audioguru Posted February 23, 2011 Report Posted February 23, 2011 The BD139 will take the entire load if the base and emitter of one 2N3055 is shorted together or if both 2N3055 transistors do not have their collectors (their metal cases) connected to +35V. Quote
lighty Posted February 23, 2011 Report Posted February 23, 2011 I feel like a idiot now >:(, you have hit the nail on the head, only one of the 2N3055 cases where connected to the +35V.Will connect both and test! Quote
audioguru Posted February 23, 2011 Report Posted February 23, 2011 only one of the 2N3055 cases was connected to the +35VThen the 2N3055 transistor that was connected to +35V does not work. Quote
lighty Posted February 23, 2011 Report Posted February 23, 2011 Thanks for all your patient help.Tested to 3amps! all ok Quote
audioguru Posted February 23, 2011 Report Posted February 23, 2011 Goodie! I am glad you fixed it. Quote
lighty Posted February 24, 2011 Report Posted February 24, 2011 Ok, now that I have eventually got my PSU unit working 100%, I'm wanting to build a LCD Display for it.I'm hope to have the following displayed on it.Actual VoltageSet voltageActual currentSet currentTemp of heatsinkSo here is my question, once calibrated, are the voltages from the wipers of P1 and P2 linear to the voltage and current limits, Or would the voltages change as the circuit regulates the voltage/current? The reason I ask is I'm wanting the use the ADC to read the voltages (through voltage divider resistor) from the the wiper to show the "set" V and I.Would this work? Quote
lighty Posted February 24, 2011 Report Posted February 24, 2011 MmmmmOk, the "SET" values don't look like it will work, the voltages change when circuit goes into CC. :( Quote
PicMaster Posted February 24, 2011 Report Posted February 24, 2011 MmmmmOk, the "SET" values don't look like it will work, the voltages change when circuit goes into CC. :(You could not have set voltage anyway, You could set the voltage with the wiper but you would have no way of limiting it, if you where to move the pot. The only way would be remove pots and use PWM from the pic. The same goes for the current control. You can read real time voltage,current and temp of the heatsink,I did sometime time ago remove the pots and used pic to control the PSU but never got around to finishing it may be I will blow the cob webs off it and start again. Quote
lighty Posted February 24, 2011 Report Posted February 24, 2011 Hi PicMasterI wasn't intending to control the PSU with a pic, but rather just use the voltages of the wiper to show where the Voltage and Current pots are situated.Eg, lets say the Vpot is set to 12 and current to 1 Amp, it would show this on the LCD, along with the realtime Volts and Amps. but at least you know the PSU wouldn't deliver More than 1 amp should something go wrong, wouldn't be nice to find out that the pot was set at 2 Amp... similarly for the voltage, to pervent over voltage should the load drop from the PSU, while you have something else connected to... If you know what I mean?I suppose you could use a tandem ganged Pot, using the second Pot to drive the "SET" voltages to the pic. Quote
lighty Posted February 25, 2011 Report Posted February 25, 2011 I'm wanting to add a Fine Adjustments pots to the circuit for the vltage and current, as I find the Pots are very sensitive.I was thinking of putting a 1K Pot between P2 and R18, and P1 and the output od U1. Would this work? Quote
audioguru Posted February 25, 2011 Report Posted February 25, 2011 A pot used for "fine" adjustment is always in the wrong position and might be forgotten.Simply use a very big knob on one pot then it can be turned a lot or turned a little. Quote
morpheous87 Posted March 13, 2011 Report Posted March 13, 2011 Could be used a 31V transformer for the PSU, ot it needs some changes? Quote
audioguru Posted March 13, 2011 Report Posted March 13, 2011 A 31V transformer might produce 32VAC without a load. Then its peak voltage is 45.3V and the bridge rectifier reduces it to 44.1V. Opamps U1 and U2 will operate or will blow up with the 44.1V supply which is higher than their max allowed supply of 44.0V. The voltage will be even higher when the mains voltage is higher and with mains voltage spikes.Maybe a couple of back-to-back zener diodes can be added in series with one transformer wire to reduce its AC voltage. Quote
redwire Posted March 22, 2011 Author Report Posted March 22, 2011 Hi Lighty Is this what you were thinking of making? Quote
surubel Posted March 28, 2011 Report Posted March 28, 2011 Hello again.I managed to finish the PSU. It worked perfectly from the first time. (except the GND trace under-dimensioned, but I fixed it ;D)Some pictures: Quote
morpheous87 Posted March 31, 2011 Report Posted March 31, 2011 For the 3A PSU version (PicMater's veersion), can two potenciometers be usedin series for coarse and fine adjustment? I saw somewhere they should be in 1:10 propotions, so 1k and 10k ? Quote
audioguru Posted March 31, 2011 Report Posted March 31, 2011 You can use 10k and 1k pots in series.I would just use a big knob on one pot. Quote
morpheous87 Posted April 1, 2011 Report Posted April 1, 2011 The biggest knob I found is 30mm in diameter. I'm wondering what would be better, this big knob or two potenciometers in series. Quote
audioguru Posted April 1, 2011 Report Posted April 1, 2011 The biggest knob I found is 30mm in diameter. I'm wondering what would be better, this big knob or two potenciometers in series.I find having a coarse control and a fine control is a nuisance. There is always one of the controls at its end but more adjustment is needed so a few adjustments on both controls is needed for one setting.My power supply has a knob for voltage that is 40mm in diameter and I can set it to very fine settings. Quote
Hero999 Posted April 1, 2011 Report Posted April 1, 2011 It's a matter of opinion.I like using a 10 turn pot so I can have course and fine control with one pot but having to turn it ten times to go from one end of the range to the other might annoy some people. Quote
morpheous87 Posted April 1, 2011 Report Posted April 1, 2011 I want to made a V-A multimer for the 30V PSU based on Aduino platform. So I have some questions about it. I need a voltage devider so the maximum voltage be <5 and put it in analog Arduino's pin. But how this devider should look? And for the current measurment I need a resistor to measure the voltage from both sides. Can the 82R resistor be used for this purpose (in PicMaster's version it's 2W resistor)? Quote
redwire Posted April 2, 2011 Author Report Posted April 2, 2011 morpheous87Attached is an example of how to calculate your voltage divider. Note that I added a potentiometer in the circuit so that once the program is written, you can calibrate it without have to reprogram the chip because of tolerance differences in resistors.For the current measurement, if you already built the PS all you need to do is measure the voltage drop across R7. V=IR. You know the resistor value, you measure the voltage drop with the ADC of your Arduino, then write code in your Arduino program to calculate and display I.Note that your common ground for will be the transformer side of R7.VoltageDivider.pdf Quote
morpheous87 Posted April 2, 2011 Report Posted April 2, 2011 redwireThis is the pdf I used to build my PSU. I'm not sure that the R7 you're talking about is the R7 in the pdf. Could you check is there some differences. Note that part's names on the last pdf's page (mounting diagram) is different from the part list page. Thanks for the help!EL_power_supply.pdf Quote
redwire Posted April 3, 2011 Author Report Posted April 3, 2011 morpheous87Well yes and no. I am refering to the 0.47Ohm resistor that is connected to TB4. I say this with a little hesitation because on the Bill of Materials, R7 is listed as a 3k9 resistor which I believe is an error. The pcb shows R7 as being connected to the led (I think this should be R22) , and the sketch describes the shunt resistor as R7, 0.47 Ohms connected off board via TB4 which looks right. The common ground is (for Ardunio) pin 2 on TB4. To measure current, you measure the voltage drop across TB4. To measure voltage output connect to Pin 2 on TB4(-) and TB3 (+). Quote
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