Timeline for Selecting a transistor for high-side switching at 5V with a 2A load current
Current License: CC BY-SA 3.0
12 events
| when toggle format | what | by | license | comment | |
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| Mar 26, 2015 at 10:14 | vote | accept | xmen | ||
| Mar 26, 2015 at 10:04 | comment | added | xmen | Let us continue this discussion in chat. | |
| Mar 26, 2015 at 10:03 | comment | added | tcrosley | @xmenW.K. The 104W figure, which is crazy large, is the maximum amount the package can dissipate. But check the notes, it gets derated to 4W under certain conditions. The actual is the same you were doing before 2A * 2A * 0.002 = a measly 8 mW. Should run very cool. | |
| Mar 26, 2015 at 9:56 | comment | added | xmen | No problem, it happens :) I have one more question. How do I calculate the heat it will create ? Max Dissipation looks very strange, its 104W. Thats alot of heat. Im using I x I x R, so its coming 0.008W. Thats almost nothing. Is it correct way to calculate ? | |
| Mar 26, 2015 at 9:38 | comment | added | tcrosley | @xmenW.K. You're quite right, I wrote that comment and then realized I had drawn the FET upside down. I updated the picture but couldn't update the comment. | |
| Mar 26, 2015 at 8:00 | comment | added | xmen | I might be wrong, but R1 seems to be on Gate to Source. | |
| Mar 26, 2015 at 7:30 | history | edited | tcrosley | CC BY-SA 3.0 |
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| Mar 26, 2015 at 6:48 | comment | added | tcrosley | @xmenW.K. Yes, you should be able to drive the P-channel FET directly from a 5v HCT595. I was going by your diagram with the uC 3.3v coming in from the side. You should also be able to eliminate the resistor R1 between the Drain and Gate (i.e. just need the FET). The Si7157DP is a bit of an overkill (max 60A), but it certainly has a low Rds(on). The 0.8W for the other FET was the maximum dissipation. | |
| Mar 26, 2015 at 3:36 | comment | added | xmen | One more thing, how DMP2035U dissipate 0.8W ? Can you tell me how did you calculate this ? My calculated value seems wrong. I did I x I x R = P. | |
| Mar 26, 2015 at 3:31 | comment | added | xmen | Thank you very much Tcrosley. Im now using HCT595, and its output will be 5V. In that case, do I still need NChannel MOSFET ? and what do you think about this MOSFET farnell.com/datasheets/1897538.pdf. It has 0.0020 Ohms resistance. | |
| Mar 25, 2015 at 21:48 | history | edited | tcrosley | CC BY-SA 3.0 |
added 70 characters in body
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| Mar 25, 2015 at 20:35 | history | answered | tcrosley | CC BY-SA 3.0 |