audioguru Posted February 13, 2011 Report Posted February 13, 2011 I seem to be having a problem, I've just finished the second board and while testing, C7 explodes into pieces about a 1 or 2 seconds after I power up, I replaced it and the same thing happened again. The transformer is the same one I use on my other board, so it can't be it.any idea where I can start? as I can test without powering it up?When I powered it up the 2nd time, I had my meter on the output, and it seemed to sit at about 30V.C7 where 10uF 50V electrolytic.ThanksC7 will blow up if its polarity is backwards or if the bridge rectifier is defective or connected wrong and applies AC to the circuit instead of DC. Another person had his C7 blow up when his power supply project was powering a switching power supply circuit.If the project has a load and is oscillating at a fairly high frequency then C7 might blow up. Quote
morpheous87 Posted February 14, 2011 Report Posted February 14, 2011 morpheous87 I would try 47R then 51R and just increase it a little until it works, I never had this trouble with mineI've changed the resistor with 47R then 51R also 68R. But there isn't change. I've made completely new board and I have the same anomaly. Both boards works same. This is not so big problem, but it's kind of annoing. Any suggestions? Quote
morpheous87 Posted February 15, 2011 Report Posted February 15, 2011 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? Quote
audioguru Posted February 15, 2011 Report Posted February 15, 2011 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 difficult to test a current regulator with a motor because the current draw by the motor changes with its mechanical load. Its current is higher when it works harder and when it starts.The current regulation reduces the output voltage until the output current is the amount of the current-setting pot. If the output current is less than set by the pot then the current regulator does nothing. Quote
fikic Posted February 15, 2011 Report Posted February 15, 2011 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.. Quote
ultima2009 Posted February 15, 2011 Report Posted February 15, 2011 Hi allcan i change the value of 10W resistor to 0.1 Ohm? (project 30V 3A output) Quote
audioguru Posted February 15, 2011 Report Posted February 15, 2011 can i change the value of 10W resistor to 0.1 Ohm? (project 30V 3A output)Maybe you are talking about the 0.47 ohm/10W resistor R7 that senses how much output current?If you change it to only 0.1 ohms then the current regulator parts also must be changed. The input offset voltage of opamp U3 must be nulled to compensate. Quote
ultima2009 Posted February 16, 2011 Report Posted February 16, 2011 Maybe you are talking about the 0.47 ohm/10W resistor R7 that senses how much output current?If you change it to only 0.1 ohms then the current regulator parts also must be changed. The input offset voltage of opamp U3 must be nulled to compensate.how calculate the current regulator parts? and i can"t set the null with trimpot and resistor between pin 1 and pin 5 of the opamp. Opamp - TLE2141, trimpot - 4.7k and resistor 1k, output voltage is change from 22mV to 33mV.. maybe i need to increase or decrease the value of resistor (1k)?Sorry for my english, iam fron russia :)Thanks Quote
adyhansolo Posted February 16, 2011 Report Posted February 16, 2011 I built this project (last version with MC34071). I tried to run the power supply in this morning. I measured the input voltage before insert the op amps in the sockets. The AC voltage was 30V, but the DC voltage was more than 50V, about 55Vdc.Hi Audioguru,I don't find the solution of my problem. I checked all the components again and the voltage still remain 54Vdc( measured at C1 pins). If I disconnect R2 the voltage found is normal, 39Vdc. What is wrong? Please help me. Quote
audioguru Posted February 16, 2011 Report Posted February 16, 2011 Hi Ultima,The input bias current of a TLE2141 opamp is 2uA max. Then its current in R21 (10k ohms) causes an input offset voltage of 20mV at U3.R17 is only 33 ohms which produces a voltage of only 4mV so increase its value to up to 200 ohms to fix your problem. Quote
audioguru Posted February 16, 2011 Report Posted February 16, 2011 Hi Audioguru,I don't find the solution of my problem. I checked all the components again and the voltage still remain 54Vdc( measured at C1 pins). If I disconnect R2 the voltage found is normal, 39Vdc. What is wrong? Please help me.I do not see how you can measure a voltage as high as +54VDC. Quote
adyhansolo Posted February 16, 2011 Report Posted February 16, 2011 It's very strange for me. Maybe if you see this photos with the measurements you can give me the solution.The second is with the circuit interrupt (rectifier bridge- R2).[img width=680 height=341] Quote
audioguru Posted February 16, 2011 Report Posted February 16, 2011 Measure the voltage with a portable voltmeter (not connected to earth). Quote
adyhansolo Posted February 16, 2011 Report Posted February 16, 2011 Measure the voltage with a portable voltmeter (not connected to earth).I measured the voltage with a portable digital multimeter (a good one). Any idea? Quote
audioguru Posted February 16, 2011 Report Posted February 16, 2011 Your voltmeter does not measure correctly. Quote
adyhansolo Posted February 16, 2011 Report Posted February 16, 2011 Your voltmeter does not measure correctly.I appreciate you waste your time with my problem.I measured with two multimeters, including a new one, with the same result. Why the measurements it's correctly in the second circuit ( without negative voltage)? Quote
lighty Posted February 16, 2011 Report Posted February 16, 2011 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. Quote
surubel Posted February 17, 2011 Report Posted February 17, 2011 How about if we replace the bd139 with tip112, and so we could drive 4 x 2N3055? Quote
audioguru Posted February 17, 2011 Report Posted February 17, 2011 The BD139 is a very fast transistor which is why it was selected. The TIP112 is far too slow and will cause the output amplifier to oscillator or have very poor transient response.Years ago I replaced the little 2N2219 with a TIP31 transistor and another member showed that its slow speed caused ringing and a poor transient response. the BD139 was tried and worked well but cannot be heatsinked for driving 4 power transistors. Quote
fikic Posted February 17, 2011 Report Posted February 17, 2011 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.. Quote
lighty Posted February 17, 2011 Report Posted February 17, 2011 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..Fikic, this it the PCB done by Audioguru, not mine. Which in my optinion is perfectly fine. Quote
fikic Posted February 17, 2011 Report Posted February 17, 2011 audioguru says, that he doesn't use Eagle..so I doubt that it is his.. Quote
lighty Posted February 17, 2011 Report Posted February 17, 2011 Sorry you right, it is Redwires' Quote
surubel Posted February 17, 2011 Report Posted February 17, 2011 the BD139 was tried and worked well but cannot be heatsinked for driving 4 power transistors.Even if we use 2 x BD139 in Darlington connection?Or you can i replace BD139 with BD681 ? Quote
audioguru Posted February 17, 2011 Report Posted February 17, 2011 Even if we use 2 x BD139 in Darlington connection?Or you can i replace BD139 with BD681?A darlington transistor or two fast transistors connected as a darlington are too slow. Why do you want four 2N3055 output transistors? To have a max output current of 6A?Then each has a max current of 1.5A when the minimum current gain of a 2N3055 transistor is about 41 then the max current in the driver transistor is 6A/41= 146mA.One BD139 driver transistor can easily be used and if the output is shorted and set to 6A then the single BD139 driver transistor can dissipate 34V x 146mA= 5W with a medium size heatsink. Quote
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