Power Design Tip 38: Use a simple latch circuit to protect the power supply design (PDF with circuit diagram!)

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LC03-3.3 SOP8 TVS Static Protection 3.3V

description:

Have you ever needed a simple, low-cost latch circuit? Figure 1 shows a circuit that provides power failure protection for a few dollars of components, basically a silicon controlled rectifier (SCR) that combines discrete components. Both transistors are normally off. To turn on the latch, you need to drive the PNP base low or drive the NPN base high until one of the transistors turns on. This will create a collector current that will turn on the other transistor, further turning on the initial transistor. The circuit performs a latch operation in a regenerative manner. Current is limited only by the source impedance and transistor characteristics, allowing the circuit to quickly discharge the capacitor.

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