27 votes
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Why have both: BJT and FET transistors on IC output?

Paragraph 2 of the description says: FAN3100 drivers incorporate MillerDriveTM architecture for the final output stage. This bipolar-MOSFET combination provides high peak current during the Miller ...
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21 votes

Is it okay to use a MOSFET in its resistive region with a heat sink?

TL;DR Use BJTs for linear operation, not FETs Most FETs are not rated for safe operating area (SOA) at DC. Bipolar junction transistors (BJT) are. If you examine the SOA graph for any FET, you'll ...
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18 votes
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Bootstrap circuit for high-side MOSFET driver

simulate this circuit – Schematic created using CircuitLab Note 1: The input voltages are only \$V_{cc}\$ and \$V_\text{High Voltage}\$. You don't apply anything at the \$V_{BS}\$ node. It is ...
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16 votes
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Do we need a resistor to discharge capacitor of MOSFETs while connected to MCU?

One good reason is to have this resistor to keep the gate low if the MCU pin is in high impedance state (e.g. during reset or after reset until the port is initialized). (Otherwise during high ...
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14 votes
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Designing a *linear* MOSFET driver stage

This is indeed an interesting problem, because of the variation of effective load capacitance with the load resistance due to Mr. Miller, and your need to not overcompensate it. I suspect a biased ...
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13 votes

Is it okay to use a MOSFET in its resistive region with a heat sink?

Unfortunately modern power MOSFETs fail when operated in the linear region at high power dissipations. MOSFETs are safe to use in the linear mode as long as the drain current decreases with ...
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12 votes
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Why does this circuit speedup the switching time and reduce losses?

If you look at the full schematic, it is easily apparent why. The MC34063 is configured in the circuit in such a way that it drives the MOSFET gate with an open emitter output: The chip can drive the ...
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12 votes

Do we need a resistor to discharge capacitor of MOSFETs while connected to MCU?

During normal operation there is no need for the resistor. However you may want it to put the FET into a known state during power up and reset. Otherwise on power up before the MCU starts to drive ...
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12 votes
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Why is my power MOSFET heating up when on?

The only mistake is using the NFET as a high side switch when it should be a low side switch with Vs=0V then with Vgs>=10V you pull down the load cathode and series R from the supply with the drain. ...
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11 votes

Why have both: BJT and FET transistors on IC output?

The CMOS and BJT output stages are combined to from one stage, the manufacturer calls this a "MillerDrive(tm)". Why they do this is explained in the datasheet: My guess is that they want to achieve ...
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10 votes
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Why is a resistor put before the gate of a transistor?

The reasons are different depending on if it is a BJT or a MOSFET. The effect, though, is the same - it's there to reduce current and protect the IO pins on the controller that are driving the ...
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10 votes

Designing a *linear* MOSFET driver stage

Outcome Report Okay, the short story is: adding a discrete buffer worked! That said, I don't think I'll design my circuit this way, rather I'll go with the recommendation of @Spehro and @...
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10 votes

Using a miniature BNC connector on a PCB to measure high-frequency content with an oscilloscope

You might consider adding an attenuator probe to your PCB consisting of a single series resistor. The 50-ohm coax cable to your oscilloscope can be any length - the oscilloscope input at the far end ...
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9 votes
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Should I use a resistor between the gate driver and MOSFET (gate pin)?

Maybe. The MC34152 datasheet pp.8 on shows a series Rg to damp oscillations, and reverse-bias Schottky diodes for catching negative ringing spikes at the driver. Wouldn't hurt to have these in your ...
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9 votes

Why have both: BJT and FET transistors on IC output?

Notice how the top NPN can only make the output reach VDD-0.7 V, I assume it is the job of the mosfet to take care of the last 0.7 V. It looks as if the BJT's are doing most of the grunt work and ...
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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 ...
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9 votes
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How does this PNP transistor improve the switching performance of MOSFET?

My guess is PNP transistor might ensure fast turn off by shunting the gate capacitance (ie, when diode is reverse biased and PNP is on) That is correct. Not sure why is the gate current limiting ...
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8 votes
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MOSFET Gate-Source protection question

Your interpretation for the reason why Z-diodes or resistors are used is corrent, in my opinion. When the driver leaves the MOSFET's gate floating, you want at least something to give you a defined ...
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8 votes
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How important is the gate threshold voltage on a MOSFET?

The Gate Threshold Voltage VGS(th) refers to the voltage below which the FET stops conducting almost completely, defined by some manufacturers as the gate voltage at which the drain current crosses ...
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8 votes

Gate resistor with "logic level" MOSFETs

If you're driving a gate directly with an MCU output you don't really need to worry about adding external resistance to the gate in most cases because the outputs are so weak they'll be the equivalent ...
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7 votes

How do I delay MOSFET turn on without slowing down the rise time?

Start with this: - And then invert the output of the OR gate. Both gates should be schmitt trigger types. The RC time constant and the schmitt trigger high and low thresholds produce the deadband ...
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7 votes

MOSFET Miller effect: length of the gate voltage flat area

MOSFET switching Let's first approximately model MOSFET inductive load switching behaviour, far from a complete study on the topic I'll just recall main points and later on focus on the voltage slope ...
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7 votes

Why is my power MOSFET heating up when on?

TL;DR: I was driving my MOSFET gate at the supply voltage I was switching/ so I didn't maintain a high enough VGS. I'd failed to consider that Vs is not 0V once the MOSFET is on. Per the accepted ...
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6 votes

Why low impedance for gate drive design

A MOSFET has a very high gate resistance because the gate is physically insulated from the other terminals on the device. This means that under DC conditions it doesn't draw any current, making you ...
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  • 4,491
6 votes
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Microcontroller incapable of driving MOSFET

I notice that you do not have a single decoupling capacitor in the schematic. Each time the MOSFET switches on or off, there can be some very high transient currents. If you don't have any decoupling ...
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  • 55.5k
6 votes

What is the difference between driving a MOSFET gate and an IGBT gate?

suitable IGBT gate driver And the key to your question is "suitable". The short answer is yes you can. The IGBT combines an isolated-gate FET for the control input and a bipolar power ...
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6 votes
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MOSFET driver without gate resistor

The chip specifies the "typical" LO output current as 1A, not an absolute maximum. This current is limited by its internal output resistance since there doesn't seem to be a limiting circuit according ...
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6 votes

Is it okay to use a MOSFET in its resistive region with a heat sink?

MOSFETs can be fine in linear mode, but extra care needs to be taken because the MOSFET will not necessarily distribute the current flow though it in a even fashion. Here is an application note from ...
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