Regulated Power Supply Circuit design

[techguru]

Dear all,
            I want to design regulated power supply for my lab which should be programmable for both voltage and current. I bought a transformer of 24V@ 5Ampere centre tap. it should provide output DC voltage from 0-30V @ 3 ampere of both polarity.I request you all to provide me the circuit which would accomplish my aim.Thank you all gentle men.

[tooki]

Assuming you want to make a linear power supply, you can't do what you want with that transformer.

When you say 0-30V/3A of both polarities, you mean you want two 0-30V outputs, each 3A*? The transformer you have is, in essence, 2x12V. Nowhere near enough.


*Though there have been power supplies that provide symmetrical "tracked" outputs (where if you set the controls to, say, 14V, then you get –14V on a – output, +14V on the + output, and one common terminal in the middle), what's more common now is to see two independent supplies, with separate + and – terminals for each supply. You can then put them in series (connect the – of one to the + of the other) as needed, or use them separately if you want.

[techguru]

Hi to all !!!!!!!!!!!!!!!!!!
 Transformer Specification

primary:230V ac
Secondary:24V-0-24V @ 5 ampere.

[eblc1388]

Transformer Specification
primary:230V ac
Secondary:24V-0-24V @ 5 ampere.

Good only for a 0~20V 3A regulated supply. If you wanted 3A at 30V, use a 35V-0-35V transformer.

[techguru]

Sir,
       How to design 0-20V power supply.as per your specification.

[eblc1388]

You should do a search on this subject in the forum. There are numerous discussions about regulated power supplies from simple to sophisticated design to suit everyone. 

[Kleinstein]

A 24 V transformer is too low to get a regulated 30 V DC output. It is more like a maximum of something around 20-25 V (maybe 28 under light load), depending on the circuit.

The usual way is to build 2 largely separate supplies, that can be connected in series and this way used as a +- supply. It is usually easier to design and more flexible. However the transformer needs fully separate windings in this case. At this power level it would also be a good idea to have a kind of pre-regulation or transformer tap switching otherwise the power dissipation can get rather high.

It is a good idea to use the search function, but be aware, that there are lot's of poor power supply circuits around. A good lab supply is a project that is way more difficult than it seems at first.
It might be a good idea to look at circuits of usually older commercial supplies, where circuit plans a available.

To release less magic smoke, it is a good idea to start with a much smaller version (e.g. like 0-20 V and 1 A). The tricky control loop is not that much different.

[Kalvin]

If the transformer had two separate 24VAC windings, you could build a decent two channel PSU using these nice modules: https://www.eevblog.com/forum/blog/eevblog-1030-$20-diy-bench-power-supply!/ With a 24-0-24 your options are now somewhat more limited.

[Lautrec]

Dear all,
            I want to design regulated power supply for my lab which should be programmable for both voltage and current. I bought a transformer of 24V@ 5Ampere centre tap. it should provide output DC voltage from 0-30V @ 3 ampere of both polarity.I request you all to provide me the circuit which would accomplish my aim.Thank you all gentle men.

I think that you can. You need 20000µF (or more) capacity + 0,1µF/50V for each diod from the rectifier. I made one one with transformer 21V to 0-30V regulated voltage. After the rectifier I add 6x 6800µF/50V and I got max 30V in output. But remember in your case you must use components as for 5A load and provide a stable voltage control to base of transistor or use IC like XL4015. My transformer is 21V/30A and PSU is with 9x TIP3055 the output is 0-30V/30A+. I love it!

[Damianos]

Dear all,
            I want to design regulated power supply for my lab which should be programmable for both voltage and current. I bought a transformer of 24V@ 5Ampere centre tap. it should provide output DC voltage from 0-30V @ 3 ampere of both polarity.I request you all to provide me the circuit which would accomplish my aim.Thank you all gentle men.

I think that you can. You need 20000µF (or more) capacity + 0,1µF/50V for each diod from the rectifier. I made one one with transformer 21V to 0-30V regulated voltage. After the rectifier I add 6x 6800µF/50V and I got max 30V in output. But remember in your case you must use components as for 5A load and provide a stable voltage control to base of transistor or use IC like XL4015. My transformer is 21V/30A and PSU is with 9x TIP3055 the output is 0-30V/30A+. I love it!

21V * 30A = 630VA,
30V * 30A = 900W
How you managed that? What physics/electrical/electronics rules apply on this?

[Kleinstein]

Transformer ratings are long term average. No problem getting more power short time if you check the transformer temperature.
On the long term, there is no way around the power limit of cause. Just a normal rectifier and filter cap even has a poor power factor. So even getting 3 A DC from an 5 A transformer might be on the edge with a stiff (e.g. toroid or large) transformer. A very large filter cap will bring the power factor down.

I have seen a power-supply circuit that uses voltage doubling rectifier (and thus a low of filter caps) as the higher transformer tap and normal rectifier for lower voltages. So it is possible to get away with the lower transformer voltage.

[Damianos]

Of course, if we short-circuit the capacitors we can have a few hundreds or even thousands of Amperes for short time ... ...
Chemistry problem?

[techguru]

Dear All,

          Could anybody give an idea to start my design with the schematic of nice design which could be simple and be a good regulator in controlling voltage and current.  help me in this regard.thank you all.

[IanB]

Could anybody give an idea to start my design with the schematic of nice design which could be simple and be a good regulator in controlling voltage and current.  help me in this regard.thank you all.

"Simple" and "good regulator" don't go together when you ask for extreme specifications like 30 V and 3 A.

If you want to keep it simple you need to aim lower. Keep the current below 500 mA or so and keep the voltage down around 20 - 25 V.

[not1xor1]

Transformer Specification
primary:230V ac
Secondary:24V-0-24V @ 5 ampere.

Good only for a 0~20V 3A regulated supply. If you wanted 3A at 30V, use a 35V-0-35V transformer.

I think it is better to give a way to get to the result rather than bare numbers

supposing the transformer is able to provide 24V at full load (resistive 5A), one has to take into account:

-1) line voltage variations (usually specified as +/-10%), so in this case the voltage might be as low as 21.6VAC (24-10%)

-2) peak voltage i.e. 21.6 * sqrt(2) that is about 30.5V

-2) rectifier drop at peak current... with a 10A bridge that should be around 2-2.5V (according to the GBJ10*, maybe optimistic, datasheet it should be 2.2V at 100A and 25°C) so worst case now is 28-28.5V

-3) ripple voltage: some books provide the formula Vpp = I / C * f, but usually the real value is a bit better (i.e. less)
in case you have a 10mF capacitor and a 50Hz frequency (100Hz thanks to the bridge) you get: 3 /( 10e-3 * 100) that is 3Vpp or more likely something around 2-2.5V, so the minimum voltage now is 25.5-26.5V

-4) regulator drop-out voltage, which might be as low as 1V using a low drop out design or more likely around 2-3V, so now you get the worst case maximum output voltage which might vary between 22.5V and 25.5V regulated DC

please correct this if there is anything wrong

[techguru]

Clear Perspective.

but my secondary Ac Voltage is 24v.Hence i could take a peak voltage of 24*sqt(2)=nearly 34Volts provided i should use good filter capacitor.Hence i think i could take about 24V dc at full load condition.

Thanks a lot sir...

[eblc1388]

The "peak" voltage information is only useful for specifying the rating of the smoothing capacitors only.

First we start from the DC load side. If the output is 24V 3A, then its rms voltage is also 24V, because it is DC. If there is no loss in rectification and regulation, then a 24V rms AC supply input is perfect. Note here we couldn't care less of the peak voltage of AC input, that's irrelevance.

But then one has to cater for ac mains fluctuation, rectification losses, regulation headroom...., that would require additional voltage headroom on the AC input voltage. So any circuits in the internet which says 30V 5A using a 25V secondary transformer is a joke. Perhaps if you look closely, what it really mean is 0-30V, 0-5A instead. It can never output 5A at 30V. Someone might tell you he can by using a very large value smoothing capacitor. No, he can't.

I challenge him to post a photo showing his regulated supply supply 30V 30A using a 21V secondary transformer. Don't forget to stick an AC voltmeter to show that it is really 21V at the secondary.

[techguru]

Hi to all,

         Can you suggest some technique to get 0V output from any voltage regulator with out going for additional transformer..

[Jeroen3]

The recent mailbag showed a SmartSupply by ThomasVDD on github.
It has a method of getting down to true 0V. I think it was based on the uSupply Dave never finished.

[Kleinstein]

It is rather simple to get a low power auxiliary supply with a kind of charge pump from the transformer. So going all the way down to 0 is not a difficult part in building the regulator.

The difficult part is getting both the voltage and current regulation stable (that is not oscillating) for any realistic load.

With circuits that start with a voltage regulator and add a kind of current limit later, there is the tendency that current regulation wil tend to oscillate quite easy. This problem is what caused Dave's µ-supply to kind of fail  .  So I would be kind of suspicious with any design that uses a voltage regulator that is not directly made for an adjustable current limit.

Transformer Specification
primary:230V ac
Secondary:24V-0-24V @ 5 ampere.

Good only for a 0~20V 3A regulated supply. If you wanted 3A at 30V, use a 35V-0-35V transformer.

I think it is better to give a way to get to the result rather than bare numbers

supposing the transformer is able to provide 24V at full load (resistive 5A), one has to take into account:

-1) line voltage variations (usually specified as +/-10%), so in this case the voltage might be as low as 21.6VAC (24-10%)

-2) peak voltage i.e. 21.6 * sqrt(2) that is about 30.5V

-2) rectifier drop at peak current... with a 10A bridge that should be around 2-2.5V (according to the GBJ10*, maybe optimistic, datasheet it should be 2.2V at 100A and 25°C) so worst case now is 28-28.5V

-3) ripple voltage: some books provide the formula Vpp = I / C * f, but usually the real value is a bit better (i.e. less)
in case you have a 10mF capacitor and a 50Hz frequency (100Hz thanks to the bridge) you get: 3 /( 10e-3 * 100) that is 3Vpp or more likely something around 2-2.5V, so the minimum voltage now is 25.5-26.5V

-4) regulator drop-out voltage, which might be as low as 1V using a low drop out design or more likely around 2-3V, so now you get the worst case maximum output voltage which might vary between 22.5V and 25.5V regulated DC

please correct this if there is anything wrong

With a 24-0-24 V transformer one can use a 2 diode rectifier and thus reduce the rectifier drop to about half.

[techguru]

Hi sir,,,

      What should i do know. where to start and how to proceed. how to start my design with out conventional voltage regulators.yes i came to know the difficulty in building 3 ampere from your kind previous reply sir.  help me in this perspective.

[techguru]

Hi to all,

               
                     Looking for beginner circruits, that are instructive and useful to  understand to construct my regulated power supply. thank you all.

[mariush]

Here's a schematic for a commercial power supply designed for up to 18v and 2 A of current

It uses a transformer with two big windings each capable of probably around 12v AC and depending on the desired output voltage, a relay switches between using only one 12v winding or both windings for higher AC voltage.

The transformer also has a winding which gives around 15v AC which is rectified using a separate bridge rectifier to provide 12v for the relay and maybe fan (so low current) , and two separate windings of around 8v each to create  +5v and -5v for opamps and the digital multimeter chips ICL7106 that would show the voltage and current on LCD displays (with old style segments).

Basically, you can buy all the components for this power supply separately, and even the lcd displays you can buy maybe not exactly the same but something with a few seven segment digits and dots is easy to find.  ( or you can buy the icl7106 chips designed for seven segment led displays instead, since these multimeter chips are available in both lcd and led display versions)

I'm also linking to  a PDF with the project for making a bench power supply which also has a good amount of information in it :  http://savedonthe.net/download/2010/Variable-Adjustable-Linear-Power-Supply.html

[techguru]

Thanks a lot sir...

[rstofer]

There is a falacy in using gigantic capacitors to hold up the average voltage and it is related to conduction angle of the rectifiers.

http://www-personal.engin.umd.umich.edu/~fmeral/CIRCUITS/05*Unit%205/Diode%20Rectifiers.pdf

Bottom line:  If the conduction angle is very short, the rectifiers have to deliver the total energy in a short period of time.  The current goes way up!  Of course, the transformer also sees the high peak current and drops its output voltage.

I wonder why anybody wants to go through the anguish of trying to build a PSU when they are dirt cheap:

https://www.banggood.com/DPS3003-32V-3A-Buck-Adjustable-DC-Constant-Voltage-Power-Supply-Module-Integrated-Voltmeter-Ammeter-p-1062475.html

Here's another thread re: DIY power supplies (among other things):
https://www.eevblog.com/forum/beginners/cheap-oscilloscopes-and-psus/

It's real easy to build PSUs based on the 7805,7905,7812 etc.  But these are fixed voltage with built-in current limiting.  Unfortunately, the current limiting can't be set down to a really low number like 100 mA.

The LM317 is a better approach for adjustable supplies but current limiting may take a 2d 317.

Overall, you will wind up with a bunch of op amps around a current loop and voltage loop all working to drive a pass transistor.

Search around this site and the rest of the Internet.  There are a lot of projects and none of them are simple.  Adjustable current limiting is a bit hard to do.

Here's one approach to creating a PSU with current limit.  It is a lightweight PS though, it only delivers 1.5A 0..26V.  But it does serve to show the complexity of a PSU with adjustable voltage and current limiting.

http://dangerousprototypes.com/blog/2014/04/27/app-note-simple-current-limiting-power-supply/

Where does the 3A requirement come from?  Is it just copied from a catalog?  I can't imagine building up a breadboard that needed even 1A, much less 3A.  If I needed more than 3A, I would probably use a purpose bought fixed PS or a set of batteries.  In my corner of the sandbox, 100 mA is a lot!

I do like the idea of adjustable current limiting when I bring up a new project.  It kind of keeps the smoke inside the chips.

For fixed voltages, a PC PS works well.  It won't have adjustable current limiting so it is more useful for things like motors.  It also provides very high current so the smoke will leak out in a great big hurry!

Add a connector:

https://www.sparkfun.com/products/12867

Here's a teardown video of the Rigol DP832.  Ignore the UI components and the CPU/networking and you still have a bunch of parts involved in a 3 output supply.