| Electronics > Projects, Designs, and Technical Stuff |
| 723 psu issue |
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| not1xor1:
--- Quote from: stj on November 14, 2018, 04:42:06 pm ---why parallel drive? i have stuff i repair that can do atleast 7A that just uses a single 2n6057 darlington. --- End quote --- It looks like you do not know the meaning of SOA, so please do not spread potentially dangerous misinformation. A 2N6057 cannot withstand more than 20Vce at 7A and that just in ideal conditions (i.e. infinite heatsink) while the schematic provided by the original poster mentions an input voltage of 40VDC. So a single 2N6057 would work with 7A just for a low voltage PSU. Low voltage, even in a fixed voltage PSU, because you must not forget to take into account Vce in case of shortcircuit. |
| not1xor1:
--- Quote from: m3vuv on November 14, 2018, 12:53:29 pm ---Hi all,im putting together a psu using a 723,im using this schematic,the iss use a lower value sense resistorue i have is,i want the current feed back to work from about 100ma upwards,the issue i have is to get 600mv from the current sense resistor,it has to be a high value to produce 600mv across it for 723,this lowers the output to much overall,is it possible to amplify the sense voltage to feed the 723 cl and cl pins,therefor use a lower value sense resistor,ive thought of using a sg3532 but they are expensive!,cheers m3vuv. --- End quote --- If you want to build a variable voltage/current PSU (i.e. lab PSU) then it is better to use a 2 opamps design rather than the 723. Any current regulation with the 723 would always be quite coarse and tend to drift unless you add another opamp and at that point IMHO it just does not make sense to use a 723. |
| xavier60:
Using a Base Emitter junction for sensing the shunt voltage is such a blunt instrument, only good for about five to one control range. I built a floating type, two op-amp bench supply that is happy to regulate current over a range of 20ma to 20a with a 10 milliohm shunt. I paralleled ten 0.1 ohm resistors. |
| m3vuv:
interesting,would you have the schematic? |
| xavier60:
Yes, it can be found in another thread. I show only the regulator section. I explain the reason for it having a negative reference voltage and some extra circuitry that fixes a problem sometimes mentioned where op-amp current control loops are usually slow to respond to sudden overloads. https://www.eevblog.com/forum/projects/lab-power-supply-the-lost-current/100/ |
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