9

4752B–INDCO–09/05

U211B

7.4

Design Hints

Practical trials are normally needed for the exact determination of the values of the relevant

components for load limiting. To make this evaluation easier, the following table shows the effect

of the circuitry on the important parameters for load limiting and summarizes the general

tendencies.

Table 7-1.

Load Limiting Parameters

P

max

- Maximum continuous power dissipationP

P

min

- Power dissipation with no rotation

P

t

d

- Operation delay time

t

r

- Recovery time

n.e.

- No effect

7.5

Pulse-output Stage

The pulse-output stage is short-circuit protected and can typically deliver currents of 125 mA.

For the design of smaller triggering currents, the function I

10-12 on page 18.

7.6

Automatic Retriggering

The variable automatic retriggering prevents half cycles without current flow, even if the triac has

been turned off earlier, e.g., due to a collector which is not exactly centered (brush lifter) or in the

event of unsuccessful triggering. If necessary, another triggering pulse is generated after a time

lapse which is determined by the repetition rate set by resistance between pin 5 and pin 3 (R

With the maximum repetition rate (pin 5 directly connected to pin 3), the next attempt to trigger

comes after a pause of 4.5 t

ishes. If pin 5 is not connected, only one trigger pulse per half cycle is generated. Since the

value of R

for a fixed value of C

Parameters

Component

Component

Component

R

R

C

Increases

Decreases

n.e.

P

min

Increases

Decreases

n.e.

P

max/min

Increases

n.e.

n.e.

n.e.

Increases

Increases

t

r

n.e.

Increases

Increases