I just designed a power out circuit, if power goes out the 12v lead acid battery kicks in...
After several redesigns, my main issues were due to using too much current when the power was on, 100k worked fine but resulted in the transistor switching the led on was not saturated, so I used another transistor too boost the signal..
Anyway, the critiques among you will surely point out the flaws in my design, please do, once the final design is made I'll move it to perfboard for a blackout light.
Edit, helps to include the cicuit!
My issues are reducing the current when the 5v supply is on....
How about a CMOS 555 timer? Some aren't meant to run from more than low Vcc, so make sure the one you choose does. Should draw on the order of microamps when the LED is off.
The TS555 is rated to 16V. Just put an appropriate resistor on pin 5 so pins 2 and 6 trigger when the 5V line drops to where you want it to trigger. Built-in hysteresis. It acts as an inverting schmitt trigger.
Not sure what the Arduino has to do with it. I gather you are switching on the basis of the presence of 5V from some sort of Arduino, but not obvious what the overall project design is. Always nice to know what you really wish to do.
A lead-acid or "gel cell" is float charged at 13.6V, not 14.4. Your circuit does not show the regulator for such float charging.
Somewhat strange way of using the 500 ohm current limiting resistor in the emitter circuit. If you are using extra transistors as inverters (but "4000" series CMOS gates would do that with no static current draw) then you might as well use a "constant current" circuit.
Would not FETs do a better job if you are concerned about current consumption?
100k resistor at 5V - something of the order of 50 µA (microAmps). This is significant why?
Poly, I thought about using a 555 or logic chips, I'm trying to develop my bare metal skills is all... if it had of been say 12v in and if the power went out, a simple pnp would handle it..
But because I want the 5v to control the circuit, a 5v high would not switch off a pnp when the emitter has 12v on it..
I was after criticism of this circuit, alternatives would be quite simple I have a draw full of logic chips to do such a job, but it's about learning, I could add schmitt trigger in transistor form...
Paul, where does it state it has to be arduino related? This is /general electronics/
cjdelphi:
Paul, where does it state it has to be Arduino related? This is /general electronics/
And indeed it is, but given that it is an Arduino forum, one does kind of expect it to be "general electronics matters used in conjunction with Arduinox".
cjdelphi:
Paul, where does it state it has to be Arduino related? This is /general electronics/
And indeed it is, but given that it is an Arduino forum, one does kind of expect it to be "general electronics matters used in conjunction with Arduinox".
You better get busy then, there's hundreds of posts not related to an arduino in any way shape or form... feel free to start here in general electronics and move into off topic last and let everyone else know their posts are not Arduino related!
Hah! Yeah, I don't think we need to limit "General Electronics" to strictly Arduino related or nothing.
How about this? It relies on only about 15uA pulled from the 5V supply to the base of an NPN, then that draws about 140uA through a resistor from the 14.4V supply. No other power when the 5V supply is present.
When 5V goes dead, the 2nd transistor gets turned on through the 100k resistor. This pulls the base of the 3rd transistor, a PNP, low through a 10k resistor and turns it on. lighting the LED.
The 10k from 14.4V to the PNP base is to make sure it is kept OFF when the 2nd transistor is OFF.
Edit:That first resistor should be 3.3M. Somehow my decimal point got lost... and 1.3uA from the 5V supply. I'd feel more comfortable with a slightly smaller resistor here, like 1M.
They missed the point (as most do in this field) that the 5v source could simply be a 5v signal from any logic voltage source, no arduino required oh well.
