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AN436 APPLICATION NOTE

In practice the area of the pulse has to be lower than 60 or 70% of the maximum voltage.time product

Vo.to.

The maximum pulse duration in the output is:

These two formulæ allow us to define the pulse transformer according to the triac sensitivity.

Example: Numerical application with a transformer having the following characteristics:

N2/N1 = 1

Vo.to = 250Vµs

Triac: BTA08-700CW

Power supply:

U = 12V; R1 = 100

We have measured:

CONCLUSION

The pulse transformer provides an excellent method to trigger a triac when galvanic insulation is required.

This system is appropriate to microprocessor systems.

Nevertheless it needs some precautions to avoid a decrease of the triac commutation behavior.

This precaution is achieved by adding a diode in series with the gate.

t

P

0.7Vo.to

V

F

V

GK

–

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=