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121 Threads found on edaboard.com: Fet Drive Circuit
in battery charger section there is two Mosfets named AO4435 AND AO4409 if i remove the AO4409 MOSfet THEN the charger adapter pin shows me the 18volts reading and if i replace it then it shows 0 volts , and that AO4409 is got shorted I tested it . My question is what is the substitute Mosfet that i can use here and how to solve further (...)
Use a logic MOSfet switch or a semiconductor relay (photocoupler input).
I need to design a drive circuit for a pm2515-03 stepper motor, rated at 5V and 0.5A (Unipolar). I am looking for advice on the best switching device to use for this project. You may either use Mosfets or transistors or dedicated stepper driver Ic's. All are "best switching devices" but depends on your design and requiremnets
You need to hook up a 'scope and look at some things. First off, huge ground currents need to be kept to very tight, short loops. If they can, they will corrupt your analog and possibly digital sections. Among common behaviors from this, is a reswitching or chatter on the fet drive signals, which can suck a lot of current. Second, if y
1/2CV^2 is the energy delivered to the gate, but in the process of charging it through a resistor you will also dissipate 1/2CV^2 (this is independent of the resistor value). Then when turning the fet off, the 1/2CV^2 stored in the gate capacitance will be dissipated in the driver. So your circuit overall consumes CV^2 per switching cycle.
Hi all, I am trying to work out a circuit to drive the windings of a stepper motor. I have done plenty of digging around and know the basics that I can use wither a fet or a Darlington pair to do the power switching. The problem that I am having is working out the power supply and matching it to the motor I have. The motor I have is a (...)
Do you want to test the optocoupler or the fet? And is this an in-circuit detection, or do you want to check components on the bench?
hello friends, I've been using BJT for a long time, #B#C#3#3#7#, #B#C#5#4#8# 2#N#2#2#2#2# and others... but I've no experience in using fet's, could you experienced guys tell me some models that are cheap, easy to find and TO/SMD package available and multi purpose fets? regards, 2000
Hi, u can also use a small fet instead of a bipolar transistor. But as mentioned before: NEVER forget the protection diode antiparallel to the coil in order to avoid damage of the transistor/fet and the PLD. Those ULN-devices are great but if u want to drive only one relais a transistor might be easier and requires less space. One good (...)
Yes it is exactly that. A led (or 2 inverse parallel for AC) on the input side. Use series resistor to supply about 10ma. Output side is photosensitive Transistor/fet/SCR ect, depending on type. Isolation is usually at least 2000v. I you give me more details of what you are trying to achieve, maybe I can assist further.
How accuracy do you need? I don't think 1% is required for LED. At this point of view, a power MOSfet and a adjustable resistor will do the job. adjust the pot till the current reachs 1A. carefully deal with the heat sink issue. the temp may be very high at 48V input. mike ------------------------------ high
The gate drive of SCR will have a low impeadance. The work off of current to drive them not voltage like a fet. You should probably be hitting about 1-1.5 V peak on the gate drive of with the SCR connected. The attached drawing is one that I have done myself. I did neglect to put in all the gate pulses you would get from (...)
I'm using a DTMF Decoder kit from Ramsey Electronics ( ) to sense touch tones from an audio channel. I used it to drive relays to trigger pneumatic solenoid valves. Apparently the EMF from the coil turning off was blowing the big chip in the kit. I have a new circ
It looks like you are trying to build an H-Bridge.See this You need to pull an N-fet gate above the source by at least the data sheet threshold voltage (Vths) usually with a safety margin as well, and you also have to be sure that at the Vgs you are supplying that the Mosf
You need the 555 12v output to drive small N transistor like 2n2222 or N fet 2n7000 The N transistor / N fet connected as inverter driver to power P fet so the 555 12v output will switch on the power P fet on
i think your circuit will meet some problem, if your output voltage will not feedback to adjust the drive signal of the power mosfet
Your mosfet source will allways remain at potential = 28V-Gate threshold of fet - drop across 1E depending upon load current. In turn your load will never see 28V. - if your application / load accepts that there is no problem else there will not be sufficient voltage to drive the load
Hello, I'm having problems with gate drive transformers. My circuit is the test signal (buck_fire_2) i used 250kHz PWM at 50% duty cycle. The output (gate side) is terible; just a sine wave with about 40V amplitude (which probably destroyed my fet). If I lower the frequency the output is
I'm designing a mosfet based single phase inverter using h-bridge I'm using PIC controller to control the mosfets The problem is that even for low duty cycle pulses, the mosfet keeps conducting for a much longer period than it should and at high frequencies (close to 40Hz), one of the high side transistors starts heating up... so.. i (...)
Your circuit will have large turn_on and turn_off times using a 10KΩ resistor in series with the fet gate (because of the gate´s capacitance at transitions), but if it is not a problem it´s OK. I would like suggesting your changing the value to about 100Ω if you need faster transitions. The more voltage on the gate the lower the Rds_on, s
You are expecting to much from this poor MOSfet .. It is not designed to switch at 2MHz (20%) pulses of the duration of 0.1us .. Also, to switch the MOSfet’s gate you need a proper driver (for example complementary emitter follower) and a microcontroller pin is definitely not the one to do so .. Take a look at:
The switching speed of the fet is slow and so there is an extended period where there is voltage across it while current flows through it. This is probably caused by the limited drive current sent to the capacitive gate-source part of the fet. I would suggest that you use and IC specifically designed to drive (...)
Hi, I'm looking for building a custom protection circuit for rechargeable lithium ion polymer batteries. The three protection offered by the standard PCM are : - overcharge voltage - over discharge current - cut-off voltage Assuming, the charge voltage is regulated and controlled by the charger IC, the over discharge current is limited by
I have prepared this on seimens IC TCA785 and power module 26 amp 1200 volts one double diode and double SCR and this works as half bridge. circuit is similer to TCA785 PDF example but with some changes I have used fet IRF540 to drive the SCR. pulse transformers I have build myself. with 2:1 ratio. when i gives 0 to 10 Volts. it (...)
While I was reading the spec sheet, I was having trouble simulating a demo circuit for the LTC4440 (trying to drive a 70 volt high side MOSfet switch). I provided 12 volts input, and drove the logic at 5 volts. I've included the schematic. What am I doing incorrectly?
Hi, I have come up with two cheap fet gate driver circuits for driving the gate of a power mosfet in a switch mode solenoid driver. The PWM signal is provided by the output pin of a microcontroller. The solenoid current is 200mA. The fet Vgs(th) should be between 0.8V and 3.5V (...)
Greetings, I'm working on a video project and I need to reproduce a composite output that matches an existing device (the TMS-9918A if you want to know.) Let me try to be as brief as possible. I am a little confused by the original device's output, which according to the data sheet is: Vwhite: 3.0V Vblack: 2.3V Vsync: 2.0V Test conditi
That's a boost converter not a buck. Also, you need a sensible base drive circuit for the transistor (e.g. A base resistor) and drive it with a voltage with respect to ground, not the output voltage. Maybe you are hoping that will provide feedback but it will just short out the output with the transistor as the output voltage rises. You (...)
Could someone please give me an idea of what could be the problem with my electric golf trolley, the motor when switched on goes on fast speed, with no control from the pot. There are no battery condition lights either. There is one P60NF06 Mosfet, a Shottsky rectifier, 3 transistors S8050x2/S8550, and 1 78L05 regulater. I do realise this is al
I've seen such gate drive circuits used when driving relatively large IGBTs over long leads (like over a foot of twisted pair). That's generally because of the problem you're referring to, with parasitic turn on of devices (which can happen to both low and high side switches). But if your driver circuit has a low impedance (...)
Hi - I'm trying to build a discrete low side fet driver. My plan is to use it to drive a fet as part of a fairly fast DC/DC boost converter (probably switching at 250KHz). Thus I'm looking to minimize rise and fall times on the gate of the fet. Please see the attached LTSpice schematic and simulation (...)
I wish to use the HM42-40002LF gate drive transformer in a two transistor flyback converter at 67KHz ...however, the datasheet doesnt state the value. I cannot understand how i am supposed to work out if it will saturate or not. For my application, i require of T(sw)*12 = 180. (
it will just be a digital output where the load(realy most probably) will be driven using a fet for transistor. the input supply will be from 24 to 60v but we have to implement a limit of .5A at 60V. at other voltages also shortcircuit protection must be there
You are only trying to generate 1 watt. Should be pretty easy to find a modern fet or Transistor that can easily put out that much current (i.e ~ 1 A rms) and do the frequency. My point is if you have a < 1 ohm input impedance, don't use a 50 ohm output impedance amp--if for no other reason that you can not accurately measure the actual anten
Hi, i need to drive a logic level mofet from a LPC1758 microcontroller. For the mosfet i will be using 3.3V is too low so i will need 5V at the gate. As a initial idea i will be using a npn transisor to drive the mosfet. I will get an inverted logic, but that is not a big problem. My doubt is about the (...)
Hi everyone, I'm new on this forum, and i'm hoping for your help! I'm currently working on the design of an ultrasonic sensor. I'm using a 40kHz ultrasonic transceiver (both receive and transmit). The transceiver is driven by a transformer with 1:10 turn ratio. Parallel to the transducer i want to implement a variable resistor with high resis
Hello all, I would like to ask about cell balancing circuit. This is the very simple balancing circuit for a first cell: 72991 I can't test this circuit till I make a PCB. Li-ion battery cells' voltage is 4.2. I'm using a microcontroller (3.3V) to drive this fet. fet is logic (...)
Are you trying to drive the fets directly with the optocoupler, or are the optocouplers driving other gate drive ICs? You should post the actual gate drive schematic. Insufficient current in the isolators can cause several problems. Of most concern is the possibility that the turn off time of each fet (...)
Yes perhaps you should choose another part. 30,000 to choose from
Yes, you can do it. Will the mixer performance be "optimized"? Maybe not. Specifically, the port to port leakage and the spurious signal levels (M x N products) may be different if you drive the IF port with the high power instead of the LO port. Sometimes the only way to tell is to actually test a unit. Similarly, for some applications,
The current limiter circuit forces the fet into linear operation. If the pulse energy dissipated by the fet before supply shutdown exceeds the SOA, the transistor will be damaged. As the capacitor is storing 9 Ws at 300 V, the transistor seems to be predestinated to damage. You may want to clarify the exact control sequence and (...)
A PWM regulator LM2576, Lm2696 could be a solution. --------------- [img
Hello, I am building a battery switch using low side topology, see schematic below. MCU has control lines at logic levels, one to drive Q2 to allow load , the other to drive Q1 to allow charge. If I use logic level gate type Q2 MOSfet, I can drive it directly via MCU line. But I can't figure out how to (...)
Hi dark night, Look at it carefully, And you will see that when the uC outputs a HIGH, that causes the fet to conduct, which means node 3 is at GND potential. This causes the PNP BJT to conduct while at the same time the NPN BJT dosent conduct because the common emitter would be sitting at 0.7V above the base(node 3 which is GND) of the NPN BJT,
Hello! I am biasing fet oscillator with three resistors. After choosing optimal load line and Q point I calculated Rd and Rs values. Additionaly put Rg resistor to "isolate" from voltage ground. I use multimeter to measure Vgs and Vds. When i measure Vgs voltage, it is almost -0.6v (i need -0.3v). Then i discovered that have additional -0.3 vol
Pls check these 2 links.
It's not surprising that the simulation gives different results than reality. The simulation probably assumes not conduction losses in the passive components, and perfect gate drive for the fet. You should at least try and verify that you're getting ZVS or ZCS when expected, so that your fet switching losses are low. Then you can start (...)
A few approaches are viable, such as using a resonant topology (LLC or phase shift bridge converter) or using better fet technology which mitigates the dissipation from hard switching (like GaN fets).
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.
To refer to suitable fet OPs: For a lower supply/output voltage range, OP356 is fine, for higher range OPA656 or THS4631. Only the latter can achieve full 100 MHz power bandwidth, however. For best pulse transmission and higher power bandwidth, I would probably accept the finite input impedance of a bipolar amplifier and adjust the input resista