Reducing voltage from 9 to 5 volts

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Pallen33

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I've got a feeling this might be far too simple, but just wondering if anyone could help me with a little problem I have. I have a 9 volt DC supply voltage (battery) and just simply want to reduce this down to about 5 volts (or less, not too critical). I've read about voltage regulators, but really know nothing about them and how simple it would be to include one in a circuit- what's the simplest solution to reduce the voltage, without mentioning too many weird and complicated sounding components! thanks a lot :roll:
 
voltage regulators are EXTRMELY simple.

they only have three legs!!

connect a 78L05 as shown below (in the pic called 'reg.gif')

assuming you don't need huge ammouts of current, you won't need a heatsink or anything fancy.

If you really wanted to, you could make a potential divider instead - see the green coloured picture, but the regulator is better because it can cope with changes in the input voltage.
 

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One more thing on regulators: You should put a capcitor from the input to ground and from the output to ground (make sure you connect the - side to ground). These two capacitors will make the regulator work better and avoid any potential problems. About 10uF should be good. Regulators are probably the easiest IC out there - well worth learing how to use and there's a regulator in almost every electronics product out there.

Brent
 
true, I was just trying to keep it as simple as possible, and there shouldn't be too many probs, and he/she is running it from a PP3
 
grrr_arrghh said:
true, I was just trying to keep it as simple as possible, and there shouldn't be too many probs, and he/she is running it from a PP3
Click to expand...

Yes, but it is very important to fit the capacitors!.

If Pallen33 looks at the hardware processor boards used in my PIC tutorials they all use a 5V regulator from a 9V battery.
 
thanks

Thanks everyone, really appreciated and I think I'm starting to understand it now. Just a couple of quick further questions which I've thought of:
1) Would it be possible to go down to any other voltage from a 9 volt battery apart from 5 volts? Ideally I need 4.5v so there is still a chance that 5v might be too much, but it should hopefully be ok (haven't had chance to try it yet unfortunately)
2) Concerning the issue of capacitors (don't want to stir up trouble or anything!) what is the benefit of putting them in the circuit and have I understood it correctly with the adapted diagram below (not sure on symbol for capacitor!)? Also bmcculla, when you said "make sure you connect the - side to ground" were you talking about the capacitors, and if so, how do you tell which side is the -'ive ? (sorry for embarassing level of knowledge).... I understand that adding capacitors might not be absolutely necessary, but I might as well learn about how they would work in this circuit all the same. Really appreciating all this help....by just searching on the web I was getting nowhere for quite a while!! Thanks.
 

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capps...

well i have also a sheme whit a pic from every range running whit out caps....


but the best reason could be that it simple keeps working because the i supply already a good voltage soow it is very difficult to say if it is nececary in your circuit..

another point wy not do it to be sure..???

the - side is 1 leg of the think.. if you use the big onse that mount vertical..they have a colour common blue or grey..and then you see the - side nearby one leg..don't have a cam but will do it one day..

the simbol of a capp looks like a battery,,,and the values are in uF common soow if you can search for a sheme you will find fast one..

greetz,

Walter
 
You 'might' be lucky without capacitors, but all manufacturers state they are essential - I certainly wouldn't build a project without them. Unless you have access to a scope, and can check for instability, I wouldn't advise you to either - even then, you are only checking under a limited range of circumstances, for the cost of two cheap capacitors you should always fit them!.

As for the negative side of a capacitor, they are clearly marked with their polarity, usually with a large white stripe with negative signs printed on it. The positive leg is usually longer as well. This only applies to electrolytic capacitors, smaller capacitors are usually non-electrolytic and non-polarised.
 
thanks again

Ok, I agree that as you say you might as well add the capacitors because don't exactly cost much. Just to check, is my circuit diagram correct? (even if it is a touch on the amateur side!)... heading for maplin in a bit to get the components so just want to make sure I've got the right end of the stick...
 
Re: thanks again

Pallen33 said:
Just to check, is my circuit diagram correct? (even if it is a touch on the amateur side!)... heading for maplin in a bit to get the components so just want to make sure I've got the right end of the stick...
Click to expand...

Yes it's fine, if you look at my tutorial diagrams (as I mentioned previously) they use a 7805 off a 9V battery, complete with capacitors.

BTW, I forgot to ask previously, you mention you would really like 4.5V, what is it actually for?.
 
electronics

Cheers nigel. If I'm totally honest didn't actually check those links before because thought they might refer to stuff out of my league, but I'll have a look now...

What's it for...hmm, interesting question. It's actually an invention so can't actually go into any kind of detail, but what I can tell you is that I'm using one of those remote doorbells as the basis of the design. The doorbell ringer conventionally just runs on 2 AA batteries (i.e 3v) but it I've had it running up to 4.5v without a problem. The thing is I need it to run from a source which will be around 9v, although the exact size of the battery could be a bit less or a bit more, probably somewhere between 7 and 10 volts (sorry for the vagueness, but difficult to explain without going into details). Presumably from what people have been saying, the regulator should produce a reliable output of 5v (or whatever) no matter what the battery size is (within reason). I was just intrigued as to whether you can get regulators which produce a voltage lower than 5v, although in my case 5v should probably be ok.
 
if maplin is your local, then have a look at **broken link removed**, it is variable regulator, so you could get exactly what voltage you want, provided the input voltage is several volts higher than the output voltage that you want.

Tim
 
regulator

Cheers Tim, I appreciate some specific component advice because I generally feel quite at a loss when I go to Maplin. One question which again might be stupid, how do you vary what output voltage you get? Is it just dependent on what you put in (i.e you get 75% out of whatever you put in), or can you actually vary it even with the same input voltage?
Paul
 
you can specify it, using something like the circuit below. (the circuit below is infact for a 'LM338K 1.2 to 30 Volt 5 Amp Regulator', which is way overkill for your needs, but the circuit should work the same) R1 is a 5K Pot (although i'm thinking it will be easier to get hold of a 4.7K...), and R2 is a 240 Ohm 1/4 W Resistor (again, a slightly obscure value, I should think that a similar value should do fine)

Is that helpful?

Tim

P.S. I am right in thinkin that all variable regulators work in the same way, aren't I? Please correct me if i'm wrong...
 

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hmmm

Think I'm starting to get out my depth Tim, but thanks very much for your advice all the same. I think I might just go for a fixed regulator to keep things simple, I was thinking of getting the first one on this list from Maplin (i.e. the L7805CP)....

**broken link removed**

I'm was also going to get two capacitors as Nigel advised just to be on the safe side and have a go at building the circuit originally posted (but with capacitors). 5v might be too much, but if it isn't taking this route looks like the simplest option!...
 
Re: hmmm

Pallen33 said:
Think I'm starting to get out my depth Tim
Click to expand...
I think your are giving up too easily.

Whats complicated about the circuit diagram? It has two extra components on it - thats all. If you want I can draw do a vero board layout, with pin numbers for all the components, anything you need, just ask, its what we are here for (although ask nigel rather than me, cos he know more... :lol

If you are not sure if you can work with 5v, then you really need a variable regulator. Either check that you can work with 5v, or go with the variable. You won't be on your own, and you'll learn something from it.

Tim
 
Re: electronics


Right, that's the info we needed (the actual device itself doesn't really matter).

Perhaps you didn't know you can get 3.3V fixed regulators?. You probably can't get them at Maplin, but RS Components list four different ones - I suspect the LM1086CT-3.3 would be the best one for you, it comes in a TO220 case, like a 7805. They also list one 4V regulator, but that's a surface mount device and only low current.
 
Where next....

Point taken Tim, but my electronics knowledge is so poor that you may regret offering assistance! For starters, just to highlight how embarrisingly cack I am, I don't know what C1, C2, C3 and C4 are in your diagram- I'd hazard a guess at capacitors on the basis of what's been said before, but what size should they be (10uF as you mentioned before??)? I'm also assuming that where the two parallel lines go off the diagram on the left hand side of the page that the top one would be connected to the +'ve terminal of the battery, and the bottom one to the -'ve side of the battery.

Thanks for those details Nigel about other smaller voltage regulators- they may well turn out to be the best option if either a fixed 5v regulator is too much voltage or if, in the process of building Tim's circuit, I get scared and run away :?

I'm extremely grateful for all this (I've probably said that a couple of times by now...)
 
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