Mosfet Driver

Discussion in 'The Projects Forum' started by capjam38, Sep 30, 2010.

  1. capjam38

    Thread Starter New Member

    Sep 30, 2010
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    I have a circuit where I want to replace the relays with Mosfet's. It is an H-Bridge design. I have chosen a mosfet to act as a switch, the IRL3803VPbf, which works perfectly. However, I have a gate driver that I cannot get to work correctly. The IXDN430 chip has a schematic on the pdf that simply says put VCC to 18V, Gnd to Gnd, Tie Enable high, then you have your input and output. My input is a sqaure wave from the function generator for testing purposes, and my output goes straight to my mosfet switch, which is tied to a LED to test the circuit switch. Everytime the driver is hooked up it draws a large amount of current and burns up. Does anyone have any ideas or a example circuit using a simliiar gate driver and mosfet switch?
     
  2. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Post the circuit you are using. John
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    Did you know that the IXDN430 is a low-side gate driver?

    You need a high-side gate driver for the upper two MOSFETs.
     
  4. capjam38

    Thread Starter New Member

    Sep 30, 2010
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    1. The diagram for the circuit can be found in the IXDN430 pdf. It is the characteristics Test Diagram. All I do then is hook the output up to the gate of my mosfet, and the input goes to a function generator supplying a square wave with a frequency that should be seen by the human eye. Then my LED is tied to the drain, to Vcc, and source is grounded.

    2. I have noticed the difference between high side and low side between the mosfets. I have never actually used a driver before (maybe explain the use, as far as I see it is more of a protection component for the mosfet). Is there any way I can still use these two chips, or would it be wise to look into a new gate driver. Or on the other hand would you think that I even need the gate driver. As said this is to replace a relay in a circuit.
     
  5. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    OK, I took the time, went to the actual datasheet and could not find any example where that chip is being used to drive an H-bridge.

    I suspected, as did SgtWookie, that you were trying to drive the top mosfets with the same chip. It won't work.

    Now, maybe you will take the time to actually show your schematic. You will get out of these forums much more than you put in, but you do have to add some of your own effort.

    John
     
  6. capjam38

    Thread Starter New Member

    Sep 30, 2010
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    I do appreciate your help, but being "smart" to me will not help. I cannot post the schematic for what I am doing because of classified reasons, I was merely coming here to ask about a gate driver or if anyone has ever used/has a schematic or an example for what they did. As I meantioned before I told you exactly how I am testing my circuit. I am using their characteristics test diagram and merely hooking it up to a mosfet (1 mosfet) to test and see if it will work correctly. I have not moved to my circuit yet, I am still in the testing phase, which is another reason I cannot post a schematic. I simply needed insite, and for that I am greatful. Now if anyone else has any suggestions on what a gate driver is supposed to do, I would be greatful.
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    He's really not trying to "be smart" with you.

    The posting of a schematic diagram is considered to be a vital tool towards eliminating ambiguities. Without such documentation, all we can do is make guesses. Frankly, I don't like guessing, because the probability is all too high that I'll be wrong, and everyone will wind up wasting time on a wild goose chase.

    If you are trying to breadboard or prototype your circuit using long interconnecting wires (more than an inch) you risk "ringing" due to the inductance of the wiring. All I can do is assume that you are powering the circuit with 18v. If the rise/fall times are very short, you will most likely exceed the +/-20v limit for Vgs, which will destroy either the gate driver or the MOSFETs that you are attempting to drive.

    You may find that the MOSFET in your test setup has already been destroyed due to static or excessive Vgs. Connect a 10k resistor from the gate to the source terminal, and measure the resistance from the drain to the gate (should be nearly infinite or open) and the gate to the source (should measure 10k due to the resistor).

    A typical failure mode is for the gate to short to the drain. This would quickly destroy your gate driver due to excessive current.
     
  8. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    You failed to start your story with ..... this is no $hit.

    You could have posted a schematic with the spec'd load, then you wouldn't have to tell the tale of "classified work". I did enjoy the laugh though.

    If I told you the load was 2.75 -j 18 ... do you know what the load is?
     
  9. beenthere

    Retired Moderator

    Apr 20, 2004
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    Before this gets out of hand, it would probably be a good idea to remind the OP that the AAC forums are public in nature. Persons with questions or who need advice should realize that it is usual to post the schematic of the circuit in question in order to get good answers/advice.

    If the FET is merely replacing a relay, the need for an H bridge setup is odd. The relay completes or opens a circuit. If the FET is in circuit with the source grounded, raising the gate to between 10 & 16 volts above ground will switch the device on. If it's in circuit with a resistance in the source line, then a driver has to be used in order to keep the gat at least 10 volts more positive than the source.

    Something has to be incorrect if the driver keeps burning up. Is the FET okay?
     
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