Two different circuits - Need some help :-)

[DeeJay86]

Hello there.
I'm quite blank to the electronics world, atleast about how to put together circuits so therefore i'm asking for some help here.

First about my project... I have 2x3.6V batteries connected to have an output of 7.2v and from those i will need to be able to reduce the voltage and be using a tactile switch.

Circuit #1: I need to use a tactile button, but those i've found only does like 0.05amp, so i got told to build a circuit to avoid the button to melt down - But how will that be done? I know i need some kind of small circuit to make the button usable with 7.2v

Circuit #2: I need a circuit to regulate my 7.2v up and down between 0-7.2v (Not exactly 0 but close to 1v atleast) and for that i know that i can use the LM337 regulator, and some kind of trimmer potentiometer but that is all i can figure out at the moment. After the regulator i will mount a LED display to display the voltage, which i'll buy premade (I'm that lazy)


I hope someone out there can help me figure out what parts that i need to buy to make these two circuits and how to put them together - I'm not that good at reading circuit plans but it'll do anyway.

Thanks in advance!

 

[Reloadron]

The LM337 is a negative regulator, I don't think that is what you want. You likely want a positive regulator. That said another problem is the positive regulator you choose will have a "dropout voltage" so if you want to get close to your supply voltage you need what is called a "low dropout regulator". If the current is low then something like this. as an example.

As to the tactile switch, you need to better explain exactly what you want it to do.

My bad as this would be a better choice as to a low dropout regulator for what you seem to want.

Oh yeah Welcome to The Forums!

Hope that helps...
Ron

 

[DeeJay86]

Thanks for the reply.

The Tactile switch should just work as a off-(On) switch, when its pressed it will powerup something with the regulated voltage, and when released its off again.

Can this be used, this is where i read about the LM338 - **broken link removed**

 

[Reloadron]

The LM338 (see the data sheet) is a 5 amp adjustable regulator having about a 1.2 volt dropout voltage. So with an input of about 7.2 volts you would get an adjustment range of approximately 1.2 to 6 volts out. If you can live with that range it is a good choice. If you plan to run it close to max current (5 amps) it would need a heat sink.

Most tactile switches are designed as a momentary push button switch. The switch works only when the button is held. If you have a link to the switch you have in mind I can tell you more. If you want a press for On and then a Press for off it would require adding a small flip flop circuit driving a small relay or transistor depending on the load.

Ron

 

[DeeJay86]

Well, the button should only work when i press it. The thing i am building should only be "ON" when holding down the button, but all the buttons i've found (tactile) only holds for 50 micro amp, which is way too low since the thing thats beeing activated by the button uses about 3amp at 7.2volts


I guess the LM338 wont be good then, i need the 7.2 voltage at some point :O

The tactile button i've been looking at is on ebay on this link
**broken link removed**

 

[Reloadron]

OK, the button woule drive a transistor (like a MOSFET) capable of supporting the load current. I would consider using what is called a logic level MOSFET transistor. Meaning the MOSFET transistor requires a low gate voltage to act as a switch.

The problem with adjustable (or any) voltage regulators is that Vout will not give you a range of 0 to Vin. Back to that dropout voltage. Even low dropout regulators will have a dropout voltage. The following is taken from your link:

•The minimum output voltage is 1.24 volts.
•There is a 1.6 volt drop across the regulator, so the input voltage has to be 1.6 volts higher than the highest voltage that you would want out. For example, to get a 10 volt output, you would have to set the input voltage at 11.6. You can use the voltage meter on your power supply to adjust the input voltage or if more precision is desired, use a multimeter.•To protect against a reverse connection, a 6 amp diode could be placed between the plus input and pin 3 of the LM 338T. The input voltage would have to be increased to compensate for the 0.7 volt drop across the diode.
•If the power supply is not filtered it would be a good idea to put a 2200 µF 35 volt polarized capacitor across the plus and minus inputs. The minus side of a polarized capacitor is the one that is marked with a stripe.

Later I can check the tactile button link. I am at work and Ebay content (as well as other content) is blocked.

Ron

 

[DeeJay86]

It's still hard for me to understand how i should make this :O

Diagrams for me is like codes to read

 

[Reloadron]

It's still hard for me to understand how i should make this :O

Diagrams for me is like codes to read

Do you have any friends with electronic skills? Another solution might be an over the counter solution. Building something like this while not overly difficult is also not easy for someone who can't read and understand electronic drawings (schematics) as well as the theory behind a design.

Ron

 

[DeeJay86]

Unfortunately not, but if you was to draw a schematic of a voltage regulator that suits my specification, would that take alot of time? If so then dont, if not would you do such thing? Then I'll see if its readable by my skills, i had a month of eletronic education a few years back.

Is there anyway to boost the 7.2v to 8.2 before the volt regulator so that i wont loose the 1.2v? The top of what i can afford to loose is 0.2v out of the 7.2v

Thanks in advance

 

[Reloadron]

There is no easy way around the dropout factor. The only way to get more out is put more in unfortunately. The LM338 is a good choice but you would need about 9 volts in to assure 7.2 out and you would still have a low end in the 1.2 volt area. The data sheets on these have schematics. Also, when working with regulators like this the capacitors are important even when a battery is the power source.

Ron

 

[4pyros]

DeeJay; Are you using this for slot cars or some other purpose?

 

[DeeJay86]

Ron: I guess I could make it with 3x3.6V batteries or buy low resistant heat champers for my project to be able to use it at 5volts and find a decent small schematic to do this.

4pyros: It's for an home build eletronic cigarette actually...

 

[Reloadron]

Oh man, I saw the E-Cigarette thing. How small are we talking here?

Ron

 

[DeeJay86]

Well the casing i've build is 90x31x31mm for the one without voltage regulation - The one with voltage regulation is 80x50x27mm