Pag. 51
SIRIO 2000T
SIRIO 2000T
SIRIO 2000T
SIRIO 2000T
SIRIO 2000T
Electronic Broadcast Equipment
THE AUXILIARY POWER SUPPLY REGULATOR
Also this small power supply regulator is an high-efficiency, low-voltage switch-mode type. Its input is
derived by the main nominally reg48V.
The main switch-mode regulator is buit around IC1 which controls the conduction duty-cycle of its
internal series-pass power MOSFET to obtain a 28.0 ±0.1 V DC regulated voltage. The oscillation
frequency is fixed, around 100 kHz.
L1 and C26/C27 form the main integration cell, which averages the pulsed voltage at IC1 output. A
second filtering cell, L2, C28/C29 further removes high frequency noise contents from the main regulated
output.
A 30V zener diode, D8, is in parallel with the main regulated output for safety purpose. Should the internal
switch transistor fail short, D8 would break-down blowing the series input fuse on the board, avoiding more
costly overvoltage damages to the rest of the transmitter. It is imperative not to exceed the n28.0V
(+0.1V max) on the main regulated output to avoid overstress on this component and consequent failure.
Neverthless in this transmitter the main regulated voltage is usually set to +20V and limited to 22-23V max,
as needed by the RF driver amplifier to deliver 18 to 20W.
Another lower power switch-mode IC regulator derives the auxiliary reg12.5V voltage (±0.5V/
0.5A, average) and a losely regulated -12.5 ±1V.
The efficiency of the whole circuitry is very high and manages a substantial amount of power versus mains
voltage changes, dissipating little energy, so keeping overall temperature low with no extensive heatsinking,
required by conventional linear regulators.
