1-5
1-20.
SCR CONTROLLED RECTIFIER CIRCUIT.
1-21.
The ac line voltage is rectified into a main dc supply for the modulator and amplifier cirĆ
cuitry by an SCR controlled bridge rectifier circuit. Primary ac power for the main dc
supply is applied to ac line filter FL1. FL1 is a modular line filter designed to protect the
circuitry from EMI. The ac from filter FL1 is applied to fuses F1 and F2. The fuses pro-
tect the power supply circuitry from over-current conditions. Metal-Oxide-Varistor
MOV1 prevents damage to the rectifier circuitry from ac line voltage surge potentials.
1-22.
The SCR controlled rectifier circuit consists of diodes D15 through D17 and SCRs D13
and D14. The rectifier circuit is controlled by the soft-start control circuit. When power
is required from the circuit, the soft-start circuit will output synchronized ac line pulses
to SCRs D13 and D14. The SCRs will respond by slowly biasing the rectifier circuit on.
The rectifier will output an unregulated and unfiltered dc supply at a maximum of 300V
to an inductor and capacitor filter network located on the power supply panel.
1-23.
FILTER CIRCUIT.
1-24.
The output of the rectifier circuit is applied to a filter network consisting of inductor L1
and capacitors C24 through C27. The filter is designed to remove the ripple in the supply.
The output of the capacitor network generates the positive leg of the B supply. The B supĆ
ply is the main operating supply for the RF power modules. The negative leg of the B
supply is generated by a switching regulator circuit (refer to the following text).
1-25.
POWER SUPPLY ENABLE CIRCUIT.
1-26.
The power supply is controlled by a: 1) power supply enable signal from the controller
and 2) power supply mute signal from the modulator circuit boards. When power supply
operation is required, the controller will output a LOW power supply enable signal to optiĆ
cal coupler U8. With no mute signals present, U8 will output a HIGH to AND gate U12A.
With a HIGH ac OK signal from U9 indicating the presence of ac power and no power
supply faults, U12A will output a HIGH to U12B. With a HIGH from U21A/U21B, U12B
will output a HIGH to U12C and to Q12. With a HIGH from U14 indicating the crowbar
circuit is off, U12C will output a HIGH after a one second delay to: 1) transistor Q10,
2) AND gate U12D, and 3) NAND gate U21C. The HIGH biases Q12 and U15 on to dis-
able the crowbar circuit. Q10 will respond by routing a HIGH power supply enable signal
to optical coupler U1. U1 will output a dc voltage to enable the power supply soft-start
circuit. AND gate U12D will output a HIGH to transistor Q11. The HIGH biases Q11 on
to enable regulator controller U13 and bias Q13 off.
1-27.
When a power supply mute operation is required, an RF power module modulator circuit
board will output a mute signal to optical coupler U8. U8 will output a LOW to AND gate
U12A. With a HIGH ac OK signal from U9, U12A will output a LOW to U12B. U12B will
output a LOW to U12C and to Q12. The LOW biases Q12 and U15 off to enable the crowĆ
bar circuit. U12C will output a LOW to: 1) transistor Q10, 2) AND gate U12D. Q10 will
be biased off to terminate power supply operation by disabling the drive to the SCR rectifiĆ
er circuit. U12D will disable Q11 which allows a HIGH to disable regulator controller
U13 and bias Q13 on. Q13 will output a LOW to disable the fault detection circuit to preĆ
vent erroneous fault indications during mute conditions.
1-28.
SWITCHING REGULATOR CIRCUIT.
1-29.
The B supply is regulated and controlled by a switching regulator circuit. The switching
regulator circuit generates the - leg of the B supply and consists of: 1) a low voltage pow-
er supply circuit, 2) a power control network, 3) optical coupler U17, 4) inverting buffer
U19, and 5) switching regulator transistors Q21 and Q22.
