| Electronics > Projects, Designs, and Technical Stuff |
| When constant current isn't constant.... on LED driver. |
| << < (4/6) > >> |
| 1sciguy:
Interesting chip.. |
| nctnico:
I wouldn't make it this way. The variations between the MOSFETs will be too big. You could do a current sink like with an NPN transistor (even less components) but you might see a way to large variation between the devices. I strongly recommend not to go cheap and buy NPN transistors so you can fix the circuit properly and make it reliable. That will probably result in satisfied customers. In the end they'll remember you fixed the problem once and for all. Edit: the NSI50010YT1G could also be a fix of your circuit. Just place it where the LM317 used to be. I'd be worried about power dissipation though. Adding a series resistor which takes care of most of the dissipation might be a good idea. |
| 1sciguy:
--- Quote from: mariush on March 22, 2019, 06:44:28 pm ---You could just replace your Lm317 with something simpler like this : https://uk.farnell.com/on-semiconductor/nsi50010yt1g/ic-led-driver-50v-0-01a-sod123/dp/1794979 10mA +/- 30% , up to 50v ... cheap in quantity. You could probably solder it between the IN and ADJ in the lm317 footprint so you don't have to throw out the boards Or this one (10mA +/- 10% preset, up to 350mA with external resistor), up to 40v : https://uk.farnell.com/diodes-inc/bcr420ufd-7/led-driver-linear-1khz-udfn-6/dp/2748559 This could also work but you may have to put it on a tiny pcb and then solder pcb to lm317 footprint on old board. --- End quote --- Wow! Never knew they existed! I can use the 15mA version and be absolutely fine. A little brighter too, without fear of burning out LED's. Thanks! And yes, I use this same layout on two different boards, so that is going to save me from redesigning two 4-layer boards. https://uk.farnell.com/on-semiconductor/nsi45015wt1g/led-driver-55-to-150deg-c-sod/dp/2985371 |
| mariush:
Yes, but keep in mind that it's +/- 20% , so you may have up to 18mA ... which should still be fine for modern leds. The 10mA is +/- 30% |
| Datman:
You could drive the LM317 by the Adj, making PWM by it. Put a resistor in series with the Adj: when you short Adj to Gnd, you obtain only 1.25V at the output. |
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