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Using the enable pin in a linear regulator as a voltage supervisor

Posted: 24 Nov 2008 ?? ?Print Version ?Bookmark and Share

Keywords:voltage supervisor? linear regulator? configuration circuit? application note?

The combination of a voltage regulator and a voltage supervisor, shown in Figure 1, is a popular circuit configuration. The addition of the supervisor ensures that the regulated output turns on and off at sufficient input voltages, as well as giving the system the luxury of a safe and ordered startup. An inexpensive alternative, shown in Figure 2, uses the enable pin of a regulator and an external delay network to provide a safe and ordered startup. Unlike the supervisor solution, this circuit does not immediately shutdown the output once it drops below an unacceptable level.

Furthermore, since the delay starts directly after the enable pin goes high, there is no insurance that the output will be at the desired regulated output voltage. The circuit proposed in Figure 3 fixes the problems of Figure 2 by cleverly replacing the single resister with a resister divider network.

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