I have no doubt this circuit will work, although it's a bit of overkill for the application. I would have used a simpler circuit.
The LM7808 device is an 8 volt regulator. The 1N4002 diode provides a .6 volt drop, and the base-to-emitter junction of the 2N5881 drops the voltage another .6 volts to get you to 6.8 volts. The 2N5881 has a maximum collector current of 15 amps, so you have up to 15 amps available to drive your gauges. Note that at 15 amps, the 2N5881 will need to dissipate 120 watts, so you'll need a healthy heat sink to do that. I would ditch the two capacitors from this design (potential failure points that don't do much), but otherwise it looks fine.
Note that the TO-3 package of the 2N5881 is a bit of a pain to work with. If you can get by with only 1 amp, the LM7808 can do that on its own. You can put a pair of 1N4002 diodes in series with the voltage regulator output to get your voltage drop.
Another solution is to use an LM350K adjustable regulator, which can provide up to 3 amps, requiring only a couple of resistors in addition to the VR. The LM350K is a TO-3 package. In a TO-220 package you can get the LM317 which is good for 1.5 amps.
We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today. [ About Us ]
Today's Featured Article - Sunday Drives - by Cowboy. Summer was finally upon us here in Northern Maine. We have two types of industry up here, one being "Forestry" (Wood Products) and the other "Farming" (Potatoes). There is no shortage of farm tractors and equipment around here! I have been restoring old Farm Tractors for the past 6 years, and have found it easier and less expensive to hit all the auctions and purchase whole tractors for parts needed. My wife who works at a local school, and only has weekends and summers off, while on t
... [Read Article]
Latest Ad:
1964 I-H 140 tractor with cultivators and sidedresser. Starts and runs good. Asking 2650. CALL RON AT 502-319-1952
[More Ads]
All Rights Reserved. Reproduction of any part of this website, including design and content, without written permission is strictly prohibited. Trade Marks and Trade Names contained and used in this Website are those of others, and are used in this Website in a descriptive sense to refer to the products of others. Use of this Web site constitutes acceptance of our User Agreement and Privacy Policy
TRADEMARK DISCLAIMER: Tradenames and Trademarks referred to within Yesterday's Tractor Co. products and within the Yesterday's Tractor Co. websites are the property of their respective trademark holders. None of these trademark holders are affiliated with Yesterday's Tractor Co., our products, or our website nor are we sponsored by them. John Deere and its logos are the registered trademarks of the John Deere Corporation. Agco, Agco Allis, White, Massey Ferguson and their logos are the registered trademarks of AGCO Corporation. Case, Case-IH, Farmall, International Harvester, New Holland and their logos are registered trademarks of CNH Global N.V.
