login
fikic
-
Posts
87 -
Joined
-
Last visited
Never
Content Type
Profiles
Forums
Events
Posts posted by fikic
-
-
So, I need at least 28V 120VA transformer? But output with 28V or 30V transformer has also hum at maximum output voltage, yes?
-
With this hum, you mean just noise, or it has impact on quality of output?
-
My transformer is 250VA, so current isn't the problem. So 24V output is just fine?
-
No, I have 3A version with 24V AC toroid transformer.
-
I changed output transistors and it works. I get maximum 24V on output. Is this ok?
-
Ok, so Ohm-meter must show nothing between collector and emmitter of 2n3055, becouse it's infinite resistance? Mine show something between 100 and 200 kOhm (on both of them, on one even less).
-
I replaced BD139 with BD135, becouse I don't have any BD139 left. Is this ok? How can I check 2N3055 transistors - I don't have transistor tester. Should one conduct between base and emmiter and between collector and emittor? If not, where it should?
-
Hy guys. I've made a little mistake, when I connected a diode bridge. I accidentally swapped - and AC connector. I then saw some smoke and litle bang. On the output of psu, I now only get constant 33V and I can't regulate it. I thought, that opamps may be the reason and I replaced them, but this is not the case. So, what should I check next. What could happen in that case, when you swap - and AC of rectifier.
PS.: PSU worked perfect before that. -
audioguru says, that he doesn't use Eagle..so I doubt that it is his..
-
Audioguru / Adyhansolo
I might be way off of here, but learning from my last problem (previous page)
I didn't have the header pins for the off board LED soldered in place when I testing, this cause the C7 (rated 50V) to pop within a few sesconds of powering up. I assume it is due to the one pin is acting as a "via" to gound some of the circuit, could this not be Adyhansolos' problem?
Just a guess :-\
Image attached.
Your PCB is very negligent drawn.. Don't use autorouter, where you can draw PCB on your own. This one is really easy, especially if you have double-sided board like you..Just for an advice, your PCB could be much smaller for double-sided board, and much more accurate.. -
Thre is something I want to ask. If I connected for example DC motor which needs 1A, and the A regulator is below 1A, current limit led is lit. When the current is near the nessesary value, the Led start slightly turning off. Then the current reach these 1A, the led is off. Is it normal?
It is normal..when the LED is on, your output voltage on PSU should drop. But try it with a bulb or something that has a constant current consumption.. -
@audioguru, thank you for all of your help. I replaced D5 and D6 and PSU works perfect! Current regulation works and everything is fine! Thank you hundred times for your help. :-*
-
Hi Fikic,
Your schematic is correct. Your pcb is an Eagle file that I cannot open because I do not use Eagle.
Check the values of R2, R3, C2 and C3. Replace diodes D5 and D6.
PCB is not Eagle, it's Kicad..I will send you pdf.. -
Ok, I replaced D7 (two diodes) and it doesn't make any difference, so this is not the case. Diodes are fine. Voltage drop across both of them is just about 400mV. ???
Can you pleeeeease take a look at my schematic and PCB, becouse I don't see any mistake now..please.. -
Please look at my post again, I edited it and you replied faster..
-
audioguru, I mounted transistors on heatsink and tryed PSU. I shorted its output and measure current. At voltage set to 30V and current regulation pot set to highest value, I calibrated it to max current 3A. But when I get near the minimum setting of current adjustment pot, it took about 5-10A. I quickly powered it off to prevent any damage. Why is that? Current regulation doesn't work fine. At highest value of current adjustment pot, I measured 3A, then I was slowly turning it down. Current was always not less than 2,96A at same voltage (30V). But when I got near minimum, LED turned on and that happend (5-10V). What could be wrong with my current regulation?
PS.: I forgot to mention, that I used 25k for RV2 instead of 20k...does this makes any difference?
PPS.: We talked about D8, if you remember. I used BZX85C instead of BZX79C and you said that BZX85C regulates porely. I don't have BZX79C, but I have BZX55C. Can I use it?
PPPS.: Is it possible, that one of D7 diodes in series is faulted, becouse voltage drop across theese two is just 400mv..(they are not shorted, I checked)... -
But R21 is supposed to be 10k and it connects pin 2 of U3 to R7. When current-setting pot P2 is minimum then R21 has a max of 0.5uA (for an MC34071 opamp) to 2uA (for a TLE2141 opamp) of input bias current which makes pin2 a max of 5mV to 20mV, not 95mV.
This input bias current in R21 turns off the current regulation when the load current is low.
Yesterday I explained why R7 has a small voltage drop when there is no load current.
You didn't understand me. At P2 minimum pin 2 of U3 is 45.5mV, at its maximum pin 2 of U3 is 95.5mV. Anyway, Too high... -
R7 is 0.47 ohms so with 95.5mV across it the load current of the project is 203mA which is 28 times too high. The current should be only 5.6mA in R4 plus 1.2mA in P1 plus 0.56mA in R6.
Check the few connections along the output of the project for a connection to something that is wrong.
The heating in Q2 depends on the voltage across it and the current in Q4 and Q5 and on their amount of current gain that could be only 35 or could be more than 100. When the load current is 3.0A and the output voltage is low then Q2, Q4 and Q5 heat the most.
The voltage drop across R7 is just 5mV. 95mV voltage drop is just on pin 2 of U3. -
Hi Fikic,
With no load on the project, the output pin 6 of U3 should always be high at about +24V to +28V. So it does not reduce the output voltage through D9 and it does not turn on Q3 to light the LED.
The slider of the current adjusting pot P2 applies a small positive voltage to the (+) input pin 3 of U3. The voltage should be +0.005V when P2 is turned to minimum and should be +1.414V when P2 is turned to maximum. Without a load, there is no voltage across R7 so the (-) input pin 2 is 0V. Then the output pin 6 of U3 should be always be high.
What range of voltage at pin 3 of U3 do you measure when P2 is turned from minimum to maximum?
Maybe the terminals of P2 are connected wrong.
Maybe U3 is defective. Replace it.
P2 is connected ok. When P2 is at it's minimum, the voltage on pin 3 of U3 is 15.05mV, at it's maximum it's 2.07V. Is that normal? At P2 minimum, the voltage on pin 2 of U3 is 45.5mV, at it's maximum is 95.5mV. So there is voltage drop on R7 in any case. Why is that?
PS.: Is normal, that when I connect a load on PSU, just Q4 and Q5 get warm, Q2 is like nothing is on it..
-
I know that your circuit works wrong. I explained how it is supposed to work so you can fix it.
1) U3 works wrong so double-check that its inputs are not connected backwards or shorted together.
2) Make sure that the output pin 6 of U3 is not shorted to ground or to -1.3V. What is the voltage of pin 6?
3) Make sure that pin 7 of U3 is about +24VDC.
4) Try replacing U3.
Thank you audioguru, I am closer now. I figured out, that I turned Q3 backwards. But still, it doesn't work perfect. At current adjustment pot turned to lowest value, LED is not on. It turns on somewhere on the end of turn of current adjustment pot.
Voltage of pin 6 is 28V, when LED is not on. When it turns on, it falls to 13-10V.
Pin 7 is always 24V or higher. All pins of U3 are ok.
The LED is turning on with unknown reason. The voltages on U3 changes like I said with changing value of current adjustment pot. What do you say? Could be Q3 fault?
PS.: all measurements applies to NO LOAD.. -
I don't understand you. You are saying, like my circuit was perfect. But I am telling you, that LED is always on, without a load... -
Of course it didn't work without C1.
That is normal. it regulates the output current by reducing the output voltage which reduces the output current according to Ohm's Law.
The LED should turn on only when it is reducing the output voltage.
That is normal. The output voltage of U3 drops when it regulates the output current and it turns on the LED.
All this I wrote applies to the case, when I have no load on output... -
I made a mistake when I was drawing schematic. I didn't connect - of C1 to gnd. I corrected PCB now, and PSU works when I connect a load. But only in some cases, when I turn pot for current regulation, the voltage drops. LED is still on the whole time. Now the voltage on output of U3 is 24V but not all the time. In some cases it's 17V when I turn current adjustment pot.
-
That is normal when there is a load on the output of the power supply.
When you turn down the current-setting pot then the current regulating circuit reduces the output voltage to keep the output current at the setting of the current adjustment pot. The LED lights to warn you that the output voltage is not regulated anymore because the current-regulating circuit is reducing the output voltage.
Your circuit has a serious problem if the output voltage drops when you turn the current adjustment pot and there is no load current.
Yes, it has and if I connect a load on it the voltage drops unnormally and there is no power. What could it be?
0-30 Vdc Stabilized Power Supply
in Projects Q/A
Posted
Somewhere in this topic, somebody said, that some capacitor must be changed from electrolytic to tantal or something. Try to browse a little.