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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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Dropping 1V from a Regulated 6V Wall Wart
I needed to drop 1V from a 6VDC 200 mA regulated wall wart, so I tried a 3 amp rectifier, but it varied by more than .2V over a range of loads. So I tried this: (view with courier font) + From wall wart --+ | +---+------+ | | | | 400 \ / 2SC2334 or TIP31 ohm / |/ NPN power TO-220 WW \-----| Heatsink optional pot / |\ | E\ | | | | +----+-----+ | | +------ + output to load - -------------- - From wall wart This has some advantages and disadvantages. It's simple and cheap, and keeps the output at 5V within a tenth of a volt over a current range. But it has a minimum current below which it loses regulation and the output starts to go up to 6V, because the transistor is not conducting and the current is being supplied thru the ww pot. This circuit is sometimes used in the bias circuit for the output transistors in high powered amplifiers. Also Win Hill showed us here how to use a similar circuit to maintain the voltage steady for a current regulator circuit used on four AA cell rechargeable batteries. I'm thinking about putting a 5.1V zener on the output so that if the voltage climbs above that, it just shunts the excess current. Oh, yeah, I set the pot to various values to see what the output voltage was with various loads. The two resistances were 120 ohms for the upper and 280 ohms for the lower. I suppose the 400 ohms total could be raised to a higher value, but the transistor needs enough base current to do its job. There's only 1V available minus the .6V E-B voltage, so even at 400 ohms, that's not a lot of current. -- @@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@ h@e@r@e@@ ###Got a Question about ELECTRONICS? Check HERE First:### http://users.pandora.be/educypedia/e...s/databank.htm My email address is whitelisted. *All* email sent to it goes directly to the trash unless you add NOSPAM in the Subject: line with other stuff. alondra101 at hotmail.com Don't be ripped off by the big book dealers. Go to the URL that will give you a choice and save you money(up to half). http://www.everybookstore.com You'll be glad you did! Just when you thought you had all this figured out, the gov't changed it: http://physics.nist.gov/cuu/Units/binary.html @@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@ u@e@n@t@@ |
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