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lab power supply

hi to all i'm an italian electronics hobbyist, i'm sorry for my bad english :( in this holiday i try to build my first lab fully adjustable power supply unit i try to hack the scheme at pag.8 of the datasheet of the lm317 http://www.ortodoxism.ro/datasheets/nationalsemiconductor/DS009063.PDF for add the negative section, the tracking voltage mode, the transistor for increase the output current, and a costant current output protection.. i ' ve implemented 5V reference due to start the regulation from 0V instead of 1.2V (normal limit of an LM317) i would like to use an lm705 for the 5 volt reference using this voltage for an ausiliary power supply for TTL boards i obtained this basic principle scheme , not yet dimensionated i will have an opinion about eventual problem or improvements

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thanks to all for the patience

Reply to
dunsscoto2
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lm317http://www.ortodoxism.ro/datasheets/nationalsemiconductor/DS009063.PDF

improvements

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ASCII ART: Sense ! ! ---------- --+-/\\/-+-- ! \\ /e R2 ! ! --- ! ! R1 ! R3 ! +-/\\/\\- --+--/\\/\\------+ ! e\\ / ! ! --- ! ! ! ! ----+-/\\/\\/--+--! LM317 !-----+------------ R4

R1 makes the transistor's E-B drop less important so temperature has less effect on the performance.

Moving the R3 connection does the same for the other transistor at no cost in parts.

You have Q24 flipped.

What are ypou trying to do with Q26?

Reply to
MooseFET

lm317http://www.ortodoxism.ro/datasheets/nationalsemiconductor/DS009063.PDF

improvements

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when r108*imax it becomes approximately equal to the Q26 Vbe, Q26 is turned on ,it short circuit R109 and then switch off Q25 and it limits therefore the output current http://www.ortodoxism.ro/datasheets/fairchild/LM7805.pdf pag.23 fig.13

what do you think about of the current regulator? you have some idea to avoid to use a double potenziometer for the current adjust? we could be taking advantage of the advanced operational U2A

this is the updated scheme:

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Reply to
dunsscoto2

lm317http://www.ortodoxism.ro/datasheets/nationalsemiconductor/DS009063.PDF

improvements

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currenthttp://www.ortodoxism.ro/datasheets/fairchild/LM7805.pdf

scheme:

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Sorry MooseFET I have mistaken to copy! excuse me! the problem is that in Italy it is late night :D and I am distracted of nature now I understand why the regolator did not seem correct! many thanks!! I have corrected the scheme from many errors this is the new one link

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aspect suggestions in particular for the regulation of the current thanks to all!

Reply to
dunsscoto2

lm317http://www.ortodoxism.ro/datasheets/nationalsemiconductor/DS009063.PDF

improvements

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currenthttp://www.ortodoxism.ro/datasheets/fairchild/LM7805.pdf

scheme:

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I don't like what you have done with R4. Transistors should not be uses such that their HFE matters. You want an emitter resistor and not a base resistor. The has an indirect effect on the current limit issue.

I worry that the current limit circuit will overshoot, ring and do other bad things. When the current limit is not active, the LM358 will have its output as high as it can manage. This is bad.

A diode or the like on the LM358 so that it never tries to take its output all the way up would help to make the current limit engage more quickly.

Reply to
MooseFET

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