Here is my circuits, simple, yet, when I disconnect the MOSFET and load from the circuits, the waveform, duty cycle, amplitude, everything else is correct. After I connect the mosfet and load (here I didn't use a laser diode, in stead I use a 1 ohm power resistor), all 're in a messy! MOSFET is hot coz it's not fully on, square wave form contains a lot of ringing, overshoot, duty cycle? no duty cycle but some weired square waves with spikes.
It is a very common circuits but I wonder something wrong?
A gate resistor is not always needed, but it seems more likely there is not enough bypass capacitance on the driver circuit. When the driver tries to turn on, it needs to get its current from a voltage source that can handle a high speed pulse. The driver should be bypassed with a low ESR capacitor at least 10x the MOSFET gate capacitance. Also, the gate drive and return tracks should be very short.
The source resistor shown in the schematic should be of low inductance, and careful consideration must be given to the ground path for the high current output. It is not even clear why the source resistor is present, unless it is used for desaturation detection or current mode PWM.
Please provide the entire circuit, including details on what sort of power supply is being used, and a PCB layout or sketch of wiring if it is on a protoboard.
There is good information on high speed circuit design in a Linear Technology app note AN47. It is more about amplifiers, but applies to this as well. And AN25, "Switching regulators for poets". Also look at International Rectifier app note AN-944 on gate charge and drivers for MOSFETs.
now it's an open loop circuits. the 0.015 is for further close loop circuits use. even I remove 0.015 ohm res the problem is still there. I did it on bread board. I think it is caused by the inductance of load, power supply wires. I don't know how to solve it. I added some big capacitors between vcc and ground, I use separate power supply for that mosfet, it didn't improve too much.
Just a 0.1 uF or so bypass capacitor directly across the driver power terminals should help a lot (like you said, decoupling). Also the connection to the gate and back to the ground pin should be reasonably short. I have a circuit that uses a Fairchild HUF75645 which is almost as beastly as the IRL3803, and I have driven it up to at least 300 kHz with an inductive load without problems, using a TI 9 amp driver. UCC27321. And my first prototype on a perfboard was OK at 100 kHz.
The IRL2803 has 5000 pF gate capacitance, but it has 230 nSec rise time, so a super fast gate driver is not really necessary. A 9 amp driver can provide about 1.8 V/nSec, and realistically about 20 nSec to full on, but the device itself will take ten times that to conduct fully.
There is an app note on the UCC35705 that is used to provide the PWM signal:
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This is a 4 MHz part, which may be overkill for the application (or at least the MOSFET). More information is really needed, such as supply voltage and drive frequency.
That's with just 4.5 volts of gate drive (Fig 10a. in the datasheet) through a 1.3 ohm gate resistor, but 12v and a hot driver could do the job much faster.
You can do a lot on a smart perfboard. The OP's "breadboard" though clearly isn't cutting it, so recommending a groundplane makes up for a lot.
It all comes down to what the OP is doing, which he hasn't told us.
If he's trying to get 15nS pulses from a laser diode with this setup...
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