# Tag Info

### P-MOSFET always conducting

It's not the FET conducting. If you turn off the FET, you have an unpowered sensor or potentially multiple unpowered sensors on SPI bus. If any pin is set high from the MCU to the unpowered chips, ...
• 159k

### Designing a Circuit to Connect and Disconnect a Load to a DC-DC Converter @3 MHz

My first idea for switching "medium" current at high frequency above 1 MHz was to use a GAN-FET, but the required low leakage current and low output capacitance changed the game a bit. I ...
• 7,395
Accepted

### Why do many mosfet models exclude Cds ​ in parasitic capacitances?

The capacitance model in your middle image is correct for monolithic MOSFETs, which are used in integrated circuit design. There are three gate capacitances ($C_{GD}$, $C_{GB}$, $C_{GS}$), and ...
• 4,717

### Designing a Circuit to Connect and Disconnect a Load to a DC-DC Converter @3 MHz

When switching at 3 MHz you can't use a relay but, to decide what might be suitable requires a stronger definition of what performance needs to be. For instance "ON" needs to be stated as a ...
• 465k

### Superposition principle and Small signal analysis

The bias point V-I curve is nonlinear so cannot be used with superposition. It can be added to the small signal ac voltage to obtain a result. But is is not superposition. The bias point can influence ...
• 17k

### Superposition principle and Small signal analysis

Quoting from this comment by OP Abdelrahman: superposition States that I take every source independently and short the other one, if I took the small signal voltage and Short the Dc bias voltage, the ...
• 131k

### Superposition principle and Small signal analysis

From your comments, it seems you misunderstood my explanation. I said that you can apply superposition to the small signal obtained by linearizing the circuit around the operating point. However, your ...
• 292
Accepted

### Tried making a "poor man's" active/MOSFET rectifier. It doesn't work, and I didn't expect it to, but I don't understand why

If you want to build a MOSFET rectifier, you need to first arrange the circuit such that the rectification is done through the body diodes even when the MOSFETs are off. Keeping the MOSFETs off is ...
• 36.4k

### Confusion regarding driving a MOSFET through optoisolator

The opto-coupler coupler has a minimum CTR of 50%, so if its LED current is $I_{LED}=17mA$, then the largest transistor collector/emitter current you can expect is:  I_{C(MAX)} = 50\% \times I_{...
• 39.2k

### Common N-channel mosfet for multiple voltages

Not only should you use separate MOSFETs but probably you should use high-side switches for some or all of those devices. It's not necessary for something like a non-addressable LED or a motor, but ...
• 408k
Accepted

### Common N-channel mosfet for multiple voltages

No. Connecting the three loads together like this will drive current backwards through the lower-voltage ones. You might be able to make this work by adding one diode per load, but it'd be better to ...
• 35.3k

### Troubleshoot Simple MOSFET switching circuit (automotive 12V - 5A)

I am concerned about these two parts of your circuit: My question: How is GND connected to CGND? Assuming the issues with GND and CGND are sorted, then the next issue is how the buck converter is ...
• 5,452

### Confusion regarding driving a MOSFET through optoisolator

As mentioned, the rise time isn't very important, and gate current only flows during transition (gate is a capacitor, and I = C dV/dt). This can simply be whatever current the opto is capable of, and ...
• 39.9k
1 vote

### Why do trench MOSFETs typically have a narrower FBSOA than planar MOSFETs?

Realize that all MOSFETs have negative tempco of Vgs(th) in linear mode, at least over a significant portion of their operating range. Thermal runaway is a necessary and ever-present characteristic ...
• 39.9k
1 vote
Accepted

### The role of Q33 and the connection of pre-discharge circuit in the BMS circuit

Here is where the circuit in question lies in relation to the over-all system: Figure 1 (Above). Link for above image: https://www.ti.com/lit/df/tidmb13/tidmb13.pdf?ts=1721547693534 The two MOSFETs ...
• 5,452
1 vote

### How is junction-to-ambient temperature measured?

There are a bunch of assumptions, often not stated or hard to find. For example, with diodes they may make assumptions about lead length, copper pads and type of board. The loss down the leads can be ...
• 408k

### Finding relationship between saturation current and Vgs for MOSFET?

There's never a guarantee that a certain amount of current will flow, given some particular $V_{GS}$, because it varies so much even between devices from the same batch. Even if a datasheet does ...
• 39.2k
Accepted

### Strange Behavior with Soft Latching Power Circuit: LED Inconsistently Staying On

Switch bounce is likely to cause MCU power to switch rapidly on and off, and no doubt this will wreak havoc with the reset circuitry inside the MCU. It's probably crashing. You absolutely must ...
• 39.2k

### Strange Behavior with Soft Latching Power Circuit: LED Inconsistently Staying On

Try adding a short ground wire from distribution to the microprocessor GND pin with minimum length [below drawn in black], place ceramic 0.1uF capacitor across the VCC and Ground pins [as drawn in ...
• 345
1 vote

### Switching ON/OFF an ADC line

Well, there's a couple possibilities: Don't care. If the input currents are small enough, there's no wear on the ESD clamp diodes*, and VCC lifts imperceptibly against the normal loads on it (MCU ...
• 39.9k

### Switching ON/OFF an ADC line

which electronic component could one use to switch ON/OFF several external lines for ADC? Analog switches and multiplexers come to mind, most designs have two parallel mosfets, one pmos and one nmos ...
• 85k
Accepted

### Why is the MOSFET in this fan control circuit overheating?

It looks like you have an N-channel MOSFET operating as a "source-follower", otherwise known as "common-drain". That means the source is always a few volts lower than the gate (by ...
• 39.2k

### Why is the MOSFET in this fan control circuit overheating?

The problem is you have the fan in the wrong spot - your MOSFET is operating in its ohmic region. To correct your circuit, tie the source of the MOSFET to ground. And put the fan between the Key ...
• 4,983
Accepted

### Replacing the BJT in the current limiting circuit with a MOSFET

Yes this should work without issue in the present case. Note that the transistor will dissipate up to around 10 W in a short circuit case, so good heat sinking is mandatory. The difference is that ...
• 22.5k

### MOSFET or relay for controlling a PC fan?

Update: I measured the running current and it was a little over 60 mA. Going with the assumption that the start current is 3x the running current, it's pushing the limit of 200 mA. So I did end up ...

### How to know what size diode to use for inductive spiking?

The diode needs to be able to handle the current that is flowing through the inductor when the transistor is conducting. This is because the current through an inductor can't change abruptly. However ...
• 3,446

### How to know what size diode to use for inductive spiking?

You really should look into Transorbs for this, acronym TSB. Although they have a power ratings, they are designed for short duration surge events. Incidentally they are available in both unipolar ...
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1 vote

### Designing battery voltage measurement with passive balancing

If you use a P-FET to switch the bleeder current, you don't need an additional supply voltage at the high side. Just pulling the gate down to GND would exceed the maximum gate voltage, so I added a ...
• 7,395
Accepted

### Designing battery voltage measurement with passive balancing

You could use opt-isolators to switch them something like this: This would allow each one to be isolated from the micro circuit (R5 is just so LTspice doesn't complain). Each one would use the ...
• 25.1k
Accepted

### Transformer-coupled MOSFET gate drive circuits

However, how does the capacitor reduces the outpus pulse by Vc ? You are feeding a single-ended pulse train (0-VDRV). You can think of this as the sum of a DC offset and an AC pulse train: Since you ...
• 36.4k
1 vote

### Transformer-coupled MOSFET gate drive circuits

First schematic: After few periods the Vc becomes stable at some value Vc. If duty is 50% the primary has equal positive and negative voltage levels. If the duty is different the Vc gets steady at ...
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### Transformer-coupled MOSFET gate drive circuits

The figure is for single ended drive. This means you will have 0-10V (or something) and thus you will have a DC voltage across your transformer. This will saturate the transformer, at any duty cycle ...
• 153
1 vote

### Chip Identification - SAW part marking

It is a BSS123 from Nexperia. Marking information: (% is the assembly location code, W in your case and 22 is a datecode) Picture from lcsc:
• 1,148
Accepted

### Best method to dampen inductive spiking from pulsing coil with MOSFET?

You have some element connected across the coil, the purpose of which will be to receive the coil's energy. Being an inductor, the coil will decide current $I$; it will be whatever current was ...
• 39.2k

### Best method to dampen inductive spiking from pulsing coil with MOSFET?

You are mixing up some equivalent solutions. To collapse the current quickly you need to allow a high reverse voltage across the inductor. A simple diode only allows 0.7 V. A zener from D-S allows ...
• 19.4k
Accepted

### Unable to use a MOSFET to connect two capacitors in series

The transistor has no DC bias. The source and drain need a path for DC current but the capacitors block DC. You could add some resistors across the capacitors to bias the transistor. The resistor ...
• 25.1k

### Switching 3.3V with 3.3V signal

Something like this should work for you: simulate this circuit – Schematic created using CircuitLab You should drive the outputs from the ESP32 low before turning off the module and make sure ...
• 408k

### Switching 3.3V with 3.3V signal

It looks like you are trying to use an N-channel mosfet as a high-side switch, which cannot work unless you have a gate voltage above the 'controlled' voltage. So using 5V works as you have found. If ...
• 521
1 vote
Accepted

### Switching 3.3V with 3.3V signal

For MOSFET switching applications, the source terminal should be connected to the "switched" rail, i.e. the positive supply for P-channel and ground for N-channel; yours is backwards. ...
• 20.4k

### How can I slow down the rise and fall time of a power MOSFET without adding a delay before the switching begins?

No, you cannot. That's simply logically impossible: you want an N ms rise time. Because the rise can't start before you press the button (otherwise, your circuit would need clairvoyance) the rise can ...
• 96.9k

### Why does a MOSFET fail on fast signals, even if they're much longer than the turn on + turn off times?

While you may not have drawn a resistor in series with V2, the mosfet model most certainly contains one. See LTSPICE wiki: https://ltwiki.org/LTspiceHelp/LTspiceHelp/M_MOSFET.htm which in the table ...
• 153

### IGBT with double emitter

That's a standard (if perhaps less common today?) IGBT symbol. The collector part implies the emitter of the internal PNP structure; gate and dashed base/body, the MOSFET structure; and the, I think, ...
• 39.9k

### MOSFET Datasheet Confusion

The second graph you showed is annotated with $I_D=31A$, which is well beyond your own requirement, and only represents behaviour along that line on the $I_D$ vs. $V_{DS}$: The graph of \\$R_{DS(...
• 39.2k

### MOSFET Datasheet Confusion

Based on a comment I assume 100mA is required when the solenoid is energized. I am having a hard time reconciling all that info. Feels like each one contradicts the others. Would someone please help ...
• 17k

### MOSFET Datasheet Confusion

Instead of playing roulette with uncertainties and variability of bare MOSFETS, you can use an industrial-grade solution called "power distribution switches and load drivers", check, for ...
• 41.1k
Accepted

### MOSFET Datasheet Confusion

For one thing, these graphs are typical values, not guaranteed values. Threshold voltage is one of the more variable parameters in a FET, and it's not unusual for it to differ by hundreds of mV ...
• 35.3k

### Two P-Channel MOSFETs for battery disconnection during charging

That should work as long as the MOSFETs are fully turned on by the battery voltage (Vgs in data sheet for the Rds(on) value). Not sure it makes a difference but normally the two MOSFETs are connected ...
Accepted

### Identify IC marking LCSZ

It's an Analog Devices LTC3563EDC step-down converter. (Source: lcsc.com)
• 5,947
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### MOSFET switch unreliable

The MOSFET gate is not connected to the resistors. The red circle marks the issue. There may be a weak connection with very high resistance, that provides partial functionality. The intended ...
• 7,395
1 vote

### Understanding taser circuit with MOSFET and push pull transformer

This is not a push pull voltage converter. The topology is called flyback. The integrated simulator CircuitLab can at least show the operation of the first part of your schematic. The MOSTFET gate ...
• 7,395

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