| Electronics > Beginners |
| RPS with from 0-30V and Current variable up to 3 A design Circuit Please.... |
| << < (4/8) > >> |
| David Hess:
--- Quote from: rstofer on January 08, 2019, 10:31:31 pm ---That National LB-28 design seems pretty nice. --- End quote --- Although as shown it requires a -5 to -10 volt negative supply. --- Quote ---Minimal components, reasonable specs and the LM395 is still available albeit expensive ($4). Still, a quality supply just can't be built for a buck ninety five. --- End quote --- Check the schematic carefully; the LB-28 design uses 7 LM395s in parallel for 8 total although new big TO-3 power transistors are not much less expensive. --- Quote ---Changing to normal transistors will be a challenge for a newcomer. The LM395s only take 10 uA of base current (3 uA typical) so the op amp can easily drive several. In addition, the LM395 has a lot of built-in protection, well beyond that of a 2N3055. --- End quote --- I brought it up more as an example to study. What I might do is use one LM395 to drive a bunch of big current boosting transistors but like you said, this would be a challenge for a newcomer. |
| not1xor1:
--- Quote from: rstofer on January 08, 2019, 06:02:46 pm --- --- Quote from: techguru on January 08, 2019, 09:54:01 am ---If any other possibility are there? Like Mr.bravo said I am trying this project for more than a year.now I came to know that linear mode that is class A mode of design is intractable. You all guide in design class s amplifier (smps), where my efficiency is nearly 100 percent. Buck topology.I think I am moving in right direction.help me in this regard. --- End quote --- If there was a circuit out in the wild that would actually deliver 0-30V and 0-3A, it would be all over this forum. It would be a sticky on every forum. Everybody on the Internet would know where to find it. Instead of dozens of replies, the matter would be settled with a simple link and the comment to "build this". --- End quote --- I do not think there is a lack of such schematic diagrams neither that it would be more difficult to design than e.g. a 0-15V 1A PSU. 4 large heatsinks and 8 TO3 BJTs can work for more than 120W of wasted power even without the help of fans. It just does make little sense and would be more expensive than using a suitable multi-tap transformer based PSU. |
| Zero999:
--- Quote from: not1xor1 on January 09, 2019, 07:48:42 am --- --- Quote from: rstofer on January 08, 2019, 06:02:46 pm --- --- Quote from: techguru on January 08, 2019, 09:54:01 am ---If any other possibility are there? Like Mr.bravo said I am trying this project for more than a year.now I came to know that linear mode that is class A mode of design is intractable. You all guide in design class s amplifier (smps), where my efficiency is nearly 100 percent. Buck topology.I think I am moving in right direction.help me in this regard. --- End quote --- If there was a circuit out in the wild that would actually deliver 0-30V and 0-3A, it would be all over this forum. It would be a sticky on every forum. Everybody on the Internet would know where to find it. Instead of dozens of replies, the matter would be settled with a simple link and the comment to "build this". --- End quote --- I do not think there is a lack of such schematic diagrams neither that it would be more difficult to design than e.g. a 0-15V 1A PSU. 4 large heatsinks and 8 TO3 BJTs can work for more than 120W of wasted power even without the help of fans. It just does make little sense and would be more expensive than using a suitable multi-tap transformer based PSU. --- End quote --- Go on, post your design. . . He's right. It's not so much the current, but the voltage which is the problem. At 15V, an ordinary op-amp can be run from the unfiltered rectifier voltage. With 30V something more elaborate is required. The absolute maximum voltage rating of most standard op-amps is under 44V, which would be an AC voltage of just over 30V on the transformer secondary. A lower voltage transformer could be used, but that doesn't leave much headroom for voltage ripple. |
| David Hess:
--- Quote from: Zero999 on January 09, 2019, 09:20:40 am ---He's right. It's not so much the current, but the voltage which is the problem. At 15V, an ordinary op-amp can be run from the unfiltered rectifier voltage. With 30V something more elaborate is required. The absolute maximum voltage rating of most standard op-amps is under 44V, which would be an AC voltage of just over 30V on the transformer secondary. A lower voltage transformer could be used, but that doesn't leave much headroom for voltage ripple. --- End quote --- So use a separate 40 volt low power regulator for the control circuits; it might be as simple as a zener shunt regulator. Or configure the control circuits in a floating configuration with a low power negative regulator following the output voltage; this is more suitable for even higher voltage supplies. With a floating design, low voltage operational amplifiers can be used. The alternative to a floating design is to add high voltage level shifting between the operational amplifier and pass transistors which is a whole different set of problems; most new designers go this route. |
| Zero999:
--- Quote from: David Hess on January 09, 2019, 12:35:19 pm --- --- Quote from: Zero999 on January 09, 2019, 09:20:40 am ---He's right. It's not so much the current, but the voltage which is the problem. At 15V, an ordinary op-amp can be run from the unfiltered rectifier voltage. With 30V something more elaborate is required. The absolute maximum voltage rating of most standard op-amps is under 44V, which would be an AC voltage of just over 30V on the transformer secondary. A lower voltage transformer could be used, but that doesn't leave much headroom for voltage ripple. --- End quote --- So use a separate 40 volt low power regulator for the control circuits; it might be as simple as a zener shunt regulator. Or configure the control circuits in a floating configuration with a low power negative regulator following the output voltage; this is more suitable for even higher voltage supplies. With a floating design, low voltage operational amplifiers can be used. The alternative to a floating design is to add high voltage level shifting between the operational amplifier and pass transistors which is a whole different set of problems; most new designers go this route. --- End quote --- My point was that none of that is necessary with a 0 to 15V supply. |
| Navigation |
| Message Index |
| Next page |
| Previous page |