0-30V Stabilized Power Supply

[audioguru2]

PicMaster's version has 3 OPAMPs, so I need 3 zener diodes on their positive pins?

The opamp U3 on my schematic and the transistor that drives the LED already have a 10V zener diode in series with their positive supply because the max output of U3 is only 28V to 30V.

 

[audioguru2]

Is it like i drew it?

No.
Pin 7 is the positive power supply pin. You have the zener diodes on an input pin instead which is wrong.
The cathode of the zener diode connects to the positive supply and the anode connects to pin 7 of an opamp.

 

[morpheous87]

How much Watts should be the 4V7 zener?

 

[audioguru2]

How much Watts should be the 4V7 zener?

Power is measaured in Watts. Power is volts multiplied by amps. The volts for a 4.7V zener diode is 4.7V and some of the current can be found on the datasheet for the opamps which is 4.5mA max. Each opamp has a load current of 5.5mA so the total current in each zener diode is 10mA.
Then the power in the zener diode is only 0.047W which is nothing so a 1/4W zener diode is fine. Use a zener diode tested at 5mA or 10mA like a 1N5992B, BZX55C4V7, BZX83C4V7 or BZX79C4V7.

 

[morpheous87]

Could be used 5,1V or 5,6V zeners instead of 4,7V ?

 

[jrhodes]

audioguru you are unbelievable you know i had the bd139 on the board and changed them out with a tip3055 cause i could only get the bd139 into126 package thinking the plastic case would needa larger heatsink i have tip3055s as output transisters but these are much larger than the tip3055 i got at radioshack and replaced the bd139s with well iguess i switch them back cause you are correct the pins are backwards hope i dont fry them with all this soldering and desoldering. cant believe i missed this. audioguru your incredible thanks for getting me straight ill let you know how it works 

 

[audioguru2]

Your unloaded supply is 46V which is 2V higher than the 44V absolute max supply for the opamps. Try reducing it with 5.1V or 5.6V zener diodes to see if the output will be 30V with a current of 3A.

 

[morpheous87]

On the first of the PCBs I put 2 4,7V zeners, on the second i put 4,7V on U2 and 5,1V on U1 (i hadn't one more 4,7V). When only one of them is turned on (the one with the 2 4,7V) has 30,4V ouput. When I turn and the second one on, maximum output is 29,7V. The PCB with the 5,1V zener has ~ 27V when both are turned on. So I suggest to put less than 4,7V zeners (4,3V may be) ?

 

[audioguru2]

Morpheous,
If your transformer produces an unregulated 46VDC without a load, then it must be producing only 41VDC with a load which is horrible voltage regulation.
Or maybe the value of the main filter capacitor is too low.

Maybe your transistors were damaged when you had them connected backwards.

 

[morpheous87]

The main filter capacitor is formed by 2 4700uF. Yestarday without the zeners on the OAMPs, the ouput voltage went over 31V.  Now when both PCBs are powered the input voltage from the transformer is 33,5V.

 

[jrhodes]

i turned the driver transisters around and the powersupply worked great right up until i hooked up my 18v dewalt drill test motor i may have over amped the circuit i dont know i didnt have ampmeter tied in but now i get 34 volts through the output nothing less on picmasters verion theres a seperate board for the driver transister and output transisters. ive disconected them and still get 34v0lts at pin 6. in audiogurus version c9,c6,r12,r11are all that are connected to pin 6 i dont see how any of these could have failed and output 34volts to pin 6 i have switched chips same thing

also i do get 0 t0 11 volts at inveting pin 3 just noninverting pin 2 stays at 0 volts

also i do get 0 t0 11 volts at[glow=red,2,300] noninveting [/glow]pin 3 just [glow=red,2,300]inverting pin [/glow]2 stays at 0 volts sorry had these backwards

Posts merged by moderator. Please use the modify button (it looks like this

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[audioguru2]

the powersupply worked great right up until i hooked up my 18v dewalt drill test motor .....
now i get 34 volts through the output nothing less

Maybe the current regulation is not working and you overloaded this power supply circuit. Then the output transistors and/or driver transistor and/or opamp are shorted.

ive disconected the driver transister and output transistors and still get 34 volts at pin 6.

That is normal because you disconnected the negative feedback from the output to pin 2 so the voltage on pin 2 is much too low which causes the output pin 6 to go as high as it can.

in audiogurus version c9,c6,r12,r11are all that are connected to pin 6

R11 and R12 are a volage divider that divide the output voltage by about 2.68 times to feed negative feedback to pin 2. When pin 3 is +11.2V then the output of the project will be +30V and pin 2 will also be +11.2V.

Measure the output transistors and driver transistor with an ohm meter to see if they are shorted. If they are not shorted then connect them in the circuit and with the voltage setting pot at zero tell us the voltages at pin 2, pin 3 and pin 6 of the opamp and the voltage at the output of the project.

 

[jrhodes]

right again it was the bd139 now i get my variable back and i checked my amps with just a led and i can control my amps thanks guys for all your help will try to get pics when done

 

[jrhodes]

alright it happened again i fried my driver chip right away now this is after i ran the supply with just a led as a load. i hooked up my ampmeter and and showed from voltages 0 to 30v, 0 to 93 millamps my current limiter was funtioning correctlly cause i was able to set my current at 20 millamps and my voltage would come up i cant remember but i think it was about 6 some volts and then it would go no higher unless i adjusted current limiter.  the light was working properly. everything was great until i hooked up my motor. it was only on ten sec or so i preset my voltage to 18v cause its a 18v motor. then i turned my current down to almost nothing. then hooked in the motor. nothing. so i turned up the current regulator and after so far the motor kicked in and almost immediattly bd139 started to smoke. the ampmeter read only 83 milliamps. but it almost seemed to me like it fried right away and was just running on 30v which is where my mains are at. im not sure it all happened so fast. i built this supply to operate this motor. i actually built 2 side by side one to run the pic chip and circutry. and one to power the motor that the pic controlls with pwm. i kept frying the motor controller chip L6203 when ever i stop the pic cycling which some times you cant stop the moter during testing so it may be running one direction then you stop the pic its outputs go 0v which 0v is a full speed reverse signal to the l6203 throwing the motor in full reverse next thing i know the l6203 is fried. so i wanted some current limiting thus this circuit. i believe this power supply should work for my prototype its just why does it fry bd139 thers no current  flowing here except for maybe through r16. in all fairness i should say i didnt put heat transfer compound under my chip to heatsink i planned to but i was only running it for a few seconds.

 

[audioguru2]

Hi J Rhodes,
The BD139 powers the load if the two 2N3055 output transistors are shorted, are wired wrong or their 0.33 ohm emitter resistors have a value much too high. Then it will burn.
If the 2N3055 output transistors have minimum gain then the max current in the BD139 is 75mA and is 38mA when the 2N3055 transistors have typical gain. Then when the output voltage is 18V the BD139 has about 22V across it then it dissipates 38mA x 22V= 0.8W to 75mA x 22V= 1.7W which is not much. With a little heatsink it will be fine but without a heatsink its junction will be above its allowed max temperature.

Maybe the BD139 is failing because the motor produces an inductive voltage spike each time the PWM turns it off unless it has a fast free-wheeling diode connected to it.

 

[jpmhdbest]

sir can a CD4071BE be a replacement for MC34071?

thanks..

 

[Hero999]

sir can a CD4071BE be a replacement for MC34071?

What do you think?

Google for the datasheets and read them.

 

[jpmhdbest]

i guess its the same..
because they have same ...4071..
therefore CD4071 can be substituted to MC34071..

 

[audioguru2]

i guess its the same..
because they have same ...4071..
therefore CD4071 can be substituted to MC34071..

No.
They are completely different. Why don't you look at their datasheets?
The CD4071 is a Cmos digital quad 2-input OR gate. It has 14 pins.
An MC34071 is a single linear bipolar opamp with some special features that ordinary opamps do not have. It has 8 pins.

A TLE2141 is also an opamp with the same special features as an MC34071. 

 

[jpmhdbest]

ok.. how about this?

MC33071/72/74, MC34071/72/74

are they all the same?

also.. i cant find a 12000uF 63V..

can i just put a 10000uF+1000uF+1000uF in a parallel as substitution?