| Electronics > Beginners |
| [SOLVED: Broken mosfet] Low-side switching of resistive load not working |
| (1/1) |
| ppff:
Hi everybody, Doing some research on the web about my problem, I found out about this forum and decided to give it a try. As you can see on my schematic, I have a battery connected to a heating resistor, their low sides are separated by a NMOS (https://www.infineon.com/dgdl/IPB039N10N3+G_Rev2.1.pdf?folderId=db3a304313b8b5a60113cee8763b02d7&fileId=db3a30431ce5fb52011d1ed1fd3915e0) BATT- is then connected to the GND of my circuit through a sensing resistor (10 mOhms) for other purposes. I tried this circuit with a power supply in place of the battery and noticed it would immediately drain current. To be sure it wasn't a command problem, I removed the gate resistor (R12), but it's still happening. When my power supply is at 20V, Vds = 2V and Vgs = 300mV, and the mosfet acts as a very small resistor. But it should act as an open circuit! I tried with R13=10k, R13=0 and without R13, and it's always conducting. What is going on? Everything I've found elsewhere displayed the exact same schematic, even a board I've already used worked the same way. What am I missing here? Thank you for your help, strangers! |
| wraper:
Probably your MOSFET already failed. Also from your circuit is not obvious if BATT- is connected to GND as it should be to work properly. |
| ppff:
God damn that was it. It had no reason to be broken, but it was :) Thanks for the idea! |
| Ian.M:
Leave a MOSFET gate floating and it can get biased into its linear region by static charge. If you powered it up without a gate pulldown resistor or good gate drive it probably fried itself due to excessive dissipation in a fraction of a second. |
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