Dc Power Supply N418 - Sailor RT2047 Technical Manual

2 CIRCUIT DESCRIPTION

2.15 DC POWER SUPPLY N418

GENERAL DESCRIPTION
The power supply N418 is constructed for supplying a 13.2V VHF from a 24V DC system. In order to obtain
high efficiency regulation is obtained by the switch mode principle.
TECHNICAL DATA:
The power supply N418 is controlled from the connected VHF unit by on/off.
Input voltage
Output voltage
Output current
Operation temperature range
Switch frequency
2.15.1 PRINCIPLE OF OPERATION
The on/off information from the connected VHF unit is controlling the N418 via pin 4 of P201.
The regulation takes place after the forward principle, which means that during the "on time" of the
switching element T202, the coil L105 is connected directly from the input to the output.
When switching element T202 is turned off the stored energy in L105 maintains the supply current to the
output via diode D201.
Regulation of the output voltage takes place via pulse width regulation, which means that the "on time"
(duty cycle) of the switching element T202 is controlled. The regulation gives long "on time" when the input
voltage is low, a further decrease of input voltage allows the T202 to be on, continuously. If the input
voltage is increased the "on time" is shortened.
In order to limit the rush in current during switching there's a built in soft start, thus enabling a short "on
time" for T202 immediately after the switching on, and afterwards the "on time" is slowly increased.
Current limitation is established by sensing the voltage over the resistor R126. If the current is too high,
the pulse width is shortened in order to reduce the output current.
2.15.2 CIRCUIT DESCRIPTION
When N418 is switched on R113 is connected to the negative terminal of the supply in the VHF and
transistor T102 is on. IC101 starts functioning. The voltage level on pin 9 of IC101 controls the duty cycle
and the voltage always starts from low level because C108 is discharged via transistor T101 every time
the N418 is switched off.
Pin 16 of IC101 is a 5V reference voltage, which is divided down in R104, R105, and R106 and connected
to pin 2 (the non-inverted input). Pin 1 of IC101 is connected to the output voltage via voltage divider R117
and R122, the two levels are compared and the pulse width is controlled so that the output voltage stays
stable. Pin 11 and 14 are outputs connected in parallel, the signal forms the drive signal for the switching
element T202 via T103 and T201 . The components L103, L104, R123, R124, R125, and C121 control
the on and off switching of T202 and D201. D105 prevents inverse polarity across T202.
The IC102 senses the output current via the voltage over R126. If this voltage is too high - due to an
overload - the pulse width and thus the output voltage is reduced.
The capacitors and coils in input and output suppresses switching noise enabling N418 to fulfill the CISPR
noice regulations.
9543
16-32V DC
13.2V DC
Max. 7A DC
-15 - +55 °C
Approx 40 KHz
RT2047 DSC - PART II
PAGE 2-39