Re: voltage controller circuit

alishadevochka@xxxxxxxxx wrote:
On Jun 29, 8:24 pm, ehsjr <e...@xxxxxxxxxxxxxxxx> wrote:

alishadevoc...@xxxxxxxxx wrote:

On Jun 29, 5:02 pm, alishadevoc...@xxxxxxxxx wrote:

Hi

I have 30 volt regulated adapter. I would like to create a circuit
which will allow me to control the voltage from 0 to 30.

Can anyone tell me where I can find a diagram for such circuit? I am
very new to electronic. I am creating this for my ety class -- mostly
to test series and parallel circuits, and few other lab work.
However, I may use it for other things too.

Thanks in advance

Update

I built following circuit on a breadboard and voltage regulator (5K
LM317 regulator) was burned -- sparking were coming out it...

http://vancouver-webpages.com/peter/lm317.gif<--- this was the c

This is what I did with LM317

LM317 has three input (a,b,c)
a goes to ground,
b connectedt o resistor 240, -- i was using resistor 220om cause I
don't have 240ohm
c connected to LM317?

what went wrong?

The diagram is correct, as far as it goes, except that
your input voltage is way higher than it needs to be at
40 volts, which would cause a whole bunch of extra heat.

For a maximum of 12.71 volts output, you want to keep the
input voltage to no more than ~16 volts. The 220 ohm
resistor is not a problem. Your table of resistances
and output voltage, if those are measurements, suggest
a high current draw and no heatsink. For example, with
220 R1 and 2200 R2 and a measured output of 12.71, you
are over a volt low. Makes me believe you are cooking
the LM317.

What to do?
1) Make _absolutely_ sure you set the 10-40 volt input supply
to *no more* than 16 volts when you want <13 volts out.
2) Tell us what the load is - how much current does it draw?
3) Put the LM317 on a heat sink.
4) Depending on your answer to 1) you may need to add pass
transistors.

Let's get the ~12 volt supply sorted out before going
to the ~30 volt supply.

Ed


Tomorrow, I will buy two new potentiometer. In some of my lab
expirement I need 20-25v output. I still don't understand how my
potentiometer end up sparking, and smoking.

I am sure I put it in a wrong way, I just don't know which way would
be right though...


Your diagram does not show a potientiometer. It
sounds like you have connected the potentiometer
to the wrong place. Post a schematic that shows
the potentiometer.

You can get 20-25v output. But first, you need
to get the basic circuit to work properly. Then
you can add pass transistors.

You can measure how much current is drawn to
get a fairly close ball park figure this way:
put a 1 ohm 5 watt resistor in series between
the Vout from the 317 and the load. Connect
your voltmeter across the 1 ohm resistor.
The reading you get is the current in amperes
that the load is drawing.

Ed
.

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