| Electronics > Projects, Designs, and Technical Stuff |
| 5v cc source |
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| Nerull:
--- Quote from: quadzillatech on March 24, 2019, 11:59:25 pm ---i wasnt asking how to regulate the votage!,i need a way of trying to get a 1300ma max from a 7805!,is it not clear now??,regards Paul. --- End quote --- If you weren't asking how to regulate the voltage, maybe your first post shouldn't state that you want 5V. |
| jeroen79:
--- Quote from: hamster_nz on March 25, 2019, 12:29:59 am ---Wire a it up as a current source, with a 3.9 Ohm 10W resistor for R1. That will limit in the load to ~ 1.28A. Will need careful attention to heatsinking.. if Rload is a dead short then the 7805 will be dissipating ~10W. --- End quote --- But then an LM317 will be more useful. That will drop only 1.2V across the resistor instead of 5V with the 7805. |
| ogden:
--- Quote from: Nerull on March 25, 2019, 12:56:35 am --- --- Quote from: quadzillatech on March 24, 2019, 11:59:25 pm ---i wasnt asking how to regulate the votage!,i need a way of trying to get a 1300ma max from a 7805!,is it not clear now??,regards Paul. --- End quote --- If you weren't asking how to regulate the voltage, maybe your first post shouldn't state that you want 5V. --- End quote --- Right. Initial post seemingly asked for 5V **and** 1300mA regulation meaning 5V supply with 1.3A current limit. Using 7805 to build constant current supply is bad idea - because it does not regulate current but voltage, 5V. To get constant 1.3A out of 5V voltage regulator, you need 5/1.3 ohms resistor which will dissipate 1.3*5 = 6.5 watts of waste power. Better just buy LED driver for < 2$, eBay search: "LM2596 LED Driver DC-DC Step-down Adjustable CC/CV" |
| Zero999:
--- Quote from: quadzillatech on March 24, 2019, 11:59:25 pm ---i wasnt asking how to regulate the votage!,i need a way of trying to get a 1300ma max from a 7805!,is it not clear now??,regards Paul. --- End quote --- Why do you want to use the LM7805? It's most likely not needed! Anyway, to answer the question. A current regulator needs to be connected in series, before with the LM7805. Purely for educational purposes. Attached are two solutions: an LM317 current regulator and an op-amp controlling a Darlington pair, with the TL431 used as a voltage reference. The laser is just an LED. Scrap the LM7805 and use either of the circuits I posted previously, with the laser connected between where the LM7805's input pin was connected and 0V. https://jtechphotonics.com/wp-content/uploads/2013/05/Instruction-Manual-2W-445nm-Laser-Diode-Component-V6.pdf |
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