[SOLVED] PWM H-bridge using TIP122 and IRF540

[eXnol]

Hi everyone,
I am trying to 'DESIGN' an H-Bridge with PWM support. I have decided on the components to be 4xIRF540 as Motor driver, 4xTIP122 (or TIP127) as gate driver for the MOSFETs. The IRFs are used for the High side as well.

I have found out that the total time for the FETs to go from OFF to ON (full) is about 100nS and the total gate charge to be about 109nC. so I have decided to use about 1Amp gate drive current using the TIP.

I know the TIPS may be overkill but they seem to do the job and I have many available. I am planning to use a PWM freq of 200KHz (5uS) and the ON time being 100nS was wondering whether the TIP providing 1A at base bias of 5V and a gain of around 100-150 will be able to drive the FETs at 200KHz. The gain bandwidth product is around 250-300MHz and the switching diagram shows at 1Amp the TIP switiching time to be anywhere down till .05uS.

can I use the TIPs to drive MOSFET gates? Does my idea have any problems?

datasheet

TIP120 etc :http://www.onsemi.com/pub_link/Collateral/TIP120-D.PDF
IRF540 :http://www.irf.com/product-info/datasheets/data/irf540.pdf

 

[IanP]

I don’t think tips are good candidates for switching 200kHz PWM ..
Not always you should use components that you just happen to have ..

Try to drop frequency to, say 10kHz, and even then you cannot expect top performance from your TIPs .. see attached picture ..

IanP
:|

 

[eXnol]

But the datasheet doesn't show any contradictions. Switching times are fine for such small frequency GBP is also fine.


I only need 1Amp gate current...Can you please explain?

 

[IanP]

The gain bandwidth product is around 250-300MHz and the switching diagram shows at 1Amp the TIP switiching time to be anywhere down till .05uS

I don't know where do you have this from ..
Once more, have a look at the graph from my previous post; for 10kHz switching time can be tolerated but 200kHz is just out of reach ..

IanP
:|

 

[Tahmid]

Hi,
I think you shouldn't be using this transistor. The first line in the datasheet states: "Designed for general-purpose amplifier and low-speed switching
applications."

200kHz is by no means low-speed switching.
For H-bridge, I think 200kHz is off limits, you should be keeping frequency below 100kHz, around 50-60 kHz is ideal, I guess.

You also need to realize, this is a MOSFET based H-bridge circuit and you need hi-side, lo-side drive. So I suggest, instead of using transistors and discrete circuitry, directly go to using a hi-side, lo-side driver. One of the most common is IR2110.

You should use IR2110 or any similar driver, this will spare you the hassle of designing your own transistor-based driver, that too for a hi-side drive at high frequency, which becomes quite complicated.

You should take a look at the datasheet and application notes:

www.irf.com/product-info/datasheets/data/ir2110.pdf

www.irf.com/technical-info/appnotes/an-978.pdf

Hope this helps.
Tahmid.