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Registered Member #258
Joined: Sun Feb 26 2006, 03:58PM
Location:
Posts: 21
Hi everyone,
I have a newbie question regarding Mosfet driver TC4422. Currently using 555 PWM setup to feed signals to TC4422 which drives a IRFP460. I noticed the waveform for the shutdown portion did not completely went down to 0V, but instead hovers around 2.47V. If I connect the Mosfet Gate directly to the output of 555 (pin 3) the off is at 0V. What's wrong ?
Registered Member #1024
Joined: Sun Sept 23 2007, 10:56AM
Location: Northern NSW, Australia
Posts: 95
Mmm, nope thats not right. Do you have another TC4422 you can substitute to see if its the actual chip thats fried? Can you post a pic / schematic of your circuit? My guess is either your TC4422 is fried, or for some reason the ground at the driver out is floating above the ground you are measuring from.
Registered Member #258
Joined: Sun Feb 26 2006, 03:58PM
Location:
Posts: 21
Hi Dylan,
Thanks for the feedback. I did tried a different TC4422 but still getting the same waveform. I included the current schematic for my 555 driver, the waveform shown on the schematic is taken at those two blue points. As you can see the turn off did not fully shut down to 0v.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
Dylan wrote ...
Remove the 100 Ohm resistor , and simply connect the gnd pins of the driver directly to ground.
Yep, i have to second(or actually third) this. I guess at higher frequency, resistance becomes more noticeable, for instance, in a sstc you want small wires for low inductance and resistance and good connections for very low resistance. Makes sense to me.
Registered Member #540
Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969
I would think that you would need short wires to minimize stray inductance. Also, you would need good connections at the place where high current is flowing because if there is a poor connection, the will be a lot of power dissipated at that connection.
Registered Member #258
Joined: Sun Feb 26 2006, 03:58PM
Location:
Posts: 21
ITWORKS NOW! Thanks a lot guys especially Dylan
The rise and fall waveform generated by TC4422 seems to be taking a longer period (sloped) compared with pulses from a 555. Why is it a better mosfet driver ?
Registered Member #989
Joined: Sat Sept 08 2007, 02:15AM
Location: São Paulo, Brazil
Posts: 476
As the frequency increases, the current at gate increases too (think about the gate-source as a capacitor, and the driver charging and discharging it, as high frequency, more current flows) after some frequency the 555 cannot supply more current, and it doesnt "discharge" the mosfet gate complete, or charge it. So the mosfet only will be half turned on, the RDS on increases, the heat dissipation too, and the 555 will suffer more current.
With mosfet driver, it can handle 6A (compared that 555 that can handle a few mA) that is better to driving mosfets gates.
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TC4422 driver waveform
Thanks a lot guys especially Dylan 