Get the SoR Robotics Android App on Android Market for FREE. See this forum post for details.
0 Members and 1 Guest are viewing this topic.
so, the regulator will get a continuous flow. Then, the output from regulator will be used to power up the Micro controller. Is my understanding correct?
i'd consider upgrading your regulator, linear ones like the 7805 waste energy...
I found my regulator was getting hot in a minute if I left the circuit powered on.
I will use another 6v battery pack instead of 9v and see if that will keep my regulator cool !!
7805 has a typical dropout of 2V at 1A according to the datasheet.
Also, I know how the datasheet says it has thermal shutdown, but I HAVE blown up a 7805 before, so I'm not too sure what's happening.I ran it from a lab power supply at 9V/4A and probably shorted the output. It blew up literally (a black piece flew away) after a few seconds. TO-220 without heatsink.
I am using a 6V battery with a LDO. Works perfectly. It's a lot more picky about the output capacitor, though. Both ESR and capacitance need to be in a certain range to stop the output from oscillating. Apparently modern ones are a lot less picky, but still harder to use than 78xx.
(you seem to scoot quite indifferent past stuff like eg. line and load regulation)
AND you verify the sample you've got AND you bake a batch of them at around 110°C for 3..4 hours AND you retest them after that.Short of a single one of them, you can either take my word and add 3.5V or design inferior supplies most of the time, but I don't base my designs on luck.
Even if you really don't wanna see the light, at least get datasheets from as many manufacturers as possible and base your advice to people that you don't know and hence have no idea what they have at hand, on worst case data, then nothing will go too wrong. Even with the best (at least on paper) 78xx regulators, 2.5V should be the worst case drop. Some regulators have a combined line and load regulation of up to around 0.25V Total so far 2.75V (for one of the good regulators).Since this is a battery fed regulator, luckily, there is no AC to take into account, or it would have been worse.
Thermal shutdown was never meant for short circuit protection, but for an overload that takes some time to reach a critical temperature, as the temp. needs time to reach the thermal detector circuit.I wonder how anyone can mix up "thermal shutdown" with short circuit protection"? It's not even spelled the same way
Running it from a lab supply could mean LF ripple if conventional iron and HF ripple if a switcher was involved. Further, if you used long (i.e. >10 cm) leads from the supply, the induction of the leads may have helped in creating oscillations.If the regulator wasn't properly capped, oscillation was surely involved (those regulators are quite high gain amplifiers).
So you are basically saying, screw what the datasheet says, and test it yourself?
The one I am using, made by fairchild, says 2.0V typical at 1A and Tj = 25C. National Semiconductor's 7805 datasheet also says 2V.I usually trust datasheets.
Do you seriously go test every parameter on the datasheet? Why do we even need datasheets then?Why stop at 3V? Why not 4 or 5?
Which 7805 datasheet exactly says 3V?
The fairchild datasheet says max load and line reg are 100mV, the national one says 50mV for both, but with a 10V input. Although it does say minimum 7.5V to maintain line regulation.
Thank you very much. I do know perfectly well the difference between thermal shutdown and short circuit protection. As you noted, they are even spelled differently!I was just under the impression that short circuit/oscillation should have triggered thermal shutdown before the case blows up.
That is possible. The input was capped, though (don't remember about output, it was quite some time ago).