Figure 4 : Application Circuit (SO–16).

CIRCUIT OPERATION

The L482control the conduction time (dwell) and the

peak value of the primary current in the coil over the

full range of operating conditions.

The coil current is limited to a predetermined level

by means of a negative feedback circuit including a

current sensing resistor, a comparator, the driver

stage and the power switch.

The dwell control circuit maintains the output stage

in its active region during current limitation. The time

the output stage is in the active region (desaturation

time) is sufficient to compensate for possible varia-

tions in the nergy stored due to the acceleration of

the motor ; moreover this time is limited to avoid ex-

cessive power dissipation.

CONTROL OF THE DWELL ANGLE (fig. 1 and 4)

The dwell angle control circuit calculates the con-

duction time D for the output transistor in relation to

the speed of rotation, to the supply voltage and to

the characteristic of the coil.

On the negative edge of the Hall-effect input signal

rent is reached, this capacitor charges with a con-

kept constant by desaturating the driver stage and

the external darlington.

edge of the Hall-effect input signal with a constant

The dwell angle, and consequentlythe starting point

of the coil current production, is decided by the com-

is added to the dwell comparator to avoid spurious

edge of Hall-effects input signal.

the motor speed decreases and viceversa in order

to maintain constant the ratiotd at any motor speed.

T

td is kept constant (and not d = cost) to control the

power dissipation and to have sufficient time to

avoid low energy sparks during acceleration.

The charging time D – td depends on the coil and

the voltage supply.

DESATURATION TIMES IN STATIC CONDI-

ded and if the values of the application circuit of fig.

3, 4 are used.

td

1

=

L482

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