EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: danater on September 01, 2013, 04:07:07 pm
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I am designing a small circuit
1) 12 volt (motorcycle battery voltage) input
2) it will have a voltage follower/buffer to make sure there is no feedback/ overload of mc circuits
3) its going to be used to relay a signal that is read from input to an external device
I have come up with a decent circuit for it However!
I have been looking at the lt1086
assuming that I have a worst case scenario and the circuit goes to a maximum of 1.5a
Ill have to dissipate almost 11 watts of power. Now I don't know how that would ever happen
but I want this thing pretty much bulletproof.
the 5v supply will be pushing a low noise follower, signal should never go above the 5v max on the output and I suspect approx 400 ma would be norm.
so the questions I have are
1) would it be wise to put in a 5v diode to make sure of no spikes on the output?
2) would it be wiser to use a 5v .1% diode to regulate the 1086 or would 2x 1% resistors work just as good?
3) I am thinking of putting a LED in the line for the regulator to show that it is working as far as power in is concerned, is that a good idea or just a waste of a LED?
Thanks all for the help and reading my ramblings
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Huh. A switchmode power supply might be a better choice. The TI LM2594-5 might be a better choice, due to the fact that there is no heat dissipation problem, and the spikes occur very rarely.
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It may not be as bad with a motorcycle alternator as in a car, but the term you're looking for is "load dump". There's some pretty good suggestions and links here: http://electronics.stackexchange.com/questions/8798/how-do-i-protect-against-an-automotive-load-dump (http://electronics.stackexchange.com/questions/8798/how-do-i-protect-against-an-automotive-load-dump)
I'd put the protection on the input of your regulator though.
11 watts is a pretty decent amount of power to dissipate in a small space (under the seat?). I'd second the switching regulator suggestion, some of them are not that hard to apply.
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awesome! thanks echen.
I found that information very helpful mmagin.
Basically what I am doing is making a vehicle speed sensor output to computer, then ill be able to go on with some other plans from that. It looks like 3.5W at max .5A with the lm2594. Hopefully I wont need more than .5A.
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awesome! thanks echen.
I found that information very helpful mmagin.
Basically what I am doing is making a vehicle speed sensor output to computer, then ill be able to go on with some other plans from that. It looks like 3.5W at max .5A with the lm2594. Hopefully I wont need more than .5A.
I'm not quite sure you understand the concept of a Switching Power Supply. A linear regulator takes the excess voltage, and burns it off as heat. This results in very low efficiencies, and thus lots of heat. A switchmode, on the other hand, takes the input voltage, and turns it into high frequency AC. It switches rapidly between full voltage, low current, and full current, low voltage. By varying the ratio of these, you can vary the output voltage. This allows in very high efficiencies, upwards of 80%. However, this requires more external components, such as an inductor-capacitor(L-C) filter, but that shouldn't be that much of a problem.
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looks like the best bet for me would be
regulator: TI lm2595 5.0 fixed regulator @ 1A
input cap : panasonic 220 micro Farads @ 50V
output cap: panasonic 220 micro Farads @ 50V
catch diode: fairchild 1n5821 schottky diode 3A
now I have a choice, I can either go with the 40V max inductor or the 15V max inductor
I chose the 220 caps @ 50v for max amount of ripple rejection.