Sallala

1n5402 protect the 2n3055 transistors, but how to protect U2? In a switched off PSU, current can be flown from the output througt D10->R15 and into U2 output. Isn't it? What about to use a Shotky diode? It have only 0,3V drop. Or you can limit the maximum voltage with a trimmer potentiometer series to the voltage adjust pot. I see your diode on various circuits. But I don't understand, how it works. For example, how can it discharge a loaded capacitor on the output? I'm interesting this protection, because I use my psu to slow charge my accumlators. I haven't add the diode on my image yet. Just use it in series on the output. But this isn't good for the voltage stability. And what about D11. This is for protect the psu from a reverse polarity charged capacitor fr example? The original schematic, this is a low current diode. It's enough? (I'm not an electircal expert, please forgive me if I asked stupid a question, or just forward me to a beginner forum..) :-X

Dear Bongo! Why do you place the 1n5402 diode to the top of the 2n3055 transistors? To save the transistors, when the PSU is off, and there is a voltage connected to the output? (A charged big capacitor, orr accumlators for eaxmple) Maybe it isn't enough. As Audioguru says in an earlyer post, big current can be flown through U2's input Audioguru suggested a diode in the feedback, like the image below. I' m waiting for your response. (Sorry for bad English)

Audioguru: Something wrong in my workplace's internet access. I can't see any pictures attached to the forum at work. At home everíthing fine ??? But it's doesn't matter. I'm sorry: T3=Q3 (In my country, Transistor=T) Huhh, I checked it, but I don't remember exactly. It wasn't conduct between E-B or B-C. But I'm sure: the LED was bright always. Even if the supply was in constant voltage mode. Hmm, of course. As the diode, that you drawed. I must to modify the PCB. But this is not makes a problem, if the fuse at the output glowed, and it's in the negative feedback? But how can it's temp exceed 200 degress, when I turned down the votlage potentiometer? As I wrote, while I working, tha supply was good, and Q2 wasn't too hot. Then I leave the 2Ohm load at the output, but turned down the voltage potetntiometer. When I go back, fuse at the bridge rectifier burned. :o

I have got another problem: - My fuse (5A) at the secunder side of the transformer glowed. - T3 went out - Fuse at the output (5A) desn't damaged I used a 1,5-3Ohm load at 3-4V at 3A. (Cutting polystirol foam with hot wire) I use only one 2n3055 at this time, with heatsink and a big fan. This worked with no poblem. When I change the foam, I just turn the voltage and the current potentiometer down. (Or maybe just the curent pot?) But later, when I like to continoue the cutting see the problem. What happend? Why the fuseage burnt?

Audioguru: My browser (Firefox) can show PNG files. I don't know, what was the problem. Now I can see the images twice... Thank you anyway! I will buy a high current shotky diode, and will build into the pcb or inside to the supply's case. OK, I understand, what you tell about the batteries.

Audioguru! I can't see your pictures attached!

While the voltage keeps climbing, your batteryes doesn't fully charged. See it's technical manual! When the voltage stops climbing, and start decrease about a few millivolts, at this point your batteryes fully charged. The newer -dV chargers stops charging at this point too.

Hey, it's neccesarry for everyone isn't it? For example, if I put a circuit with a bigger puffer condensator on it's input, that can damage the power supply if the mains off. Not? I remember, on some three terminal stabilizer IC's manufacturer suggest a bypass diode between the leg 1 and 3. So the puffer condensator can discharge over the diode and the transformer. What can I waste, if I place permanently a series diode into tha supply's case? 0,6V voltage drop, 3W additional dissipation. Any other thing? Because who's care about that 600mV if it can be save your circuit?

If I use a 4,8V battery pack for example, and set the voltage to 5,2V the curent can't remain constant. A fully charged 4,8V NiMH batterypack's voltage about 5,2V. No voltage difference between the supply and the battery, -> no current isn't it? I use several type of batteries, I need the adjustable curent, so I'm happy, that I have an adjustable current batery charger too :-)

Audioguru: thank you for the quick answers again! - Yes, I'm thought to use a series diode too! (But I'm sure now because you confirm) - I think, timer doesn't neccesarry, only once. 1. Just charge the battery pack, with full voltage and adjusted current according to the battery. 2. Measure the fully charged battery's voltage 3. Next time, adjust the voltage to the measured in the 2. point. The constant current charging automatically "switches" to something like drop charging at the end. Somebody suggested this method. It's right? (Of course, this method not the same as use a timer. Just for start charging in the afternoon, and stop tomorrow morning.. And sometimes need to repeat to measure the fully loaded voltage)

Can I list all of the posts on one page in this topic somehow?

Ok, then Q1 emitter go back to 0V. I will make the modification. Just a new hole :-X I made a summarize about the project on my homepage: http://sala.sallala.hu/elektronika/szab_dc_tapegyseg/tapegyseg.html This time only for my language, (Hungarian) I will update this. And then what about the suggested 10..47uF capacitor paralell to D7 ? When the mains turns off, and there is a capacitor, -5V will go down slowly, not quickly. Isn't it? It's not a problem? Other question: Can I charge NiMH and NiCd batteryes with my powersupply? NiCd and NiMH bateryes doesn't need any special thing, just constant current, when you charge it in slow charge mode. (With 1/10C, 14h) Can the batteryes damage my supply? For example, when I stay connected it to the output, and switch off the supply? Or other reason?

Great tipp Alun! Thank you, I will try this. But you know, to print something to a leser printer, you must to draw it with a computer. ;-)

As I read in the topic: Q1 for pull down the output voltage, if you decrease the voltage adjust potentiometer. The current flows throught R7, Q1's emitter voltage increased, and T1 won't conduct->U2 can drive T2 If thers no current flow througth R7, then Q1's emiter go down, it's base higher than it's base->T1 conduct->pull down the output throught D10. But this is not clear to me. Wait for others' answer!

Twentyone century. Nevermind! I plan and made my PCB-s with my hand :-) 1. plan the connections on a papper 2. put the paper to the pcb, and sign the holes with a sharp prod 3. clean the brass plate well 4. now, you can see the place of holes on the brass plate, draw the pcb with water resist ink. Or you can use special pen. Water resist ink makes coherent surface, but hard to draw. You can draw easyer with a pen, but the surface will be ragged after the etchwork. 5. put the pcb into Ferric chloride (Fe2Cl3) solute in hot water, with face down 6. 15...30min and your pcb are ready 7. clean the pcb That's it! Take care, to read usage instructions for the ferric chloride!!!

T1's emitter connected to the input voltage's null point. This is wrong! T1's emitter must to connect to the output's 0V, otherwise it doesn't make it's job.

Spagbol: Oh, I missed. You need to modify the Q1's emitter, not Q2. Now I will correct my post. (at Q1, you know, what to modify?)

Ok, I will unsoldier the potentiometers, and measure they. My R4 is 1k, as according to the modified part list. I promised the pcb plans. Here they are: My finished PCB's picture. My modified soldier side plan My modified pcb side My finished circuit, and my transformator. This time, with only one power transistor. My finished circuit, closer look. PCB side, with the bypass capacitors for the OPAMP's. You can see, I use a shortcut for the powertransistor's emitter resistance. I will replace this with an 0,1 Ohm R, if I place a second 2n3055 The PCB plans are contain the "Q1's emitter" modification, and ready for bridge rectifier. They are draw for the BD139 transistors and ready for two 2n3055. Contain two fuse. Sallala

I measured the DC voltage again. It's 42VDC on C1. (I measured the 46V before I put the IC's into the panel. Maybe this makes the difference?) My pots are 10K. (as the label says) U1 output is just 10,56V for me. (I sed BZX 5v6 as D8) U(D8) is 5,25V Something wrong with my reference? I'am sorry. My old RFT scope dead. I must to go to the service :-S I can't measure the ripple now. :-[

Thank you for the reply Audioguru! I have a very poor English knowledge. I mean: split = not conduct ::) Of yourse, I use a metal case 2n3055, as the picture that you attached. Spagbol: thank you, I know that, and use a heatshink with a fan. But it' true, not a good resistor value for the start :-) I'am go to eat something, and after start a correct exact test with oscilloscope. The fast tests with an 50W 12V bulb: - Circuit can drive more than 4Amps at ~11V - The curent regulator regulate ~4,8A at the maximum potentiometer turn - With a 2-3Amp load, the voltage jump 10-20mV if I remove the load (Now, I used only one 2n3055) I made many photos whlie I building. I made small modification on the original PCB according to Audioguru's posts. (Q2 emitter, dual 2n3055, recifier diode bridge, BD139 feet layout. I will upload everithyng soon. Thank you! Gábor Salamon

Ehh, I solved my problem. 1. I measured wrong the 2n3055. But is still dead. There is a split between it's emitter and base. 2. I think it was wrong before I soldered it. (I have got three 2n3055 at home. I remember, once I test one of them. Maybe this was, beacuse I remember it's red painted text) OK, now I try to start testing the circuit under heavy load.

OK, I unsoldier the 2n3055 and the circuit now 0-31,5V again. I'm happy, that my opa455"s alive :-) The 2n3055 have a split between it's collector and base. But what happend? It's a very big problem, when the 2n3055 go wrong, the output jump to 13v isn't it? If I use the supply for an expensive circuit to supply 5V for example, and the 3055-> die. Now, I start to find another one in my boxes....

Hi! Finally I built the circuit. It started working and I was very happy. Without a load, I can adjust the voltage from 0-31,8V, tested with a multimeter. I use an old 32VAC transformer. The DC voltage is 46V at the rectifier. The negative supply is -5V exactly. I use OPA445 it's max supply +-45V :o but the absolute maximum rating at +-50V. My happyness gone when I tryed to test the circuit under a load :'( I started to test the circuit, with an 1 Ohm resistance at 2-3V. 1. I adjusted the voltage 2. cureant adjsutment potentiometer at the center 3 turn on the corcuit. Everithing seems to be ok. 4. I tryed to adjust the voltage and something happend: Current supply mode led flash ones, and the output is jumped to 13V Now, I can adjust the voltage only from 13V-31,8V DC. The DC voltage at the rectifier decreased to 42V What happend? Where can I find the bug?

Hi all! I'm, who start this topic some years earlyer. My parts are in a box one years ago, now there is the time to build the PSU. :-) I think, I visit the topic, before start building. It was a good idea ;) I readed through the topic. Thank you everybody, who help to correct the circuit, especially audioguru! I updated the parts list, TI shipped the three free OPA445 today. (I ordered it July 5 evening, and FedEx knocked the dor July 8 in the morning Whoaa. (I'am in Europe/Hungary) Maybe I will finish it the end of the next week. (I will busy in the weekend) I will post my experience. Gabor Salamon

Thank You! Exactly: +-5V AC, or +-5V DC? But maybe I must buy a tranformer, I haven't got a 3A one at home. When I ready with the circuit I will add comments.