0-30V Stabilized Power Supply

[audioguru2]

I measured the input voltage before insert the op amps in the sockets. The AC voltage was 30V, but the DC voltage was more than 50V, about 55Vdc.

The peak voltage is 30V x 1.414= 42.4V and the bridge rectifier reduces it to 41.0V with no load.
Maybe your filter capacitor was charged to a higher voltage. R1 should slowly discharge it.

 

[morpheous87]

Your opamp U3 has a high input offset voltage. Null it with a pot (like at U2) or increase the value of R17.

How exactly to null it? I'm using PicMaster's schematic and there isn't R17. What value it should be?

 

[adyhansolo]

The peak voltage is 30V x 1.414= 42.4V and the bridge rectifier reduces it to 41.0V with no load.
Maybe your filter capacitor was charged to a higher voltage. R1 should slowly discharge it.

Thank you Audioguru for your replay. I know the peak voltage should be around 42 Vdc, but I don't understand what is wrong. The filter capacitor is ok, it's discharged by R1. Could be the bridge rectifier defective ?  I measured the negative voltage ,too. It was 1.47 Vdc. It's ok or it's too high?

 

[PicMaster]

How exactly to null it? I'm using PicMaster's schematic and there isn't R17. What value it should be?

R17 is R16 on my schematic They are both laid out the same order so you can cross referaence from the original version. If I get time I will correct my version so it's the same has the original

 

[morpheous87]

So, will help only increasing R17(R16) value or I need something more?

 

[audioguru2]

How exactly to null it?

I said to null the input offset voltage of the opamp in the current regulator circuit exactly the same as it is done with the opamp that is in the output voltage amplifier. With a trimpot and resistor between pin 1 and pin 5 of the opamp.

I'm using PicMaster's schematic and there isn't R17. What value it should be?

Again we are sorry that PicMaster changed all the parts designation numbers. R17 on my schematic is 33 ohms. If its value is increased a little then the current regulator will stay off without a load.

 

[morpheous87]

I said to null the input offset voltage of the opamp in the current regulator circuit exactly the same as it is done with the opamp that is in the output voltage amplifier. With a trimpot and resistor between pin 1 and pin 5 of the opamp.

Again we are sorry that PicMaster changed all the parts designation numbers. R17 on my schematic is 33 ohms. If its value is increased a little then the current regulator will stay off without a load.

So, what value should I use, 68 ohms or ?

 

[lighty]

Hi Audioguru

I seem to be having a problem, I've just finished the second board and while testing, C7 explodes into pieces about a 1 or 2 seconds after I power up, I replaced it and the same thing happened again. The transformer is the same one I use on my other board, so it can't be it.

any idea where I can start? as I can test without powering it up?

When I powered it up the 2nd time, I had my meter on the output, and it seemed to sit at about 30V.

C7 where 10uF 50V electrolytic.

Thanks

 

[PicMaster]

I remember now why I created a new BOM is that some of the parts do not exist now like the .33R power transistors resistors . I will check that all the values are correct and I have decided to leave my version has it is, After all it is so simple to cross reference between the two drawings and BOM but I can't see the reason or nay need to, Has I built my PSU off my version including the bom. I will correct the last sheet which is the Assembly drawing

morpheous87  I would try 47R then 51R and just increase it a little until it works, I never had this trouble with mine

 

[morpheous87]

morpheous87  I would try 47R then 51R and just increase it a little until it works, I never had this trouble with mine

May be there is something wrong with U3 oamp. I'll try first with a new one, then increasing the resistor's value.

 

[lighty]

Hi Audioguru

I seem to be having a problem, I've just finished the second board and while testing, C7 explodes into pieces about a 1 or 2 seconds after I power up, I replaced it and the same thing happened again. The transformer is the same one I use on my other board, so it can't be it.

any idea where I can start? as I can test without powering it up?

When I powered it up the 2nd time, I had my meter on the output, and it seemed to sit at about 30V.

C7 where 10uF 50V electrolytic.

Thanks

Ok, found the fault, didn't fit the header for the off board LED, which one the the legs acts as a "via"

Will get new caps tomorrow and test again.

 

[audioguru2]

I seem to be having a problem, I've just finished the second board and while testing, C7 explodes into pieces about a 1 or 2 seconds after I power up, I replaced it and the same thing happened again. The transformer is the same one I use on my other board, so it can't be it.

any idea where I can start? as I can test without powering it up?

When I powered it up the 2nd time, I had my meter on the output, and it seemed to sit at about 30V.

C7 where 10uF 50V electrolytic.

Thanks

C7 will blow up if its polarity is backwards or if the bridge rectifier is defective or connected wrong and applies AC to the circuit instead of DC. Another person had his C7 blow up when his power supply project was powering a switching power supply circuit.

If the project has a load and is oscillating at a fairly high frequency then C7 might blow up.

 

[morpheous87]

morpheous87  I would try 47R then 51R and just increase it a little until it works, I never had this trouble with mine

I've changed the resistor with 47R then 51R also 68R. But there isn't change. I've made completely new board and I have the same anomaly. Both boards works same. This is not so big problem, but it's kind of annoing.  Any suggestions?

 

[morpheous87]

Thre is something I want to ask. If I connected for example DC motor which needs 1A, and the A regulator is below 1A, current limit led is lit. When the current is near the nessesary value, the Led start slightly turning off. Then the current reach these 1A, the led is off. Is it normal?

 

[audioguru2]

Thre is something I want to ask. If I connected for example DC motor which needs 1A, and the A regulator is below 1A, current limit led is lit. When the current is near the nessesary value, the Led start slightly turning off. Then the current reach these 1A, the led is off. Is it normal?

It is difficult to test a current regulator with a motor because the current draw by the motor changes with its mechanical load. Its current is higher when it works harder and when it starts.

The current regulation reduces the output voltage until the output current is the amount of the current-setting pot. If the output current is less than set by the pot then the current regulator does nothing.

 

[fikic]

Thre is something I want to ask. If I connected for example DC motor which needs 1A, and the A regulator is below 1A, current limit led is lit. When the current is near the nessesary value, the Led start slightly turning off. Then the current reach these 1A, the led is off. Is it normal?

It is normal..when the LED is on, your output voltage on PSU should drop. But try it with a bulb or something that has a constant current consumption..

 

[ultima2009]

Hi all
can i change the value of 10W resistor to 0.1 Ohm? (project 30V 3A output)

 

[audioguru2]

can i change the value of 10W resistor to 0.1 Ohm? (project 30V 3A output)

Maybe you are talking about the 0.47 ohm/10W resistor R7 that senses how much output current?
If you change it to only 0.1 ohms then the current regulator parts also must be changed. The input offset voltage of opamp U3 must be nulled to compensate.

 

[ultima2009]

Maybe you are talking about the 0.47 ohm/10W resistor R7 that senses how much output current?
If you change it to only 0.1 ohms then the current regulator parts also must be changed. The input offset voltage of opamp U3 must be nulled to compensate.

how calculate  the current regulator parts? and i can"t set the null with trimpot and resistor between pin 1 and pin 5 of the opamp. Opamp - TLE2141, trimpot - 4.7k and resistor 1k, output voltage is change from 22mV to 33mV.. maybe i need to increase or decrease the value of resistor (1k)?
Sorry for my english, iam fron russia
Thanks

 

[adyhansolo]

I built this project (last version with MC34071). I tried to run the power supply in this morning. I measured the input voltage before insert the op amps in the sockets. The AC voltage was 30V, but the DC voltage was more than 50V, about 55Vdc.

Hi Audioguru,
I don't find the solution of my problem. I checked all the components again and the voltage still remain 54Vdc( measured at C1 pins). If I disconnect R2 the voltage found is normal, 39Vdc. What is wrong? Please help me.