AN871 APPLICATION NOTE

4/13

Figure 4. Ignition circuit with SCR: storage capacitor connected across input voltage source

In these circuits the diode D acts as a freewheel diode to ensure the complete discharge of the energy

stored in the capacitor C.

The current through the transformer is oscillating in the cases 3A and 4A and unidirectional in the cases

4A and 4B.

Utilization of triac

The triac can be used as a very flexible unidirectional or bidirectional switch in such a circuit.

Moreover, it can be triggered with a negative gate current. This feature allows the use of standard buffer

circuit for the gate control (see Figure 5).

(A)

D

+V

(B)

D

+V