A high perfomance Crowbar Circuit

The MC3423 can protect sensitive circuity from power supply transients or regulator failure when used with an external "Crowbar" SCR. The device senses voltage and compares it to an internal 2.6 Volts reference. Overvoltage trip is adjustable by means of an external resistive voltage divider (R1, R2 on Fig 2).
A minimum duration before trip is programmable with an external capacitor. Other features include a 300 mA high current output for driving the gate of SCR, an open-collector indicator output and remote activation capability. Fig. 1 below shows the internal configuration of MC3223.

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FIG. 1

Fig. 2 shows a sample. R1-R1 divides the output voltage. For 13,2 Volts Power Supply output, R1 it must be 50 K and R2 = 10 K. The resistor for SCR gate driving = 330 Ohms. The capacitor on pin 4 = 0,1uF

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FIG. 2