Front End; Bias Supply; Main Supply - Crown XLS1000 Service Manual

The power supplies of the XLS series of amplifiers are efficient and light weight, but yet
extremely robust switchmode designs. The topology of the main supply employed is a
half-bridge series resonant converter. The use of this topology allows for soft switching
of the main semiconductors Q903 and Q906 reducing dissipation at idle and throughout
the operating power range. Two other buck derived switching power supplies are
employed. One serves as a bias supply for the main power supply and the other generates
the +5V from the low voltage output of the main supply

Front end

This power supply is equipped with an internal EMI filter that both reduces the transfer
of power supply related noises onto the power line, and improves the power supplies
immunity from voltage transients on the power line.
The AC line voltage is converted to DC by a bridge rectifier D901. 120Vac and 100Vac
models use voltage doubler, while 220V and 230-240Vac models use a full wave
rectifier. Z901 determines this operating mode. It is present on the 120Vac and 100V
models, and is open on the 220V and 230-240Vac models
When switch S901 is closed the bulk storage capacitors C911, C912, C955, and C956
begin charging thru the PTC (RT901). This PTC limits the inrush current, eliminating
circuit breaker trips at turn on. After the charging cycle is complete the soft start relay
(K901) bypass the PTC.

Bias Supply

The main supply's integrated control IC & gate driver (U902) is powered by a primary
referenced 15V buck power converter that is supplied by the "V_BULK" rail. The heart
of this bias supply is the Power Integration LinkSwitch-TN control IC (U901). This IC
contains an integrated MOSFET, control circuitry, current limit, and thermal protection.
It provides a regulated 15V during power up, normal operation, brownouts and line
transients.
The Buck converters major components are the integrated MOSFET in U901,
freewheeling diode D903, filter inductor L903, and filter capacitor C915. Voltage
feedback to the control IC is feedback thru D902 which charges C914 only when the
freewheeling diode D903 is conducting. The voltage stored on C914 is scaled down by
R909 and R908 which feed pin #2 of U901. The control loop within U901 adjusts the
duty cycle of the MOSFET in the order of 60,000 times per second such that the voltage
on Pin #2 remains constant. This mechanism regulates the +15V output voltage.

Main supply

The main supply consists of a half-bridge power converter utilizing two IGBT power
devices, a center tapped secondary transformer, a full-wave secondary rectifier, a half