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P2 also provides an unbalanced audio input pin. This unbalanced audio is also protected from RF
interference by using a choke (L3) and suppression capacitor C12. Coupling capacitor C1 removes any DC
component from the audio line before passing the audio to Amplifier U1B. U1B is used as a summing
amplifier to combine all of the audio signals into one unbalanced audio signal for the transceiver. This
amplifier has a gain of 1.
Voltage regulator U3 generates the +5V supply used as signal bias and as an external supply on pin C of
connector P3.
Optocoupler U4 provides electrical isolation between the input data signal from the ESU (External
Synchronising Unit) and the transceiver.
Internal charger PCB
The internal charger operates as a constant voltage current limited source. The input voltage of 17 to 29
volts is stepped down to 16 volts. The battery and the transceiver are connected in parallel. Current in
excess of what is used by the transceiver is available for battery charging. Hence with transceiver off,
maximum (depending upon the source current) of 2 amperes can be available for battery charging. The
input voltage of 17-29 volts is switched by the Q3 (a FET) at high frequency of > 250 KHz. This operates
as a step down converter, with L1, C7 and C8 smoothing the ripple. D4 is a high speed freewheeling diode.
R10, 11 and 27 form a voltage divider for giving feedback voltage to the controller IC U1 (BQ 24700). VR2
and VR1 provide voltage to U1 for setting Input and output current limits, respectively. These currents are
senses by the drop across R7 and R8 respectively, and fed to pins 11, 12 and 16, 13 respectively. The
U1 compares all these signals and adjusts the PWM on time accordingly. The PWM out put of the U1
drives Q3 switch via R3.
The inductors L4 and L2 along with various capacitors of 1 uF and 0.1 uF form EMC filters.
The D11 is a low voltage drop Shottky diode for preventing reverse current flows when the input voltage is
absent and the charger is connected to a battery. This prevents battery from being drained.
The Q4, Q5, Relay, Q6 and D8 protect the system from over voltage and reverse polarity. If the voltage
goes too high the D7 and Q4 conduct turning off Q5, turning off relay. If the polarity is revered the D8 does
not conduct and the relay remains off.
The only adjustments are for setting of input and output current limit by VR2 and VR1 respectively.
Specifications
Voltage Input
+ 17 to 29 VDC
Maximum input voltage
+/ - 35 VDC. (No AC)
High input voltage protection
Turns off above 29 VDC
Reverse polarity protection
Inbuilt
Max input current
2 Amperes
Max output current
2
Amperes
Содержание 2000 Series
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Страница 29: ...29 To access components on the battery charger PCB the RF shield must be un soldered ...
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