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| Simple DIY Linear PSU |
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| xavier60:
--- Quote from: panoss on March 07, 2020, 11:10:29 am ---So you 're saying the circuit is ok? I should built it and after this experiment with the value of R10? --- End quote --- That's right. Aim for a gm of 10 to 15. That is the amount of output current change to change of Q1's Base voltage. A gm of 10 would mean that the output current changes by 1A for a change of 0.1V at Q1's Base. |
| panoss:
Output current change gm = ----------------------------------- Q1's Base voltage change Is this correct? e.g if Q1's Base voltage increases by 10% and Output current increases by 100%, this is a gm of 10? |
| xavier60:
--- Quote from: panoss on March 07, 2020, 11:50:38 am --- Output current change gm = ----------------------------------- Q1's Base voltage change Is this correct? e.g if Q1's Base voltage increases by 10% and Output current increases by 100%, this is a gm of 10? --- End quote --- You have the right idea but use absolute changes, not percentages. Use 2 resistors in parallel for R17 so that the LM317 output can be easily set to the desired voltage. It is important that the unreg voltage stays high enough to prevent the LM317 from dropping out of regulation. I don't expect a problem with a 15VAC secondary. The regulation stability can only be as good as that of the LM317 which I think is reasonably good. |
| panoss:
--- Quote from: xavier60 on March 07, 2020, 12:07:31 pm ---I don't expect a problem with a 15VAC secondary. --- End quote --- I 'll try with 15VAC and 30VAC as these are my transformer 's output voltages. Another question: Which resistors should be power resistors? I think R13, R14 and R18 should be 5W rated? |
| xavier60:
At 5A the dissipation is 0.625W for each of the 100mΩ resistors and 1.25W for the 50mΩ resistor which can be 2x 100mΩ resistors in parallel. So 2 or 3 watt resistors will be fine. 5W resistor on ebay are likely to be cheaper. I like to place larger areas of copper print under power resistors.` |
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