All About Circuits Forum  

Go Back   All About Circuits Forum > Electronics Forums > The Projects Forum

Notices

The Projects Forum Working on an electronics project and would like some suggestions, help or critiques? If you would like to comment or assist others with their projects, this is the place to do it.

Reply   Post New Thread
 
Thread Tools Display Modes
  #1  
Old 08-25-2011, 08:24 AM
Schniz2 Schniz2 is offline
Junior Member
 
Join Date: Apr 2010
Location: Australia GMT+10 DST
Posts: 22
Unhappy Buck Converter MOSFET + Driver Selection

I am building a Buck converter with a max output current of 3A @ 45V. Supply is 50V. I want the build to be relatively simple, im not concerned with efficiency or component cost (within reason). I am switching at 20kHz with a 3.3V microcontroller output.
My first question is whether i would be better off using an NMOS and high side driver or a PMOS? Would i need a high side driver for a PMOS anyway?

As far as i can tell the important parameters for the MOSFET woudl be (i want overrated components to be safe):
Drain current = 8A+
Vds = 100V+


For the MOSFET Driver:
I am looking at this one, not sure if i totally understand the parameters given:
http://au.element14.com/internationa...011/dp/1080612

Does the peak output current relate to how quickly it can charge the capacitance of the MOSFET?
Also, the following parameters are given... the way i understand it is, i need at least 10V above my 50V supply to drive an N Channel MOSFET. This module would allow me to have a 20V pk-pk square wave sitting on top of up to 200V DC (or in my case 50VDC)
  • Output Voltage:220V
  • Output Voltage Max:20V
  • Output Voltage Min:10V
Reply With Quote
  #2  
Old 08-27-2011, 12:44 AM
praondevou's Avatar
praondevou praondevou is offline
Senior Member
 
Join Date: Jul 2011
Location: Canada
Posts: 2,887
Default

Quote:
Originally Posted by Schniz2 View Post
My first question is whether i would be better off using an NMOS and high side driver or a PMOS? Would i need a high side driver for a PMOS anyway?
I'd use the same MOSFET for high and low side, so I don't have to think about different parameters. If you use the driver you suggested it already has high and low side driver in one chip.

Quote:
Originally Posted by Schniz2 View Post
As far as i can tell the important parameters for the MOSFET woudl be (i want overrated components to be safe):
Drain current = 8A+
Vds = 100V+
That's ok.

Quote:
Originally Posted by Schniz2 View Post
For the MOSFET Driver:
I am looking at this one, not sure if i totally understand the parameters given:
http://au.element14.com/internationa...011/dp/1080612

Does the peak output current relate to how quickly it can charge the capacitance of the MOSFET?
Yes, the higher the output current the faster you'll charge the gate capacitance, depending on the value of the gate resistor of course.

Quote:
Originally Posted by Schniz2 View Post
Also, the following parameters are given... the way i understand it is, i need at least 10V above my 50V supply to drive an N Channel MOSFET. This module would allow me to have a 20V pk-pk square wave sitting on top of up to 200V DC (or in my case 50VDC)
??? No. You drive a MOSFET with a gate signal within it's voltage ratings, which is usually between 10V and 20V, most commonly used is 15V.

You provide one supply voltage for the driver IC. It charges the high side driver capacitor when the lower power MOSFET is conducting. Then the lower MOSFET turns of and the energy stored in the upper driver capacitor is used to charge the gate of the upper power MOSFET.


If you use this driver IC you will not be able to separate logic and power GND. Proper layout is therefore extremely important.
There are isolated drivers too like the HCPL3180, but you'd need one for each MOSFET.
Reply With Quote
The Following User Says Thank You to praondevou For This Useful Post:
Schniz2 (09-14-2011)
  #3  
Old 09-14-2011, 05:53 AM
Schniz2 Schniz2 is offline
Junior Member
 
Join Date: Apr 2010
Location: Australia GMT+10 DST
Posts: 22
Question Gate Driver

Thanks for your help, i ended up going with the IR2011, but i am only using one mosfet and one diode (ie im not implementing a synchronous buck).
I am a little bit confused how to choose the capacitors and resistor for the following diagram ("Typical Connection" diagram from the datasheet) http://www.irf.com/product-info/data...ata/ir2011.pdf
Im going to use a Vcc of 15V for the gate driver.

I assume i would leave the LIN and LO pins unconnected.
The resistor value would let me choose how fast to charge the gate capacitor... my MOSFET has a Typical gate charge of 27.4nC... i could use the equation Q=IT to select my gate turn-on... but what is the output current of the gate driver? The datasheet has IO+/- (Output High/Low Short circuit pulsed current <10us).. is this the current i would calculate it on? What do i use to calculate a gate turn-on time? The MOSFET dV/dt ruggedness? This is my MOSFET datasheet http://www.fairchildsemi.com/ds/FC/FCPF11N60NT.pdf

And im not sure what the capacitors are for and how to choose them from Vcc to COM, Drain to COM and Vb to Vs (i guess this last one is to hold the 15V voltage for turning the gate on)
Attached Images
File Type: jpg driver.JPG (54.6 KB, 44 views)
Reply With Quote
Reply   Post New Thread

Tags
, , , ,


Related Site Pages
Section Title
Textbook The Unijunction Transistor (UJT) : Thyristors


Similar Threads
Thread Thread Starter Forum Replies Last Post
Help on MOSFET and buck converter MatheusLPS The Projects Forum 4 07-22-2011 01:23 AM
Buck Boost converter - Driver thedinuka The Projects Forum 4 05-04-2011 04:03 AM
Buck converter and Boost converter porky67 General Electronics Chat 12 12-09-2010 04:39 AM
DC DC boost converter design S_adnan General Electronics Chat 16 07-29-2010 08:30 PM
MOSFET Driver Selection milon The Projects Forum 0 04-08-2009 08:35 PM

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT. The time now is 05:45 AM.


User-posted content, unless source quoted, is licensed under a Creative Commons Public Domain License.
Powered by vBulletin
Copyright ©2000 - 2014, vBulletin Solutions, Inc.