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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 ...
Tom Carpenter's user avatar
26 votes

Do MOSFET logic gates necessarily need an N channel MOSFET?

Couldn't it be replaced with a simple resistor into ground like this? Yes it can and is has been done: PMOS logic there's also the complementary version: NMOS logic We've been there and done that! So ...
Bimpelrekkie's user avatar
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15 votes
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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 ...
DKNguyen's user avatar
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12 votes
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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 ...
Jim's user avatar
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12 votes

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 ...
Andy aka's user avatar
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12 votes
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Why do we need transmission gate for XOR (transistor level design)?

There are practical concerns with real transistors that you do not see in the digital diagram. MOSFETs require the correct difference between the gate and source terminals to conduct. You can always ...
DKNguyen's user avatar
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11 votes
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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 ...
Bimpelrekkie's user avatar
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10 votes
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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 ...
Vladimir Cravero's user avatar
10 votes

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 ...
Olin Lathrop's user avatar
10 votes

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, ...
John Doty's user avatar
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10 votes
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Why is the gate resistance of this PMOS so low? It should be very high

The gate resistance in this datasheet refers to the series resistance between the gate (pin) and the actual gate on the substrate. This resistance is made up by the pin, bond wire, the substrate ...
Klas-Kenny's user avatar
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9 votes
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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 ...
Bimpelrekkie's user avatar
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9 votes

Load Selector/Load Switch

I want to do something to perform the same as a Relay [...] I want something fast CMOS IC switches are fast. Blazingly fast. 50ns pulses are no big deal for them. Look for integrated RF switches. ...
Kuba hasn't forgotten Monica's user avatar
8 votes

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: ...
Renan's user avatar
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8 votes
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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 ...
Dave Tweed's user avatar
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8 votes

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, ...
BEE's user avatar
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8 votes
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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}(...
G36's user avatar
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8 votes

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 ...
AnalogKid's user avatar
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8 votes
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What happens when Vdrain is greater than Vsource in PMOS Transistor?

The only thing that determines the "on/off" state of the MOSFET (channel conductance) is the potential difference between gate and source, \$V_{GS}\$. As long as \$V_G\$ is significantly ...
Simon Fitch's user avatar
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7 votes
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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 ...
Curd's user avatar
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7 votes

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 ...
Phil Frost's user avatar
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7 votes

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,...
tobalt's user avatar
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7 votes
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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 ...
Bimpelrekkie's user avatar
  • 80.8k
7 votes

P-channel MOSFET gating circuit that passes voltages above 17 V

The NPN bipolar transistor Q1 is being used as a comparator, and an inverter. When the input voltage rises to 17V, the base of this transistor is at: $$ \begin{aligned} V_B &= 17 \times \frac{R_1}{...
Simon Fitch's user avatar
  • 32.7k
6 votes

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 ...
jms's user avatar
  • 8,611
6 votes

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 ...
Justme's user avatar
  • 144k
6 votes

Low-side NMOS switch circuit

I suspect you've got drain and source swapped, for Q1, the P-channel MOSFET. When PWM-IN is low, the gates are both high (because of the inversion by Q6). If this circuit was working, then Q2 would be ...
Simon Fitch's user avatar
  • 32.7k
6 votes

Driving a motor with a high-side PMOS switch. Does it need a flyback diode?

Is it necessary to add a flyback diode for this implementation? And if so, how/where exactly should it be added? Yes, usually necessary and, it goes here: - You've also drawn M2 upside down.
Andy aka's user avatar
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5 votes

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 ...
722204's user avatar
  • 51
5 votes
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Simple Mosfet driver

Yes, the transistor-resistor driver is helping. A quick look at the datasheet of the MOSFET show Qin = 38nC and Cin = 860pF. With I=2mA direct drive, switch time is t=Q/I=19us. With your driver, ...
jpcgt's user avatar
  • 400

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