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Due to size constraints, adding a heat sink may be difficult. Attached is some temperature data from the fets at stall for 1 minute. This seems much improved; however, the capacitor is having a weird affect when both FETS are used, the stall current will drop and the motor makes a strange...
I put two of the same FETs in parallel and am getting strange results. both fets will heat up initially then one seems to turn off and the other one takes the grunt of the load. Any ideas as to why this is?
I calculated 175C-25C = 150C (Tjmax - Ambient). Then (150C)/(50C/W) = 3W (Heat limit/Rja) Max power dissipation for the FET before reaching the critical limit in ambient air. If I were to add another fet in parallel wouldn't that half the 3.6W power dissipation to 1.8W? Would this be more...
So if I take the voltage drop across the circuit while the motor is stalled I get 6V, and with a 0.6A current limit the FET will be dissipating 3.6W? That seems pretty low, but the FET is getting very hot.
Hello,
I am having an issue with my PCB. The circuit is a current limiting circuit in which the limit threshold is controlled by R1. The output is to a motor spinning a wire which must stall at the specified current in order to prevent damage. The P-Mosfet is heating up when the motor is at or...
I didn't think it had anything to do with the layout, i figured it had more to do with the way I soldered the SMD FET. The source, gate, and drain are all in the correct positions. Attached is the schematic.
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And here's the fet layout, I am attempting to connect the "new"...
I am trying to solder a SMD FET to my PCB, this is a different fet than the PCB was originally designed for (Drain and Source switched places). When i solder it up like this the R1 on my PCB ignites. Is there a reason you cant solder SMD FETs like this?
I also tried to solder the through hole...
Thanks for the help. I tried it and it works well except that R3 is affecting the current limit. Also, why would R3's value affect the delay, and how exactly is this model causing a delay?
I am using a simple current limiting circuit design to limit the torque applied by a motor. The problem is; the initial start-up of the motor requires a lot of torque, but once it's rotating I would like to have a lower limit. How would I add a delay or bypass for the initial start-up?
This circuit has been working well, but I have a few questions. What attributes should I look for in a P-MOSFET so that I have as little voltage drop as possible when it's on, is that the Rds value? Also, we are using alkaline 9V batteries and we are seeing a non-linear drop in voltage over...
Everything worked great, there was some speed drop, but not as bad as the resistor we were using. The p-mosfet does get very hot (smoking) with stalls longer than ~10 seconds.
I am trying to understand what's happening in this circuit. The current passed R2 controls the PNP gate to open/close, this then determines whether enough voltage is present to open the PMOS which is then supplied to the motor, otherwise it's pushed to R1? I'm still a bit confused on what...
I am currently working on a project that requires some sort of current limiting circuit with minimized voltage drop. I have a 9V battery powering an electric motor that spins a wire. I want to limit the current draw to approx 0.5A, otherwise the wire over-torques and can break. I can’t change...
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