seek automobile 5.5V power

5.5v at what current?

around 800mA.

The National Semiconductor LM2575T-ADJ will handle that. They make a high-voltage input variety, but even the normal one handles 40-volts in, or something like that. 1.5A out. It's a switcher, so you'll need a Shottkey diode, an inductor, and input & output caps. Switching frequency is 52kHz, so parts size / availability / cost / real estate are all within reason.

For protection, you could design circuits ahead of this (don't forget the fuse too). Also, the LM2575T has a shutdown pin if that helps? And because it's a switcher, it'll produce less heat compared to a linear regulator, and you might not need a heat sink.

ON Semiconductor 2nd sources the LM2575T-ADJ, so look there too.

Note: Take this for what's its worth. There may be better options out there for you...

-mpm

Thank you mpm. Can you tell me where to look for over voltage (when car is jump start), over current, surge and transient protection circuits. Also, I was told to use a PTC (Positive Temperature Coefficient) device. Can you tell me where to find this kind of devices & circuit?

So far, I found Vishay 2381 PTC Thermistors seems to be applicable to over temperature. Zener Diode with SCR thyristor seems to protect on over-voltage. But how about protection of over-current, surge and transient?

Restart you quest for information by learning about 'load dump'. Both ISO and SAE have standards for this automotive problem that must be addressed in the design of that power supply.

For example, a 40 volt regulator is not sufficient. Load dump on 12 volts is defined as up to 260 volts - but designs should make at least

60 volt electronics protection sufficient. SGS Thompson put this in a 1996 application note of numbers your design must address: "The overvoltage is named the load dump and can be defined by the following figures:

- Peak voltage 80 to 100 volts

- Duration 300 to 400 milliseconds

- Series resistance 0.2 to 1 ohms"

Thank you Tom. Can you tell me what kind of device or circuit I should look at for 'load dump' protection? I understand to simulate "load dump", you charge capacitors in test fixture, and then discharge into Device under test.

Can you give me the link to this SGS Thompson 1996 app note? Are you talking about STMicro's RBO40-40 type of devices?

Thanks.

Similar to auto cigarette plug to power wireless prototype boards.

The SGS Thompson part is installed in auto electronics by the manufacturers. But as the app notes says, that still is not sufficient protection. As noted earlier, your designs must be undamaged by 60 volts on the 12 volt circuit. That is why some semiconductor manufacturers make a different line of regulators for automotive service. How reliable must your electronics be. Then the power supply must withstand even high voltages without damage.

There was a thread discussing some of these issues few months ago:

--

John Devereux

I remember awhile back touching on this topic.. Car More Dead from Boosting a Dead Car Battery Dec. 2006

D from BC