MOSFET Ideal Diode Controller Provides Fast Turn-On and Turn-Off for Robust Power Supply ORing in Low Voltage Applications. Consider the cross-sectional view of an n-channel MOSFET operating in linear mode (picture below). We assume the threshold voltage is constant along the channel. The channel voltage V c has.
by Crutschow
When you parallel a battery with another battery or other source, the batteries are often required to be back charged. This can be done with standard diodes, but that gives close to a half volt drop — even with Schottky diodes. This is especially problematic with low-voltage batteries, where that drop is a significant percentage of the battery voltage, noticeably reducing efficiency and battery life.
Exicon lateral MOSFET are ideal for audio amplifier designs. Banerjee 'Building An Ideal MOSFET' As our electronics continue to proliferate and become more sophisticated, the race continues for more power efficient and scaleable semiconductor devices — components that use minimal power while being small enough to. ▀▄▀▄ Answer: 1 📌📌📌 question ➜ An ideal n-channel mosfet has the following parameters: w 50 1-5 μm, tox 0.05 rn, na-10 15 cm, 3, n+ independent of vg). Ignore the bulk charge effect and velocity.
To minimize this forward drop you can configure a MOSFET as an ideal diode, which has a very low drop in the forward direction (equal to the current times the MOSFET’s ON resistance) while blocking the current in the reverse direction.
Below is the LTspice simulation of a simple ideal-diode MOSFET circuit. It uses inexpensive components consisting of a P-MOSFET (for use in the positive rail) with a dual PNP transistor and two resistors.
Q1 and Q2 form a current mirror circuit. The indicated values of R1 and R2 cause Q2 to be on and thus M1 off (Vgs ≈0V), when there is no voltage difference between the drain and source of M1. The mirror has a gain of ≈130 from the voltage difference between the two emitters to Q2’s collector voltage change.
In the forward direction (output voltage lower than the battery voltage) the current mirror becomes unbalanced due to the difference in emitter voltages, such as to turn Q2 off, which puts the P-MOSFET gate near ground potential, turning it on. This allows current to flow from the battery to the output (left to right) with a low drop. (MOSFETs conduct equally well in either direction when on.)
When the output voltage becomes slightly higher than the battery voltage, this voltage reversal across the MOSFET unbalances the current mirror in the opposite direction, causing Q2 to turn on. This causes the MOSFET gate voltage to rise, reducing Vgs [V(G,Out) in plot], which turns it off and prevents reverse current flow.
This can be seen in the simulation, as the current only goes out of the V1 battery when the V2 output voltage is lower than the battery voltage, and doesn’t flow in the reverse direction when the output voltage is greater than the battery voltage. The maximum voltage drop, when the battery is providing 2A current is ≈32mV with the MOSFET shown, demonstrating the near ideal diode operation.
The current mirror operation is very sensitive to any offset between the two transistor base-emitter voltages, which could possibly allow some current conduction in the reverse direction. It is thus recommended that a matched transistor pair be used, such as the DMMT3906W shown on the schematic (basically two 2N3906’s in one package), which have their Vbe matched to within 2mV max and are thermally connected.
(The simulation was done with 2N3906‘s which are perfectly matched in the simulation, unlike real life.) The DMMT3906W pair are quite inexpensive, selling for U$0.37 here, for example.
The P-MOSFET selected should have an on-resistance small enough to give a low voltage drop when conducting the maximum battery load current. If the battery voltage is less than 10V then a logic-level type MOSFET should be used which have gate-source threshold voltages (Vgsth) of less than 2V.
One of these circuits can be used at the output of each battery; however, many are in parallel.
You can read more articles by Electro-Tech-Online “Well-known” member, Crutschow, here.
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Ideal Mosfet In Saturation
Prof. Kaustav Banerjee and ECE researchers demystify the role of negative capacitance in modern MOSFETs after over a decade since its conception
As our electronics continue to proliferate and become more sophisticated, the race continues for more power efficient and scaleable semiconductor devices — components that use minimal power while being small enough to pack into increasingly dense integrated circuits.
MOSFETs (metal-oxide field-effect transistors) are an example of such a breakthrough. Developed in the 1960s, their low power consumption, scalability, compactness and ease of mass manufacture made them the go-to logic switch for a wide array of electronics. The rapid miniaturization and densification of these transistors (without a concurrent increase in power consumption) was what led Intel executive Gordon Moore to formulate his famous law: that the number of transistors in an integrated circuit would double every two years. The result has been a steady increase in the performance of our computers for several decades, from desktops and laptops to our smart devices and wearables. Today’s smartphones have billions of nanoscale MOSFETs.
However, the benefits of downward scaleability — at least in terms of conventional FETs — seems to be hitting a limit, according to UC Santa Barbara electrical and computer engineering professor Kaustav Banerjee, a renowned expert in nanoelectronics and one of the world’s most influential scientific minds, according to Clarivate Analytics. And though a certain type of transistor called a negative-capacitance FET (NC-FET) has been touted as a way to maintain performance, Banerjee thinks it’s time to reconsider its role.
“After over a decade of misconception and confusion in the scientific community, we have essentially blasted the myth that NC-FET is a steep-slope device,” Banerjee said of his paper, “Is negative capacitance FET a steep-slope logic switch?,” recently published in Nature Communications.
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The UCSB Current – 'Building An Ideal MOSFET' (full article)