Jump to content
Electronics-Lab.com Community

0-30V Stabilized Power Supply


redwire
 Share

Recommended Posts

Guest liquibyte

Yes it is with Q1, R13, R14 and D10.  The picture is when I unplug the transformer and the voltage is decreasing.

The picture makes sense in relation to the second one now.  It seems to be falling off a lot better than it was without Q1 though, no more huge spike there.  What's it looking like at power on?  That's where I'm seeing the big issue.
Link to comment
Share on other sites

Guest liquibyte

So, if my thinking is right on this, the blue region represents Q1 activating and pulling the power to ground and the red region is where Q1 shuts off and the caps drain on their own.

Have you tried the TIP141 idea yet?  I'm curious as to what effect that might have, it looks like a good idea but I'm wondering about what kind of heating would be going on if there were 3 amps at 30 volts going through it.  Either way, it would be easy to add off board on an external heatsink if required.  My parts order is on hold for now as we just can't afford the expense at the moment so I can't even try my idea unless I can find a relay in some old discarded equipment.  Minus the relay for my idea and a TIP141 or equivalent (which I may have somewhere), I have everything else I need though.

post-107142-14279144757796_thumb.png

Link to comment
Share on other sites

Guest liquibyte

I just found this appnote from TI.  Figures 4 and 5 show promising results but I'm not sure if this would work at higher currents, they only talk about and around 300mA.  Figures 2 and 3 and the associated text state that careful consideration of the capacitor values must be taken into account for proper circuit operation.

Link to comment
Share on other sites

Have you tried the TIP141 idea yet?  I'm curious as to what effect that might have, it looks like a good idea but I'm wondering about what kind of heating would be going on if there were 3 amps at 30 volts going through it.  Either way, it would be easy to add off board on an external heatsink if required.  My parts order is on hold for now as we just can't afford the expense at the moment so I can't even try my idea unless I can find a relay in some old discarded equipment.  Minus the relay for my idea and a TIP141 or equivalent (which I may have somewhere), I have everything else I need though.


No, I have been focused on the shut down issues.  I'm confident a soft start can take care of the inititial startup spike.  I just sent you a TIP 141 today.  It will likely be next week before you get it.  It is estimated that at full output (3 amps), the TIP will be using about 3.6 watts.  So if it is mounted to some metal or a small heatsink it should be ok.  A MOSFET may be a better solution but for testing purposes  the TIP should work.
Link to comment
Share on other sites

Guest liquibyte

No, I have been focused on the shut down issues.  I'm confident a soft start can take care of the inititial startup spike.

I only see a drop in voltage at power off with just the Q1 circuit soldered in.  I'm not seeing any spikes unless it's happening too fast for my scope and my eyes.  I'll do more testing at various settings loaded and unloaded and see if I can capture it.


I just sent you a TIP 141 today.  It will likely be next week before you get it.  It is estimated that at full output (3 amps), the TIP will be using about 3.6 watts.  So if it is mounted to some metal or a small heatsink it should be ok.  A MOSFET may be a better solution but for testing purposes  the TIP should work.

I certainly appreciate it.  I'll wedge it in as soon as it gets here and let you know what I see and try and get some screen grabs from a movie.  I'm going to rig up a mount today so I can film with a phone and hope it's good enough to capture what's going on.  I think I should probably watch the o-scope training class they had over at eevblog too, I could just be missing a setting or two that I need.
Link to comment
Share on other sites

Guest Luisitou

Hi to everyone!
I'm building this proyect but with little mods from the page that I have seen, the design is the same: http://electronics-lab.com/projects/power/028/index.html.  What changes would you recommend?
I'm using a transformer 120V to 24 V 3A
Because I have seen in this topic a lot of mods but my teacher wants exactly the same design with minimal changes
Best regards

Link to comment
Share on other sites

The original project has errors and problems:
1) Many of its parts are overloaded so it is not reliable. The transformer, driver transistor and single output transistor overheat. Your 24V/3A transformer is rated at 72VA maximum but the full wave bridge rectifier operates from the peak which is 24V x 1.414= 34V and with an output of 3A then the transformer power is 34V x 3A= 102VA. You can calculate the heating in the driver and output transistors yourself.
2) Without a load the peak voltage from the transformer is about 36V which is reduced to about +34.8V by the bridge rectifier.  The opamps use an additional negative -5.6V supply so their total supply is 34.8V + 5.6V= 40.4V but their absolute maximum rating is only 36V.
3) There is no way the project can supply 30VDC at 3A because the circuit losses reduce the output to about 25V at 3A. If you increase the transformer voltage then the opamps will be destroyed even quicker and more heat will destroy the driver and output transistors quicker.

Therefore we fixed the circuit and improved the parts.

Maybe you should research the original parts and calculate how much they are overloaded. Also show your teacher the losses that prevent 30V at 3A.

The original circuit would be reliable if it uses a 20V/4.3A transformer. But its maximum output at 3A would be only about 18VDC or 20VDC.

Link to comment
Share on other sites

Guest Luisitou

Wow... so quickly. Thanks for answering.
I'm seeing that the original project isn't reliable, so I have to make some changes, I don't care if my teacher gets angry with me :)
Actually I'm looking for mods that some people have made, and I found that in general some changes are: 2 x 2N3055 in parallel with resistors, some transistors have changed, added a zener 10V, and other minor changes. 
So I hope it works fine.
What do you think?
Sorry for delay but I had lost internet connection.

post-114438-14279144757934_thumb.png

Link to comment
Share on other sites

Guest liquibyte

I've been doing a little more work on the board.  I added in the TIP141 soft start circuit redwire came up with and I added R15 and D10 back in.  I figure that if I had these made and R15 and D10 isn't needed or causes unexpected results a jumper can be soldered in instead.  Since I measured overhead to spare I figure it couldn't hurt to try them out.

Since I've done the work and people keep asking about it, I'm going to put the Eagle files up.  I haven't made this yet and I haven't tested the the power supply with the added components yet so if you want to make this it's at your own risk.  If you do make it, let me know how it works.  I plan on doing testing of the added stuff later on next week and if everything works out I'll probably have these made.

Quick edit: redwire reminded me that spacing on fills and traces should probably be bigger for home etching.  If you got this before I edited the post, try downloading again for the updated spacing.  I changed the spacing from 6mil to 10mil.

Another edit: I wasn't happy with a few things so I tweaked some stuff.  I'm happy now.

post-107142-14279144762747_thumb.png

post-107142-1427914476334_thumb.png

0-30V-rev-8.zip

Link to comment
Share on other sites

Guest liquibyte

I took the liberty of making gerbers using Elecrow's cam file if anyone wants to have these made super cheap.  You can get 10 boards made for around $20 including shipping.  I'm confident in the design of the board and redwire is sure the soft start should take care of the problem with the startup transient.  I'll be doing testing on this sometime this week and report the results with pics.  If you do have this made, report back on how it works for you.  If you want to test without the soft start, just jumper the TIP141 header from the collector to the emitter and leave out the 12K resistor.  If you want to test without D10 and R15, leave out D10 and use a jumper in place of R15.  The Q1 circuit seems to now be required so leave that in.

In addition to the edit in my previous post, I redid the gerbers and I made a new schematic with the added parts.

post-107142-1427914476372_thumb.png

gerber.zip

post-107142-14279144764352_thumb.png

Link to comment
Share on other sites


I took the liberty of making gerbers using Elecrow's cam file if anyone wants to have these made super cheap.  You can get 10 boards made for around $20 including shipping.  I'm confident in the design of the board and redwire is sure the soft start should take care of the problem with the startup transient.  I'll be doing testing on this sometime this week and report the results with pics.  If you do have this made, report back on how it works for you.  If you want to test without the soft start, just jumper the TIP141 header from the collector to the emitter and leave out the 12K resistor.  If you want to test without D10 and R15, leave out D10 and use a jumper in place of R15.  The Q1 circuit seems to now be required so leave that in.

In addition to the edit in my previous post, I redid the gerbers and I made a new schematic with the added parts.


Hold off on populating the soft start.  I started testing last night and the arrangement and values will likely need to be tweaked.    As drawn, the PS kicked on at the same time as the main cap -no good.  I then rearranged the set up by connecting the 47uf cap directly to ground and used  a 39k resistor connected between the collector and cap.  I then used a 18k resistor to the base of the TIP141.  Timing seemed pretty good (about 1 sec delay to reach 12V) with reasonable ramp up on the scope.  I did not test it with a load.  After running through the numbers (39k and 18K resistors) and the data sheet for the TIP, I am concerned that the base current of approximately  0.7mA to the TIP may be a little low under a 3-5 Amp load.  I may need to change up the resistors to increase the base current to the TIP without shortening the delay period.  Otherwise I may need to increase the value of the cap.    Will keep you posted.
Link to comment
Share on other sites

Guest liquibyte

Hold off on populating the soft start.  I started testing last night and the arrangement and values will likely need to be tweaked.    As drawn, the PS kicked on at the same time as the main cap -no good.  I then rearranged the set up by connecting the 47uf cap directly to ground and used  a 39k resistor connected between the collector and cap.  I then used a 18k resistor to the base of the TIP141.  Timing seemed pretty good (about 1 sec delay to reach 12V) with reasonable ramp up on the scope.  I did not test it with a load.  After running through the numbers (39k and 18K resistors) and the data sheet for the TIP, I am concerned that the base current of approximately  0.7mA to the TIP may be a little low under a 3-5 Amp load.  I may need to change up the resistors to increase the base current to the TIP without shortening the delay period.  Otherwise I may need to increase the value of the cap.    Will keep you posted.

Something like this?  The transistor showed up today so I'll be able to do a bit of testing as well, thanks again.

post-107142-14279144765162_thumb.png

Link to comment
Share on other sites

Guest liquibyte

After some experimenting, I'm not thrilled with the soft start results.  I don't know if adding all those parts are worth the benefit.

What kinds of results are you getting?  I thought you had a delay going on before and just needed to tweak the time a bit.

I've been looking at solutions using basic transistors and there seem to be limited options there.  Is it maybe because it's not an ideal solution?  My thinking on this is that we should be using the transistor as a switch and not try to make it slowly ramp the voltage.  Isn't fast turn on ok as long as it happens after initial power is applied to the transformer, rectifier, filter cap circuit by at least the time domain that the spike lives in?  How would you delay the voltage to the base so the transistor stays off for say 200 milliseconds or so?  From what I've been reading mosfets seem to be the going rage for inrush current limiting so wouldn't this be adaptable to what we're trying to accomplish?  Something from this app note perhaps?  Figures 5a and 5b on page 9 look interesting but reading the calculations the whole thing seems to be way over my head.  The pic is from something that has to do with the usb spec and gets posted a lot.

post-107142-14279144765314_thumb.png

Link to comment
Share on other sites

Attached is a picture of the charge on the main cap vs output to a 12.4 V setting under a 0.5 Amp load.  The turn on is a flatter curve and slower but  I don't know what I saw yesterday when I thought I had a 1 sec delay.  I must have misread the time period.  I agree that the turn on after the cap charges is the ultimate goal and using a mosfet has many advantages. 

post-34537-14279144765417_thumb.png

Link to comment
Share on other sites

Guest liquibyte

I just did a more thorough reading of that app note and I think this may be the way to go here.  I'll try and work through the calculations tomorrow and see what I can come up with.  The circuit in 5b makes a lot of sense after reading through the whole thing.  I'm sure this kind of thing came about due to switching supplies but I don't see why it couldn't be adapted to solve our problem.

Link to comment
Share on other sites


Can someone who might know better tell me if this would work and if not, why?

I think there is a certain supply voltage where the opamps in the project suddenly begin working, maybe with severe overshoot.
maybe why most audio amplifiers do not have soft start. Instead they use a relay for delayed start so that the circuit can stabilize before it has an output.
Link to comment
Share on other sites

Guest liquibyte

I've measured the spike before and without the power supply attached so I'm thinking that even though the circuit is handling things to a certain level it's just not enough and may eventually damage the op amps themselves by being continuously subjected to +60V at power on.

If I put this before the op amps and if f I have a VGS(th) of 3.5-5.5V such as with this one, then at around 850ms or so this would turn on with the above circuit given the values of 100K and 100uF according to the calculation that I got here.  My settled voltage after rectification and filtering is 43.7V and is consistent between two separate power supplies.  So, given that value, the 100K resistor, the 100uF cap, and the equation 43.7*(1-2.71828^(-85/100000*100)) I get 3.56V @ 849.7476ms.  I made sure I verified the calculation and didn't just rely on the page itself to do it right so I'm confident in the values but I'm not sure how well it would work as I've never tried something like this before.

I don't have the mosfet I linked but I do have quite a few laying around to try this out with but am wondering if I'm just wasting my time with such a simple solution.  Should I be looking into the app note above and calculating out a circuit for either figure 5a or 5b and trying that instead?

Link to comment
Share on other sites

Ok I've gotten something that seems to be working fairly well  I have a 39k connect to the high side, then a 2.2k connected to the 39k then a 47uf connected between the 2.2k and ground.    Then I have 4K7 resistor connected at the voltage divider between the 39K and 2.2k.  The other end of the 4k7 is connected to the Base of the TIP141.  Start up is nice  and shutdown occurs nearly instantly .  The first picture is startup the second is shutdown.  The blue line is connected to the main cap (10,000uf) and the yellow is the output.  Test was taken with about a 0.5amp bulb.

post-34537-14279144765743_thumb.png

post-34537-14279144765865_thumb.png

Link to comment
Share on other sites

  • 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...