I have a circuit with a pair of MOSFETs (one n-channel IRF7201 that is the input to drive a p-channel SSM6J507). It's supposed to be a gate to either turn on the output or turn it off. After reading several other threads on here about driving MOSFETs with digital outputs, I chose the IRF7201 because it has a Vgs(th) of only 1.0V. It's controlled by a TLC7705 which is supposed to sense when the voltage coming from a regulator is actually good or not and then wait a bit of time and create a reset signal to drive this output circuit. It's a bit weird since the circuit almost works. The output is 12V and works correctly, but when I put any load on it (about 1A load), the output drops to 2V or so which is exactly what I was trying to avoid. While the 7705 is supposed to be able to drive up to 10mA max, I have a feeling that in this configuration (with an external voltage divider, and also with some extra voltage dividers from the regulator) that the 7705 is not the right part for the job and I should have used a 7701. (The 7705 has an internal voltage divider in addition to all of these, and perhaps it has more going on inside of it as well). In any case, while I can swap out the 7705 for a 7701 and change the resistors, etc, I'm more concerned because it seems to take 38mA of current to actually turn on the output MOSFETs. I measured this by hooking it up directly to the 5V and measuring the current (voltage drop) across R22 (I replaced the 0-ohm with a 1.37k-ohm). The output circuit worked well when I hooked it up to a wire directly to +5 or ground (and it also even enabled the output after a while of being disconnected and allowing it to "float" high). Looking back at the datasheet of the IRF7201, I think I missed something that was pointed out in another thread here. It's that the 1V Vgs(th) is specified with a drain current (Id) of only 250uA. With R21 at 10K, I would have 1.2mA instead. So would I just be okay to replace R21 with a 48k resistor instead? I'll be trying that tomorrow. Anything else I should be concerned about? Thanks!
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