ITT - Index of

____
TBA840, TCA840
WRIST-WATCH BALANCE WHEEL DRIVERS
Circuit Design Information
The optimum position for an output pulse is
when the switch-on threshold VSI and the
switchcoff threshold Vs, are equal. This is dependent
upon the capacitor, C, chosen, the
mechanical clockwork, induced coH voltage
Vin s, driving frequency, fd, duty cycle tilT and
the coU resistance RL •
r
RI
c
With two-magnet systems, the output drive
pulse must appear only once per total oscUlation
because the polarity of the induced volttage
changes with each change in oscillation
direction. Care must be taken when designing
the external components with this system.
TIJ------;--------r---~
L _________________ ~
o
The switching threshold is changed together
with the induced coil voltage. For optimum
pulse conditions, i.e. VSI = VS2, the switching
threshold is only dependent on the maximum
induced voltage.
The self-starting properties of the system are
dependent on the operation of the oscillator
and coil. The start-up time is limited by the
movement of the balance wheel, magnets,
value of the induced voltage and the coil resistance.
3 ,
r- --TBA 840-----------,
I
I
I R, I
I T3 RS I
I R, R2
I
I
I
I
I
I
.f?]
I T1}------+-------+--~
I
I
L ____________ ~
c
J I
o
Circuit Diagram
Fig. 2--lnternal circuit diagrams TBA840,
TCA840 .
o~--~----------~~------~-­ _I
Fig. 3--0perating waveforms for Veoil and leoll
with a 3-magnet balance system. (Vc & Ie)
Fig. 4--Test Circuits
8-98