0-30V Stabilized Power Supply

[audioguru2]

The problem I am having is that I have no current control.  If P1 is at max and I turn P2 to max, then both the voltage and current drops to zero, and vice versa.  The LED never lights up.  And the max current never gets above 0.9A.

Tesseract's schematic does not show P1 or P2.
On my schematic, P1 is the voltage control and P2 is thew current control. If P1 is at max and the voltage trimpot is calibrated then the output voltage is 30V (or less when the current is higher than the current control setting). Since your voltage and current drop to zero when P2 is at max then you probably have P2 wired backwards.

R7 senses the output current. U3 controls the output current and compares the voltage across R7 with the setting of P2 and reduces the output voltage so that the output current (and the current in R7) is the same as the setting of P2.

 

[jpmhdbest]

please fix my schematics.. i don't know why it is not working properly..

how should i set the 2 potentiometers and the 3 trimmers to know the maximum and minimum voltage i can get?

i couldnt find MC34071 here in philippines.. then i researched about its equivalent.. there i found TL081.. so thats what i used as substitute for MC34071.. is this right?

i will be using 30V 4A = 120W Transformer.. is my AC source in the schematic right?

why is my output voltage varying and not stable..

thx in advance.

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[audioguru2]

please fix my schematics.. i don't know why it is not working properly.

how should i set the 2 potentiometers and the 3 trimmers to know the maximum and minimum voltage i can get?

i couldnt find MC34071 here in philippines.. then i researched about its equivalent.. there i found TL081.. so thats what i used as substitute for MC34071.. is this right?

i will be using 30V 4A = 120W Transformer.. is my AC source in the schematic right?

The fixed and corrected project will not work with TL081 opamps!!!!
I selected Motorola (ON Semi or another name today) and Texas Instruments opamps because they do what is required and are available almost everywhere. Their max allowed supply is 44V.
The max supply for a TL081 is only 36V so it will probably blow up. (the 30VAC transformer will have an output of 31V or more with no load, then the positive unregulated supply will be 42V. The TL081 needs a negative supply that is at least -4V which is not provided and would result in a total supply of 46V which is 10V more than its max allowed supply!

The MC34071 and TLE2141 opamps do not need a negative supply but the TL081 opamp needs a negative supply of at least 4V. The 1.3V negative supply is provided in the improved circuit so that U3 can turn on the diode to reduce the output voltage when the current is too high.

 

[jpmhdbest]

now its MC34071.. its voltage is at 53V.. still not correct..

what seems to be the problem here?

i really wanted to build this power supply.. i really cant find MC34071 or TL081.. help me please..

how about this OP Amp Dual GP22V/44V 8-Pin SOIC

http://philippines.rs-online.com/web/p/products/7092154/

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[fly3rman]

@audioguru, wolud you please approve the files i posted here:
http://www.electronics-lab.com/forum/index.php?topic=19066.msg100521#msg100521

before i start to build i have to know =)

 

[audioguru2]

now its MC34071.. its voltage is at 53V.. still not correct..

It is impossible to get +53V when you rectify and filter 30VAC.
The peak voltage is 30V x 1.414= +42.4V and the full-wave bridge rectifier drops it to +40.4V.
The max output from the project is about +35V when it is loaded then the calibration trimpot drops it to a max output of 30.0V.

i really cant find MC34071 or TL081.

You do not want TL081 opamps. You need MC34071 or TLE2141 opamps.
Farnell used to have an office in the Philippines but now it is called http://ph.element14.com and they stock both opamps.

how about this OP Amp Dual GP22V/44V 8-Pin SOIC
http://philippines.rs-online.com/web/p/products/7092154/

Why don't they call it by its real name? It is a surface mount TLE2142 which has two TLE2141 opamps inside. But it is tiny so it might over-heat.
RS components have the TLE2141 in a normal DIL package.

Your "remake schematic" has the wrong value for RV3.  It should be 100k ohms.

 

[audioguru2]

@audioguru, wolud you please approve the files i posted here:
http://www.electronics-lab.com/forum/index.php?topic=19066.msg100521#msg100521

before i start to build i have to know =)

You show my latest schematic and parts list. I don't know anything about the pcb design.

 

[redwire]

Fly3rman ,    The pcb you reference was copied from the 1st post  on page 1 and is still current.    Given it is a double sided board it is a little more difficult to build at home.  I had some commercially made pcb's  from that board file so I know it works.

 

[jpmhdbest]

they finally restocked MC34071 here in philippines.. i hope when i buy they wont run out again..

is my 30V 3 A transformer the right transformer to use?
(JUST FOR SURE I GOTTA ASK FOR THE LAST TIME.. thanks a lot for the patience)

i am also having a problem how to set the potentiometer and trimmers in the multisim to know the minimum and maximum voltages..

pls correct my schematic again.. if i set my trimmers to 100(i prefer 100 is the maximum) and potentiometers to 100.. voltage is somewhere 20 then an error message.. what to do?

is it alright to have MDA980-1 as bridge on multisim.. which has 12-30 Amps and 50 to 600 volts.. or should i stick with the 4 1n4148 diodes?

later il buy this KBPC10005 which is a 10 A 50V diode bridge available in the philippines.. is this alright?

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[fly3rman]

Fly3rman ,    The pcb you reference was copied from the 1st post  on page 1 and is still current.    Given it is a double sided board it is a little more difficult to build at home.   I had some commercially made pcb's  from that board file so I know it works.

Thanks for answering and thanks for the PCB. I also crosschecked it yesterday and and seems to be fine, only some values differs.

Alignments its a little bit tricky but there is still some leeway. Ill finish the toner transfer to the 2nd side today and etch this one.

 

[audioguru2]

is my 30V 3 A transformer the right transformer to use?
(JUST FOR SURE I GOTTA ASK FOR THE LAST TIME.

No.
It will overheat. It can supply 30V at 3A which is 90VA.
But the rectifier works with the peak voltage that is 42.4V so when the project has an output of 3A then the transformer must supply 42.4V x 3A= 127.2VA.
Use a 28V or 30V transformer rated at 4.2A.

i am also having a problem how to set the potentiometer and trimmers in the multisim to know the minimum and maximum voltages.

Build it and adjust it without fiddling around with Multisim.

pls correct my schematic again.. if i set my trimmers to 100(i prefer 100 is the maximum) and potentiometers to 100.. voltage is somewhere 20 then an error message.. what to do?

Multisim doesn't work properly.
If the pots are at maximum then reduce the settings of the trimmers until the max voltage is 30.0V and the max current is 3.0A.

is it alright to have MDA980-1 as bridge on multisim.. which has 12-30 Amps and 50 to 600 volts.. or should i stick with the 4 1n4148 diodes?

Forget about Multisim.
The MDA980-1 has a max voltage rating of only 50V which is very close to the peak voltage of 42.4V produced by the transformer. The peak voltage might be 44V without a load and power line spikes will be higher. Use a MDA980-2 that is rated at 100V.
A 1N4148 is a tiny low current signal diode, not a power rectifier.

later il buy this KBPC10005 which is a 10 A 50V diode bridge available in the philippines.. is this alright?

No.
Use a diode bridge with a 100V rating.

 

[jpmhdbest]

what about 30 V 4 A transformer? can i use this?

correction.. KBPC10005 can have REVERSE VOLTAGE from 50 to 1k V.. FORWARD CURRENT 10.0/15.0/25.0/35.0 A.. now can i use this?

http://www.datasheetcatalog.org/datasheet/good-ark/KBPC3502.pdf

MANY THANKS AUDIOGURU^

 

[audioguru2]

A 4A transformer is 95% of what is needed (4.2A) so it can be used.
The KBPC10005 has a voltage rating of only 50V which is not enough. Use a KBPC1001 which has a voltage rating of 100V.

 

[jpmhdbest]

i thought this project's Bridge needs to be 6-10 A / 50V diode bridge module..

may i also ask if the 2 pcs. 2N3055 needs heat sinks also.. 1 for each?

 

[audioguru2]

i thought this project's Bridge needs to be 6-10 A / 50V diode bridge module.

Correct. But a 100V one is much better.

may i also ask if the 2 pcs. 2N3055 needs heat sinks also.. 1 for each?

Of course the output transistors get very hot and must have a heatsink. Use one very big heatsink for both or use a smaller but still pretty big heatsink for each one. When the output voltage is low or shorted and the current is set to 3A then each 2N3055 transistor must dissipate about 59W of heat.

 

[jpmhdbest]

ok.. many thanks again.. il start building it nowadays.. any reminders you want to add more..?

 

[jpmhdbest]

in the schematic you have given.. U1 has its #2 & #3 pins flipped right? why doesnt #7 & #4 pin flipped also? is the schematic wrong?

 

[audioguru2]

in the schematic you have given.. U1 has its #2 & #3 pins flipped right? why doesnt #7 & #4 pin flipped also? is the schematic wrong?

Whose schematic are you looking at? My schematic is correct. U1 does not have its pins flipped.
U1 is the 11.2V reference voltage circuit.View attachment 41563

 

[fly3rman]

just to check: this one ok as bridge? (asking because of the glass)
http://diodes.com/datasheets/ds21221.pdf
25A GLASS PASSIVATED BRIDGE RECTIFIER 600V

4700 or 6800uF/63VDC  should be enough for stable voltage at low currents right?

 

[peckcj]

Hello all,

My PCB is made, and all components have been purchased, but I had one question I need some assistance with.  I am making the 5A version, with three MJ11016G paralleled transistors.

My question is:  I'll be using three emitter resistors (0.33 Ohm 5W), but I'm a little unclear on how I should wire them.  My initial thought is to wire each one in series with the emitter before I connect all three emitters together for the parallel connection.  See pic.

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