HP HP-97 - Page 25

HP-97 Theory of Operation
2-U48. When the power is applied, Q1 is turned off. VSS rises and the
voltage across C3 also rises, resetting the ACT. If VB drops a certain
level below VSS, Q1 turns on and discharges C3, forcing the ACT to reset
again. This sequence repeats until VB and VSS are stable, thereby
eliminating the effect of ON-OFF switch contact noise.
AC Adapter/
Recharger
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Voo)
Figure 2-10. Battery Charging Circuit
T——Z(To ACT)
=ac3
(To Vso)
Figure 2-11. Power-On Reset Circuit
2-11/2-12