elrond@ccwf.cc.utexas.edu (hlista) (12/27/90)
I have been looking for a transformer to take 12V from the ligter and convert it to 3V for a portable CD player. I have found some for 25 dollars and was hoping that someone might have a simple design for one. I have a 120V AC adapter that is rated at 3V DC 600 mA. Does anyone have a schematic for a 12V DC to 3V DC 600 mA ? Thanks for any help. elrond@titan.tsd.arlut.utexas.edu
roy@phri.nyu.edu (Roy Smith) (12/27/90)
elrond@ccwf.cc.utexas.edu (hlista) writes: > Does anyone have a schematic for a 12V DC to 3V DC 600 mA? > Thanks for any help. Seems like a perfect application for a 7803 three-terminal regulator. Can't get much simplier than that. Should run you a couple of bucks at Radio Schlock. If they don't have the 7803 (it's an unusual value), they will probably have the variable version, which just requires adding a couple of passive components to set the output voltage. The only question is whether a 7803 is hardy enough to handle all the horribleness that goes on in a automobile electrical system (I'm mostly worried about voltage spikes). You might want to protect it with something like a 20V zeiner across its inputs, and a 1-ohm power resister in series with the input, after the zeiner. -- Roy Smith, Public Health Research Institute 455 First Avenue, New York, NY 10016 roy@alanine.phri.nyu.edu -OR- {att,cmcl2,rutgers,hombre}!phri!roy "Arcane? Did you say arcane? It wouldn't be Unix if it wasn't arcane!"
rambler@pnet51.orb.mn.org (Dan Meyer) (12/28/90)
12v input --> 7805 3 terminal regulator --> 2 or 3 regular diodes should get
you }in the ballpark.
-- Dan
Remember: " Buffalo never Oink " Seen on a South Dakota travel brocure.
Advertisment: Try the Railway Post Office , a railfan BBS ! (612) 377-2197.
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INET: rambler@pnet51.orb.mn.orgmurray@sun13.scri.fsu.edu (John Murray) (12/28/90)
In article <1990Dec27.141809.2856@phri.nyu.edu> roy@phri.nyu.edu (Roy Smith) writes: >elrond@ccwf.cc.utexas.edu (hlista) writes: >> Does anyone have a schematic for a 12V DC to 3V DC 600 mA? >> Thanks for any help. > > Seems like a perfect application for a 7803 three-terminal >regulator. Can't get much simplier than that. Should run you a couple of >bucks at Radio Schlock. If they don't have the 7803 (it's an unusual >value), they will probably have the variable version, which just requires >adding a couple of passive components to set the output voltage. I'm pretty sure the Schlock only carries 2-4 78xx or 79xx. '05's and '12's and such. > The only question is whether a 7803 is hardy enough to handle all >the horribleness that goes on in a automobile electrical system (I'm mostly >worried about voltage spikes). You might want to protect it with something >like a 20V zeiner across its inputs, and a 1-ohm power resister in series >with the input, after the zeiner. Anybody happen to know what is likely to occur when a 7{8,9}xx or a 317 melts down? Specifically, I am wondering if it is reasonably safe (for the load) to go with the quick-and-dirty circuit below in a less than benign environment: |---------------| +12V O--------------| Radio Schlock |------o----------O adjustable, approx. | LM317 | | . +1.5 to +12 |_______________| | . |------| | | . | V | | ----- .01 uF capacitor (can o--\/\/\/\/\/\---o---\/\/\/\/\--| ----- you get away without it?) | 10K variable 5K 1/4W resistor . | . ground O---o------------------------------------------O ground About $3.00 in parts at Radio Schlock, or about $4.00 if you get a 15-turn variable resistor (I recommend it). If the LM317 blows up, buy another one for $1.79 :-). If it blows up the load along with it, buy another CD player for $100 :-| Educational notes: a 78xx is a 3-terminal voltage regulator which takes a somewhat higher positive DC voltage and regulates it down to xx volts. A 79xx does the same thing for negative voltages. An LM317 does the same thing, but the output voltage is adjustable. An LM337 does the same thing as an LM317, but for negative voltages. 78xx's and 79xx's in TO-220 cases (the flat kind with the metal tab sticking out the top, like you see at RS) are rated to 1 amp, properly heatsinked (heatsunk?) LM317's and LM337's in TO-220 cases are rated to 1.5 amps. 78xx's and 79xx's have the advantage of needing no external components. >-- >Roy Smith, Public Health Research Institute -- Disclaimer: Yeah, right, like you really believe I run this place. John R. Murray | "Never code anything murray@vsjrm.scri.fsu.edu | bigger than your head.." Supercomputer Research Inst.| - Me
mcovingt@athena.cs.uga.edu (Michael A. Covington) (12/28/90)
Well done. One can add that... (1) There is no such thing as a 7803. The circuit with the LM317 looks good. Another alternative would be to use a 7805 followed by a series of diodes, each introducing about 0.6V additional drop. (2) The 317 does not absolutely require a capacitor across the output, but putting one there will help to reduce noise. (3) If you're worried about meltdown, put a fuse upstream from the 317.
roy@phri.nyu.edu (Roy Smith) (12/28/90)
elrond@ccwf.cc.utexas.edu (hlista) writes: > Does anyone have a schematic for a 12V DC to 3V DC 600 mA? In <1990Dec27.141809.2856@phri.nyu.edu> I suggested a 7803 and added: > You might want to protect it with something like a 20V zeiner across its in- > puts, and a 1-ohm power resister in series with the input, after the zeiner. David Lesher <wb8foz@mthvax.cs.miami.edu> pointed out to me that I'd be asking the zeiner to dump enough current to de-spike the entire car's electrical system, something which it is not going to be happy doing. One very likely mode of expressing its unhappiness is to simply open, but quick, and end up doing nothing useful at all. I agree with David, and so ammend my proposal to be: 2W-1ohm 2W-1ohm +------+ +12 O------/\/\/----+-------/\/\/\------| 7803 |------O +3 R1 | R2 +------+ __|__/ | / /_\ 20V zeiner | | | | | Gnd O---------------+-----------------------+---------O Gnd If your +3 load is drawing 600 mA, the I^2*R loss in R2 should be 360 mW so 2W seems like a reasonable safety factor. If you like, put a 1A slow-blow fuse in series with R2 to protect both it and the 7803 against an overload. I'm assuming the zeiner will only be called upon to zap low duty cycle spikes, so while R1 may have to handle big spike currents, the average power shouldn't be significantly higher than R2, so 2W should be OK for it too. At 600 mA, you'll see a 1.2V drop between the car's nominal +12 and the input terminal of the 7803, but since you'll only need something like 5V in to regulate properly, that's no big problem. -- Roy Smith, Public Health Research Institute 455 First Avenue, New York, NY 10016 roy@alanine.phri.nyu.edu -OR- {att,cmcl2,rutgers,hombre}!phri!roy "Arcane? Did you say arcane? It wouldn't be Unix if it wasn't arcane!"
rambler@pnet51.orb.mn.org (Dan Meyer) (12/28/90)
In article <1990Dec27.141809.2856@phri.nyu.edu> roy@phri.nyu.edu (Roy Smith) writes: >elrond@ccwf.cc.utexas.edu (hlista) writes: >> Does anyone have a schematic for a 12V DC to 3V DC 600 mA? >> Thanks for any help. > > Seems like a perfect application for a 7803 three-terminal >regulator. Can't get much simplier than that. Should run you a couple of >bucks at Radio Schlock. If they don't have the 7803 (it's an unusual >value), they will probably have the variable version, which just requires >adding a couple of passive components to set the output voltage. > The only question is whether a 7803 is hardy enough to handle all >the horribleness that goes on in a automobile electrical system (I'm mostly >worried about voltage spikes). You might want to protect it with something >like a 20V zeiner across its inputs, and a 1-ohm power resister in series >with the input, after the zeiner. Even Simpler - And output overvoltage protection is included! The diodesin series with the output of the 7805 drop 0.7v per diode: 5v-1.4v=3.6 v. add another one if you want run off of 2.9 v. The Diodes paralell with the output (which are installed the wrong way in the schematic!) form a crowbar circut. if the output rises above 0.7 * 6 = 4.2 v you pop the 1 amp fuse (be sure to use diodes of 1a or greater capacity!) 1a |---------------| +12V O--####--------| Generic |->|- >|-o------o----------O output fuse | LM7805 | | . |_______________| - . | ^ . | | ----- .01 uF capacitor (can | - ----- you get away without | ^ . it? Probably!) | | . | | . | - . | ^ . | | . | - . | ^ . | | . | - . | ^ . | | . | - . | ^ . | | . ground O--------------------o----------------o------o---O ground Come to think of it, simplify the circut a little, use a 4.1 ( or so ) zener instead of several standard diodes for the crowbar. Simpler and still almost all junk box parts! -- Dan Meyer Remember: " Buffalo never Oink " Seen on a South Dakota travel brocure. Advertisment: Try the Railway Post Office , a railfan BBS ! (612) 377-2197. UUCP: {crash tcnet}!orbit!pnet51!rambler ARPA: crash!orbit!pnet51!rambler@nosc.mil INET: rambler@pnet51.orb.mn.org
al@qiclab.uucp (Al Peterman) (12/29/90)
In article <1990Dec27.141809.2856@phri.nyu.edu> roy@phri.nyu.edu (Roy Smith) writes: > > The only question is whether a 7803 is hardy enough to handle all >the horribleness that goes on in a automobile electrical system (I'm mostly >worried about voltage spikes). You might want to protect it with something >like a 20V zeiner across its inputs, and a 1-ohm power resister in series >with the input, after the zeiner. I can't vouch for 7803's but I am using 7809's to run my garage door openers in both cars. Never a problem. BTW - It's really neat having a working button on the dash to raise the door. Ther's also the security angle that if you get power from a source that turns on with the accessories, someone can't raise the door by breaking into your car when it's parked in the driveway. Also no need to think about opener batteries... -- Alan L. Peterman (503)-684-1984 hm cse.ogi.edu!qiclab!al
dt@yenta.alb.nm.us (David B. Thomas) (12/31/90)
A hint: Take the 12v from the battery terminal with its own wire. Other wires from the battery have finite resistance and may have high, varying currents through them, thus providing noisier power. In particular, avoid the ignition switch wire. The "accessory" wire is probably okay. My car doesn't have one. I had a digital circuit that ran from a 7805 connected to the ignition switch wire, and it would fail when starting the car. Running a separate wire from the battery fixed the problem. I have a big digital circuit in my car (patent pending!) which uses TTL. 7400 series. Ouch! Moocho current, poor noise immunity. But the LM309K does it just fine. It has its own wire from the battery, switched on by a relay controlled by the ignition wire. (The new version uses CMOS -- I learned those lessons!) little david -- This is my .sig. n?e .sgurd no gis. ym si sihT
squishy@casbah.acns.nwu.edu (Shishin Yamada) (12/31/90)
From my past high school experience playing with my custom sound
installation (40 watts/channel, 7 band graphic eq, and Sony D-4 portable cd
player) in of all things, an '83 Sentra, I can tell you you should expect a
lot of electrical noise. It is inherent in a car. My first impulse was to
try filtering, then came tunable notch filters, then Radio Shack car
audio patches. Finally, I sat down and thought about it. The brunt of the
noise seems to always come from the car's ignition system. The tunable
notch filter failed because the oscilation frequency depends on the
engine's RPM multiplied by an intergral number (the number of cylinders).
Eventually, I worked it down to a simple circuit with a little back up
protection, noise filtering, and one power regulator transistor for a 9
volt, 500 mA cd player (yes, 4 watts of power! And it was PORTABLE!!!).
First thing is to select the type of power you want: Constant
(Always on, for example the clock) or Ignition (Only on when key is on). My
car didn't have many problems with either one. Then, once the +12V is
selected, you need to run it in series first through a auto Fuse, then a
reasonable sized inductor (first filtering defense). These are my two new
suggestions. I would also use a 7805 then place rectifying diodes in series
at the output. See circuit below:
+12V Fuse L1 1 _________ 2 D1 D2 D3
O-------O~O---UUUUU---+------+---| |-----+---->|--->|--->|----O +3V
+| | | 7805 | |
=== === |_______| === C3
Ground | C1 | C2 |3 |
O---------------------+------+-------+---------+--------------------O Ground
Where, L1 is say 1 uH, C1 is say 2200uF, C2 is 0.33uF, C3 is 0.1uF,
D1 D2 and D3 are silicon rectifying diodes (like 1N4001). All components
should be rated at least to 16 volts.
In operation, L1 provides the first filter against spikes. C1 is a
large capacitor to guard against large changes in voltage. C2 is there if
it's far from the battery. C3 provides high-frequency filtering. C3 should
filter out most of the ignition coil noise (assuming you have a
dristributor coil type ignition). Finally, each of the forward-biased
diodes provides a 0.7V voltage drop. The final output should be about +2.9
volts.
As a last note, I could never fully filter out all noise from the
system. I had barely audible noise enter the cd player simply from the fact
that I think it was electromagnetically induced into the system. My cabling
(especially the audio cables) were never the best. In MY '85 Honda Prelude
(not my father's car, My own), things work much better with good cabling.
Please note that this is all for a +12V car system with NEGATIVE
GROUND. You might need to rework this circuit for positive ground and/or 6V
cars. Have fun and Happy New Years!
-----------------------------------------------------------------------------
Shishin "Squish" Yamada | Electrical Engineering (Class of '91)
BitNet: Squishy@Casbah.acns.nwu.edu | Northwestern Univeristy
-----------------------------------------------------------------------------wrf@mab.ecse.rpi.edu (Wm Randolph Franklin) (01/01/91)
In article <2374@casbah.acns.nwu.edu> squishy@casbah.acns.nwu.edu (Shishin Yamada) writes: > >+12V Fuse L1 1 _________ 2 D1 D2 D3 >O-------O~O---UUUUU---+------+---| |-----+---->|--->|--->|----O +3V > +| | | 7805 | | > === === |_______| === C3 >Ground | C1 | C2 |3 | >O---------------------+------+-------+---------+--------------------O Ground > > Where, L1 is say 1 uH, C1 is say 2200uF, C2 is 0.33uF, C3 is 0.1uF, >D1 D2 and D3 are silicon rectifying diodes (like 1N4001). All components >should be rated at least to 16 volts. What does C2 do since it's so much smaller than C1? My guess it that it also has a smaller inductance and so traps hi freqs better. Is this right? Thanks. -- Wm. Randolph Franklin Internet: wrf@ecse.rpi.edu (or @cs.rpi.edu) Bitnet: Wrfrankl@Rpitsmts Telephone: (518) 276-6077; Telex: 6716050 RPI TROU; Fax: (518) 276-6261 Paper: ECSE Dept., 6026 JEC, Rensselaer Polytechnic Inst, Troy NY, 12180
mcovingt@athena.cs.uga.edu (Michael A. Covington) (01/01/91)
In article <%BS^BG*@rpi.edu> wrf@mab.ecse.rpi.edu (Wm Randolph Franklin) writes: >In article <2374@casbah.acns.nwu.edu> squishy@casbah.acns.nwu.edu (Shishin Yamada) writes: >> >>+12V Fuse L1 1 _________ 2 D1 D2 D3 >>O-------O~O---UUUUU---+------+---| |-----+---->|--->|--->|----O +3V >> +| | | 7805 | | >> === === |_______| === C3 >>Ground | C1 | C2 |3 | >>O---------------------+------+-------+---------+--------------------O Ground >> >> Where, L1 is say 1 uH, C1 is say 2200uF, C2 is 0.33uF, C3 is 0.1uF, >>D1 D2 and D3 are silicon rectifying diodes (like 1N4001). All components >>should be rated at least to 16 volts. > >What does C2 do since it's so much smaller than C1? My guess it that it >also has a smaller inductance and so traps hi freqs better. Is this >right? Thanks. > Series resistance. A big electrolytic capacitor, especially if not tantalum, will have a couple of ohms of series resistance, and to that extent will not be a good filter for high frequencies. That's why a capacitor of the conventional type (polyester, or whatever), much lower capacitance, is put in parallel with it.
squishy@casbah.acns.nwu.edu (Shishin Yamada) (01/01/91)
In article <%BS^BG*@rpi.edu> wrf@mab.ecse.rpi.edu (Wm Randolph Franklin) writes: >In article <2374@casbah.acns.nwu.edu> squishy@casbah.acns.nwu.edu (Shishin Yamada) writes: >> >>+12V Fuse L1 1 _________ 2 D1 D2 D3 >>O-------O~O---UUUUU---+------+---| |-----+---->|--->|--->|----O +3V >> +| | | 7805 | | >> === === |_______| === C3 >>Ground | C1 | C2 |3 | >>O---------------------+------+-------+---------+--------------------O Ground >> >> Where, L1 is say 1 uH, C1 is say 2200uF, C2 is 0.33uF, C3 is 0.1uF, >>D1 D2 and D3 are silicon rectifying diodes (like 1N4001). All components >>should be rated at least to 16 volts. > >What does C2 do since it's so much smaller than C1? My guess it that it >also has a smaller inductance and so traps hi freqs better. Is this >right? Thanks. > You hit the nose right on the button! C1 is large to filter out very slow changes in the power supply (like smoothing out power ripples in typical AC to DC converters). C2 is for filtering out high frequencies that are typical of cars. C2 is required since the DC regulator is far from the power source (battery). It helps to filter out high frequencies from both sides of the 7805. By the way, I only wrote down 0.33uF and 0.1uF because they are typical values. 0.33uF was given in the chip data book, and 0.1uF is common when using digital circuits (notably TTL) to block spikes. These higher frequencies are typically from the ignition coil as it fires the spark plugs. Finally, C3 is also there for high frquencies developed in the right hand side of the circuit. It is common practice with any digital circuits to place 0.1uF caps around the power supply as close as possible to logic chips (especially TTL), because they help to stabilize the power supply during changes of the logic gate's state. ---------------------------------------------------------------------- Shishin "Squish" Yamada * squishy @ casbah.acns.nwu.edu Electrical Engineering (class of '91) * Northwestern University ----------------------------------------------------------------------
ken@csis.dit.csiro.au (Ken Yap) (01/02/91)
Wow, does anybody have a circuit that will do the reverse? I wouldn't mind getting a car from a CD player. Especially if the car's a BMW. :-) :-) :-)
dunphy@col.hp.com (Dan Dunphy) (01/05/91)
You should use capacitors at least double the available voltage. I would use an output capacitor of at least 1 uF.