KX-TEB308CA, KX-TE82460X, KX-TE82493X, KX-A227X - Panasonic PBX Service Manual (repair manual). Page 11

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1) AC-DC Inverter Function
The AC input voltage is rectified and smoothed by D10-13 and C5. The obtained DC voltage is converted into a rectangular wave by
the switching transistor Q1, then isolated and transduced by T1. This converted rectangular wave is rectified and smoothed by
D101 and C101 to output DC27V. The DC27V is transmitted to the primary side by PC1 and then PWM- controlled to keep con-
stant. The switching frequency of Q1 is approximately 60KHz.
2) DC-DC Inverter Function
The DC 27V DC is converted into a rectangular wave by control IC201, and then output as an output voltage of +15V by the
smoothing circuit which is composed of D201, L201, C201.
The 27V DC is converted into rectangular wave by control IC301 and then output as an output voltage of +3.3V by the smoothing
circuit which is composed of D301, L301, C301.
3) Battery back up function
This back up battery adaptor circuit has DC supply function, from battery (+24V) to service unit and DC charge from service unit to

battery (+24V). Charge current is typ. 0.3A.

AC-DC Inverter Function

This function isolates and converts the AC input voltage to DC 

input and output of DC27V.

DC-DC Converter Function

This function outputs DC+15V and 3.3V from the inputted
DC27V.

Battery Back Up Adaptor Function

This function connects battery and service unit without battery
adaptor, only needs a cable connected to the battery and ser-
vice unit.