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108 Threads found on Fet Switching
Most often the chosen frequency is not limited by the fet's own capability, but outcome tradeoffs like the switching losses you can stand, EMI, available external components and the BOM cost thereof. Often MOSfet selection is done to optimize the efficiency and cost, without regard to the ultimate cutoff frequency or the like. A rough (...)
The "problem" is that even if the fet turns off instantly, the rise time of VDS will be determined by its drain source capacitance (Coss) and the load current. If your load is just a 1K resistor, this will result in a fairly slow rise time of VDS. You need to increase the load current greatly to see the true switching times of the fet. (...)
i don't think that will make difference No big difference. But you should analyze the switching behavior (fet current and voltage) to be sure that the circuit doesn't involve additional switching losses, due to diode reverse recovery, slow switching caused by unsuitable gate signals or whatsoever.
Because dynamic current does flow through the gate to charge and discharge the gate capacitance when the MOSfet switches. So a low gate poly resistance will reduce the gate charge and discharge time, increasing the maximum operating switching speed of the transistor.
As Klaus says, Burst mode is often seen in pwm controllers which are controlling a power supply which has gone into light load?(often called ?low power burst mode?)?in light load, you don?t want to keep switching the fet on and off, as it results in too-large switching losses, so what you do instead , is you just have the controller pulsing (...)
when I am using the HCPL3120 for driving the high side (cascaded BUCk+Boost converter for high voltage around 600V) fet, there is dip in the gate drive supply voltage and negative current flowing through to gate drive supply during the switching period. please someone help me, thank you127638
Hi, I am working on this Infineon IC ICL8201, which is an AC/DC Buck Controller with PFC for LED Lamps. Here is a ref design for the IC. 127563 I quote from the datasheet, "art 4.2.3. In it's normal regulation operation, power MOSfet is turned on by valley detection through DRAIN pin, is turned off by con
Hello, Have you ever seen a sync buck controller that does not have the facility to detect overly high reverse current flow in the synchronous fet?
ZCS converter is like many DCM converters, where the fet current is zero at the point that the fet is switched on. ZVS , is like in the Quasi resonant flyback where you have ?valley detection?, so that you switch the fet on at the point where its voltage is zero and avoid Cds capacitive switching loss??however, its not (...)
I picked one igbt from mouser with 600 V voltage and 11 A current rating. The IGBT is optimized for 40 kHz and could be ok for SMPS but I don't know if it is better choice than mosfet. Saying this iGBT is "optimized for 40 kHz" somehow abridges the facts. I think you would better say it can be operated up to 40 kHz under circumstanc
Hello, In Full Bridge SMPS type converters, why do people use pulse transformers on the bottom fet drives as well as the hi side fet drives? I mean, presumably its so that the propagation delay of the switching signal is equal for both top and bottom fets, but isn?t this pointless? The 70ns or so delay is too short to be of any
What's the highest switching frequency that the method of page 12, figure 4 (datasheet below) can be used for? This is with reference to a full bridge LLC converter with vin = 400VDC. The actual signal to drive the fet drive ic is coupled up to the hi-side via a pulse transformer. 1EDI60N datasheet
any calculation of fet switching losses will be subject to considerable error. There are a huge number of factors involved. The following by Balogh though, summarises the process of calculation. As you can see from Balogh document, there is a turn-on switching loss associated with the gate voltage rising from Vth to Vgs(miller)?this (...)
what are the switching conditions for fetIn short words: The driver need to have enough peak current to quickly charge the gate capacitance, the supplied voltage to gate has to be higher than VTH.
Hi, ..and you can also use a Pchannel fet for highside switching, then you don`t need a charge pump. *** N-Ch fets are more common and easy to drive. There are logic level MOSfetS that can be directely driven by a 5V or even 3.3V logic output. But in cars you have a common "minus" system. All the chassis is connected to (...)
As you connect the secondary, can you confirm what waveform the mosfets produce at that moment? Is it narrow pulses (narrow duty cycle)? Or do they conduct continually so that they burn up?
..more than .. just a guess MARKING CODE LIST P(2) * , ** , *** , ****,_=date code,Lot No. etc. PM RTL035N03 ROHM - TUMT6 6 2.5V drive N-ch MOS fet for symbol : PM - - - Upda
Even if you want the negative output voltage, the simple non-isolated buckboost still has some unique disadvantages. First, if you want to use an N channel fet, its source will be at the switching node, and must swing above and below ground. One trick to deal with this is to reference your whole control IC to the switching node (though then (...)
For the first look, this MP3 fet is used to preventing cut-off of a MP2 when the output is in low state. Yes, apparently a clamp circuit for the MN3/MP2 drain node to speed up comparator switching.
Try getting the caps across the fet H bridge as close as possible, and up the C to 1uF on all the power pins on the IC, shortest leads possible. Failing that try some gate turn on resistors to limit dv/dt at turn on and if needed snubbers across the fets.
Hi, You could use the 9v signal to control a MOS fet transistor Gate via diode into a 3 sec Res/Cap time out, the relay would be in the Drain of the MOSfet. Do you follow that OK.? E EDIT: This is one option, the LTSpice sim shows the level switch Opening but the relay remains energised for ~1 second, to increase the
fets have voltage controlled resistance with a threshold effect determined by geometry and fab this has improved over the decades in Enhancement mode MOSfets standardized from 4.5V to 2.5 ... to 400mV for LVC2 logic level drive. High Threshold CMOS such as HCMOS series has a wide Vdd range and
Hi, I have a new system developed using 5 SPI devices and am having major issues with it. After a large amount of testing over the past number of weeks the issue appears to be a brand new ST chip that is not setting its SDO line to high impedance when it has been De-Selected. It is always holding the line preventing any other chips controlling t
106608 Hi there! I have an op amp acting as a comparator (which might not be too ideal) comparing ground and an inverted signal from a coil that, when nothing magnetic is moving near it, is pretty close to ground (?1mV or so). I'm using this comparator (Vcc=7.4V from the +ve terminal of a battery, Vee=-7.4V from the 76
When the fet switches on it draws some current through the snubber Cap (limited by its series resistoor), so the fet dissipation does increase,though not by much. Frank
I'd start with estimating your worst case charge per cycle (you know t, you know a (rated) static Icc for the driver so there's that; probably know Qgg for your fet; have to take a guess at how much of a switching impulse pair's charge you have to make up). Now figure out what kind of droop you can stand across max on time (dV) and C=Qsum/dV. Now
transistor or fet or MOSfet in common-emitter mode between the switch and power MOSFT
Can I use an RF MOSfet in switching application? I need to turn on and off about 200mA current at a rate of 100MHz. Can I use an RF MOSfet for this? Those fets that are marketed as switching fets have turn on and turn off times in the range of 20ns or much more. To be able to nicely (...)
The diode is used as a protective element for the MOSfet. It is called a freewheeling diode which is used to protect the fet from any transient voltages that are generated across it when the fet is involved in switching any inductances. While normal conduction, this diode remains reverse biased. When the (...)
Hello, The Active clamp forward can certainly be arranged to have zero switch_on switching loss (by suitable sizing of the leakage inductance). Since at switch off, much of the fet drain current is diverted into the clamp capacitor, (ie rather than it going through the drain_source of the fet) can we also say that the switch_off (...)
In a high side driver configuration consisting of a P-type fet for the pass function and an N-type fet for the switching function, how do I calculate the value of the pull-up resistor which connects the gate of the pass transistor to the source (input supply)?
A car battery is at least 12V, meaning you have a decent voltage to drive a fet on why do pwm controllers like TLE8386 only have 5V fet drive.?....fet switching losses are far worse with such low voltage gate drive.....I know car batteries go down to 6v when cold cranking, but thats just a short transient condition. (...)
The easiest way is to use the motor as the drain load on a switching fet, and put PWM on its gate. Frank
That's a fine technique for doing it. The fet is not switching, it's biased in its saturation region so it will act like a linearly controlled voltage source. It will probably dissipate a large amount of power at 10A, so make sure it is a large device with a good heatsink. Also to do the measurement you only want to look at the component of the wa
Hello, The switching loss of a DCM flyback is virtually zero at turn on (because theres no current flowing)...........however, it has high switching loss at turn off.......supposing I add an RCD snubber to the fet...............can I confirm that this doesn't make for overall efficiency increase, but does make dissipation in the (...)
I don't believe that it actually helps in loss estimation, but we would refer to ideal fet characteristic gm ~ √Id in case of doubt.
You'll find that the typical leakage current of small logic level MOSfets like Si2301 is below 0.1 ?A, but unfortunately the guaranteed (maximum) value is considerably higher. It's essentially the same with MCU idle current.
Hi unipolar motors are easy to drive the center taps of the coils go to the supply voltage. the coils can then be pulled to GND using a fet. you will need 4 fet's in total one for each coil. Don't for get to add diodes across the cols to help with back EMF from the switching. If you need more help let me know.
You could make it work but you have left out the DC biassing components. A better starting place would be to use a fet or a digital transmission gate (4066) Frank
From both, because will be an avalanche failure. Initially will be a breakdown followed by temperature degradation. Is a common failure for fets used in switching power supplies.
By design, the fet switches are shorting the input signal to the trigger circuit. I don't believe that the circuit can work without basic changes.
Hi, What are the basic difference in application of BJT,fet,MOSfet and IGBT.... i.e; for example all this are used for switching applications but in some circuits BJT wont work but a MOSfet will... also i would like to know the pros and cons for each if used in different situations.... Thanks Hi demetal A (...)
I don't think it will work. When a switch is open, the related fet gates are "floating" at an indeterminate voltage. I don't think you can guarantee that they will all turn off. There may be other problems but I didn't bother to look further than this.
I am designing a two transistor forward converter where the upper fet is driven by a pulse transformer, (fron the controller's gate drive output) but the lower fet is driven on straight from the controller's gate drive output , with no pulse transformer. ........because of leakage in the pulse transformer (its too expensive too wind for the su
is this too short a time for a fet to be on? No, but transistor switching times and related switching losses are giving a practical lower limit.
HI; i want to measure the wattage of my own designed power supply That i've designed usign 4 LM338 ICs in parallel. moreover how can i find the wattage/VA of different powersupplies/Invertors/UPSes that use Transistors or MOSfets in parallel. is it enough that i just add the given wattage in the Datasheets of the components to get the total wat
Hi, I need Transistors to replace these relays in the attached schematic. fets for RL1, RL2 and RL3 and one poles of RL4 need to be extremely low stray capacitance if possible. Currents for RL4 would not exceed 100mA and the others not more than 5mA. I need to stick to TO-92 if possible please. Can you recommend some transistors and configurat
a simple fet amp has a very high gain v can get volts from micro volts in put and use bridge rectifier or diode and capacitor instead of speaker ..checkout "sch_ZCA.png" at this link
If you put a stiff gate drive on any fet, the Cgso & Cgdo, and the gate-channel capacitance (which partitions to D, S) all are shunt losses. If you take a hint from CMOS and fet / HEMT RF switches and isolate the gate with a resistor, this is much improved and you are left with the Ron (insertion loss) and Coff (isolation) if the bulk parasitics a
For paralleling fets or IGBTs, you have to look at the characteristics of the specific device, and its operating point. Many fets can't be paralleled due to a high negative coefficient of Vth, or a negative Rdson coefficient. switching losses pretty much always have a positive temperature coefficient, so watch out at high frequency (...)