Timeline for MOSFET voltage drop and LED flickering
Current License: CC BY-SA 4.0
12 events
| when toggle format | what | by | license | comment | |
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| Jul 27, 2019 at 10:21 | comment | added | Marek | @SpehroPefhany I have bought IRL530N and IRL540N as these were the only logic mosfets a store had, but the problem is still occuring, Vmax on output is 17.17 V. I have also tried with TIP120 with base pullup resistor 1k to 12 V and a 1k base resistor and output is 22.5 V which is fine, but I can't control it with mcu, changing PWM does nothing. | |
| Jul 26, 2019 at 15:14 | comment | added | Spehro 'speff' Pefhany | You drive it on with the full 3.3V from the MCU. It will have less than 24 milliohm resistance typically (that's the typical with 2.5V drive and it will be less at 3.3V), so it will drop only about 12mV at 0.5A. 0V is off. Vgs(th) just gives you an idea of where it's almost off. You want to drive it fully on and fully off (or it will burn up). | |
| Jul 26, 2019 at 15:11 | vote | accept | Marek | ||
| Jul 26, 2019 at 15:10 | comment | added | Marek | Thanks @SpehroPefhany, BTW. If AO3400A has a max Vds(th) = 1.45 V it means that max output voltage will be at PWM equal 113? (1.45V*255)/3.3V, and all over will provide same output voltage? | |
| Jul 26, 2019 at 15:01 | comment | added | rothloup | Marek, the 20V spec on Vgs for the 16NF06FP is the absolute max voltage. The recommended drive voltage to turn the FET fully ON is 10V. | |
| Jul 26, 2019 at 14:50 | comment | added | Spehro 'speff' Pefhany | You'll find that most modern logic level MOSFETs are SMT only. Worth acquiring the skill set to work with them. | |
| Jul 26, 2019 at 14:49 | comment | added | Marek | Damn, these are SMD and my hand is also flickering so I was thinking of THT more. Yeah I can add it and I think I will, as my voltage regulator is getting very hot right now | |
| Jul 26, 2019 at 14:45 | comment | added | Spehro 'speff' Pefhany | You could add a 78L12 or 78M12 etc. For only 0.5A I'd probably use a AO3400A because I happen to have a reel of them on hand, but the SOT-23 is pretty easy to fry if anything bad happens (like input floating) so a 10K-100K gate-source is a good idea. | |
| Jul 26, 2019 at 14:41 | comment | added | Marek | I've got no 12 V in my circuit, though isn't TIP120 an NPN BJT? I think I will go with logic level mosfets, maybe I will buy more of them just to have them. Is there any you could recommend for my specification? | |
| Jul 26, 2019 at 14:23 | comment | added | Spehro 'speff' Pefhany | If your PWM frequency is slow you could use a jellybean NPN BJT with a base resistor and pullup to +12. Eg. 1K for each resistor. 1/4W for the pullup. PWM logic is reversed (high = off). | |
| Jul 26, 2019 at 14:20 | comment | added | Marek | According to my datasheet Vgs is 20 V, but I see now. Is it smart to use second transistor to control this one or is it an overkill and I should buy for example: PSMN2R7-30PL? | |
| Jul 26, 2019 at 14:01 | history | answered | Spehro 'speff' Pefhany | CC BY-SA 4.0 |