Jump to content
Electronics-Lab.com Community
Sallala

0-30 Vdc Stabilized Power Supply

Recommended Posts

Hello subodhthok,

I've been building this circuit last week, I can tell you that it works perfect. But, there are some thinks that I have changed in the original circuit. In stead of using three TL081 IC's, I've been using one LT081 IC,U1 in the scematic, and an LT082 IS for U3 and U2 (same supply voltages...). The TL082 is an Dual JFET Input Operational Amplifier. This works great, and you don't need to add RV1 and R10 to the circuit, these are unnecessary if you use the TL082.

There also a little note you need to keep in mind... The maximum supply voltage of an TL081/TL0872 is about a 36Volts (+/-18V). In the circuit, the supply voltage of these IC's is around a 38Vots (positive maximum of the tranfo= 24V*1.41, neg voltage =-5.6V).
Further... there is a 2N3055 transistor used as power transistor. The worst case powwer dissipation of this transistor =90W (30V*3A). When you check the thermal design, you will see that the junction temperature can rise to 250

Share this post


Link to post
Share on other sites

Hi Kolonel,
I agree that Q4 gets too hot in this project.
When a 30VAC transformer is used so that the output can reach 30VDC at 3A then the Q4 gets much hotter. Then high voltage opamps must be used.

Does your project exceed an output voltage of only 25VDC at 3A?

Did you use the original little 2N2219 for Q2? It will melt if the gain of the output transistors is low, with a 3A low voltage load.

RV1 is used to adjust the output for exactly 0V. The opamp could have an input offset voltage of up to 6mV which is amplified to plus or minus 18mV at the output. RV1 can reduce it to zero.

Share this post


Link to post
Share on other sites

Hello Audioguru,

The high voltage opamps aren't really needed, the supply works perfect...no problems untill now.

For Q2 I use a BD137 beceause I hadn't a 2N2219 in my stock. I've mounted a little heatsink at the transisto and it works good,doesn't get too heat at all...

I'l check one of these days if I can measure the 18mV noise at the output with my scope...

BTW, is there someone who has built the LCD panel meter for this supply? Witch are the results?

Greetings

T.K.

Share this post


Link to post
Share on other sites

I tried to build it, but...ha some troubles with programming atmega8 ( dil28 package) and finally voltage regulator 78L05 fried to short circuit...result? Atmega8 had 13V between Vcc and GND...it fried...haven't got new one yet. By the way....is it me, or the ISCP part of DIP package Atmega ( on the original page) has serious bugs in it...there are'nt all the pins needed for programming present in LCD connector... 

Share this post


Link to post
Share on other sites

I admit I was wrong... :-[. But I'm a newbie...& sometimes confused :-*. But I'm very much keen in electronics....and hope that one day I understand all.

Please tell me what are the functions of R7 & Power Transistor Q4.


Pls Somebody why is Q4 & R7 used?

Share this post


Link to post
Share on other sites

I'l check one of these days if I can measure the 18mV noise at the output with my scope.

It is not noise, it is a DC voltage that is up to positive or negative 18mV at the output of the project when the voltage control is all the way down. It is caused by the opamp U2's input offset voltage which could be from -6mV to +6mV and it is amplified 3 times by the circuit. The output voltage is supposed to be zero which is adjusted with RV1.

Share this post


Link to post
Share on other sites

[Pls Somebody why is Q4 & R7 used?

Q4 is the main power transistor in the project. It acts like an automatically variable resistor. It automatically keeps the output voltage or output current constant even if the load current changes. It gets very hot when it has up to 30V across it and up to 3A through it which is 90W of heat. A single 2N3055 transistor cannot dissipate that much heat so two should be used to share the heat.

R7 develops a voltage across it that represents the load current. It is 0.47 ohms so 1A through it creates 0.47V. The opamp U3 uses the voltage across R7 to regulate the load's current.

Share this post


Link to post
Share on other sites

Listen very carefully,

The 0-30 Vdc stabilized supply is a very advanced design.
Truthfully, it is a marvel but can also become a problem.

Example:

In the event you plan to use this supply on your bench to test homebrew digital circuits "BEWARE".
The advanced shut-off is the most amazing i have ever noted.

Example:

Let's say for instance you designed a multi-timer circuit using the 555 - 556 group of timers.
The latter timer circuit eventually is used to light a few LEDs along with activating a relay etc...
Powering and testing the timer project you are using the 0-30V stabilized supply.
However, you plan to make an on-board constant 12V supply for the timer project.

You test the timer and every aspect will work perfectly, you try a fast-on, fast-off then back again; multiple times in extremely fast order.
Additionally, while the 0-30V is powering the timer project you pull the AC plug out of the wall then immediately push it back into the wall.
Regardless, as to what you try your timer project will time-out and work perfectly!

Next, after you design the PCB for the timer project you build a small +12VDC supply onboard to power the timer circuit; basic supply.

Wow, will you be let down...

All of a sudden when you try a fast on/off/on cycle the timer does not respond correctly, relay is engaging immediately, LEDs are flashing out of order etc...
The basic 12V supply cannot perform like your test bench 0-30V supply, you then try to load the 12V PCB mounted project supply to clamp the output voltage to zero but the minimal delay is still a problem; im talking strapping a 50ohm resistor across the 12V PCB supply is too slow!

The 0-30V is the ultimate supply but in real-world situations it is too perfect, unless you plan to buy or build another just to place in your project you may find the latter supply more of a tease than anything!

Trust me, i found out the hard way!

-Omni  ???

Share this post


Link to post
Share on other sites

Hi Omni,
This power supply project reduces its output voltage to zero very quickly with its transistor Q1 when its power is turned off, so that the output voltage doesn't rise when the opamps lose some of their supply voltage. You don't want the output voltage to rise because  then it might destroy your load.

Share this post


Link to post
Share on other sites

"very quickly" cannot be measured...

I would like to duplicate this feature on the link below.

My digital timer module will not work properly unless i have the "very quickly" feature!
The below link is the supply i am trying to use for a timer circuit but the decay on the output is creating havoc, i tried a 50 ohm shunt across the output it does help but not flawless like the 0-30VDC stabilized supply when adjusted to 12V.



If possible, please be specific as to how it may be performed.
Additionally, i understand if it is not possible etc...

Any help would be appreciated.

Share this post


Link to post
Share on other sites

Actually, if i spend the time i can get the posted pic (12VDC) circuit to simulate the clamp as designed on the 0-30V stabilized supply.
I was hoping someone had already designed a working model...

Your theory would not work in my situation since the LM317 would still produce a decay when power is turned-off, the timer circuit i designed will only draw 200mA of current when power is applied.
The latter circuit will also operate slightly below 4V at which time the extremely low current relay disengages.
Circuit current consumtion in today's digital designs are very low.
When a worst case scenario is applied such as power-on/off/on applied at both AC and DC levels digital design can take on a whole new meaning!


Although, i thank you for your concern.

-Omni

Share this post


Link to post
Share on other sites

The original design will operate perfectly, i have completely tested the 0-30V supply and feel it is one of the best i have ever used.
I fabricated my own PCB using the internet supplied artwork along with PnP.
The only addition i added was a digital voltage & current meter; link provided.

http://www.hobbytron.com/UK203.html

I ordered all the parts for the supply from Futurlec, their prices are excellent!
The enclosure is a ventilated Bud (champion series).

http://www.budind.com/pdf/hb11202.pdf

Furthermore, the green (stock) 7-segment LEDs were replaced with Red since i fabricated the front panel enclosure out of dark red plexiglass.
However, you could also use a dark green plexiglass and use the stock LEDs.
(the Digital I & V meter uses stock green/yellow LEDs)

Plexiglass can be purchased in very small sizes from ebay, be carefuly when drilling, do not attempt to immediately drill a large hole (.25) above, start very small and work your way up.
Plexi has a tendency to grab the bit and a crack will easily occur (drill very slow), no pressure!

I hope i can get some time to post a few pics; perhaps this weekend.

Share this post


Link to post
Share on other sites

Hi Omni,
How can your power supply have an output voltage of 30VDC with some current, with a 24VAC transformer that makes rectified only 32VDC?

Isn't the output full of ripple if the voltage is higher than 25VDC and the current is more than about only 2A?

How can the 24VDC/3A (72VA) transformer supply 32VDC x 3A= 96VA?

How can the 2N3055 dissipate 30VDC x 3A= 90W without overheating?

How can the little 2N2219 dissipate up to 3.6W without melting?

Share this post


Link to post
Share on other sites

Hi Omni,
How can your power supply have an output voltage of 30VDC with some current, with a 24VAC transformer that makes rectified only 32VDC?

Isn't the output full of ripple if the voltage is higher than 25VDC and the current is more than about only 2A?

How can the 24VDC/3A (72VA) transformer supply 32VDC x 3A= 96VA?

How can the 2N3055 dissipate 30VDC x 3A= 90W without overheating?

How can the little 2N2219 dissipate up to 3.6W without melting?


You don

Share this post


Link to post
Share on other sites

One has to understand how a precision op-amp output biasing is performed before understanding the advanced principles of the stabilized output.
Within the circuit are many feedback paths that form/conduct the Vout in a very controlled manner.
Additionally, view the unique shunting path that is performed, the original circuit is a marvel!


The superb design of the DC clamp upon shut-off is magnificent.
However, it could never be easily performed on a basic 78xx series regulator using the design implemented on the 0-30V supply.
Although, there is always a work around that will perform a similar function using a more passive characteristic.
I provided the pic/link, one could also use an SCR in place of the relay but the region of operation can become subjective, using a basic high-quality sealed relay will remove all aspects of the subjective content.



One could tap from the P/S bridge but an excessive capacitance is noted that would generally require a zener/resistor to the relay.
Using an isolated bridge with very minimal capacitance is the key since a relay is a basic coil, non-silicon device.
However, make sure to select the relay coil for minimal current consumption; 30mA etc...
The above can also be replaced with a relay on the AC side but i do not like the idea of RAW AC engaging a relay.
Although, arc supression can be be implemented it is far easier to use the secondary side to eliminate the large contact potential.
Please, understand higher current devices (project circuit) would cater to using an SCR but for low current applications like the timer circuit the 12VDC supply is powering (300mA) a relay is perfect.

Far too many designers reduce the secondary capacitive filtering along with installing a fixed load to pull the output decay rapidly, the latter causes excessive component wear along with increased loading on the P/S; heat generated is high!

Share this post


Link to post
Share on other sites

Within the circuit are many feedback paths that form/conduct the Vout in a very controlled manner.

The voltage setting pot has its voltage (0V to 11.2V) amplified by opamp U2. Its only negative feedback path is R12 and R11 which set its voltage gain to 3.074.

Share this post


Link to post
Share on other sites

A feedback path can also be viewed as a dynamic feedback.

Ugh, different executions are performed throughout the circuit when required, bias shunting etc...

Including, certain parameters (power, voltage or current), establishing set points occur in a much more controlled level when using an op-amp design.

Enroll in a class (semester) concerning "Advanced Power supply design and circuit application", the latter is usually available at any University.





Share this post


Link to post
Share on other sites

Hello Omni

Enroll in a class (semester) concerning "Advanced Power supply design and circuit application"...


The original design will operate perfectly, i have completely tested the 0-30V supply and feel it is one of the best i have ever used.


Perhaps you could share with us the results of your "complete" testing? What were your results for things like gain and phase margine, cross over frequency, transient response time, short circuit recovery time, start-up time, line and load regulation, thermal derating... etc.

Share this post


Link to post
Share on other sites

I remember at PENN a variety of students that always wanted me to provide an outline concerning a completed project; always looking for the answers without making any attempt on their own.   :'(

I would kindly state the below in a very respectful manner:

The only way you will learn the questions you are asking is to pull the legs one by one from the centipede.
When you have completed the above you will gain a much better understanding.  :)


I truly honor the individual that has presented this project, PCB artwork along with a brief functionality is so difficult to find today!
I view far too many circuits/projects on the internet that are continual copies of a basic format.
Today, we must learn how to work outside the box!

-Omni   :)



Share this post


Link to post
Share on other sites

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...

×
×
  • Create New...