Auto-shutdown Regulator

[MFB]

The attached schematic shows a low drop 200mA regulator that can be shutdown by the host PICAXE. There are a number of reasons why it can be an advantage to automatically power down a battery-powered system in an orderly way. For example, when a logger has filled memory and wants to save power, or to protect a rechargeable battery from dropping to a damagingly low voltage.

The regulator is powered-up by momentarily activating the push-button. The first action required by the PICAXE, when it comes out of reset, is to hold the regulator on by taking OUT high. Provided that the push-button is no longer activated, the system can be powered-down at any time by taking OUT low. One reason for the PICAXE to do this might be when a low battery (< 5.5V) warning has been detected at IN. There is not normally a need for a separate ON/OFF switch because battery drain in the powered-down state is only in the order of micro Amps.

 

[MFB]

Oops! The top of the 43K resistor should have gone to the other side of the push-button (to battery +). I should also have mentioned that if low battery detection is not required both of these potential divider resistor can be left out and the LB input (pin8) linked directly to IN (pin 5).

 

[fernando_g]

Thanks for sharing. Another reference circuit for future projects.

One of the best things about this IC, is that it is still available in the P-DIP package, for the SMT-impaired among us.

 

[MFB]

Even without the shutdown and low battery detection options this device is a pretty useful regulator. The input voltage can drop to 5.22 volts before effecting the output, and the excellent voltage stability makes it a good choice as an ADC reference for the PICAXE. However, keep an eye on the 727mW maximum dissipation limit (either 200mA out or 11.5Vin, not both at the same time!) but it is over temperature and current protected. Best of all, Maxim may also supply a free samples.