Kevin Weddle Posted July 29, 2013 Report Share Posted July 29, 2013 I modfied this posting. Quote Link to comment Share on other sites More sharing options...
Kevin Weddle Posted July 29, 2013 Report Share Posted July 29, 2013 Impedance is slightly different from maxing opamp current. Especially when Q2 handles all the current. Quote Link to comment Share on other sites More sharing options...
audioguru Posted July 29, 2013 Report Share Posted July 29, 2013 The voltage reference from U1 is 11.2V and the maximum output from the project is 30.0V. Then the output amplifier must have a gain of 30V/11.2V= 2.679 times.The power output transistors operate poorly at high frequencies. C6 and C9 make sure that their phase shift does not cause oscillation at a high frequency.C7 makes the output a low impedance at high frequencies.Usually a circuit that is powered has a supply bypass capacitor so its supply is a low impedance at high frequencies.Q2 is the driver transistor and is an emitter-follower. Its base is fed from opamp U2 and its emitter feeds the bases of the output transistor emitter-followers Q4 and Q5. The output is fed back to U2 as negative feedback so the entire amplifier is very accurate and stable.The output voltage of U2 (and the base voltage of Q2, Q4 and Q5) vary a little when the output current varies so that the output voltage is constant.Kevin, your idea will allow the output voltage to bounce up and down when the output current changes. Quote Link to comment Share on other sites More sharing options...
jegues Posted July 31, 2013 Report Share Posted July 31, 2013 Hello,I'm looking to build my own lab power supply, but am still fairly new to the "practical" aspects of electronics.(i.e. wiring circuits up to mains voltages) I've taken two university level courses on electronics, but I still feel I have a lot to learn. (Currently reading "The Art of Electronics")Is this a good first power supply project for me, or should I go for something easier to start with? If so, is there a "latest and greatest" version of the schematic and BOM?Thanks for your input! Quote Link to comment Share on other sites More sharing options...
deepak.roy.alchemist Posted July 31, 2013 Report Share Posted July 31, 2013 Hello Jegues! the latest schematic posted here would prove to be too complicated for you as you would not be able to detect any flaw in its working as i can make out that you are still a beginner in this field. i would rather suggest you to try certain basic level circuits using LM723. That is all time proven chip to start with. Quote Link to comment Share on other sites More sharing options...
xristost Posted August 1, 2013 Report Share Posted August 1, 2013 I'm sorry to interrupt the conversation. I know it isn't said here often enough. But our programmers are what makes are world all the possible. Even you can take a lesson. Remember.Your latest posts are very cryptic, weird and not connected with the subject. Are you OK? Quote Link to comment Share on other sites More sharing options...
audioguru Posted August 1, 2013 Report Share Posted August 1, 2013 Your latest posts are very cryptic, weird and not connected with the subject. Are you OK?Maybe Kevin needs to be de-fragged or re-formatted. Quote Link to comment Share on other sites More sharing options...
deepak.roy.alchemist Posted August 1, 2013 Report Share Posted August 1, 2013 everybody needs to see the mirror once in a while to keep one self grounded. Quote Link to comment Share on other sites More sharing options...
WinDTrek Posted August 18, 2013 Report Share Posted August 18, 2013 How do I connect an ammeter to this project? Quote Link to comment Share on other sites More sharing options...
audioguru Posted August 19, 2013 Report Share Posted August 19, 2013 How do I connect an ammeter to this project?An ammeter has a resistance that spoils the excellent voltage regulation of this project because its resistance is in series with the load.Instead, measure the voltage aross R7 then calibrate it in Amps.R7 is inside the negative feedback loop so it does not affect the output voltage. Quote Link to comment Share on other sites More sharing options...
WinDTrek Posted August 22, 2013 Report Share Posted August 22, 2013 Thanks Guru. One more question, i have completed already the 5A version. I made 2 actually and put some switches to interconnect the 2 x 5A version in series (to get 60V max) or in parallel (to double the amperage). However, one thing i noticed is that when I turn on the power supply the LED of the 2 x 5Aversion will light up (P2 or the current limiter pot is at minimum position). What i do normally is rotate P2 about /8 turn clockwise and the LED will turn of. After that putting P2 back to min LED will no longer light. Is this normal? Aside from that everything works fine. I will post some pictures later. Quote Link to comment Share on other sites More sharing options...
WinDTrek Posted August 22, 2013 Report Share Posted August 22, 2013 or if I put P2 to >1/8 position before powering on the power supply LED will not light up. It will only light up when I put load into it but it will turn the LED of once I adjust P2 towards max position. Quote Link to comment Share on other sites More sharing options...
audioguru Posted August 22, 2013 Report Share Posted August 22, 2013 This power supply should not have two or more connected in parallel because the voltage and current regulators will fight each other. It will be very difficult to set the output voltages exactly the same anyway. The current regulator reduces the output voltage when the output current exceeds the settting of P2 so that the output voltage and current are both reduced. Then the LED lights to warn you that the output voltage is reduced. Quote Link to comment Share on other sites More sharing options...
WinDTrek Posted August 23, 2013 Report Share Posted August 23, 2013 i think i found the reason why LED lights up when power is applied to this power supply. Pin 3 of U3 is less than 5.6mV (1.2mV and 0.6mV) when P2 is at minimum position. Adjusting the P2 to 1/8 turn will give me around 5.6mV. At this position of P2 LED will not light up when power is applied. I'm thinking of replacing R17 (33 ohms) to a higher value to get 5.6mV. Also, what is the maximum voltage should i set Pin 3 of U3 to get 5A maximum? Quote Link to comment Share on other sites More sharing options...
audioguru Posted August 23, 2013 Report Share Posted August 23, 2013 i think i found the reason why LED lights up when power is applied to this power supply. Pin 3 of U3 is less than 5.6mV (1.2mV and 0.6mV) when P2 is at minimum position. Adjusting the P2 to 1/8 turn will give me around 5.6mV. At this position of P2 LED will not light up when power is applied. I'm thinking of replacing R17 (33 ohms) to a higher value to get 5.6mV. Also, what is the maximum voltage should i set Pin 3 of U3 to get 5A maximum?If you use 56k for R18 or 33k with a 100k series calibration trimpot set to about 23k, your P2 is 10k and R17 is 33 ohms then pin 3 of U3 should be about +5.6mV when P2 is at minimum.The LED will be off if your opamp has normal very low input current and low input offset voltage.But I do not know the value of your R18 or if you have a calibration trimpot in series with it and I do not know which opamp you are using.Increase the value of R17 to fix your problem.The value of R7 and the setting of the calibration trimpot in series with R18 set the maximum current. I do not know the values you are using. Simply short the output and set the current to 5.0A by adjusting the trimpot. Quote Link to comment Share on other sites More sharing options...
WinDTrek Posted August 23, 2013 Report Share Posted August 23, 2013 My R18 is 20K with a 200K trimpot. P2 is 10K R17 is 33 ohms . Just check redwire's schematic page 1 and values is already been changed to the values that you have specified. RV2 and Rf11 was also changed. I will replace this then and see what happens. Btw 'm using MC34071. Thanks Guru.. Quote Link to comment Share on other sites More sharing options...
audioguru Posted August 23, 2013 Report Share Posted August 23, 2013 What points of circuit should be measured, when RV1 is turned to make 0V (and what value should be)?The modified parts list shows that a 5k trimpot if the opamp U2 is a TLE2141 and should be a 10k trimpot if the opamp U2 is an MC34071.Also, R10 should be 1k if the opamp is a TLE2141 and R10 should be a piece of wire for an MC34071.RV1 should be adjusted so that the output with or without a load is 0.0V when the voltage control pot P1 is set to minimum.I still have a problem with glowing LED when P2 is set to minimum. I tried to increase R17 to 100ohm, 150ohm; short R10; use 10uF film capacitor with a resistor on the output; but none of this helpsThe LED lights to show that the current regulator is reducing the output voltage. With P2 set to minimum then it provides about +5.6V to the non-inverting input of U3 when R17 is 33 ohms and provides +25.5mV when R17 is 150 ohms. With no load then there is no current in R7 and no voltage across it so the inverting input of U3 is 0.0V. Then the output of U3 will go as high as it can and NOT turn on Q3 and the LED.Which opamps are you using? Quote Link to comment Share on other sites More sharing options...
Guest _pike Posted August 24, 2013 Report Share Posted August 24, 2013 Hello to all!!!!! I am intrested of building this power supply but i saw that lot of modifications have been made and i would like to know if someone can tell me where to find the final parts with the improvements that have been made...Best Regards Quote Link to comment Share on other sites More sharing options...
audioguru Posted August 24, 2013 Report Share Posted August 24, 2013 I am using TLE2141, so those trimpots and resistors are exactly as you said for TLE2141.I think, that adjusting RV1 does not change anything..With the voltage control P1 set to zero then adjusting RV1 should change the output voltage of the project from about -30mV to +30mV. Then it can be set to 0.0V. Quote Link to comment Share on other sites More sharing options...
audioguru Posted August 25, 2013 Report Share Posted August 25, 2013 The output voltage stays -19mV when P1 and P2 are set to minimum (adjusting RV1 do not change it at all) (at this time LED is glowing).When I turn P2 a little, so the LED does not glow, I am able to see the change in the output when adjust RV1, and it is from +19mV to +32mV. What is wrong here?The LED lights to warn you that the current regulation is reducing the output voltage because it senses that the load current is higher than a few mA set by the value (33 ohms) of R21.I notice now that the idle current and load of U1 is part of the load and the idle current of the TLE2141 is higher than the original TL081.So increase the value of R17 until the LED does not glow with no output load. Quote Link to comment Share on other sites More sharing options...
audioguru Posted August 25, 2013 Report Share Posted August 25, 2013 I tried several values of R21 from 10kOhm to 50kOhm, but changing it does not change anything at all, and the problem still remains..Sorry, It is R17 that should be increased a little.Here I show that when R17 is the original value of 33 ohms, the TLE2141 opamp U1 has its maximum supply current of 4.4mA, its load is 5.6mA and its input offset voltage is at its maximum of 1.4mV. Then the output of U3 is low and turns on the LED.I also show if R17 is increased to 56 ohms then the output of U3 is high and the LED is turned off. Maybe 47 ohms will work fine. Quote Link to comment Share on other sites More sharing options...
WinDTrek Posted August 26, 2013 Report Share Posted August 26, 2013 i have the same problem. when i apply power to my power supply LED will light up. moving the current pot 1/8 clockwise will turn off the LED. increasing the value of R17 to 56 ohms fix this problem. Quote Link to comment Share on other sites More sharing options...
WinDTrek Posted August 26, 2013 Report Share Posted August 26, 2013 Preview of the PSU that 'I'm working on.. Please visit Quote Link to comment Share on other sites More sharing options...
WinDTrek Posted August 27, 2013 Report Share Posted August 27, 2013 Actually the problem I have was when I power on my power supply LED lights up. This problem goes a way when you turn P2 1/8 clockwise. After that returning P2 while the power is still on to minimum LED remain off. The problem only occurs upon powering up the power supply. Changing the value of R7 from 33 to 56 ohm fixed the problem. Before I'm getting 0.6mV at Pin 3 when P2 is minimum. Now I'm getting 4.5mV. In the video noticed that when I power up the power supply LED did not turn on. Maybe the one you saw was when I put load into it. Quote Link to comment Share on other sites More sharing options...
Kevin Weddle Posted August 28, 2013 Report Share Posted August 28, 2013 Jfet input opamps are a great improvement because they are square law devices. Their input voltage needs to be very close to the supply voltage based on Jfet VGS. Maybe 5V less. Does this opamp need a transistor bias voltage so that the bias impedance is higher than would be a resistor. Quote Link to comment Share on other sites More sharing options...
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