Sallala

0-30 Vdc Stabilized Power Supply

Recommended Posts

Your photo of a no-name-brand Chinese power supply does not show any specifications and does not show its schematic and parts list.

The photo shows its 30VDC output when its current is zero. The defective Greek kit and Chinese copies do that but cannot produce 30VDC at 3A. Instead they produce about 25VDC with a lot of ripple at 2.5A and the parts are burning.

Share this post


Link to post
Share on other sites
Quote

Your photo of a no-name-brand Chinese power supply does not show any specifications and does not show its schematic and parts list.

I found this. Since the same model number is shared by other 4 brands. I can't tell if the actual hardware still true to the schematic.

599978a3b763f_EsquemaSchematicfontePs-305dYaxun.jpg.1e5dd519ca41ae7d6536e3a3e962cd9c.jpg

Share this post


Link to post
Share on other sites

The Chinese power supply uses relays to switch the transformer voltage into voltage ranges so that the output transistor does not get too hot. I do not know if any parts are overloaded and I do not know how good or bad is its regulation. Its LM741 opamps were designed 50 years ago (!).

Share this post


Link to post
Share on other sites
2 hours ago, audioguru said:

The Chinese power supply uses relays to switch the transformer voltage into voltage ranges so that the output transistor does not get too hot. I do not know if any parts are overloaded and I do not know how good or bad is its regulation. Its LM741 opamps were designed 50 years ago (!).

Thank you.

I will choose this project in that case.

 

 

Share this post


Link to post
Share on other sites

Hi! ,Everybody 

I made this 30v lab supply using mc34072 and everything is working fine except the voltage at output is not.going below 15mv as it should go to 0 and the current limit is not working below 36ma as the current limit should work till 2ma as stated, please help.

The voltage at 

Voltage pot 1st pin=11.2 v, 3rd pin=0.008

Current pot 1st pin=1.2v, 3rd pin=0.014

Current shunt are two .22ohm resisitors in series which gives me 1.22v voltage drop at 30v 3amp 

My concern is that ,1- voltage should go to zero which is not going and is about to 15mv whe voltage pot turned to zero.

2-current limit is working till only 36ma and not below it..

Please i appreciate any help..

 

               

Share this post


Link to post
Share on other sites

Every opamp has an input offset voltage error. Single opamps like the recommended MC34071 and the TLE2141 have input offset voltage adjustment pins. The project uses trimpot RV1 to null the offset voltage but your MC34072 does not have offset adjustment pins. Since your MC34072 has two opamps then it has double the heating and I think it becomes too hot.

The original project used the wrong value for R10 connected to RV1 and R10 was connected to the wrong voltage. Here is how it was and how it should be:

 

0V-30V offset adjustment.PNG

Share this post


Link to post
Share on other sites
On 2/2/2018 at 8:31 PM, audioguru said:

Every opamp has an input offset voltage error. Single opamps like the recommended MC34071 and the TLE2141 have input offset voltage adjustment pins. The project uses trimpot RV1 to null the offset voltage but your MC34072 does not have offset adjustment pins. Since your MC34072 has two opamps then it has double the heating and I think it becomes too hot.

The original project used the wrong value for R10 connected to RV1 and R10 was connected to the wrong voltage. Here is how it was and how it should be:

 

0V-30V offset adjustment.PNG

 

22 minutes ago, electron234 said:

 

I have a 30V, 8A transformer. Will this do the job. I want to make this project  on Breadboard for professional  purpose.  Is it possible ?

Share this post


Link to post
Share on other sites
On 2/2/2018 at 8:31 PM, audioguru said:

Every opamp has an input offset voltage error. Single opamps like the recommended MC34071 and the TLE2141 have input offset voltage adjustment pins. The project uses trimpot RV1 to null the offset voltage but your MC34072 does not have offset adjustment pins. Since your MC34072 has two opamps then it has double the heating and I think it becomes too hot.

The original project used the wrong value for R10 connected to RV1 and R10 was connected to the wrong voltage. Here is how it was and how it should be:

 

0V-30V offset adjustment.PNG

 

Share this post


Link to post
Share on other sites

A solderless breadboard has intermittent contacts that cannot handle the high currents of this project. The many rows of contacts and wires all over the place have capacitance between them that frequently causes a circuit like in this project to oscillate at a high frequency.

 

In my career I made all my prototypes soldered together on stripboard where I planned the layout to be compact and the strips were cut to length so that each strip was used for many parts of the circuit. Some of the circuits were very complex but worked perfectly and looked good enough to be sold as the final professional product. 

Share this post


Link to post
Share on other sites
On 3/7/2018 at 2:38 AM, audioguru said:

A solderless breadboard has intermittent contacts that cannot handle the high currents of this project. The many rows of contacts and wires all over the place have capacitance between them that frequently causes a circuit like in this project to oscillate at a high frequency.

 

In my career I made all my prototypes soldered together on stripboard where I planned the layout to be compact and the strips were cut to length so that each strip was used for many parts of the circuit. Some of the circuits were very complex but worked perfectly and looked good enough to be sold as the final professional product. 

Thanks audioguru for  your endless effort to the fulfillment of  passion .

Can i use  30V, 8A transformer  for the Project of  " 0-30V PSU Rev-7, 14-Aug-2014 Latest By Guest-liquibyte ". 

Attached file below. 

Waiting for you.

 

0-30V PSU Rev-7, 14-Aug-2014 Latest By Guest-liquibyte.pdf

Share this post


Link to post
Share on other sites

Hello, I make a PCB with this schematic, with a 24VAC transformer, who give normally 36VDC after main capacitor.
I test my PCB without AOPs and Tmain transistor (BD139 and TIP3055) and I measure Voltage after main capacitor C1 :
-The voltage start to 36VDC and grow up to 44VDC and stabilize.
-After inspection, I remove R1 (in my schematic R1 1K+R1-1 1k2) and I have 36VDC, ok.
-I put a 1K resistor for R1 (R1+R-1) and I have 36VDC for testing.
-I put a 2k2 resistor for R1(R1+R-1) and I have 44VDC...
-I I remove R1(R1+R-1) and I have 44VDC !!!
-I replace 1K resistor and I have finally correct 36VDC...

What is the explanation of this ?

Thanks and sorry for my english.

IMGP8086_DxO.jpg

Alimentation_0_30V-afa1cff4a81a4e6380fbe4d075b36b12.png

Share this post


Link to post
Share on other sites

This project will not produce 30.0VDC at 3.0A with a 24V transformer. It might produce 25VDC at 2A with a lot of unregulated ripple.The transformer must be 28VAC or 30VAC at 4.2A.

A 24V transformer will produce about 25VDC when it has a small load current which has a peak of 25V x 1.414= +35.4V and the bridge rectifier reduces it to about +34.0V.

Maybe your transformer is cheap and has a small maximum current so it is made to produce a much higher voltage when it has a small load current (your 2.2k resistors) then its voltage drops when it is loaded with your 1k resistor. Or maybe your meter is measuring the AC ripple that is caused by the value of the total capacitance of C1 is too small. 

Share this post


Link to post
Share on other sites
9 hours ago, audioguru said:

This project will not produce 30.0VDC at 3.0A with a 24V transformer. It might produce 25VDC at 2A with a lot of unregulated ripple.The transformer must be 28VAC or 30VAC at 4.2A.

A 24V transformer will produce about 25VDC when it has a small load current which has a peak of 25V x 1.414= +35.4V and the bridge rectifier reduces it to about +34.0V.

Maybe your transformer is cheap and has a small maximum current so it is made to produce a much higher voltage when it has a small load current (your 2.2k resistors) then its voltage drops when it is loaded with your 1k resistor. Or maybe your meter is measuring the AC ripple that is caused by the value of the total capacitance of C1 is too small. 

Hi : I am not sure if you understand my problem : I measure Voltage on the PCB without AOPs and Transistor, to make sure all is ok before put the AOPs.
The voltage I give is on The collector of TIP3055, just after the KBK.

1)My transformer is not cheap : I test him on breadboard with same main capacitor and Resistor, it give me with small charge 27VAC and 36VDC after bridge rectifier on BreadBOARD

 

2)I don't understand why on my PCB, I have 36VDC after bridge rectifier only with 1K resistor... With 2k2 or without resistor the voltage after bridge rectifier go up to 44VDC...

3) The question is why, with same component, I have a problem only on my PCB... Maybe a ground loop problem ? I checked many times all connections and all is fine, so...

 

Share this post


Link to post
Share on other sites

Ok, finally I replace R1et R1-1 (1K+1K2) by two 2k2 1W in // and it's works very well. The first test are pretty good.
If you want I made a final review when I will finish my Power supply ;).
The odd things is the fact that the transformer need a small charge (not too small - 30mA) on PCB to works well and on Protoboard it not need a charge at all to make 36VDC...
Thanks audioguru for your answer !

Share this post


Link to post
Share on other sites

Hi Tintin,

Now you say you measured 27VAC from your 24V transformer when its load current is low. Then it is cheap and has a high resistance so they made its voltage 27VAC instead of if it had low resistance and an output closer to 24VAC. Or maybe the voltage of your AC electricity is higher than normal. The peak of 27VAC is 27V x 1.414= 38.2V and the full wave rectifier drops it to about 36.8VDC, not 44VDC. 

Share this post


Link to post
Share on other sites

Hi audioguru,

You are right with the fact with 27VAV =>  44VDC after bridge rectifier is not normal, even without a charge.
My hypothesis is on my PCB :
-we see the wrong side of the things : maybe it is not the V+ who go up to 44VDC but the V- who go down to -8VDC when there is no charge (or <20mA) between + and - of the bridge rectifier
-and so, if my hypothesis was good, we have to find why and where is the new "zero point"
-Maybe the rôle of the section D5-D6-C2-C3 is important : on simulation on LTspice, whe have a sinusoïdal voltage between -4V and -12V (so the mean is -8V !) between D6 and C3 on normal situation...

My point of view is, even it's working well with a charge >25mA, I would want to know (because of my scientist brain) the cause of this fealure, in order to not make the same error the next time !

Share this post


Link to post
Share on other sites

Which schematic are you using? Years ago when I replaced the low voltage TL081 opamps with higher voltage MC34071 or TLE2141 I replaced the D7 zener diode with  two diodes so that the negative supply is only -1.3V. The 0V reference (zero point) for making measurements has always been the negative wire of C1, the main filter capacitor. 

Share this post


Link to post
Share on other sites

Hi,
I made a lot of test yesterday and it's works fine, i.e it could deliver 3A <20V, 2.5A<24V and 1A to 30V. It's ok for me, I thinks what did you say and maybe I will buy a 28VAC 160VA toroïdal transformer.
So I test for ripple  voltage for 5V 1-2-3A, and it was pretty good. I test start and my "disable output" and the results were good, particularly the limitation of current peak.

Well finally I test de current limit function, and, after adjusting trimmer RV3 for 1.41V (max 3A), when I make a short-circuit with the Potentiometer 10K at full the current go up to 6A and it blows up my primary fuse (630mA).

1)Ok, I replace the fuse, and I wonder why the max current is 6A !
2)So I test to 5V with a 10R Power Resistor, and, instead of having 5V500mA on my Chineese Multimeter like this : https://fr.aliexpress.com/item/Digital-DC-200V-0-10A-Red-Blue-LED-Dual-Display-Voltage-Current-Meter-Voltmeter-Ammeter-Power/32605098792.html?spm=a2g0s.9042311.0.0.L5o1rg

I have this : 5V with 0.390mA...

3) I test with my multimeter and it is not 5V but 3.90V with 0.390mA !

 

4)So I have 3 problems :

a) Why with the pot2 to max and with RV3 for 1.41V or even to make it at fully (100K), the current limiter is over 6A !

b)Why now the voltage regulation go down with a small charge, go 5V=>3.90V with only a 10R Power resistor. It's the same with 10V=>7.5V and 8V=>6.90V for example.

c)Why the chineese digital multimeter see 5V and not 3.90V ? I test with other and it was the same things. Or yesterday when i make test, when I put a 2A load on 30VDC the chineese meter saw the same fall than my Multimeter, so why now it did not see the voltage fall ?

I Checked AOPs, Transistors and voltage on AOP, main capacitor, and all is fine.

I give you my schematic and how the digital meter is plugged.

Thanks

Alimentation_0_30V-afa1cff4a81a4e6380fbe4d075b36b12.png

multimeter.jpg

Share this post


Link to post
Share on other sites

The Chinese meter is messing up the voltage and current of the power supply project.

Try the power supply project without the Chinese meter. Measure the voltage across R7 then calculate the current in it.

The voltage across R7 will never be more than 1.414V when the current in it is 3.0A or less.

Here are my calculations for the current calibration trimpot RV3: 

current control calibration.png

Share this post


Link to post
Share on other sites

Ok thanks Audioguru for your explanation, I wil take measure but I have one questions :

When you write on shematic +1.41V above R21, it is between Circuit OV, not the output ? I wonder if the ground have to be before or after R7 ? Is there any importance ?

 

Share this post


Link to post
Share on other sites

So I make my measure and this is result :

1) If a have no load (D is my ground) :
-UR7 (U_CD )= -12.6mV

-U_AC= 0.745V with RV3 set  to 100K
-U_AC=2.47V with RV3 set to 0K

-U_BD=11.7mV

-U_BC= 24.8mV (11.7-(-12.6))


If I put a 10R load for 5V to output :

 

-UR7=-115mV, so I=0.115/0.47=245mA

-U_AC = 0.635V with RV3 set to 100K

 

-U_BD = 11.7mV
-U_BD= 128mV

ex.png

Share this post


Link to post
Share on other sites

Oh I measure without my my chineese multimeter and so I have 3.90V on the 10R charge load.
I decided to measure voltage directly on the output of the PCB and surprise I have 5V !

So I think It was the cable between the negative output and the banana-plug who make this voltage fall !

Sorry for this disturbance, I will say you if this is it or not !

Share this post


Link to post
Share on other sites

5V on 10 ohms produces a current of 500mA (0.5A). Then the voltage across R7 is 0.235V.

On your schematic, C is the ground for the current regulator. The output ground is its input signal and the 11.2V is its reference voltage.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now