wally@cbnewsl.att.com (Brian S Walden) (02/11/91)
I want to take my old Sony Dicsman D-5 in the car with me, the problem is that it requires 9 volts and 1/2 amp. I'm not a e.e., but from the course in college (a few years, now) I remember something like this (12 to 9 volts) is just a resistor, a zener diode, and an NPN transistor. I figure someone should have done this already with real parts. So if you'd like to share a schematic with me, I'd be very grateful. Thanks in advance, Brian S Walden -- Brian S Walden AT&T Bell Labs, Whippany, NJ att!attbl!brian.s.walden
ee5391aa@triton.unm.edu (Duke McMullan n5gax) (02/11/91)
In article <1991Feb10.220719.17078@cbnewsl.att.com> wally@cbnewsl.att.com (Brian S Walden) writes: >I want to take my old Sony Dicsman D-5 in the car with me, >the problem is that it requires 9 volts and 1/2 amp. OK: First, let's think 13.6 volts, not 12. That's the actual (as opposed to nominal) voltage when you're running the engine. Second, you _can_ use a resistor/zener_diode/buffer_transistor circuit such as the one you mention, but there are easier ways. We want to carve about 4.6 volts off that 13.6. If we call it 4.5, and you can come up with a 4.5 volt zener, then just put the zener in series with the load: + 12V o----------------|<-----------o + 9.1V 4.5V zener diode Negative is ground, of course. Note that the zener diode is installed "back- ward" to the way normal diodes are placed. It's used in "reverse conduction" mode. A problem is that that diode is dropping 4.5 volts at half an amp... that comes to 2.25 watts. As a safety fudge, you'd want a diode that could handle twice that...say, 5 watts. 5 watt zeners aren't cheap. Also, note that that drop assumes a significant current being drawn. As the current gets very small (<1mA, typically), the voltage will start to rise. This _usually_ isn't a problem, but for a CYA it can't hurt to put a small load...say, an LED with a current-limiting resistor (2.2 kilohms or so)...across the 9V side. This will stabilize the current, and give you a pilot lamp to boot. Stick a 3/4 amp or so fuse in the circuit, too. Slo-blo is recommended. Again, note the polarity of that diode. Also, be warned: If that zener should develop an internal short, the full 13.6 volts will be dumped into your load. If you install it backward, you will get just under 13 volts into your load. If you're lucky, the fuse will go before your DiskMan. _If_ you're lucky.... There's also a junk-box solution: 1 amp silicon rectifiers are widely avail- able, cheap, and many of us have a bunch lying around. The forward drop on a silicon diode is nominally 0.7V; actually 0.626 is a _very_ good average fig- gure. Lesee...0.626 into 4.6 is...7.3bleep, so if we use seven rectifiers in series, we lose about 4.4 volts leaving us with just under 9.2 volts. The circuit looks like this: +12V o------->|-->|-->|-->|-->|-->|-->|-------------o +9V seven silicon rectifiers, 1A at 50V or so. This time, note that the diodes all point downstream the way they're "sup- posed" to. If you need more current, it's easy to find 6A or even 10A rectifiers. Consider the rectifiers as all one component, then install the fuse and pilot light as before. Each diode dissapates about 0.626 times the current. Stay under 1 amp, and you should be safe. The PIV of the rectifiers isn't a worry, and 50V is about the lowest (and cheapest) type you'll find. You have some more safety here, too. Failure of more than one of the diodes (shorting-type failure, that is) is pretty unlikely in any situation that doesn't involve a blown fuse. Another advantage is that all the components pass the strongest test of availability that I know. Radio Schlock carries 'em.... Best o' luck, d PS -- A final caveat: It's unlikely to happen, but make sure you have _sili- con_ (not germanium) diodes, and make sure they're not Schottky or "hot car- rier" silicon diodes. All those diodes have a forward drop of about 0.3V, and if you're using a rectifier chain, you're like to do unpleasant things to your load. Germanium rectifiers are rare, and Schottky rectifiers are both rare and expensive. If you're worried about it, you can measure the forward drop very easily: Just put the diode in series with a small load (say, a flash- light lamp) powered with a battery, and measure the drop with a voltmeter. It should be between 0.6 and 0.7 volts. d -- "Got to slap these Goddamn Third World nations around, Flynn," he said, "until they learn some manners." -- Gregory MacDonald, from _Flynn_ Duke McMullan n5gax nss13429r phon505-255-4642 ee5391aa@triton.cirt.unm.edu
mcovingt@athena.cs.uga.edu (Michael A. Covington) (02/11/91)
In article <1991Feb11.012255.3022@ariel.unm.edu> ee5391aa@triton.unm.edu (Duke McMullan n5gax) writes: >In article <1991Feb10.220719.17078@cbnewsl.att.com> wally@cbnewsl.att.com >(Brian S Walden) writes: >>I want to take my old Sony Dicsman D-5 in the car with me, >>the problem is that it requires 9 volts and 1/2 amp. > >OK: First, let's think 13.6 volts, not 12. That's the actual (as opposed to >nominal) voltage when you're running the engine. > >Second, you _can_ use a resistor/zener_diode/buffer_transistor circuit such as >the one you mention, but there are easier ways. > >We want to carve about 4.6 volts off that 13.6. If we call it 4.5, and you >can come up with a 4.5 volt zener, then just put the zener in series with the >load: > >+ 12V o----------------|<-----------o + 9.1V > 4.5V > zener > diode > NO! You'll fry a Discman. The voltage in the car is not a constant 13.6V; it varies from 11 to 17 volts!!!!! (Measure it if you don't believe me.) You don't want a constant voltage DROP, you want a constant voltage OUTPUT. A 7809 regulator chip will do the trick.
ee5391aa@triton.unm.edu (Duke McMullan n5gax) (02/11/91)
In article <1991Feb11.051608.2280@athena.cs.uga.edu> mcovingt@athena.cs.uga.edu (Michael A. Covington) writes: >>We want to carve about 4.6 volts off that 13.6. If we call it 4.5, and you >>can come up with a 4.5 volt zener, then just put the zener in series with the >>load: >> >>+ 12V o----------------|<-----------o + 9.1V >> 4.5V >> zener >> diode >> > NO! You'll fry a Discman. > The voltage in the car is not a constant 13.6V; > it varies from 11 to 17 volts!!!!! (Measure it if you don't believe me.) > > You don't want a constant voltage DROP, you want a constant > voltage OUTPUT. A 7809 regulator chip will do the trick. Well, on your car, perhaps. ;^) Seriously, Mike, I'm going by experience here...so your mileage may vary. I've used the chain-of-seven diodes for quite a few years, and never any damage to any electronics. Some years back, I used a 7806 in TO-3, nicely mounted on a heat sink, to power a little tape player. It worked just fine -- for about seven months. Then something went wrong with the '06. Fortunately, I was wearing the headset at the time. The volume increased significantly, and the motor speeded up. I didn't know what the problem was, but I had the instinct to yank the plug out of the cassette player. It survived without damage; I didn't. I burned my hand when I thoughtlessly picked up the regu- lator. I've observed battery voltages below 12V on occasion -- when the motor wasn't running, and when the battery was getting a bit low. I've never -- NEVER -- observed anything that would push a meter up to 17V on any vehicle I've worked with. Measured with a 'scope, things might be different, but it's likely the power supply filter caps would swallow such transients without difficulty. In any event, I've never had any equipment failures of this sort, nor of the voltage reducer, either. One could easily add a voltage clamp if this is worrisome, however. Across the output, put a string of diodes (or a zener) with a conduction voltage of say, 10 to 10.5 volts (16 or 17 rectifiers, if you're doing it that way). If the output voltage rises enough to turn that diode/diode-string on, it will clamp the output voltage at that point, and will blow the fuse if the voltage tries to rise much higher. Messy? Sure, but unless you have a pretty shaky voltage regulator, it should give you sufficient reduction to operate your equipment, and sufficient saf- ety with the shunt circuit to protect it. Twenty-four rectifiers take up a bit of room, but what's your equipment worth? A safety shunt of this sort is also a good idea with IC regulators. I've seen those fail often enough (not just the tale told above) to make me pretty wary of relying only on God and Mammon to see that they don't wind up with their pass transistor shorted. The same thing applies to discrete circuitry. Note that I have not installed a shunt on the reducers I use: risky, perhaps. But, again, I've not had any problems with those circuits...ever. d PS -- Now, watch me smoke a nine-volt appliance later this week.... d PPS -- Recently, someone's .sig said: "If there's one thing software types are sure of, it's that smoke is a hardware problem." d -- "Got to slap these Goddamn Third World nations around, Flynn," he said, "until they learn some manners." -- Gregory MacDonald, from _Flynn_ Duke McMullan n5gax nss13429r phon505-255-4642 ee5391aa@triton.cirt.unm.edu
depolo@eniac.seas.upenn.edu (Jeff DePolo) (02/12/91)
In article <1991Feb11.051608.2280@athena.cs.uga.edu> mcovingt@athena.cs.uga.edu (Michael A. Covington) writes:> >>We want to carve about 4.6 volts off that 13.6. If we call it 4.5, and you >>can come up with a 4.5 volt zener, then just put the zener in series with the >>load: > NO! You'll fry a Discman. > The voltage in the car is not a constant 13.6V; > it varies from 11 to 17 volts!!!!! (Measure it if you don't believe me.) > > You don't want a constant voltage DROP, you want a constant > voltage OUTPUT. A 7809 regulator chip will do the trick. Amen to that. At idle speed, my car shows right around 14 volts, slightly higher on cold days. At 1000+ RPM's, it's right around 14.5 volts. With the engine off, it's in the 12.5 volt range. I have seen voltages above 15 in some cars, especially when cold as some of the modern systems boost up the altnerator voltage to quickly charge the battery (the premise here is that when a battery is at less than full charge, it should be brought back up ASAP in case the trip is going to be too short to fully charge it at a normal voltage, according to a mechanic). The 7809 should handle your 1/2 amp, but may need a heat sink. A better way to go is to use a 78H09 (H for high-current) and mount it to some sort of a metal object, preferably using a heatsink. The cost of a 78H09 is about $2.00. You can try a 7809 (probably available at *gasp* Radio Shack) first, but if it gets too hot, it will (or should I say, it is supposed to) shut itself off. It's definately going to be warm, so don't touch it if you've been using it for a while. I wouldn't use a zener unless I had a crowber with it as well (requires another zener, an SCR, and a few resistors). --- Jeff -- -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Jeff DePolo N3HBZ Twisted Pair: (215) 386-7199 depolo@eniac.seas.upenn.edu RF: 146.685- 442.70+ 144.455s (Philadelphia) University of Pennsylvania Carrier Pigeon: 420 S. 42nd St. Phila PA 19104
panek@hp-and.HP.COM (Jon Panek) (02/13/91)
I'd have to agree... my Toyota Celica voltage meter regularly floats around 15-16V while the engine's running. A constant voltage drop setup, like the in-line zener, or the chain of Si diodes is not a very robust solution. The simple solution is the 7809. Make sure the power rating on the '09 is enough to handle the expected dissipation: P = EI, where E is the voltage *difference* between the engine (use 15-18V) and the output of the device (9V) -- this gives E of ~9V. I is the current needed by the discman. This gives you power in watts. Note that devices higher than about 0.5W require proper heat-sinking to achieve their max ratings... I sure wouldn't want to risk *my* discman on a junkbox solution... Good luck! Jonathan Panek Hewlett-Packard, Andover Division panek@hp-and.an.hp.com (508) 687-1501
myers@hpfcdj.HP.COM (Bob Myers) (02/27/91)
>The circuit that you're thinking of is this (Very) basic regulator, >An Emitter follower or Current amplifier... This one uses a PNP, other >variations can be used. > > Before anyone builds the circuit shown in the referenced article, please note that it is incorrect - it WILL NOT work if built as shown. There are two problems (or one, depending on how you look at it); the transistor is backwards (C for E) and the resistor is in the wrong place. A corrected version is as follows: + 13V in -------------\ /------------------> +9V out | C \ / E \ --------- / | B NPN power transistor \ R | / | | | ---------- | ----/ / /\ / \ 9.7V (or 9.6V) Zener diode ---- | | GND -----------------------------------------> GND Here's how it works: The regulation of the output voltage depends on the fact that the B-E drop of a silicon transistor is a *fairly* constant 0.6-0.7V, depending on the current through this junction. Thus, if the base is held to a constant voltage (which it is here by the Zener), the emitter will be this voltage minus the B-E drop. So, with a 9.6-9.7V Zener, we should get about 9V out at the emitter. The "lost" voltage (the difference between the input and output voltages) is not "dumped by the Zener, but appears across the transistor C-E. This is one drawback of this type of regulator - the voltage across the transistor (which will increase as the input voltage increases), multiplied by the output current, represents power which is doing nothing more than heating up the transistor. In other words, a linear regulator (which this is) isn't particularly efficient. (And note that you MUST have some minimum drop across the transistor - at a bare minimum, about 1.4V, and more reasonably 2V - to make sure that the transistor is biased properly.) The resistor R supplies both the Zener current and the base current of the transistor. The Zener current needs to be enough such that the Zener diode is sufficiently past the "knee" in its characteristic curve such that the voltage across the diode is reasonably stable; the base current required is determined by the maximum required output current and the minimum expected beta of the transistor. A Zener current of a few tens of mA at most is usually sufficient; if we say we want 20 mA through the Zener, and expect 1A load current with a transistor beta of 20 (meaning 50 mA base current), then the resistor must supply 70 mA with a drop of (13.6 - 9.7), or 3.9V. This calls for a resistor of 3.9V/70 mA = 55.7 ohms *maximum*; we'd probably wind up with a 51 ohm part here (nearest standard value). (Note that these numbers are examples only - use you own Zener requirements and transisor beta, etc., to get the right resistor for your application.) Also, please note that using a value slightly under the calculated maximum simply means that more current will be available to the Zener/base junction - and what isn't taken by the base will go through the Zener. Check to make sure that you won't have *too much* Zener current under any possible load/transistor combination - if you're in trouble here, go to a heftier Zener. The power rating of the resistor should be selected based on its expected power dissipation under the worst-case conditions (use at least the next larger standard rating). It's also a good idea to add some additional filtering to a regulator like this, in the form of capacitance at the input and output and across the Zener. If a capacitor across the output is used, a diode connected backwards across the transistor may be a good idea as well - to prevent any possible damage from trying to "run the regulator backwards" when the input power is shut down (or any other situation arises where the "output" voltage is higher than the "input." Bob Myers KC0EW HP Graphics Tech. Div.| Opinions expressed here are not Ft. Collins, Colorado | those of my employer or any other myers@fc.hp.com | sentient life-form on this planet.
dunne@motcid.UUCP (Jim E. Dunne) (02/27/91)
From article <erk.1356@americ.UUCP>, by erk@americ.UUCP (Erick Parsons):
> Get a 9V regulator chip ! I mounted one for my Watchman TV (actually 6V) into
Can you provide part numbers and makers? When I was investigating
a power supply for my 9V electric guitar effects, I could only find
12, 8, and 5 Volt regulators in the TI book. I know there are
"adjustable" ones, but I operate on the KISS principle when it comes
to circuits! I'm trying to get 9V from a really dirty 12V wall-type
transformer, and ended up with a 12V regulator chip, and thus the very
problem that is the subject of this thread. Why do they only seem to
make those screwy values when all my DC items are 3, 6, and 9 volts???
Thanks for the circuit, anyway.
--
Jim Dunne Motorola Inc. uunet!motcid!dunne
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Things are more like they are now than they ever were before. - Eisenhowerjgk@osc.COM (Joe Keane) (02/27/91)
In article <erk.1356@americ.UUCP> erk@americ.UUCP (Erick Parsons) writes: >This is a pretty basic circuit but works well as a regulator. After all >this though, I would have to agree with about everyone else in saying ... >Get a 9V regulator chip ! I mounted one for my Watchman TV (actually 6V) into >a cigarette lighter plug. I heat sinked it through the metal contact clips >which contact the lighter receptacle *AND* drilled 8 holes in the thing >for some air flow. The thing gets warm but not half as warm as it did when >it wasn't heat sinked !! Worked from Sacramento to Las Vegas without a >hitch, about an 8 or 9 hour drive. I have to second the comment about using a regulator chip. Anything you hack together from discrete components probably won't compare. Those little guys have lots of transistors, so duplicating their functionality would be costly and take up a lot of space. Their performance is generally very good, with wide input tolerance and very low output impedence. But the more important issue is what happens under abnormal conditions. Most regulator chips have current foldback and thermal shutdown so they won't burn out or fry your device when things get bad. This is what distinguishes a good circuit from a hack.
robf@mcs213k.cs.umr.edu (Rob Fugina) (02/28/91)
In article <4591@ash17.UUCP> dunne@motcid.UUCP (Jim E. Dunne) writes: >From article <erk.1356@americ.UUCP>, by erk@americ.UUCP (Erick Parsons): >> Get a 9V regulator chip ! I mounted one for my Watchman TV (actually 6V) into > Can you provide part numbers and makers? When I was investigating Try 7809 for a +9v regulator. > "adjustable" ones, but I operate on the KISS principle when it comes What's the "KISS" principle? > problem that is the subject of this thread. Why do they only seem to > make those screwy values when all my DC items are 3, 6, and 9 volts??? > Thanks for the circuit, anyway. Why 3, 6, and 9? Because that's what corresponds to 2, 4, and 6 1.5 volt batteries... BUT, the values I've seen for voltage regulator chips are 5, 9, 12, 15, 18, and 24... Rob robf@cs.umr.edu
elliott@optilink.UUCP (Paul Elliott x225) (02/28/91)
In article <erk.1356@americ.UUCP>, erk@americ.UUCP (Erick Parsons) writes: > ---------- > The circuit that you're thinking of is this (Very) basic regulator, > An Emitter follower or Current amplifier... This one uses a PNP, other > variations can be used. [design omitted] STOP! Don't build this! It won't work! I fully expect to be one of dozens replying in horror to this circuit, so I will stop here. In the remote chance that no one else covers the details, I will probably follow up. Ok, I will stop *here* ;-) -- Paul M. Elliott Optilink Corporation (707) 795-9444 {uunet, pyramid, pixar, tekbspa}!optilink!elliott "If I had known it was harmless I would have killed it myself." - P.K. Dick
dunne@motcid.UUCP (Jim E. Dunne) (03/01/91)
From article <5170111@hplsla.HP.COM>, by tomb@hplsla.HP.COM (Tom Bruhns):
> (hee-hee-hee -- you're with Motorola and can't find semiconductors?? ;-)
OK, I'm a software hack in Cellular. Hardware devices crash when
they see me comin'! Actually, right upstairs from me, where I knew
they had scads of data books, I found out they had a cache of sample
parts too. I raided the cabinet, only to find 5, 8, and 12 V
regulators! Oh well, I grabbed an LM317 adjustable. To the mailers
who said the adjustable needed only two resistors, well the data book
shows otherwise. Nothing I can't handle, but it'd be so nice to
have it all on-chip... guess I'll hunt for a 7809 next. Thanks to
all who helped.
Long live the KISS principle...
-- Keep It Simple Stupid (Softwarejock)!
--
Jim Dunne Motorola Inc. uunet!motcid!dunne
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Things are more like they are now than they ever were before. - Eisenhoweredhall@rand.org (Ed Hall) (03/04/91)
In article <4596@ash17.UUCP> dunne@motcid.UUCP (Jim E. Dunne) writes: >From article <5170111@hplsla.HP.COM>, by tomb@hplsla.HP.COM (Tom Bruhns): > >> (hee-hee-hee -- you're with Motorola and can't find semiconductors?? ;-) > > OK, I'm a software hack in Cellular. Hardware devices crash when > they see me comin'! Actually, right upstairs from me, where I knew > they had scads of data books, I found out they had a cache of sample > parts too. I raided the cabinet, only to find 5, 8, and 12 V > regulators! Oh well, I grabbed an LM317 adjustable. To the mailers > who said the adjustable needed only two resistors, well the data book > shows otherwise. You are correct--the databook shows two bypass capacitors, both optional. One is at the regulator input, and is needed when the power supply filter capacitor is an appreciable distance from the regulator (e.g. in a wall wart, as is quite common these days). The other is at the regulator output, and improves transient response (i.e. better regulation when the load varies at a high frequency, such as with digital logic). If you look at the databook for the 78XX, you'll see the same optional capacitors. All that the LM317 adds is two resistors, and a great deal of convenience. I find that using a single part for a variety of voltages (including odd values) is a LOT simpler than having to use a different part for a different voltage. > Long live the KISS principle... > -- Keep It Simple Stupid (Softwarejock)! As a software jock myself, I agree. That's why I prefer to have a single procedure that I can call with a variety of parameters rather than a different procedure for each parameter. -Ed Hall edhall@rand.org
mckillnm@unix1.tcd.ie (Bubble Boy) (03/04/91)
Why don't U use the LM318 voltage regulater or even a 7809 regulater.
Why not try this :- (7809)
____________
1| 7809 |3
+12 V -------------------| |------------------ +9V
| ------------ |
| |2 |
------ | ------
------ | ------
100uF | | | 10nF
| | |
0 V ------------------------------------------------- GND
or this :- (LM318 <I think>)
------------
1| LM318 |2
+ 12 V -----------------| |------------------ +9v
| ------------ | |
| |3 \ R2 |
------- | / -----
======= |-/\/\/\--| -----
100uF | | R1 | 10nF
| | |
0 V ------------------------------------------------ GND
As I sit here I can't think of the relationship between R1 R2 and the
Vout (ie 9V), but any book on power supplies should have it in.
If you can't find it mail me and I'll look it up for U.
Hope this has been of some help !!
Mark at unix1
TCD Dublin, Ireland.
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