Questions tagged [pmos]

A p-channel metal-oxide semiconductor (pMOS) transistor which has has p-type carriers used in the channel. The channel is established by a negative voltage on the gate which inverts the substrate (NWell) under the gate which turns the device on. The term may also be used to describe logic circuits built around pMOS transistors.

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26
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4answers
3k views

Why old PMOS/NMOS logic needed multiple voltages?

Why does old PMOS/NMOS logic needed multiple voltages like +5, -5, and +12 volts? For example, old Intel 8080 processors, old DRAMs, e.t.c... I'm interested in the causes on the physical/layout ...
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2answers
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P-Channel MOSFET high side switch

I am trying to reduce the power dissipation of a P-Channel MOSFET high side switch. So my question is: is there any way in which this circuit can be modified so that the P-Channel MOSFET will ...
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3answers
23k views

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

Some days ago I was considering using a small signal P-Channel MOSFET in a design of mine, but could not find a suitable part. The specs I was looking for were something like the following: \$I_D = -...
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1answer
5k views

Where are the depletion PMOS transistors?

In school, I was taught about PMOS and NMOS transistors, and about enhancement- and depletion-mode transistors. Here's the short version of what I understand: Enhancement means that the channel is ...
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2answers
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Why do we use a CMOS for inverting a circuit when the PMOS already achieves that?

The output in a PMOS is as follows: I/P O/P 0 1 1 0 Why can't I just use this instead of using a CMOS for inverting logic? (Please ...
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P-Channel MOSFET Inrush Current Limiting

I have been searching EESE and Google for several weeks now for a solution to this problem, and while I found some proposals that seemed promising, the real-world implementation fell short of ...
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2answers
6k views

Reverse polarity protection - PMOS vs Schottkey diode

I have a circuit running from 2 AA cells in series, meaning I get 3.0V when fresh (or 2.4V if NIMH cells) and it goes down to 2.0V, that's when my circuit cannot function anymore (no DC/DC onboard). ...
7
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2answers
5k views

Micro SD card power circuit failure

Description I am designing a system in which there's a circuit that controls the power applied to a micro SD card (enable/disable). The circuit is the following: The power control circuit is done ...
6
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1answer
1k views

Pull up resistor on P-MOSFET gate. Not working

I am building a battery-powered datalogger that will communicate using cellular signal, based on the ATSAMD21 microcontroller and the SIM5320 cellular modem. To save power, an outside timer ...
6
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4answers
4k views

P-channel MOSFET as high-side switch gets hot

So I'm trying to control my front lights of my car using an Arduino Nano. In total there are 14 lights (including foglights and blinkers etc.). I'm using two 75HC595 shift registers to control these ...
4
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3answers
6k views

what happens when transistors are interchanged in CMOS?

A basic cmos inverter will have a P-transistor upside and N-transistor down side. what happens if we reverse the p and n transistors?
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Phase margin analysis of a [diy] PMOS LDO [with LTspice]

I'm somewhat familiar with using LTspice to do phase margin analysis for a classic i.e. obvious negative feedback path opamp circuit; in fact I've done that analysis successfully for fixing real opamp ...
4
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2answers
824 views

Problems with DC analysis of a PMOS circuit

I'm beginning with electronics and I've picked up the book from Donald. A. Neamen - Microelectronics. I'm stuck at a simple example of DC analysis for this PMOS circuit. simulate this circuit – ...
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269 views

Level shifted PMOS driver operation

simulate this circuit – Schematic created using CircuitLab Having some confusion this gate driver. It can be found in Design and Application Guide For High Speed MOSFET Gate Drive Circuits. ...
4
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1answer
6k views

Designing stable PMOS voltage regulator

As a follow-on to the question "Using forward voltage drop of diodes with linear regulator" I am looking into designing PMOS voltage regulators. General Topology A common problem with the intuitive ...
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1answer
197 views

Li-ion power supply with a charger, a booster, and a pMOS high side switch

I am designing a circuit board for a small mobile robot and there is a problem with the power supply. The circuit is powered by a 1-cell Li-ion battery (VBAT) and includes a charger (MCP73831/2), a ...
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2answers
442 views

Adding switch debounce to discharge circuit

We use the attached circuit for some diagnostic timing prior to doing experiments. Basically when the momentary switch is closed, from a location away from the generator box, the left side of C2 is ...
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5answers
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Replacing a Switch and Avoiding body diode conduction

I am trying to design a replacement for a 2:1 switch using FETs, which would be really easy if I didn't have to concern myself with the body diodes that are present on PMOS transistors. My scenario ...
3
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3answers
588 views

High Side P Mosfet Circuit

I'm designing a circuit to use a P mosfet as a high side switch. The supply will be either 12v or 24v. The circuit is being designed for 8 amps max current draw. Does this circuit look exceptable? ...
3
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3answers
877 views

Switch (Relatively) High Voltage from Logic Level

The Situation: Basically, I would like to switch a load that requires 30v using a switch that cannot have more than 5v across it. More descriptively, I am trying to drive the anode of a VFD segment ...
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2answers
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Buck using discretes - Driving p-MOSFET using n-MOSFET

We are designing a buck using discretes. I have a problem with OFF time of Control MOSFET(U1) and driver(T1). In OFF time, Gate of U1 is rising very slowly to 12V which makes U1 always ON. Which in ...
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1answer
1k views

Driving Inductive Load with MOSFET: N-Channel vs. P-Channel

Problem I am driving an inductive load from a microcontroller using a MOSFET. I have a current sense resistor in series with the load. I don't have much experience with transistors (should have paid ...
3
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1answer
734 views

CMOS technology, use a NMOS or PMOS as series switch?

A general question regarding switches in CMOS. Have a look at the schematic below (symplified current mirror) There is a input reference current, on/off switch, a PMOS mirror and the resulting output ...
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1answer
73 views

Mask Programmable Array Concept

I am having trouble understanding a lecture slide for Mask Programmable Arrays. The cell on the right is supposed to represent a 4-input NOR gate. But I just cant wrap my head around which pads ...
3
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2answers
687 views

Adjustable PMOS current source

I'm trying to design a current source that can be adjusted from 0mA to 25mA (for an input voltage of 0V to 3V) using a dual P-Channel FET (NTZD3152P). I've based my design on some PMOS current ...
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2answers
107 views

4 P-FET HBridge

The other day I got a reel of 800 P MOSFETs, my workplace threw out, as the entire company is relocating. 800 are quite some, and I need to build me a couple of HBridges anyway, so "joy, oh joy!" ...
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3answers
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Reverse polarity protection for a very low voltage devce

I want to add reverse polarity protection to a device which is powered by a single AA battery, so its voltage might go down to 0.8 V. Forward diode is too huge of a drop. I've already thought about ...
2
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1answer
607 views

Why is the current through the PMOS different to the NMOS?

I'm trying to alternate two LEDs with a shared PWM signal. When the signal is low D1 should conduct. When the signal is high D2 should conduct. I've created an LT Spice simulation of the circuit I ...
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2answers
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Will this circuit protect my digital IOs from overvoltage conditions?

I have come up with the following circuit to protect my device's IOs from overvoltage conditions. simulate this circuit – Schematic created using CircuitLab The idea is that as soon as the ...
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5answers
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Simple Mosfet driver

I need to switch 8 IRF9540 (P-Channel Mosfets) with about 32kHz (so 1 MOSFET about 4kHz) so that only one is On at one time. I thought about using the decade counter 4017 for this, and the 555 Timer ...
2
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2answers
4k views

Why is CMOS fall time faster than rise time?

I've just started a computer architecture class, and the slides from a lecture says that the reason why fall time is faster than rise time is that the NMOS electrons have more mobility than PMOS which ...
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3answers
690 views

Control inrush current

A basic question, how does the P-Mosfet reduce the inrush current. simulate this circuit – Schematic created using CircuitLab Old image link Can the P-Mosfet's drain and source orientation be ...
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1answer
2k views

Explain the use of NPN and pMOSFET in this 8x8x8 LED cube

I've got part of a circuit diagram for an 8x8x8 RGB LED cube from http://www.kevindarrah.com. See the entire schematic. I'm having trouble working out how it does what it does. I know that a high ...
2
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1answer
506 views

Turning an NMOS with substrate terminal into a PMOS

Some NMOS's come with a substrate/bulk/body terminal so the "Source Voltage" referred to in literature then Substrate Voltage. Say then we short the gate to the drain and have the substrate take the ...
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2answers
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Drive DC Motor with H Bridge(H Bridge turns off too slow and problem with current monitor)

I have two questions about my circuit, drving DC Motor with H Bridge. The picture below shows my design and how I drive it with signals. For example, when I make the motor rotate forward, I give 'S1' ...
2
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1answer
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PMOS Gate Driver using BJT

I'm (again) looking at high-side load-switching. The load shall be switched on with a controlled rise-time (=limited inrush current) and be switched-off quickly when a controller (not shown) detects ...
2
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1answer
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nMOS passing 1's poorly and pMOS passing 0's poorly

I came across the statement in a digital design book that "nMOS transistors pass 0's well but pass 1's poorly" and "pMOS pass 1's well but 0's poorly". What exactly do these statements mean and why ...
2
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2answers
72 views

Reverse-polarity protection P-channel MOSFET

There are many ways one can build a reverse-polarity protection circuit. Using diodes, Shottky diodes, n-MOS in the return path and using a P-channel MOSFET on the positive side of the circuit. My ...
2
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2answers
354 views

Motor activation using MOSFET

I need to switch a motor on and off by cutting it's battery connection and even though I could use a relay, I would rather to use a MOSFET, so things will be smaller and quieter. The problem is, I am ...
2
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1answer
515 views

How are PMOS equations different than NMOS's?

I have been googling about it and I see lots of different ways such as only flipping the signs (< becomes >) and switching variables (VGS becomes VSG). Some people even say just put absolute value ...
2
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2answers
1k views

Precharging capacitors with P mosfet slew rate control - Unwanted turn ON

I am considering using a MOSFET to control the dV/dt rise (slew rate) when power is first applied to a DCDC power supply. This will hopefully resolve both a precharging issue I am having and the ...
2
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1answer
298 views

How to determine the voltage on the drain of a “hanging” PMOS

This is likely a simple question that has an equally simple answer. Below is the associated schematic. The problem I'm having is identifying what state M2 is in, and what the voltage is at Va. I know ...
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2answers
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Create a CMOS circuit from a logic function [duplicate]

I have to create a CMOS circuit from the logic function: F= ~A + B (notA or B). I made the truth table but I'm stuck here trying to make the CMOS circuit. Any ideas anyone? Thanks! I know it's the ...
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2answers
208 views

Slew Rate Adjustability

A SPST switch connects HB1 and HB2, to control a lamp connected to HB OUT. I am looking into modifying this circuit to make the slew rate adjustable when switching the output to VCC (around 12V). I ...
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1answer
221 views

Is it possible for (W/L) of 0.18nm PMOS to become 989100?

Is it possible for (W/L) of 0.18nm PMOS to become 989100 ? If not,i wonder what the range is for (W/L) of TSMC 0.18nm PMOS and NMOS.Thanks a lot.
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What happens to a MOSFET if i apply voltage between Drain and Source leaving the Gate floating?

lately i was analyzing a simple circuit with 2 MOSFET, 1 Nmos and 1 Pmos, where the Nmos was acting as a switch and its drain was connected through a resistance to the Pmos' gate. The pmos had it's ...
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3answers
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What is the conventional circuit to control a P-MOSFET with MCU?

How a P-MOSFET works is clear, there is plenty of documentation on the web. But what's the standard circuit to use them as an ideal switch with an MCU is not that clear, in my opinion. I saw there ...
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4answers
3k views

3-pin MOSFET: P or N type?

This may be a silly one but I couldn't seem to find an explicit answer: with a 3-pin MOSFET, how do I determine whether it's an NMOS or PMOS? I'm making some assumptions here: I've already found the ...
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3answers
7k views

How can PMOS eliminate body effect but NMOS doesn't?

I have a question on the body effect of MOS transistor. In particular, how does the body effect in PMOS be eliminated (by connecting bulk to source together) while this similar technique doesn't do ...
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1answer
2k views

A good reference for modeling pmos transistors in LTspice?

I've been trying to learn how to use LTspice, and I'm attempting to create a model for a pFET I've been using/will use on a real board. However, since my specific transistor isn't already in LTspice'...