Hello there,
I was thinking about installing a power turnoff circuit on a device that could benefit from lower power dissipation. It's not a huge amount of power, but still of some concern because it runs off of a battery.
The circuit to be powered draws low current but it would be better to draw even much less current when it does not have to do anything. It only has to take measurements maybe once every 2 minutes to maybe 5 minutes or something like that.
The power turn off circuit would be such that it would apply power to the main circuit, then at some point the main circuit would turn off the power and that would also start a very very low current timer (maybe uA's if possible). After the time is up, the power timer circuit would turn the main circuit back on again, and the cycle would repeat indefinitely.
My first thoughts were to use a few transistors but it's not that great to try to get reliable time periods from a three transistor circuit, so i started to think about a 555 timer, then a CMOS version. The CMOS version should draw very low current while it is timing out. It would then turn on the main circuit through a transistor such as a small NPN type or even PNP ok, and a little extra current to drive that would be ok the base current would be small.
The CMOS version would have to work from about 10 volts up to about 15 volts. Temperatures from about -20F to about 150F.
I would like to get decent repeatability on the timeout period. To start out, 1 minute, then some days later move to 2 minutes and some weeks later 5 minutes. The timeout period should be reasonably accurate but does not have to be super accurate, maybe 20 percent would be good, and that does not have to be an absolute, it only has to be 20 percent from whatever it was to start with. So if it started at 60 seconds if it went down to 50 seconds or up to 70 seconds total over temperature that would be ok i think. If it went down to 40 seconds or up to 80 second i think that would be too much. I hate to say it but i guess this requires an electrolytic cap for the timing.
So that's with the CMOS 555 timer idea. Any other ideas or possibly more suggestions for the CMOS 555 timer idea?
I was thinking about installing a power turnoff circuit on a device that could benefit from lower power dissipation. It's not a huge amount of power, but still of some concern because it runs off of a battery.
The circuit to be powered draws low current but it would be better to draw even much less current when it does not have to do anything. It only has to take measurements maybe once every 2 minutes to maybe 5 minutes or something like that.
The power turn off circuit would be such that it would apply power to the main circuit, then at some point the main circuit would turn off the power and that would also start a very very low current timer (maybe uA's if possible). After the time is up, the power timer circuit would turn the main circuit back on again, and the cycle would repeat indefinitely.
My first thoughts were to use a few transistors but it's not that great to try to get reliable time periods from a three transistor circuit, so i started to think about a 555 timer, then a CMOS version. The CMOS version should draw very low current while it is timing out. It would then turn on the main circuit through a transistor such as a small NPN type or even PNP ok, and a little extra current to drive that would be ok the base current would be small.
The CMOS version would have to work from about 10 volts up to about 15 volts. Temperatures from about -20F to about 150F.
I would like to get decent repeatability on the timeout period. To start out, 1 minute, then some days later move to 2 minutes and some weeks later 5 minutes. The timeout period should be reasonably accurate but does not have to be super accurate, maybe 20 percent would be good, and that does not have to be an absolute, it only has to be 20 percent from whatever it was to start with. So if it started at 60 seconds if it went down to 50 seconds or up to 70 seconds total over temperature that would be ok i think. If it went down to 40 seconds or up to 80 second i think that would be too much. I hate to say it but i guess this requires an electrolytic cap for the timing.
So that's with the CMOS 555 timer idea. Any other ideas or possibly more suggestions for the CMOS 555 timer idea?