# Tag Info

Accepted

### Why do we use a CMOS for inverting a circuit when the PMOS already achieves that?

In a word: Efficiency. You can use a PMOS transistor to drive a logic output high (e.g. VDD) when the input is low (e.g. GND). However, you can't use that same PMOS transistor to drive a logic output ...
• 56.5k
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### Why is the arrow on this MOS transistor IC common?

That is the body connection. All MOSFETs have a fourth connection to the substrate, but for discrete MOSFETs this is normally connected internally to the source which results in a parasitic body diode ...
• 45.9k
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### Is there a popular small signal PFET equivalent to NFETs 2N7000 or BS170?

That is called a complementary transistor. BS250 is complementary to 2N7000. Check this list for PFETs with the characteristics you want. However I don't know what popular transistors you'll find ...
• 4,988
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### Pull up resistor on P-MOSFET gate. Not working

a better idea for this, if you want to use a PMOS high side switch, would be to have the ATSAMD21 switch a low-side NPN switch, which then switches the PMOS for the SIM530. Example: simulate this ...
• 1,617

### Can you drive a P-MOSFET as a high side switch directly from a microcontroller?

If I use a GPIO configured as open drain output, not push-pull, and use a pullup resistor between the gate and source of the P-MOSFET and It this OK to do so ? Am I correct, or am I missing ...
• 378k
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### Why is the current through the PMOS different to the NMOS?

If all the components are identical, or 'symmetrical', this is because for the PMOS the load is connected on the source. The drain current of a MOS transistor is a function of its gate to source ...
• 15.6k
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### What affirms channel current direction in nMOS and pMOS?

When talking about MOSFETs on an IC, these mostly have a symmetrical structure like this: Picture from here. Note how Drain and Source are physically identical. When using these type of MOSFETs (so ...
• 78.7k

### P-Channel MOSFET Inrush Current Limiting

You have sortof the right idea: But the capacitor is in the wrong place. For slew rate control, it should be between the drain and the gate, not the source and the gate as you show it. Putting it ...
• 306k
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### Do I really need the N-MOS driver here?

The P-Channel MOSFET needs to switch up to 20V. And that's the catch, when making the MCU output high impedance, you could have 20 V at that MCU's output. You would be violating the maximum ratings ...
• 78.7k

### Can you drive a P-MOSFET as a high side switch directly from a microcontroller?

This is a good spot for the oft-neglected common base configuration: simulate this circuit – Schematic created using CircuitLab Assuming 3.3V CMOS GPIO, if the GPIO pin is low, you turn on Q1, ...
• 1,451

### Is there a popular small signal PFET equivalent to NFETs 2N7000 or BS170?

ZVP3306A is not too bad a choice as a complimentary part to the 2N7000, rather cheaper (~30%) than the BS250, but it is still more than six times more expensive than the surface mount SOT-23 BSS84. ...
• 327k

### Why do we use a CMOS for inverting a circuit when the PMOS already achieves that?

CMOS, while more complex to make, consumes very little power when not switching, while PMOS consumes more power even when it's not switching. From here, be the circuit below for a simple inverter: ...
• 4,966
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### PMOS device in low-side switch

Yes, it's possible. But just like with a high-side NMOS switch, you'd need to drive the gate beyond the supply rail (below Gnd, in this case) in order to switch it fully on. While there's some ...
• 164k

### Why use a PMOS transistor instead of a diode for ESD protection?

The purpose of the diode and MOSFET are for reverse polarity protection, not ESD. The diode is more simplistic, but it is lossy as it will drop some voltage across it (0.4 V to 1.0 V, ...
• 546

### Buck converter without oscillator?

As above, what you have is a linear regulator. BUT If you add hysteresis to the circuit, you now have what is called a hysteretic converter, where the output bounces back and forth rapidly between ...
• 12.5k

### Will this circuit protect my digital IOs from overvoltage conditions?

One problem with your design is if the overvoltage exceeds M2's maximum drain-source voltage, M2 won't actually disconnect the circuit. Another is that when it's tripped, you'll have significant ...
• 55.3k
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### Reverse polarity protection for a very low voltage devce

Did you see (and understand) Spehro Pefhany's comment? I take the liberty of turning it into an answer because that's also what I'd suggest. Add a diode in front of your circuit that shorts the ...
• 15.7k

### How does a PMOS LDO work?

The opamp will settle such that $V_{gs}$ for the PMOS is close to its threshold. The FET is almost never fully on or off unless very briefly during startup and step changes. When Vout drops a little,...
• 10.2k
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### Why is the current flowing into the power supply?

Note that this current flowing back into the supply flows only for a fraction of a nano-second! What happens is easier to explain with a much simpler circuit like a CMOS inverter. In your latch the ...
• 78.7k
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### Replacing a Switch and Avoiding body diode conduction

There are IC's which can provide this functionality. One option would be to use a "Power Multiplexor". An example is the TPS2115. It takes the place of the diodes and switches, and is controlled by ...
• 16.3k

### P-channel MOSFET as high-side switch gets hot

The problem The /OE (output enable) pin of the 74CH595 toggles the output drivers between two states: driving the outputs (high or low) and high impedance (letting the output lines float). It is ...
• 8,314

### Simulating Power PMOS using LTSpice

To model the P-MOS transistor in LTspice you do not need to know the $W$ and $L$. The simples model used the $K$ factor and $V_{TH}$. The drain currency is equal to: I_D = \frac{K}{2}(...
• 12.2k

### Can you drive a P-MOSFET as a high side switch directly from a microcontroller?

No, the FET would always be on, no matter if MCU output 3.3 V or 0 V to gate. The Vgs would be 6.7 V or 10 V. Also the pull-up to 10 V would always force overvoltage on MCU pin, but would also limit ...
• 86.9k

### Is there a popular small signal PFET equivalent to NFETs 2N7000 or BS170?

Consider the design to be sustainable, 2N7002 usually is used to control signals. You can use BSS84 as equivalent but pmos usually is used as power switch. that's why people rarely can find 2N7002's ...
• 51
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### A good reference for modeling pmos transistors in LTspice?

In The LTSpice help file you can find this table, which I'm too lazy to figure out how to reproduce completely: The table is under LTspice IV -> LTspice -> Circuit Elements -> M. MOSFET in the help ...
• 121k
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### Buck using discretes - Driving p-MOSFET using n-MOSFET

The reason the FET turns off so slowly is because you only have 2 kΩ pulling it high. Take a look at the datasheet for that FET. It should show you the actual and effective gate capacitance ...
• 306k
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### term "fat" when referring to NMOS and PMOS

Microchip designer here... I've never heard of a "fat" MOS transistor, but there is such a thing as a "thick oxide" MOSFET transistor, sometimes referred to as just "thick" transistors. Typically, a ...
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### Phase margin analysis of a [diy] PMOS LDO [with LTspice]

I think the top graph does indicate exactly where instability occurs: - The phase angle is zero degrees and the gain is still +45 dB. In other words it's "gain margin" that is causing oscillation ...
• 378k