New answers tagged

1 vote
Accepted

Switching losses in a power supply

The transformer will indeed present as an inductive load (two of them, actually) to whatever is driving the primary. if there is a resistive load across the secondary, then there will also be a ...
user avatar
  • 25.9k
24 votes
Accepted

Why does my MOSFET always burn?

It looks like you have two problems here. Your steady state losses are excessive; you say there's no heatsink, but 1.5 W (incidentally, your current of 1.5 A will actually result in a power loss of ...
user avatar
  • 19.3k
12 votes

Why does my MOSFET always burn?

Do you have any cooling or heatsink on the MOSFET? The on resistance of the MOSFET will cause it to dissipate ~500-600mW of heat. The MOSFET has a thermal resistance of junction to ambient of about ...
user avatar
  • 25.9k
5 votes

Why does my MOSFET always burn?

If one changes the optocoupler, it can be "better" ... And adding a resistor (base Opto to ground) ... one can see the drastic diminution of the power dissipated by MOSFET ( from 26 W to ~3 ...
user avatar
  • 3,846
0 votes
Accepted

How to switch a SIM800L modem on/off with an ESP32-CAM, without a relay?

The problem with the IRF530N was that its gate voltage is too high (~4v) for the ESP32 pin signal (3.3v) to open it. I replaced it with an IRLZ24NPBF, the datasheet says Vgs 2v. This FET did open with ...
user avatar
  • 109
2 votes

How to make a MHz-fast, 5 volt thyristor with discrete components?

Yes, you can. It will be as fast as the BJTs you use. You can replace D1 with a resistor. The choice for the resistors gives a tradeoff between turn-on ease and turn-off delay. Turn-off is limited by ...
user avatar
  • 12.5k
0 votes
Accepted

How to make a MHz-fast, 5 volt thyristor with discrete components?

" Is it possible to emulate thyristor behavior at Mhz speeds? Not likely. But it can make a perfect set only latch. Maybe with the right transistor geometry in the same package that can ...
user avatar
2 votes

How to make a MHz-fast, 5 volt thyristor with discrete components?

Your BJT thrystor will be faster than a bought one .But the need for PNP and NPN will make high power/High voltage not good .One way to make it faster is to employ a baker clamp or similiar scheme to ...
user avatar
  • 12.4k
1 vote

Efficiently limit current to LED without power loss

From what I understand of this circuit is that when the voltage of R3 exceeds the voltage that is required to turn on Q1, the gate of Q2 will be pulled to GND and the Q2 will be turned off. Hence, ...
user avatar
0 votes

MOSFET Power Switching Circuit

The problem might be the internal drain/source capacitance of the P fet. If you connect your battery, the voltage of the P fet source rises very fast and feeds this delta-U forward to it's source. ...
user avatar
  • 418
1 vote

MOSFET circuit to trigger timer. Any additional safety additions to circuit required?

You have a MOSFET IRFZ44N capable of pulsed drain current of 160A. I don't think 0.25A inrush is of any concern. In any case, you're switching the START input, not the power supply, which draws ...
user avatar
2 votes

Using the WS2811 as a vibration motor control

The current the WS2811 sinks is around 16.5mA (15.5mA minimum). PWM frequency is said to be > 2kHz. Probably there is only a sink, no pull-up. Try this: simulate this circuit – Schematic ...
user avatar
1 vote
Accepted

Formula to calc Id of this IRF3205 in the linear region from this specific voltage measure point

The current in each MOSFET is the voltage across the source resistor divided by the value of the resistor. It is assumed that the gate current is negligible. In the schematic shown the source resistor ...
user avatar
  • 29.1k
3 votes
Accepted

How to prevent LED strip from flashing at full brightness when the ESP32 boots

According to Adafruit documentation, the pin "A0" is pulled up with 10k resistor onboard the PCB. According to Adaruit documentation, they don't seem to even know why ESP32 documentation ...
user avatar
  • 87.3k
5 votes

Paralleling two MOSFET Solid State Relays

This works fine. You put the LEDs in series and the output switches in parallel. That also means that you control them as if it were a single switch eventually.
user avatar
  • 10.2k
3 votes

Paralleling two MOSFET Solid State Relays

Can I drive both devices through the one gate-drive resistor? If you mean opto driven gates, YES, by putting the LEDS in series and reducing the R value for the remaining R voltage drop and desired ...
user avatar
1 vote

How to prevent LED strip from flashing at full brightness when the ESP32 boots

The pins are likely initialized to a floating, high impedance state. A floating MOSFET gate can pick up charge and spontaneously "turn on." A pull-down resistor on the gate would prevent ...
user avatar
8 votes

Paralleling two MOSFET Solid State Relays

Gate resistors do not apply at all. It does not apply because you do not have direct access to the MOSFET gate in an opto (or an SSR). You're driving an LED, not the MOSFET gate. That said, LEDs still ...
user avatar
  • 46.3k
0 votes

Full wave active rectification for lower voltages?

Threshold voltage. M2 and M4 do not begin to conduct until Vgs exceeds the FETs threshold voltage. This is the minimum gate-source voltage required for conduction at current levels greater than ...
user avatar
  • 12.6k
1 vote

How to switch a SIM800L modem on/off with an ESP32-CAM, without a relay?

The 3.3V from the module is not enough to turn on the IRF530, which has a threshold voltage of 2-4V. 5V should be enough, which gives you options. You could change the IRF530 for another device (BJT,...
user avatar
  • 6,600
0 votes

Motor voltage spike

The motor has considerable inductance (probably some ~mH), so its current cannot be set to zero instantly. An opposite voltage must be applied to cause the current to fall towards zero. This is ...
user avatar
  • 1,035
0 votes

Cascode: Which device goes into triode region first?

My intuition is that the cascode device M2 in saturation has the ability to shield M1 from supply variation, and when looking at former version of question, it seems M2 will go into triode region ...
user avatar
  • 1,702
1 vote

Bulletproof H-Bridge

I've been thinking about a couple of approaches to doing this. The cognoscenti seem to go with stepping up the DC to a high voltage (165V for 120V/60Hz, or 330V for 230V), then using a high-voltage ...
user avatar
  • 40.3k
0 votes

Bulletproof H-Bridge

If the 24V is really 24V, and not automotive 24V than can get a lot higher, I'd use a pair of cheap half-bridge MOSFET drivers with integrated adaptive dead time like NCP5901, ADP3120, ADP3110, etc. ...
user avatar
  • 57.6k
1 vote

Bulletproof H-Bridge

You need to ensure you have non-overlap on the HS and LS FETs in the H-Bridge. With an inductive load, you also need to ensure you have sufficient V rating for your FETs, and also that the VCC and GND ...
user avatar
  • 12.5k
3 votes

Why do logic gates need multiple MOSFETs?

For now I'm interested in learning why the very simple NOT gate (inverter) is designed with 2 CMOSFETs. Just conceptually, not the math of it (if that's possible). Why not just one PMOSFET (P-type ...
user avatar
  • 2,893
6 votes

Why do logic gates need multiple MOSFETs?

For now I'm ignoring the math and the correct terms, and just concentrating on the concepts... The right sequence Indeed, circuits (like everything else in life) are best understood in this sequence -...
user avatar
25 votes
Accepted

Why do logic gates need multiple MOSFETs?

The ‘C’ in ‘CMOS’ means ‘complementary’. CMOS uses both P and N FET types that work with opposite polarity. A CMOS inverter (P source to +V, N source to GND) works much like a single pole double throw ...
user avatar
  • 40.3k
1 vote

Connecting two DC-DC 0-200V SSRs in series

Two solutions come to mind. Either simply get an SSR rated for enough voltage (as your current requirements are unknown, I can't recommend a specific one here, but you can always use the SSR to switch ...
user avatar
  • 19.3k
1 vote

mosfet to protect reverse plarity from a power suply range 10v-18v DC

Use a bridge rectifier, instead.
user avatar
  • 9,907
4 votes

Selecting series resistor for a Zener diode

Your analysis is correct. If the zener is biased with a high resistance, it may regulate at a little lower than the nominal voltage. This means the MOSFET doesn't have as much gate drive and its on-...
user avatar
  • 12.5k
5 votes

Selecting series resistor for a Zener diode

Well, that sound reasonable. Personally, within those constraints I’d probably pick the 10V zener and 1M or less, but I’d check and see what typically happens at low zener current and very high ...
user avatar
0 votes

Could we use holes in an NMOS?

In an NMOS, the source and drain are N diffusions. When a channel (electrons) is formed, you can imagine a continuous conductive sheet is formed between S and D at the top surface of the channel. If ...
user avatar
  • 12.5k
0 votes

Mosfet circuit-function

Looking at that PMOS in the middle top, with f(a,b,c) at its gate, I'm guessing that device doesn't have the same drive as the others, and functions as a "weak holder" ensuring that once ...
user avatar
3 votes

Low Side Parallel MOSFET Drive

This topology will not work for several reasons: It has no back EMF diode clamp The driver impedance is not low in the off state and even with diodes is not sufficiently low compared to this FET to ...
user avatar
3 votes
Accepted

Low Side Parallel MOSFET Drive

You probably want a push pull or totem pole method between OC1 and your power MOSFETs. Direct opto drive might be insufficient for PWM at 50Hz, It certainly would be in I would omit OC1 and only have ...
user avatar
  • 46.3k
0 votes

Rectifier for bike dynamo

A MOSFET bridge as shown won't charge a capacitor since it also allows current to flow in reverse. You can add a Schottky diode at the output, or just replace the bottom 2 MOSFETs with two schottkys. ...
user avatar
  • 12.5k
2 votes
Accepted

Is this IRF9640 MOSFET operating within the recommended temperature as specified by the datasheet and why is it so hot?

I am PWM-ing a 0.85 A current through a coil with a D.C. of 20% and a period of 500 us at 12 V making the power dissipated approx. 10 W. I simulated your circuit in LTspice, adjusting RDSon to match ...
user avatar
  • 51.1k
1 vote
Accepted

Why does MOSFET N back to back switch work?

FETs have a neat party trick: they can conduct in both directions. And, a bias on gate-to-drain will turn on the FET as well as the more customary gate-to-source. In this circuit then, the left-hand ...
user avatar
  • 40.3k
0 votes

Why does MOSFET N back to back switch work?

Because the FET has a reverse diode from S to D, the S of the 'other' FET cannot be more than 0.7 V above that drain. So, the common S node is no higher than the lowest of either drain. Therefore if ...
user avatar
  • 12.5k
1 vote

Why does MOSFET N back to back switch work?

If you read the datasheet, the IC has a charge pump that produces 13.1V above Vout and the common source node never floats more than M2's body diode drop above Vout.
user avatar
  • 46.3k
1 vote
Accepted

All Mosfet terminals internally shorted in voltage controlled resistor

The DAC output voltage was set to 2.39V in order to obtain approximately 6A of current as per the VGS to ID curves. Like this: - So, when 2.39 volts are first applied (at ambient of 25°C) the ...
user avatar
  • 379k
2 votes
Accepted

Could we use holes in an NMOS?

In a N-channel MOSFET with Vgs = 0, there is a depletion region between the source and drain N+ regions and the P-type substrate that is a barrier to current flow. In normal operation with Vgs > 0,...
user avatar
  • 6,600
3 votes

Current source with MOSFET

It is common practice to put a resistor of low value before a MOSFET gate. It is particularly important when the MOSFET is to be switched ON/OFF at high frequency. MOSFET have an input capacitance ...
user avatar
7 votes

Current source with MOSFET

Power MOSFETs have very large input capacitances (thousands of pF). In conduction with the output resistance of the opamp that will cause significant phase delay that would affect the feedback loop to ...
user avatar
  • 29.1k
9 votes
Accepted

Current source with MOSFET

In my understanding the 1K along with the 200pF create an integrator topology to provide some stability Correct and, particularly when using a MOSFET in these configurations there can be a ...
user avatar
  • 379k
3 votes

How does this PNP transistor improve the switching performance of MOSFET?

The transformer load will never be sufficient to reset the primary coil even with R1 set to a 100 ohm value. R1 is redundant when the gate diode and PNP conduct the forward and negative voltage pulse. ...
user avatar
3 votes

How does this PNP transistor improve the switching performance of MOSFET?

The other answers have covered the meat of the questions, however there is one more aspect to call attention to: the right circuit needs a resistor between transformer and base. As shown, the C-B ...
user avatar
  • 1,035
0 votes

How does this PNP transistor improve the switching performance of MOSFET?

To switch the FET on, its gate capacitance must be charged and to switch it off, that capacitance must be discharged. Fig. 2.6 This uses series resistor R2 to limit the current drawn from the ...
user avatar
  • 17.7k
8 votes
Accepted

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 ...
user avatar
  • 379k

Top 50 recent answers are included