Guest _pike Posted November 6, 2013 Report Share Posted November 6, 2013 Thank you audioguru for your answer....I have built the improved circuit with the new components and i used the pcb of windtrek.I used one transistor instead of two or three because that was available to my drawer..( i hadn't second one ) i will try it again tomorrow when i will buy 2 2n3055....But do you think that this could cause the particular problem????I mean that both of them are npn transistors...I will start with that and then i will write my progress..thanks in advance Quote Link to comment Share on other sites More sharing options...
audioguru Posted November 7, 2013 Report Share Posted November 7, 2013 A 2N3055 has an allowed continuous collector current of 15A.A 2N3722 has an allowed continuous collector current of only 1A but it should work if the load current is 1A or less and if it does not get too hot.I could not find a datasheet for the 2N3722 to see which pin is which. Maybe you have its pins mixed up. Quote Link to comment Share on other sites More sharing options...
Guest _pike Posted November 9, 2013 Report Share Posted November 9, 2013 As i thought.... there wasn't any problem with the power transistor i used a 2n3055 and 2 2n3055 and i didn't get any output.... (0volts) I will now look for the bd transistor and the u2 ic..... What other measurements can i do to diagnose the fault???Regards Panagiotis Quote Link to comment Share on other sites More sharing options...
audioguru Posted November 9, 2013 Report Share Posted November 9, 2013 Connect a load of 2.7k ohms/0.5W to the output of the project.Opamp U2 and the driver and output transistors are an amplifier with a voltage gain of 2.68 times. So when the voltage setting pot is set to maximum it has +11.2V from U1 going to the input of U2 and the amplifier amplifies it to +30.0V.The output of U1 is always +11.2V. Since the driver and output transistors are simple emitter-followers in series then the output of U2 is always about 1.4V to 2V higher than 2.68 times the voltage from the voltage-setting pot. Quote Link to comment Share on other sites More sharing options...
Guest _pike Posted November 10, 2013 Report Share Posted November 10, 2013 audioguru thanks for your intrest.Well i don't get any output from pin6 of u1 (0volts) but i am measuring 41 volts from the other pcb.Does this helps you?P.s Another measure i did.ic1 pin 4(-) and pin 7(+) 41,4voltsic2 pin 4(-) and pin 7(+) 41,4voltsic3 pin 4(-) and pin 7(+) 33voltsalso when i touched my multimeter to measure ic3 the led lit up...Hope to help you....regards Quote Link to comment Share on other sites More sharing options...
audioguru Posted November 10, 2013 Report Share Posted November 10, 2013 Well i don't get any output from pin6 of u1 (0volts)U1 is a simple voltage reference. It uses an opamp U1 to amplify a 5.6V zener diode to 11.2V: Quote Link to comment Share on other sites More sharing options...
Guest _pike Posted November 10, 2013 Report Share Posted November 10, 2013 Audioguru i found the problem!!!!!! There was a short circuit between pin2 of ic1 There was so little solder but thankfully i found the problem......i will test it with loads and i will post my results I would like to thank you again for helping me....Regards Panagiotis Quote Link to comment Share on other sites More sharing options...
audioguru Posted November 10, 2013 Report Share Posted November 10, 2013 I am glad that you spotted the problem and it caused no damage. Quote Link to comment Share on other sites More sharing options...
Guest _pike Posted November 16, 2013 Report Share Posted November 16, 2013 Hello Audioguru!!!Well the power supply works fine and i'm glad for that....I used 2n3055 and i will buy a third one later.The only thing i noticed is that the transistors became very hot in a 12v load with 2,5 amps current.....Is it normal?Also if it is possible for you i would be glad to explain me how the current limiter works...Thank you in advance Panagiotis. Quote Link to comment Share on other sites More sharing options...
audioguru Posted November 16, 2013 Report Share Posted November 16, 2013 I used 2n3055 and i will buy a third one later.The only thing i noticed is that the transistors became very hot in a 12v load with 2,5 amps current.....Is it normal?The 2N3055 output transistors are powered from about 41V. If the output is 12V then the output transistors have 41V - 12V= 29V across them. Simple arithmetic calculates that they heat with 29V x 2.5A= 72.5W.If the current is set to 3A and the output voltage is low or is shorted then the output transistors heat with 41V x 3A= 123W.They need a pretty big heatsink to cool them enough. It is simple to calculate the thermal resistance needed for a heatsink and heatsink manufacturers specify the thermal resistance of their products. Also if it is possible for you i would be glad to explain me how the current limiter works...It has current regulation which is much more accurate than current limiting.R7 senses the output current using Ohm's Law. Opamp U3 is used as a comparator with the current-setting pot on one input and the voltage developed by R7 on the other input. If the actual current is higher than the pot setting then the output of U3 goes low enough for D9 to reduce the output voltage until the actual current is the same as the pot setting. Quote Link to comment Share on other sites More sharing options...
Guest _pike Posted November 17, 2013 Report Share Posted November 17, 2013 Thank you a lot audioguru!!! Can you please explain in more detail the following...."R7 senses the output current using Ohm's Law" Can you give me an example as you did before?Thank you!!! Quote Link to comment Share on other sites More sharing options...
audioguru Posted November 17, 2013 Report Share Posted November 17, 2013 Thank you a lot audioguru!!! Can you please explain in more detail the following...."R7 senses the output current using Ohm's Law" Can you give me an example as you did before?Ohm's law says that "The voltage developed across a resistor is made by the current in the resistor times the resistor value". 2A in the 0.47 ohms of R7 produces (2A x 0.47 ohms=) 0.94V. Quote Link to comment Share on other sites More sharing options...
Guest _pike Posted November 17, 2013 Report Share Posted November 17, 2013 thank you audioguru!!!! really appriciated.......Something last...R21 acts like a pull down resistor for voltage reference?and why is it used 1w for the led's resistor?wouldn't be ideal a 1/4w?thank you Quote Link to comment Share on other sites More sharing options...
audioguru Posted November 18, 2013 Report Share Posted November 18, 2013 R21 acts like a pull down resistor for voltage reference?R21 feeds the voltage across R7 into the inverting input of opamp U3 so that U3 can integrate the voltage with R21 and C8.Why is it used 1w for the led's resistor? Wouldn't be ideal a 1/4w?The original circuit used a 1W resistor that dissipated 0.37W.The LED's resistor is R22 and is 3.9k. It has 28V across it now when the LED lights. Then it dissipates (28V squared)/3.9K= 0.2W. A 1/4W resistor will get very hot so use a 1/2W resistor. Quote Link to comment Share on other sites More sharing options...
Guest danijelrd Posted November 20, 2013 Report Share Posted November 20, 2013 First of all, HY ! :)So, which one of all those schemes to use? For me, its important to get voltage and current control of max 12V and 1A. (could be bigger, but not so important for my use..) ?! I'll read all thread before I start doing it, but it would be nice to order componentes (Im from croatia, lame electronics stores...).. :) thank you ! and sorry for my little bit rude question. Quote Link to comment Share on other sites More sharing options...
audioguru Posted November 20, 2013 Report Share Posted November 20, 2013 I have posted the corrected and updated schematic and parts list hundreds of times. It is too bad that the original project is wrong and does not show my corrections.It produces regulated 0V to 30V with regulated current from a few mA to 3.0A.Since you want only a small voltage and current then maybe you should use a simple LM317 adjustable voltage regulator IC instead. Quote Link to comment Share on other sites More sharing options...
Guest danijelrd Posted November 20, 2013 Report Share Posted November 20, 2013 Those with LM317 don't have current regulator..and they dont go from 0V..At least not those what I found. Do you have any maybe with current regulation? I would be very thankful to you! If you dont, I'll try to manage somehow in this bunch of schemes here :D (saw your post, couple pages earlier)...Sorry for offtopic! Quote Link to comment Share on other sites More sharing options...
xristost Posted November 20, 2013 Report Share Posted November 20, 2013 Those with LM317 don't have current regulator..and they dont go from 0V..At least not those what I found. Do you have any maybe with current regulation? I would be very thankful to you! If you dont, I'll try to manage somehow in this bunch of schemes here :D (saw your post, couple pages earlier)...Sorry for offtopic!It's there, in the datasheet: http://www.ti.com/lit/ds/symlink/lm117.pdf (page 21). But it is from 1.2V to 30VIn the datasheet have also schematic which goes from 0V (page 20) but without constant current mode. Maybe its possible the first schematic to be modified to go from 0V. Quote Link to comment Share on other sites More sharing options...
Guest danijelrd Posted November 20, 2013 Report Share Posted November 20, 2013 I've been thinking a bit...For an example. When I on experimental board, put 74ls86 XOR or 555 timer... on output 1,2 led's or something with low current (below 0.5 A), I dont need a current regulation? Am I thinking ok ? 'cause resistors and loads would take amount of current which they need, no more no less..(except ofc if there's something wrong connected.)About low limit of voltage regulation, I think that any of IC's and componentes that I'll be using, wont need that low voltage.If that's true, Linear psu with lm317 would be perfect for my needs. Quote Link to comment Share on other sites More sharing options...
audioguru Posted November 20, 2013 Report Share Posted November 20, 2013 For an example. When I on experimental board, put 74ls86 XOR or 555 timer... on output 1,2 led's or something with low current (below 0.5 A), I dont need a current regulation? Quote Link to comment Share on other sites More sharing options...
redwire Posted November 27, 2013 Author Report Share Posted November 27, 2013 The original circuit used a 1W resistor that dissipated 0.37W.The LED's resistor is R22 and is 3.9k. It has 28V across it now when the LED lights. Then it dissipates (28V squared)/3.9K= 0.2W. A 1/4W resistor will get very hot so use a 1/2W resistor.After adding the 10V Zener, I don't think R22 was adjusted on the parts list. Shouldn't R22 be approximately 1.5K. Quote Link to comment Share on other sites More sharing options...
audioguru Posted November 27, 2013 Report Share Posted November 27, 2013 After adding the 10V Zener, I don't think R22 was adjusted on the parts list. Shouldn't R22 be approximately 1.5K.Yes, I agree.If the value of R22 is changed to 1.5k then the current in the LED will be about 19mA which is fine and will be nice and bright. The resistor will dissipate 0.53W so it should be 1W. Quote Link to comment Share on other sites More sharing options...
Guest gizmo322 Posted December 12, 2013 Report Share Posted December 12, 2013 Hello ,i just build my first circuit and this was 0-30V power supply.Now i would like to know where do i connect a digital voltage and amp lcd display? . Pleas help me ,and sorry for my bad english . Regards Quote Link to comment Share on other sites More sharing options...
red_81 Posted December 12, 2013 Report Share Posted December 12, 2013 Hi guys,I almost started to do a schematic ver.0 (the one from kit) and than stumbled upon this thread. I read it from firs to last page. What to say, u saved my life. I did PSU on last version with MC34071 from ebay and used it in school where kids do a lot of short circuits during practice and this nice piece of design survived 2 years of daily torture. I got a bit lazy to bring it home->job->home... so i decided to make another one.My problem is that there is no more ICs to find anywhere at reasonable price tag, neither MC or TLE variant. They were like 1$/piece but now i cant to find them anywhere. I live in EU and shipping from USA is insane so im kind of stuck!Any suggestions? Some replacements for IC s? im trying to find something on my own but no success.tnx in advancePs: one more time, big tnx to audioguru, redwire, picmaster and all others for effort on this one Quote Link to comment Share on other sites More sharing options...
audioguru Posted December 12, 2013 Report Share Posted December 12, 2013 where do i connect a digital voltage and amp lcd display?A voltmeter is connected to the output to show the output voltage.A current meter is connected in series between the output and the load to show the load current.Most digital meters need a power supply that is completely separate from the circuit they are measuring. Quote Link to comment Share on other sites More sharing options...
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