Timeline for MOSFET overheating and voltage drop
Current License: CC BY-SA 4.0
12 events
| when toggle format | what | by | license | comment | |
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| Aug 21, 2022 at 9:22 | history | edited | Andy aka | CC BY-SA 4.0 |
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| Aug 21, 2022 at 9:18 | comment | added | Andy aka | @RussellH oops, when I added the diode I forget to get rid of the capacitor. | |
| Aug 21, 2022 at 3:50 | comment | added | user319836 | @Andyaka: I have used this circuit quite successfully. C3 is actually detrimental. The flywheel diode should be a Schottky diode. Regular diodes cause a spike on the gate through the Miller capacitance. This is due to minority carrier in the diode. I have found that Q1 and Q2 have sufficient internal resistance that R2 may not be necessary. What I have found beneficial is a 1uF ceramic from VCC to ground located close to Q1-C. It provides a local energy store for high speed switching transients for the gate. | |
| Aug 20, 2022 at 19:40 | comment | added | Kevin White | @AndrewMorton - it would reduce dissipation but C3 is not necessary. | |
| Aug 20, 2022 at 15:29 | comment | added | Andrew Morton | @KevinWhite Would a few tens or hundreds of ohms of resistance in series with C3 be useful? | |
| Aug 19, 2022 at 20:53 | history | edited | Andy aka | CC BY-SA 4.0 |
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| Aug 19, 2022 at 20:50 | comment | added | Andy aka | @KevinWhite it's not ideal is it. The cap will limit the back emf but, it's dependent on motor current and motor leakage inductance or free-spinning. I'll amend that picture. Thanks very much. | |
| Aug 19, 2022 at 20:37 | comment | added | Kevin White | You could do with a flywheel diode across the motor or there will be a high voltage across the FET when it turns off and the energy in the motor inductance will be lost. At high frequencies the presence of C3 will cause high peak currents in the FET. | |
| Aug 19, 2022 at 17:42 | history | edited | Andy aka | CC BY-SA 4.0 |
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| Aug 19, 2022 at 17:34 | history | edited | Andy aka | CC BY-SA 4.0 |
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| Aug 19, 2022 at 17:29 | history | edited | Andy aka | CC BY-SA 4.0 |
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| Aug 19, 2022 at 17:23 | history | answered | Andy aka | CC BY-SA 4.0 |