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Forum Index : Electronics : LM723 30V-10A Power Supply Problem
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| muneeb345 Newbie  Joined: 21/09/2013 Location: PakistanPosts: 4 |
Hi! sorry for bad english I am making lm723 based power supply by backshed LM723 PowerSupply. The problem is that when ever I turn on the power supply under load the BD139 blows out.  . I cant figure it out why it is happening.Please help me I deadly need this power supply for my ongoing CNC. |
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Downwind Guru  Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Are you sure you have the BD139 in the correct way around, have you checked for a short to ground between the emitter and ground, Have you checked all the 2n3055 transistors to see if any have blown or are shorted between base and emitter or emitter and collector. Have you made any changes to any of the components shown. Pete. Sometimes it just works |
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| muneeb345 Newbie Joined: 21/09/2013 Location: PakistanPosts: 4 |
No I did not change any thing in the circuit except R8 to set the range. All 2n3055 are fine. |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Well you have something wrong or made a mistake somewhere because the circuit works fine when it is all correct. Do you have a heatsink on the BD139 Sometimes it just works |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
I can vouch for the circuit, it does work well. All you can do is troubleshoot the problem. Does it work OK under light load, say driving a light bulb? How are you using the power supply, what is the load that's causing it to fail? I've used the same circuit to drive a 24v electric DC motor on my own CNC, and found back emf and spikes from the motor were affecting the power supplies regulation, so I fitted a couple of 0.1uF caps across the motor and the fault cleared. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| muneeb345 Newbie Joined: 21/09/2013 Location: PakistanPosts: 4 |
Yes I do have but I think its not enough,I'll try again with bigger heat sink |
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| muneeb345 Newbie Joined: 21/09/2013 Location: PakistanPosts: 4 |
Thanks gizmo! I too have confidence on this circuit because it did work well once..
I think there is something wrong that I am not getting..I have connected a 9V DC motor with the power supply and after a jerk output voltage goes to constant 37V and I had a quick check for BD139 it was showing a short between BASE and Emitter |
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| novosyst Newbie Joined: 24/11/2013 Location: Czech RepublicPosts: 16 |
hello , please help me , I use R8 -120R -does not regulate the voltage and current ,chip have been changed, assembly is ok . everything was ok everything was fine until LM was varied to UA . |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
What is UA ?? micro amps. ?? well the circuit wont do micro amps if that is what you are intending to do. I designed the circuit and built it over 20 years ago, and mine still works fine, so it might be a assembly problem after all, please double check all components and wiring. There has been a few revisions to the circuit of minor components over time to allow lower settings but the basic circuit as presented should work. If not then its a construction fault somewhere, it always is, as many have built this circuit and had results, often after solving the assembly error. Pete. Sometimes it just works |
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| novosyst Newbie Joined: 24/11/2013 Location: Czech RepublicPosts: 16 |
oh sorry UA723 - new chip , but but fully equivalent . |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Ahrrr, i had a thought to your problem, it might not be a circuit fault at all. It could be your understanding of how the LM-723 works. What happens when the LM-723 reaches its preset current (amps), then it backs off the "voltage" to maintain a set current. You might be seeing the voltage drop when the current limit is reached, this is normal for how the LM-723 works. All it means is the connected circuit is drawing more current than the power supply is set to deliver, if you increase the current setting you should see the voltage rise to its per set limit. I test the circuit current control by shorting the output leads together, and start down low on the current setting and increase it, the current should increase with the dial, although voltage will read around zero because of the shorted leads. If all is working correctly then no magic smoke should escape from the circuit, just dont spend too long at full amps with the leads shorted, as the 3055 transistors will get very hot. Pete. Sometimes it just works |
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| novosyst Newbie Joined: 24/11/2013 Location: Czech RepublicPosts: 16 |
problem in the following - I collected first time -everything worked ok ))) past -short (too many beer ) , ship have been changed to ua723 ( 3 TIMES )and after that i have not any adjustment . |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Check the 0.1 ohm and 0.47 ohm 5w resistors as one of them might have gone open circuit, also check the 3055 transistors to see if one or more have become a short circuit. Pete. Sometimes it just works |
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| novosyst Newbie Joined: 24/11/2013 Location: Czech RepublicPosts: 16 |
i have 35 volts on the exit (((( have not voltsge adjustment ((( please sent me your circuit my email novosyst@seznam.cz |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
My circuit is the one posted on the forum that you are using. No voltage adjustment would imply you have blowen up 1 or more transistors, please check all transistors. What do you have for a heatsink, as you will require a rather large heatsink or the transistors will burn out. Pete. Sometimes it just works |
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| novosyst Newbie Joined: 24/11/2013 Location: Czech RepublicPosts: 16 |
ok now we have voltage (but only 27v max is it true) and have not current adjustment tell me please how it working if i have some load on the exit of power supply |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Your English is good, but your information is not so good. There is a fault in your circuit somewhere, its not a design fault, its a construction fault. This makes it very hard to help you with, because i can not see your construction of the circuit. Can you post a few clear photos of your power supply, as it might help me understand what you have built. Pete. Sometimes it just works |
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| novosyst Newbie Joined: 24/11/2013 Location: Czech RepublicPosts: 16 |
red points- pot pins. |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
That photo tells me nothing, except you have components on a board. A component side photo and a solder side photo might help, i am more interested in a photo of your transistor circuit than a photo of capacitors and resistors on a PCB. I can only work with the information you provide, i dont have a crystal ball to see your project and can only work with what you provide. Pete. Sometimes it just works |
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| novosyst Newbie Joined: 24/11/2013 Location: Czech RepublicPosts: 16 |
ok but am interesting in -is that circuit is true ( UPSB is usual with common parallel pad strips) because if every thing is all right i connect it with one transistor to begin )))))) why you need to see transistor i know TO3 pin position and how to connect legs . If i have trouble -only with chip connection )))) check it please |
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