Jump to content
Electronics-Lab.com Community

0-30V Stabilized Power Supply


redwire
 Share

Recommended Posts

The U1 opamp has a max output current of about 20mA. A fan draws a lot more current.
The 11.2V from U1 can drive a power darlington transistor which will have an output of about 9.4VDC. The power darlington will get very hot and will also need a pretty big heatsink.

Or you can use an LM317HV adjustable voltage fregulator set for an output of 12V. It will also get very hot and will need a pretty big heatsink.

Link to comment
Share on other sites

thx guru.Both method need a heatsink again  :-\ now my problem also hard to get a pretty big heatsink , heatsink is also quite exp , LM317HV 12V with mA also will very hot?can i just put it circuit on a perfboard and cooling with fan cooler also?the input of LM317 can i just borrow the current from bridge rectifier ?

Link to comment
Share on other sites


thx guru.Both method need a heatsink again  :-\ now my problem also hard to get a pretty big heatsink , heatsink is also quite exp , LM317HV 12V with mA also will very hot?can i just put it circuit on a perfboard and cooling with fan cooler also?the input of LM317 can i just borrow the current from bridge rectifier ?

hi sing,
I don't know which transformer you have.
A 28V transformer is  29.5V without a load. Then its peak voltage is 41.7V which is reduced to 40.3V by the full wave rectifier.

You need something  (an LM317HV) to reduce the 40.3V down to 12V for the fan. The voltage limiter will have 40.3V - 12V= 28.3V across it and (I don't know the current of your fan but maybe ) 0.5A so the "something" will dissipate 28.3V * 0.5A= 14.2W and will need a pretty big heatsink.
Link to comment
Share on other sites

I collected the original scheme (http://www.electronics-lab.com/projects/power/003/index.html). I have the transformer 20v - 30W. Will tell how to limit the output voltage is adjustable from 0 to 15 volts, the current from 0 to 1,5 A (no longer needed). Sorry for bad English (it's Google Translator).
P.S. Happy New Year!

Link to comment
Share on other sites

thx for guide guru,

the transformer i already series for gain 24VAC isn't i can pull one more line from one of 12VAC with a diode mean half-wave rectification = about 6VAC?

the return circuit of the fan is point to the return circuit of transformer?because when i series the transformer 12V+12V the return circuit is doesn't use.

sorry guru i don understand how filter the rectified 12V to 16V use other  rectification way?

any diode also ok ? or at least 3A diode

Link to comment
Share on other sites


thx for guide guru,

the transformer i already series for gain 24VAC isn't i can pull one more line from one of 12VAC with a diode mean half-wave rectification = about 6VAC?

the return circuit of the fan is point to the return circuit of transformer?because when i series the transformer 12V+12V the return circuit is doesn't use.

sorry guru i don understand how filter the rectified 12V to 16V use other  rectification way?

any diode also ok ? or at least 3A diode

Connect the (-) wire of the fan to one 12V wire of the transformer.
Connect the anode of a diode to the 12V tap on the transformer.
Connect the (+) wire of the fan to the cathode of the diode.

The current rating of the diode must be at least the current rating of the fan.

If the fan hums or vibrates at the mains frequency then add a filter capacitor to get smooth 16VDC and add a series resistor to reduce it to 12V for the 12V fan.

You could add a second diode to the other 12V wire of the transformer to have full-wave rectified 16VDC.
Link to comment
Share on other sites

Well I have decided to just mod the existing circuit board, using audioguru's part list, from post #2
I'll try that first, if it still isn't adaquite for 24 volts 2 amps, then I'll make a new board for Redwire's parts list.

Only part I could not locate at the supplier were the OPA445 op-amps.
So I'll see what I have in stock that is comparable.

I'm enjoying reading the posts!!!

Glen  :)

Link to comment
Share on other sites


Well I have decided to just mod the existing circuit board, using audioguru's part list, from post #2
I'll try that first, if it still isn't adaquite for 24 volts 2 amps, then I'll make a new board for Redwire's parts list.

Only part I could not locate at the supplier were the OPA445 op-amps.
So I'll see what I have in stock that is comparable.

The version with the OPA445 high voltage opamps is an old version.
Use the latest version that uses more common MC34071 or TLE2141 opamps.
Link to comment
Share on other sites



The version with the OPA445 high voltage opamps is an old version.
Use the latest version that uses more common MC34071 or TLE2141 opamps.


Ok so I can use the MC34071 or the TLE2141 as drop in replacements for the original schematic and board I built? to replace an TL081? I'll go look at the datasheets for those two op-amps.

I checked my stock of op-amps, all I have is low noise ones for making stomp boxs 18 volt max  :-\
Link to comment
Share on other sites

The original project has many errors. Changing the opamps to MC34071 or TLE2141 opamps with a max allowed supply of 44V fixes only one problem.
The tiny poorly cooled Q2 transistor will melt!
The overloaded transformer might melt or catch on fire.
Many of the resistors get too hot.
The main filter capacitor's value is way too low.

The max allowed supply voltage for ordinary opamps including the TL081 is plus and minus 18V which is a total of 36V. The 28V transformer is 29V without a load which has a peak voltage of 39.6V and is reduced to 38.2V by the full-wave rectifier.
U2 and u3 also need a negative supply voltage which is -1.3v in the latest circuit so the opamps have a max supply of 39.5V. Their max allowed supply is 44V so they are fine.

Ordinary opamps including the TL081 need at least 4V for the negative supply so their total supply of 42.2V is much higher than their max allowed supply voltage.

Link to comment
Share on other sites


The original project has many errors. Changing the opamps to MC34071 or TLE2141 opamps with a max allowed supply of 44V fixes only one problem.
The tiny poorly cooled Q2 transistor will melt!
The overloaded transformer might melt or catch on fire.
Many of the resistors get too hot.
The main filter capacitor's value is way too low.

The max allowed supply voltage for ordinary opamps including the TL081 is plus and minus 18V which is a total of 36V. The 28V transformer is 29V without a load which has a peak voltage of 39.6V and is reduced to 38.2V by the full-wave rectifier.
U2 and u3 also need a negative supply voltage which is -1.3v in the latest circuit so the opamps have a max supply of 39.5V. Their max allowed supply is 44V so they are fine.

Ordinary opamps including the TL081 need at least 4V for the negative supply so their total supply of 42.2V is much higher than their max allowed supply voltage.


I'll asume you are responding to me  :)
Yes thats why I'm upgrading the rest of the components on the original board as suggested by you in the second post on page one of this thread.
New resistors, transistors, larger cap, extra power transistor .33 Ohm 2watt resistor.......

This parts list here!
http://www.electronics-lab.com/forum/index.php?action=dlattach;topic=19066.0;attach=16238;image


Glen
Link to comment
Share on other sites

Glen,
That old version of this power supply project was made years ago when OPA445 high voltage opamps were available. Its 30VAC transformer makes about 31VAC without a load and the rectified peak voltage on C1 is 42.4V. Two of the opamps also have the -5.6V supply so their total voltage is 48V which is too high for most opamps.

Link to comment
Share on other sites

Because When I decide make this power supply the link to the forum doesnt work, so I make the PCB for the original version. Can I only change the components and increase the pcb traces? Or I have to make a new PCB? Is there any way to use a output of 0-15V 3A (or 5A)? Best Regards to all. Thanks for help.

Link to comment
Share on other sites

You are in Ontario, Canada so you can order the proper opamps online from Digikey or Newark.
If you order before 8:00PM then they are delivered the next morning.

The latest version is designed for the MC34071 or TLE2141 opamps that have inputs that work at 0V and have outputs that go close to ground. They have a 44V supply rating.

OPA445 opamps have a high voltage rating but the inputs do not work near ground and the output does not go near ground so they need the earlier version of this project.

Maybe the OPA445 opamps you bought are counterfeits.

Link to comment
Share on other sites

Ya I get my SMT parts from Newark and Mouser, they would have them too.
I''d have to wait for a while until i need lots of parts before placing an order, they charge $15-20 for shipping.
Not sure what Digikey charges for shipping.

I am using the APO445 op-amps for the old project.

If and when I make the new project I'll use the MC34071 or TLE2141
But for now I'm playing with the old board, to make it work better.

If I'm not happy with the results,
then I'll make a new board using the correct new schematic and parts list.
But for now I'm playing with the the old version and experimenting.  :)


Glen  :)

Link to comment
Share on other sites

guru isn't i can connect the fan cooler to the line about 3xV after bridge rectifier and add a resistor for reduce the voltage to the fan.

half-wave rectification ripple is too high, i hope the fan wont easy mangle, for economize diode and circuit can just borrow the current from bridge rectifier? isn't in theory full-wave rectification ripple algorithm same with bridge rectification ?

Link to comment
Share on other sites


guru isn't i can connect the fan cooler to the line about 3xV after bridge rectifier and add a resistor for reduce the voltage to the fan.

half-wave rectification ripple is too high, i hope the fan wont easy mangle, for economize diode and circuit can just borrow the current from bridge rectifier? isn't in theory full-wave rectification ripple algorithm same with bridge rectification ?

You never told us how much current the fan needs. A resistor in series to limit the current might prevent it from starting to run since it needs much more current to start running. The resistor might get very hot unless it is huge.
Link to comment
Share on other sites

  • 2 weeks later...
  • admin featured and pinned this topic

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
 Share

×
  • Create New...