Creating a negative voltage rail for MOSFET driver

  • Thread starter Thread starter DaDes
  • Start date Start date
  • Tags Tags
    Ltspice Mosfet
AI Thread Summary
Creating a negative voltage rail for a MOSFET driver can be achieved using a charge pump in conjunction with a Zener diode, which can clamp the voltage at -4.7 V. The specific MOSFET in question does not require a negative rail, as it can turn off with a gate voltage below +2.5 V. Proper gate driving is crucial due to the MOSFET's gate capacitance, which requires a driver capable of sourcing or sinking one to two amps, rather than the 17 amps currently being simulated. Additional resources and circuit design examples are available online, and using a dedicated driver IC may simplify the process. More detailed information about the specific setup is necessary to provide tailored solutions for the gate drive issues.
DaDes
Messages
1
Reaction score
0
TL;DR Summary
I am trying to create a negative voltage rail using a zener diode for driving a MOSFET
I am trying to create a negative voltage rail using a zener diode for driving a MOSFET. I've read several placed online about using a zener diode for this purpose but I cannot seem to get it to work. I am simulating using LTspice but the negative rail just isn't there. I would be very grateful if someone can help me with this and also understand what I'm doing wrong. This seems like something that should be easy but I'm missing something.

I've attached the schematic and the LTspice asc file renamed as .txt.

MOSFET Driver with Negative Rail.PNG
 

Attachments

Last edited by a moderator:
Engineering news on Phys.org
Welcome to PF.

The Zener diode will clamp the voltage at -4.7 V, but first you need a charge pump, to pull that rail negative.

The MOSFET you are using does not require a negative rail, as a gate voltage below +2.5 V will turn it fully off.

The MOSFET is a power device and has a gate capacitance of about 2 nF. It will take a good driver to charge that capacitance. At the moment, you are driving it with 17 amps from an ideal voltage source. I would expect a logic input MOSFET gate driver, would source or sink between one and two amps.

How will you control the unspecified gate driver?
 
It's hard for us to help unless you explain more about your specific problem. There are many MOSFET gate drive circuit solutions. A negative PS isn't often required, but there are some cases where it is beneficial.

The short answer is if you want a negative power supply, you have to make one (or be given one). As @Baluncore said, this is usually a charge pump of some sort, since MOSFETs don't need a lot of power.

There is also a lot of info on the web. Here's one, kind of randomly chosen, example:
https://www.ti.com/lit/ml/slua618a/slua618a.pdf?ts=1733237400369

Often you will do well to just buy an appropriate driver IC and do what they say to use it properly.
 
@DaDes
I see you are lucky to be getting circuit design help from the LTspice group.io; Normally, they will only discuss the operation of LTspice, with answers like:

The SPICE directive; VN VN 0 -5 ; will generate a negative 5V rail node called VN, without having to place a voltage source or wires on the schematic. It also conveniently provides the ground connection needed by SPICE to function.
 
Here is your circuit modified to pump the negative rail down to -4.7 volts.
The MOSFET gate now switches between -4.7 V and 15.3 V.
Note that it takes about 3 k * 10 uF = 30 ms, for the rail to stabilise.
file.asc is attached as .txt file.
Neg-Rail-Pump.png
 

Attachments

If you have extra gate 'on' voltage you can add a series capacitor to level shift your gate drive to create a negative 'off' bias. As shown below. Like the charge pump it takes several cycles to work. I've used this a few times to deal with turn off problems caused by the miller capacitor charge injection back into the gate. But, it's not a "cookbook" solution, you have to make some design choices.

Without more information we can't tell which sort of solution is best for your gate drive issues.

PXL_20241206_074221646~2.jpg
 
I have recently moved into a new (rather ancient) house and had a few trips of my Residual Current breaker. I dug out my old Socket tester which tell me the three pins are correct. But then the Red warning light tells me my socket(s) fail the loop test. I never had this before but my last house had an overhead supply with no Earth from the company. The tester said "get this checked" and the man said the (high but not ridiculous) earth resistance was acceptable. I stuck a new copper earth...
Thread 'Electromagnet magnetic field issue'
Hi Guys We are a bunch a mechanical engineers trying to build a simple electromagnet. Our design is based on a very similar magnet. However, our version is about 10 times less magnetic and we are wondering why. Our coil has exactly same length, same number of layers and turns. What is possibly wrong? PIN and bracket are made of iron and are in electrical contact, exactly like the reference design. Any help will be appreciated. Thanks. edit: even same wire diameter and coil was wounded by a...
Thread 'Beauty of old electrical and measuring things, etc.'
Even as a kid, I saw beauty in old devices. That made me want to understand how they worked. I had lots of old things that I keep and now reviving. Old things need to work to see the beauty. Here's what I've done so far. Two views of the gadgets shelves and my small work space: Here's a close up look at the meters, gauges and other measuring things: This is what I think of as surface-mount electrical components and wiring. The components are very old and shows how...
Back
Top