fever said:
yes 12v to power tacho and 5v for battery voltage indicator circuit.
@gootee
LM2937 seems to be good.but can it handle rough both the lower and higher voltages according to the output voltage. imean from 10.5 to 15v input the output shld be 12v stable.
Well, of course not. But neither will a 7805. They are both Linear Regulators. And I thought that we were talking about the 5V output. But even with a 12V LDO (Low Drop-Out) linear regulator, the input voltage has to be higher than the output voltage, by at least the drop-out spec (and a little higher is usually better), for it to be able to maintain the output at 12V.
You'd need a switchmode power supply, to get 12V output for input ranging from 10.5V to 15V. I suggest that you either download LTspice (aka SwitcherCad), at linear.com, and use the "File" - "Switch Selector Guide" automatic SMPS designer menu-option, or, go to national.com and use their on-line automatic SMPS designer. Then maybe also look for appnotes about snubbers for SMPSs. You might also want an LC filter on the output. And you'll probably want a 12V LDO linear regulator after the output.
If you meant to say "5V" instead of "12V", then yes, the 7805 and LM2937 "should" both be able to do it, although they might dissipate a fair amount of heat, especially at the higher end of the input voltage range. And the 7805, at least, might not be very happy about it, and might tend to fail. The LM2937 is a little more robust.
At any rate, it sounds like you should listen to what audioguru and Hero999 have recently posted, about your ICs' voltage requirements, and avoid some wasted time and resources.
- Tom Gootee
**broken link removed**
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