Kenwood TH-25A Service Manual

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TH-25A/AT/E BC-11 (RAPID CHARGER)6) Sensor Level Switching CircuitThis circuit receives the output of the battery recogni-tioncircuitandalignsthevoltagessuppliedtothechargingstatusdetectcircuitaccordingtothebattery type(voltage)sothattheyarenearlyequalatcompletionofcharging.El=EB+1.4VPB-5 : “H"PB-6,7,8,9 : “L”PB-6,7,9: "H"PB-5.8:"L"SHIFT Es(V}Table 5PB-6{7.2V 600mAH}Fig. 5 Sensor Level Switching Circuit Block DiagramThe pin voltages while the Ni-Cd battery is charging aréapproximately 1.2 times the voltages at the completion ofcharging. (See Figure 6.)The battery terminal voltage EB is as follows:Approximately 14.4V for the PB-8&Approximately 8.6V for the PB-5, 6, 7, 9The charging line voltage El is the EB voltage plus a 1.4Vvoltage drop added by a diode.EI=EB+14V..... (1)1.5V1.2V 144VI AY tFig. 6 The pin voltages while the Ni-CDBattery is chargingThe El voltage is output with a level shift as the voltageEO to the charging status detect circuit via Zener diodeDZ6 and diodes D17 and D18. The amount of the shift iscontrolled by switching Q11 : 2SA608E and O12QISA6OBE on and off. (See Table 5.) If Eq. (1) is sub-stitued into EO in Table 5, the results are:PB-8: EO=EB- 6.2VPB-5,6,7,9:EQO-EB O06VAt the completion of charging the value is approximatelyBV.