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# Fet Drive Circuit

121 Threads found on edaboard.com: Fet Drive Circuit

## Toshiba Laptop Power ON and Charger circuit problem.

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 (...)

## FET circuit using a micro to a BJT to a FET? what circuit?

Use a logic MOSfet switch or a semiconductor relay (photocoupler input).

## Stepper motor driver circuit

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

## Inverters built on PIC16F877A, short circuit and very noisy

Hi everybody I about to finish building my sine inverter with carrier frequency 2000hz and output voltage 110 v ac using PIC 16f877A now my problem is when I switch the N channel CMOS fet H bridge suddenly the circuit becomes very noisy and there is a short circuit on power supply. can anybody help me to overcome this short (...)

## Gate Drive CIRCUIT Power loss for switching FET?

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.

## Stepper motor drive circuit design

Stepper motors ratings should be thought of mostly on terms of current. What voltage it takes to achieve that current is almost irrelevant. The rating of 4 V on your motor means that it can take a steady state of 4 V in stopped mode without burning up. But there is nothing wrong with briefly applying 30 V to overcome the inductance and get the c

## Need Testing Circuit for opto coupler A 4504 or HPCL4504

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?

## general purpose switching FET

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

## i want to drive a small relay from PLD device.

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 (...)

## How to drive a triac from a 16c54?

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.

## Accurate 1A current source

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

## My circuit is unable to control dc motor

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 (...)

## Need advice on snubber circuit

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

## Mosfet switch problem

Hi everyone, I want to use some mosfets as switches. I will control them with a microcontroller (3.3V signals). The problem is that in some mosfets the Source is not connected to ground so I am not sure if the Vgs signal will my circuit I have two pairs of switches. Mosfe

## Need to remove a Relay from a timer circuit.

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

## Best Way to Drive FET in SMPS

I'm designing a SMPS and have looked at various circuits. This is actually going to be a battery charger. See attachment; V1 is a 15 V dc supply and V2 is a 200 kHz 5v pp square wave. The load is connected across C2. In the final version, a PIC will replace V2 to drive the fet from one of its PWM outputs and that's the bit I'm having a (...)

## Help me improve my MOSFET drive

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

## Gate drive transformer - oscilations

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

## Mosfet Based Inverter Design

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 (...)

## pull-down for FDV301N N-FET

I have a relay that is driven from a PIC 18F452. It is driven with a FDV301N N-fet. I've put a 10k in series with the uC pin to limit current to the fet. NOW I want to put a pull-down on the pin for when the micro-controller is in reset and the pin is set as input. so I don't want the input to float, So I want to put (...)

## How to drive IR LED using a FET

I wish to pulse an IR LED at 2 MHz and 20% duty cycle. I have an AVR programmed to deliver that frequency and duty cycle. I tried using a 2N3904 but it maxes out around 1MHz. Would a fet be a better way to go? I was looking at a BS170. Any thoughts as to it's suitability? I have never used fets before so selection is kind of foreign to me. Oh ya, I

## Is Driver circuit is necessary for driving mosfet in flyback

hi friends i am trying to design 12V isolated output from 24V constant DC source using flyback configuratiom. i am using ST3524 for pulse generation. operating at 40kHz, switching device is my input is constant i am using openloop configuration to obtain output, no closedloop feedback. I am getting my desi

## LiIon reduced protection circuit

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

## digital control of DC drive using TCA785 IC

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 (...)

## Hi side fet driver (LTC4440) simulation problems

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?

## Discrete FET driver turns off slowly.

i agree with logic level mosfet solution. cheap stuff and fairly reliable and 74C14 will handle most problems associated with connection between power and digital grounds. i used this for a similar circuit you are describing except my frequency was not static as i used the circuit as an "ON/OFF" switch... but otherwise worked great, (...)

## Composite video FET source follower

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

## Lame question-simulating simplest AC/DC+buck converter in PSPICE

Its output is (almost) identical with the input Yes looks like something is significantly wrong! - you put in a PMOS instead of a NMOS fet. It' simply acting as a short between input and output - the circuit won't work with a NMOS fet either, because the gate driver voltage needs to be connected between source and gate (...)

## 12v DC Motor no control

There are no battery condition lights either Ist see if ground connection to the control board is properly connected. There is one P60NF06 Mosfet, a Shottsky rectifier, 3 transistors S8050x2/S8550, and 1 78L05 regulater. First check fet this way. Disconnect motor terminal from fet output and connect a bulb of sam

## Turn off PNP for gate drive with charge-pump high side driver IC?

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 (...)

## How to improve this low side FET driver?

Designing CMOS cicruits from discrete devices would result in a higher component count. An important point in CMOS IC design is to scale the transistor areas of stages appropriately. You'll also have difficulties to find suitable small complementary fets for the input stages. What's your motivation for designing a discrete gate driver? It looks

## Gate drive transformer.....will it saturate?

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. (

## short circuit protection at 60v .5A

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

## How to drive a series LC resonance circuit?

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

## Doubs about best way to drive a logic level mosfet with 3.3V

Consider using something like a quad NOR (parallel as many as you like for drive - 74ACT02 - with the other input being a RC network with C to 5V, R to GND forming a power-on reset / holdoff. The natural state of the dormant uC + pullup (1) will not energize the fet. There may be some elevated Idd on the 5V-operated logic IC but ought to be toler

## voltage controlled resistor

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

## Cell balancing circuit

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 (...)

## effect of optocoupler input signal current on circuit behaviour

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 (...)

## NPN BJT to drive N-channel MOSFET into saturation. How would I do this?

Yes perhaps you should choose another part. 30,000 to choose from

## Help! Intend to use mini-circuit mixer IF as input, Rf as output!

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,

## MOSFET HV switch short circuit behaviour

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 (...)

## DC regulators can't drive car headlight DC bulb... why?

A PWM regulator LM2576, Lm2696 could be a solution.

## dual FET control - how to drive gates?

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 (...)

## gate drive for N-channel mosfet

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,

## FET oscillator biasing confusion. Multimeter shows voltage drop across Rg.

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

## circuit that can drive a AC loaded machine..

the dc derived from mains , is not isolated. thus it would be an issue to drive direct from micro controller. Opto isolator can be used where the diode section would be driven from micro. The output transistor should have separately derived DC from the mains and that can be stepped down to 12V by some zenor and a high value resistor. th

## Problem with Power Converter Circuit

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 (...)

## How to solve the Hard Switching iin the converter circuit?

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).

## plese help me urgently!! unipolar stepper motor driver circuit!!

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.

## Wideband 1Mohm to 50ohm unity gain Amplifier circuit

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