Special considerations for automotive use?
Eric R
Posts: 225
Plan to install a BS2 in my car but wanted some input on the best way to protect it from the battery and charging system. I know these are prone to noise and other effects that are undesirable. Anyone have some ideas? Board space will be a premium so smaller is better.
My first thought was a LM2940 with a pair of caps but then decoupling with ceramics and possibly a zener·crossed my mind. Before I was done, the little board was all power supply and conditioning.·
How much and what is actually needed here???·
My first thought was a LM2940 with a pair of caps but then decoupling with ceramics and possibly a zener·crossed my mind. Before I was done, the little board was all power supply and conditioning.·
How much and what is actually needed here???·
Comments
I built a small control system for my motorcycle that has worked for five years plus without a noise glitch of any kind. Here is what I did:
a. LM7805 regulator in a TO-220 case with a heatsink.
b. Tantalum capacitors on the input and output leads of the 7805 in parallel with standard electrolytic capacitors as well.
Points a. and b. are pretty standard fare for me and some would argue the linear regulator is not as efficient as a switcher but I will take the trade off of size and heat over extra EMI noise anyday. My own personal choice based on field experience with noisy industrial electronics. Also:
c. A wire wound power resistor between the battery voltage and the input to the regulator. This does two things: drops the voltage to minimize heating of the regulator and the inductance acts as a bit of a filter, especially in conjunction with the capacitor to act as a high pass filtering system.
d. All outputs from the stamp are run through a darlington driver or transistor buffer - even for low current loads like LED's.
e. All inputs have a tantalum capacitor between the pins and 0V. Yes I am paranoid about noise so I use tantalum capacitors quite liberally - comes from my ham radio background with power supply circuits and RF systems.
f. Input fusing for branch circuit protection.
The only thing I should have done is also put in a zener diode clamp like you have suggested but so far everything has run glitch free. My motorcycle still has a point ignition system on it so it is noisy but has not affected circuit operation so far.
Hope this helps. PM me if you have any further questions.
Gerry
Guess it's better safe than sorry!
just remember that temperature extremes might be a problem. a motorcylce will (probably) only be used on sunny, warm/hot days. it won't have cold issues or moisture to deal with. just keep that in mind if this is going to go in a car or something. most automotive components are rated from -40°C to +85°C. the stamp is rated from 0°C to 70°C. you 'may' have a little trouble if you live somewhere like the desert or the northeast (like me). but maybe not.
i'm in the process of putting a BS2P into my car, and i did pretty much the same protection: power input fuse (1A), power input filter inductor, power input filter cap (50V, 10uF), and a surge protector. it's an SM5A27 from Vishay. it's specially designed to be a surge/transient protector for automotive applications. i kept the electronics inside the cabin of the car, and a power switch so that i can disable the board if it's really cold, or until the car warms up. i don't forsee any issues, but it's better to err on the side of caution.
good luck.
-mike
Just a little bit of quick information: I have run by motorcycle as low as -5 Celsius and 40 Celsius without any problems. I also store the bike unheated during the winter months where the temperatures have dipped to -45 Celsius. And every once in awhile I did turn the electrics on to "test" the stamp and so far no problems for five years. Preheating may be a consideration and that is fairly easy to do.
I do like the MOV use as well, that's a good idea.
Regards,
Gerry Shand
So could you theoretically replace that 7805 with a LM2931 or LM2940?? Would that be overkill? Even necessary?
Actually while I'm at it, I'm confused. If you take a regulated 5v from this circuit and pass it thru to the Vin on the BS2 would that still work? I remember reading something about unregulated input to Vin being from 5.5-15V.. Of course it's obviously working for others. But am just curious as to how.. [noparse]:)[/noparse]
thanks in advance!
Post Edited (Whaleboy) : 11/18/2004 8:29:57 AM GMT