I'm looking for a component that has 12 or 15 silicon diodes in series, or an array with pinouts for diodes that I can connect in series. Low current application, a few milliamps. Might be able to work with led's, but the tempco on most led's is too low for the purposes of my project.
I need a tempco of about -25 mV/deg C. I already built a prototype using diodes in series and don't like soldering lots of diodes. It exceeds the total number of components in the rest of the circuit, and consumes time. This is a voltage regulator with temperature compensation for charging 12 volt lead acid batteries, which call for temperature compensation between -18 and -33 mv/deg C, depending on the battery construction. The batteries in question undergo extreme temperature variations and have short lives if used on fixed voltage regulators. And no, it's not for a UPS.
I decided against taking a small voltage reference, like a diode or two, and scaling it up using a resistive voltage divider. I prefer not to deal with touchy pot adjustments. I use a series of about a dozen diodes or so to get the tempco right and then stick a zener in the series to bring the voltage up the rest of the way.
I didn't think going into a long explanation would help, and it looks like I was right. This is a voltage regulator on a vehicle. Not an offline battery charger. Switchmode is too complicated. There's a max of about 2.3 amps field current to regulate, and I use hysteresis to keep the main switching element from heating up. Very simple circuit.
On 8 Jan 2006 19:18:27 -0800, snipped-for-privacy@billburg.com put finger to keyboard and composed:
Years ago I built an alternator regulator using a Motorola MC3325. It has an on-chip string of diodes (including one zener) for setting the tempco, and it is linear. I don't know what is available today, but I believe ST Microelectronics has several single-chip solutions, both linear and switchmode. My old SGS Automotive Products databook lists the L9480VB which comes in a 3-pin TO220 package. You can't get any simpler than that. :-)
- Franc Zabkar
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