmitter’s AC mains ON/OFF switch. The AC mains input of the transmitter is also
protected from voltage surges and spikes by MOVs connected between line to neutral,
line to ground, and from neutral to ground.
4.4.1.3 Transformer Secondary
The secondary of the AC input transformer has two Controller-selected taps, allowing
the power supply to provide two DC voltage outputs. The two DC output voltages
provided are +200V, and +300V.
NOTE:
Depending on the transmitter output power setting, the control system will adjust
this 200Vdc supply between 200Vdc and 80Vdc in order to optimize the trans-
mitter’s RF performance at lower power levels.
A 40A SPDT relay is used to connect the appropriate secondary tap to the full-wave
SCR bridge rectifier, with only one secondary tap selected at a time. This relay is
actuated via a MOSFET controlled by the FPGA main controller.
4.4.1.4 SCR Rectifier
The selected transformer secondary tap feeds a full-wave bridge rectifier, which
contains two SCRs, two rectifier diodes, and one free-wheeling diode. The free-
wheeling diode provides an electrical path for inductive turn-off currents.
SCR firing control, voltage regulation, and B+ power supply enable/disable functions
are provided by a vendor supplied PCB. The ENERPRO SCR firing board used in this
design is the FCRO2100, which also provides the voltage regulation function.
4.4.1.5 Output Voltage Regulation
The output voltage of the B+ supply is regulated by continuously adjusting the
conduction angle of the SCRs in the bridge rectifier. If the DC output voltage sags, the