I have some project ideas that would be targetted for use in a vehicle. I would like to consider the possibility of tapping into the car's 12V battery to power the projects, for example through the cigarette lighter port. I would put the input power from that port through a linear or switching regulator (e.g. a 7805 or similar), to give me 5V power. Am I likely to face any challenges in that approach? Are there front-end circuits that are a 'must have' for consuming automotive battery power in low voltage / low current embedded applications? Specific circuits and/or part recommendations are encouraged.
Electronic – arduino – Is Automobile Power Viable for Electronics Projects
12varduinoautomotivepower
Related Solutions
First pass:
Your schematic is confusing. What is the relationship between JP1-1, VIN, BPOS and the battery voltage?
You should have the fuse on the positive input 'ahead' of your protection circuitry (on the battery-side of things). You never know how things may fail in real life.
Given the orientation of D2, the battery feed should be JP1-1, correct? If so, and if you have reverse battery, your unidirectional TVS will conduct big current (it will indeed act like a diode) and melt things, and your PTC is powerless to help.
You may want to consider the bidirectional TVS 5.0SMDJ30CA (notice the extra C) so that it will clamp regardless of polarity.
If VIN is the battery feed, your circuit won't work as D2 will be blocking all the time.
An automotive-rated voltage regulator will necessarily be priced significantly higher than the super-cheap 7805, due to the latter's massive sales volume and lack of high voltage spike protection, if nothing else.
Setting aside the input reversal case, which is easily addressed with a high current diode at the input, the options are:
- A Transient Voltage Suppressor (TVS) and / or a clamping diode shunt at the input
- A combination of common mode auto-rated choke coil and clamping diodes at input
- A DC-DC buck regulator designed to withstand the likely extreme case voltages
The LM2937 fits that third category, but there are less expensive options available.
For instance, there has been excellent personal experience with pre-built DC-DC regulator modules based on the LM2596 buck regulator, available on eBay.com for less than $2 including free international shipping:
This module is rated for up to 35 Volts input, and copes well with transients on the input supply, as well as significant temperature swings. The output is adjustable, so one can set it to 5 Volts and forgets about it, for all general purposes.
For a supply-noise-sensitive design, a two step design is my preference: The above type of buck regulator set to say 6.5-7 Volts output, feeding into a linear regulator such as 7805 or better yet, one of its newer low drop-out counterparts such as the AMS1117, probably cheaper than a 7805 at just over 7 cents apiece for 50 units.
The added advantage of the buck regulator is that it generates less heat than a linear regulator, for any significant current, by dint of the different mechanisms of voltage regulator between the two technologies. Efficiency of 65 to 80% is common with a buck regulator, much less so with a linear regulator that needs to dump 7 Volts x Load_Current Watts through heat emission.
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Best Answer
I recommend using an Adapter from Cigarette lighter to USB (like a cell phone charger), to get your 5V. It is simple, cheap and effective. And if you tear it open you will find a linear Drop Out Regulator (for the lighter loads) or a switcher (for heavier). And they are typically already current limited and such. So I suspect they are perfect for your goal. I would readily run an Arduino such.