# Voltage Controlled Switch

This is a little circuit that i designed that could be used for a charging controller or voltage limiter. Its very useful if you are thinking of making a solar charger.

## Step 1: Get the Stuff

To build this circuit you would need the following:
2 1k ohm resistors
2 5V zener diodes
A comparator (the one it used is a KA393)
A led
A Digital Multimeter
A variable power supply ( of your choice once its in the limits of the comparator)
Some wire

## Step 2: Assemble the Circiut

In the assembly of the circuit u can alter the circuit as you please. For instance i didn't go as exact as the schematic.
Just in case you don't know how the comparator works heres a link that shows how.
home.cogeco.ca/~rpaisley4/Comparators.html

## Step 3: What its suppose to do

In the circuit that i build thats not totally the same as the in the diagram, is suppose to turn on the led at 8V because i used a 5v and 3v zener. I also used a two 9 V batteries which voltages differ. The circuit i suppose to turn the led on at 8 V and any voltage lower than it should go off.

## Step 4: Tips

If turn the comparator positive and negative leads around will have the reverse effect. I mean instead of  turning on at 8V it will turn off and any voltage thats lower than that it will be on. Sorry i don't have a picture of that particular instance, but i will put in one any way. [ for decorative purposes]
Also to increase the current of a load which it quite large the LED can be replaced with a P-MOSFET which will give you the gain.

## Step 5: Thanks

Thanks for looking at this and i hope that it was helpful .Have a good and GODLY day.
Elexa says: 10 months ago
I did not understand which component you used and why the 5V supply? Can't we use a comparator that derives the required power from the charge capacitor? Will you please explain so that it'll be easy for me to make this circuit. Please help..
josh1001 (author) says: 10 months ago
this a prototype circuit and you see how complicated it is right now, there isnt even all the components need to make it work yet.
Elexa says: 10 months ago
Elexa says: 10 months ago
Thank u for the reply. The problem is that the solar panel I am using only give 1.5 V output. So I think may be I need to use some sort of amplifier because I can not use any external power supply. And why do we need bi-stable multivibrator? Please help me by drawing up a schematic that works for me. It would be a great help...
Elexa says: 10 months ago
Hi

I need to make a circuit working between 1 V and 2.4 V. I want to make a solar charger that charges a capacitor until it reaches 2.4 V, once the voltage reach 2.4 V, the switch is closed and the led lits up. At the time, 1st capacitor is discharging, I want to charge another capacitor. When the 1st capacitor discharges to 1 V, then I want to charge the 1st capacitor again and connect the load to 2nd capacitor. Please help me with this..I'll be very thankful to you.
josh1001 (author) in reply to Elexa10 months ago
O sorry i didnt read it so properly you also need a Bi- stable multivibrator in the circuit for it work
josh1001 (author) in reply to Elexa10 months ago
the problem i see with this is that most opamps need @ least 3v to work properly. so you may have to run an external power supply or a larger voltage solar panel to power the opamp the rest is easy. i draw up a schematic for you.
Crinton says: 1 year ago
THanks for posting this, right along the lines of what I am looking for. What would I need to change to be able to control a realy with this circuit. Specifically, have a SPST relay engange at 5V or higher, or relay disengage at anything under 5 volts? Any help is appreciated.
josh1001 (author) in reply to Crinton1 year ago
O yea the K represents 1000. So 1k is 1000 ohms and 10K is 10000 ohms. ZD is the zener diode
josh1001 (author) in reply to Crinton1 year ago
hi crinton, sorry i didnt update this thing yet but there is an easier way of doing it. You can use one diode and a voltage divider plus an opamp / comparator. Ive placed a schematic on below it will show you how to connect it. The circuit is currently connected to turn on @ 5V, if you want it to do the opposite turn off @ 5V exchange the positions of pin 2 and 3. i hope you know how to use a transistor. I labeled ther transistor points B for base, C for collector and E for Emitter. Just purchase any npn low powered npn transistor and you will be fine. Transistors come in 3 different pin configurations CBE, BCE, ECB. the package will show you the pin out. if not go and reference it online. if i missed any thing message me back.
srainsdon says: 3 years ago
this is a very nice I thanks i dont understand it all but im going to collage and will ask some friends to help me out wonderful place for me to start though thanks.
awatif1989 says: 3 years ago
rpvanpatt says: 3 years ago
Hey,  I like the idea, I am looking to find specific answers for a particular setup I am trying to put together.  Could you help me?  just message me thanks!
josh1001 (author) in reply to rpvanpatt3 years ago
i'll help u, what do u need?
rpvanpatt in reply to josh10013 years ago
I am trying to create a mini solar panel battery pack/charger.  I have a mini solar panel that I would like to try to connect to a 9.6v nicd battery (2 if possible).  Also, I was thinking of putting an LED indicator that will let me know when the battery is charging/charged.  I have a drawing I am not sure if it will work or not, if so I dont know the particular parts that I would need.  Any help would be great, thanks www.instructables.com/files/deriv/F5L/T83H/G57007WW/F5LT83HG57007WW.MEDIUM.jpg

josh1001 (author) in reply to rpvanpatt3 years ago
OK I was working on a circuit to charge a 12 volt battery. Its a charge controller I designed I guess I can tweak it to meet your demands
josh1001 (author) in reply to josh10013 years ago
(removed by author or community request)
josh1001 (author) in reply to josh10013 years ago
when u open the picture view it with the windows picture and fax viewer
rpvanpatt in reply to josh10013 years ago
hey, sorry i dont have that program
josh1001 (author) in reply to rpvanpatt3 years ago

josh1001 (author) in reply to josh10013 years ago
can u see this one?

rpvanpatt in reply to josh10013 years ago
ya think if i print this and take it to radio shack they could help me figure it all out and the parts?
josh1001 (author) in reply to rpvanpatt3 years ago
well the triangular thing is a KA393 comparator and it is a small ic with 8 pins to find out the pin selections go to http://www.datasheetcatalog.com/ and type in KA393. You can use an enhancement mode p channel mosfet of our choice as the gate. To see how the comparators work check out http://home.cogeco.ca/~rpaisley4/Comparators.html
rpvanpatt in reply to josh10013 years ago
nevermind I got it, but I dont quite understand it all, can ya explain the symbols a bit? sorry ...ive never made some one, or bought stuff for it neither
nfarrow says: 4 years ago

So what if I need a 12v charge controller for something like solar? What would you recommend?

josh1001 (author) in reply to nfarrow4 years ago
I will upload a schematic too show u how to get it done. How much watts is this solar panel?

nfarrow in reply to josh10014 years ago

It’s just a 5watt solar but would like to be able to add more later on since I am working on refurbishing some old car batteries. I have about 12 now and I was told that I should hook them up in parallel.

josh1001 (author) in reply to nfarrow4 years ago
Sorry im taking a bit of time, im testing and trying to improve circuit. I should have it soon for you. Is 30W of power ok?
nfarrow in reply to josh10014 years ago
No clue, I guess that will work. thanks :)
josh1001 (author) in reply to nfarrow4 years ago

mathews says: 4 years ago
You may want to place a 330R resistor in series with the the LED output.

Also, why do you have two zener diodes in your circuit, you only need one, and the other input should be a potential divider made up of two resistors. That way if it is over 5v, it will trigger on, and if not it will be off.
josh1001 (author) in reply to mathews4 years ago
thanks for the tips, i tried the voltage divider circuit and it works.
Question isn't the comparator sinking the led current ?
What i mean is the led isn't a big load that would damage the IC, but in future i would put in a resistor just to be safe.
inventorjack says: 4 years ago
You should explain a bit more how the circuit works. If I didn't already understand comparators, zeners and the like, this instructable would be totally greek to me. Perhaps explaining why you chose those specific component values and what the components actually do would be helpful to those less experienced in electronics.
josh1001 (author) in reply to inventorjack4 years ago

This is my first time posting  an instructable, and it did realise that i could have change some things. By the way you are right abotu the lack of in fromation in the instructable, I'll update it soon.

inventorjack in reply to josh10014 years ago