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AN871 APPLICATION NOTE

Figure 5. Ignition circuit with Triac: In case B the Triac is triggered by a negative gate current. In

case A, no freewheel diode is needed

Safety equipment. The discharge of capacitor is also widely used in safety equipment which sets powder

trigger mechanism in action: Air bag, belt pretensionner, etc...

In such a system, SCR’s are generally the best choice to provide high energy pulse with less than one

microsecond response time. Usually, the gate trigger drive of the SCR circuit is very simple and therefore

provides a high reliability (see Figure 6).

+V(400V)

Conv.

DC/DC

(A)

SPARK PLUG

Vcc

DRIVER

IG

SPARK PLUG

+V(400V)

IG

+Vbat

DRIVER

(B)