Furuno FAR-2107 Series Service Manual page 364

- Heater power supply circuit
U21 is the switching power supply for the Magnetron heater outputting 7.5
VDC/1.3 A and operates at 125kHz. Q22 and C23 connected to the SS terminals of
U21 are circuits for output control and soft start. U21 is controlled by HEATER
VLT signals from the RFC board and changes heater voltage during "ST-BY" and
during "TX" in long pulses. This is intended to reduce the heater voltage during
"TX" in long pulses for extending the life of the Magnetron. The heater voltage is
adjusted at R28 during "ST-BY" and at R32 during "TX" in long pulses. Since the
heater voltage differs according to types (Magnetron), JP21 is provided to correct
different voltages.
Note: HEATER OFF signal is outputted from the RFC board to stop the heater
voltage but it is not used.
- +5 V power supply circuit
U31 is the switching power supply for +5 VDC/0.5 A and operates at 250 kHz.
Q31 and C33 connected to the SS terminals of U31 are circuits for output control
and soft start. The soft start function is provided to suppress the supply rush
current of the load. R47, R48 and U22 are output overcurrent protection detection
circuits which control the SS terminals of U31 and stops outputs when the current
of 0.8 A to 1.0 A runs through the +5 VDC line. This overcurrent protection circuit
is automatically reset.
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7.2 Antenna Unit