0-30 Vdc Stabilized Power Supply

[mixos1]

Yes, LM7805 is suitable for 24V input, it can take as input even 30V according to the datasheet i attach.

The capacitors are used to smooth the input-output voltage.

LM7805.pdf

 

[FireFly3]

If meters are to be added to this power supply, I believe they should powered by their own transformer. Am I right?

So to add a cooling fan, should that be powered by the power supplies transformer, the meters' transformer or a third transformer of its own? ???

 

[MP1]

Billy: The regulator might get hot with this amount of difference, so you should add a heat sink. Also, in regards to the capacitors, when you add a capacitor to the input side of the regulator, isn't there already one there for the other part of the power supply? When you put two capacitors in parallel on the same line, it changes the value of capacitance and will actually cause less filtering in many cases. Check your values with the capacitor parallel formula (Ctotal= (1/(1/C1+1/C2+...1/Cn))). You will probably not want the additional one there. Be sure that all capacitors are well above the max voltage range. I usually use the times2 rule when possible, but this is not necessary. This is only my own personal safeguard.

Firefly: You should not need additional transformers to run a fan or meters. If your existing transformer is capable of the added current usage, you can tap into it just after the rectifier bridge with a regulator or a zener/resistor for the correct voltage drop.
MP

 

[DerFly1]

Hello All,

Seems we are all making our modifications to this project. I hope someone can help me with mine.

I would like to use two variable resistors each for the adjustment of voltage and current to enable coarse and fine adjustment.

The circuit calls for 100k variable resistors. Is it possible someway to wire in 10k variable resistors for the fine adjustment?

How does one wire the 100k and 10k variable resistors together?

Thanks for any help. A diagram would be great.

DerFly. ???

 

[FireFly3]

Thanks MP. This site has an LCD panel meter that seems cheap enough:

http://www.circuittest.com/Default.asp?Main=/English/OnlineCat.asp?Menu=/English/Content/Categories/CatM_81.asp%26Detail=/English/Content/Items/DMD-3500B.asp

Not sure about the quality. Any thoughts on that?

The description states: "Note: Supply voltage must be independent of voltage being measured." I've seen something similar for some other meters.

Any idea what that is about? Would this meter need a separate transformer or would it be good enough if it was on its own taps?

TIA;

 

[MP1]

Firefly, they are just trying to say the supply voltage must be a fixed voltage. The other input is the measured voltage and this is what will be displayed. In other words, you would want to add a 9 volt regulator right after the rectifier bridge to supply this unit and the measured variable voltage will go into a different pin on this meter to display the output voltage of your PSU.

Here is a link to the one I have just purchased. Much better price. In fact, I have not seen one for less. It has different jumpers for decimal point on voltage ranges. 0-2mV, 0-20V, 0-200V, (up to 500V range, I think).

http://www.allelectronics.com/cgi-bin/category.cgi?category=385&item=PM-200&type=store

MP

 

[MP1]

If the link does not work, just go to www.allelectronics.com and use the search box. Enter pm-200 for the search.

MP

 

[MP1]

In reply to the question asked by Derfly, you can connect the potentiometers in series. More importantly, for the fine adjustment, you will want to use a 10 turn or a 15 turn or even possibly a 20 turn pot to give you the accuracy you want to achieve. This should be on the smaller value pot as you want maximum number of turns for smallest voltage change.
Hope that helps a little.
MP

 

[kurt2]

hi
u seems to be quite in to the electronics field
kurt

 

[DerFly1]

MP Thanks,

I undestand wiring in series but the variable resistors in this project have three connections. To wire two variable reistors in series, how is this done. Could you possible supply a diagram?

Many thanks,

DerFly

 

[MP1]

Yes, here is a diagram. Two ways to do it. Both are the same.
MP

potentiometer.pdf

 

[mixos1]

I attach it here also for fast view...

View attachment 35092

 

[KIRKCHABO]

Help!
I am new to the electronic world and i need some clarification on the
resistors in this project.

R1=2.2Kohm 1 watt (ok)
R3=220ohm 1/4watt (ok)
R4=4,7Kohm 1/4 watt (?)
R7=0,47Ohm 1/4 watt (?)
R9=2,2Kohm 1/4 watt (?)
R14=1,5Kohm 1/4 watt (?)

I kown this probibly sounds dumb but I don't get this?


Thanks In advance

 

[MP1]

Think of the commas as periods or the periods as commas. These are used differently in different continents. It means the same.

MP

 

[KIRKCHABO]

thanks mp

help I checked all solder joints and componets but when i start it up
it seems ok till i put a load or even without a load (meter) when i turn up the current dial even a little bit the led starts flashing and i go into overload.

lost in space

 

[juanpmoron1]

I have a problem with the power supply: when the output shortcircuiting, the Q2 (2N2219) burn up!

Who can I help me?

 

[ante1]

Check R16. :

 

[juanpmoron1]

Check R16. :

R16 is 1K and is OK
???

 

[MP1]

All the components around the IC are for the current limiting circuit. You should check all of these parts for correct values and orientation.
Did you leave anything out that you felt was not needed? Even the LED is part of the current limiting circuitry.

MP

 

[FireFly3]

I have a heat sink from an old stereo receiver that I think is substantial enough for this project. The project page states:

"...use the mica insulator between the transistor body and the heatsink..."

I will be able to re-use the screws and plastic hole inserts but there was a piece of clear plastic between the sink and transistor that is too small. What should I use? Is there something around the house or hardware store I can use or do I have to hope :-\ my local electonics store guys will know what I am talking about?

Also:

"Use a little amount of Heat Transfer Compound between the transistor and the heatsink..."

Would that be between the transistor and mica insulator, between the mica insulator and sink, or a layer on each side of the mica insulator?

(Curiously, the old, built-like-a-tank receiver didn't use any goo; just the piece of clear plastic between the sink and transistor.)

On another note, I received the 2N3055A and numerous other "samples" from ON Semi http://www.onsemi.com They charge $15 US for shipping and handling but I felt it is well worth it if you order enough pieces or you are having trouble finding stuff locally.

Thanks.