gate driver doesn't work on multisim

[johnsorious]

I'm trying to build a smps but want to simulate it on multisim first before I buy all the components. The buck has a 6.3V dc input and will have a 5V dc output at 2 amps.  I've designed a buck converter and it seems to work when I supply 12V dc with 400kHZ at 83% duty cycle into the gate of the mosfet. I'm trying to get my design with a gate driver but it doesn't seem to work. I put VCC at 12 and put 5V dc at the input (I'm planning on using a microcontroller). For some reason it's not working! I don't have to use a microcontroller but would need some feedback circuitry. 

[johnsold]

I do not have Multisim so I cannot look at your simulation directly.

First, it is much more informative, therefore making it more likely that you will get a helpful answer, if you provide specific information. "...it's not working!" tells us nothing about the kind of problems you are having.  Do you get convergence errors? Does the simulation run but produce results you do not consider realistic? Does your computer go up in smoke?

I have had problems simulating gate drivers. The models may use switches, which can lead to convergence errors.

Other things to consider: SPICE simulators do not like floating nodes.  It may be that the unused inputs or outputs of the driver produce such nodes. Try putting a resistor to ground at each of those points. Similarly, the MOSFET gate could be interpreted as floating, depending on the details of the output circuit in the driver model. A resistor to ground there might help. It is also good design practice to make sure unused inputs and transistor gates have defined states at power up. Those resistors to ground provide that as well.

The driver can switch on ten nanosecond timescales while your regulator is operating at timescales 200 to 4000 times longer. This can lead to either very long simulation times or inaccurate simulation outputs.

Lynn

[johnsorious]

These are the results that I'm getting. I was looking into doing the pwm with a microcontroller but it doesn't output the required voltage I need to drive the gate of the mosfet. In my simulation 12v at the gate seems to work so I was looking into using a gate driver along with a microcontroller. Unless it's easy to do other types of feedback circuit to keep the output voltage at 5v dc. 

[johnsold]

That certainly looks like the MOSFET is never turning on.

At 200 us/division on the oscilloscope it will be hard to see if the driver is doing anything.  Try setting the oscilloscope to show just the first two or three cycles of the 400 kHz clock - 5 to 10 us across the horizontal axis. If the output never goes high, then you need to work on the driver portion of the circuit.  Try disconnecting the gate. Use a 1 nF capacitor and 1 kΩ resistor for the load on the driver. As I mentioned in my previous post, connecting resistors to ground form all the unused pins of the driver may help the simulation.

From looking at the IRF530NS datasheet it appears that about 5 V gate to source is required to get it fully turned on at the current levels in your circuit. So the 12 V driver will get you there but with relatively small margin.

The combination of driver and MOSFET can switch in about 73 ns so the timesteps in the simulation may need to be smaller than that to get a good simulation. The driver can source enough current to switch the MOSFET at that rate.

I think the problem is likely with the driver circuit.

Lynn

[OStep]

That gate driver component is for schematic capture/layout only. It has no simulation model.

It is easy (but not obvious) to tell because the component appears green. 

You can also see whether or not a component has a model from Model Manufacturer list in the component browser. See attached image. If there's nothing listed, then the component has no model.

[johnsorious]

Thanks for all the input. Do you have any recommendations for a gate driver ic that will work in my situation? I would prefer through hole so I can test it on a breadboard first. Since I'm thinking of using a microcontroller to do the pwm can I just plug in a function generator into the input of the gate driver to verify operation before I start to write the code. Just to verify that the driver will work as expected. Are there any ics out there that do pwm and will adjust the duty cycle based on the output voltage of the buck converter? That could save me some time from using a microcontroller.

[WenR]

johnsorious

There are some drivers that do have a model in Multisim, like the TPS76150DBVR. There are some more in Master Database>>Power>>Voltage Regulator. Have you checked if any of the ones listed in there fit the electrical requirements of your circuit?

WenR

[petergeller]

I faced a similar issue recently and used this gate driver which resolved my issue. 

https://www.taraztechnologies.com/product/power-electronics-modules/gate-driver/gda-2a6s1/

[asghar.zabihi]

hi

please add models on the circuit, made the mentioned parts on the circuit BLUE.

have a good time with MULTISIM