Hi Dexter,
is there any particullar reason that you used 78L05 regulator? If I were you I'd use any other, low consumption one, there are chips at Linear Technology which draw less than 10 microA (!!) and deliver some 80 mA at output, which is more than enough for a microcontroller.
If you're talking about quiescent current, the quiescent current on a 78xx is about 5mA nominal which is negligible when compared to the load current. You're going to dump way more than that in pull-up resistors, uProc, and other loads.
Yes... but: go ahead and callulate energy losses with quiescent current of 78L05 (5mA) and 10 microA (in the same time). The current that device uses on load may be high however, but it takes very short time.
Let's see:
10 microA * 3 seconds =30 microA seconds (low quiescent current regulator)
5mA * 3 seconds = 15.000 microA seconds (500 times more!) 78L05
1.2A * 0.1 second = 120.000 microA seconds (load current)
I supposed that timer was in function (in the flight) 3 seconds, but, having in mind that you turn timer on maybe 1 minute or 2 minutes before flight:
10 microA * 120 seconds =1.200 microA seconds
5mA * 120 seconds = 600.000 microA seconds = 0.6 Amp second.
These are currents of only regulators. If regulator uses that much energy, less of it remains for other electronics.
I really do not see a reason why not use less energy and use low quiescent current regulator instead of 78L05?
Again, it doesn't matter if you're using a 9V battery.
A 9V battery can easily provide 5mA of continuous power for at least 100 hours.
Unless you're running with a very small battery (i.e. watch cell), it makes little difference for the durations altimeters are typically run at. Now if you were building something battery powered that was operating for months or even years at a time, than sure, your statement would make more sense.
The other advantage if using a 'modern' regulator is low drop out, which is a major plus in avoiding a MCU brownout condition, especially if the battery is of questionable freshness, when firing the e-matches. it might be nice to have the option of running on a watch battery too, so why not. its certainly not a matter of cost. the point is thee is no disadvantage in using a better regulator and no advantage in using a poorer one.
Not correct. It really doesn't matter which regulator you use, they (linear regulators) will all DISSIPATE or waste the same energy based on the load the current.
If you're talking about quiescent current, the quiescent current on a 78xx is about 5mA nominal which is negligible when compared to the load current. You're going to dump way more than that in pull-up resistors, uProc, and other loads.
So, unless you're running from a watch battery or planning on running for weeks at a time, a 78xx is fine. The only thing is that it is pretty big, however you can get 78xx series in small TO-92 (3-pin transistor) packages.
Yes... but: go ahead and callulate energy losses with quiescent current of 78L05 (5mA) and 10 microA (in the same time). The current that device uses on load may be high however, but it takes very short time.
Let's see:
10 microA * 3 seconds =30 microA seconds (low quiescent current regulator)
5mA * 3 seconds = 15.000 microA seconds (500 times more!) 78L05
1.2A * 0.1 second = 120.000 microA seconds (load current)
I supposed that timer was in function (in the flight) 3 seconds, but, having in mind that you turn timer on maybe 1 minute or 2 minutes before flight:
10 microA * 120 seconds =1.200 microA seconds
5mA * 120 seconds = 600.000 microA seconds = 0.6 Amp second.
These are currents of only regulators. If regulator uses that much energy, less of it remains for other electronics.
I really do not see a reason why not use less energy and use low quiescent current regulator instead of 78L05?
Again, it doesn't matter if you're using a 9V battery.
A 9V battery can easily provide 5mA of continuous power for at least 100 hours.
Unless you're running with a very small battery (i.e. watch cell), it makes little difference for the durations altimeters are typically run at. Now if you were building something battery powered that was operating for months or even years at a time, than sure, your statement would make more sense.
Well I could replace the 78L05 with an LDO, because this may happen to be a test board - the USART doesn't work in proteus on this pins, but I had already made the PCB when I simulated it , so I decided to test it anyway.The other advantage if using a 'modern' regulator is low drop out, which is a major plus in avoiding a MCU brownout condition, especially if the battery is of questionable freshness, when firing the e-matches. it might be nice to have the option of running on a watch battery too, so why not. its certainly not a matter of cost. the point is thee is no disadvantage in using a better regulator and no advantage in using a poorer one.
Well, thats why you filter your Uproc Vcc input, so you don't have to worry about the Vcc drooping during an ematch fire . . .
Oh wait . . . didn't we already have this discussion ? ? ?
OK now that explains everything in a few words. Thanks!Quoting myself here:
"the point is there is no disadvantage in using a better regulator and no advantage in using a poorer one."
A disadvantage of Low Dropout Regulators is less stability--they are more likely to oscillate if the bypass capacitors freeze due to extreme cold. They also need larger capacitances for stability, which have more mass. An oscillating regulator can result in unreliable circuit operation.
A disadvantage of Low Dropout Regulators is less stability--they are more likely to oscillate if the bypass capacitors freeze due to extreme cold. They also need larger capacitances for stability, which have more mass. An oscillating regulator can result in unreliable circuit operation.
A disadvantage of Low Dropout Regulators is less stability--they are more likely to oscillate if the bypass capacitors freeze due to extreme cold. They also need larger capacitances for stability, which have more mass. An oscillating regulator can result in unreliable circuit operation.
A 78L05 is stable with just one 0.47 uF capacitor close to the input for bypassing--are there any good LDOs that are fully stable without increasing the capacitance?...
https://www.national.com/ds/LM/LM2940.pdf?
A very old application note that I found quite useful 20 years ago-...
I never noticed any sign of instability--powering a VHF crystal oscillator around 90 to 100MHz and multiplying it up to 2, 3, 5 or 10GHz for Ham morse code is a pretty tough test.
I have that in mind.Keep your traces on your MOSFET outputs nice and fat! Our ignition system used the thickest copper clad available (and the widest traces that we could fit) and we had the PCB sent out and fabbed for us...
After 200+ firings, the trace had accumulated enough damage from joule heating that the last time it was used the trace vaporized and exploded. Granted, we were running 12V at ~5A through it....
It'd just be smart to do it on a single board but be very conscious of the current limits due to your conductor cross sectional area.
Using PADS to lay it out?
Keep your traces on your MOSFET outputs nice and fat! Our ignition system used the thickest copper clad available (and the widest traces that we could fit) and we had the PCB sent out and fabbed for us...
After 200+ firings, the trace had accumulated enough damage from joule heating that the last time it was used the trace vaporized and exploded. Granted, we were running 12V at ~5A through it....
It'd just be smart to do it on a single board but be very conscious of the current limits due to your conductor cross sectional area.
Using PADS to lay it out?
the point of my previous post was just to make sure you don't settle for 0.5 mm wide traces...