Hi all,

I'm sure this has probably been covered before, I've searched around a bit but am still unsure as the best way to do it!

I've found a handy looking mosfet h-bridge on a chip, nice and cheap etc. I'd like to drive a lc circuit with it for rfid purposes (mainly experimenting a bit!).

Quite a few of the circuits I've found with a search use two bjt (I think) transistors to drive the high and low side of the bridge.....



The H-bridge I have is laid out like this,



The data sheet says this!





Do I need to use four more transistors to drive the mosfets on the H-Bridge? I think its the value VGS I'm interested in? Does this mean my chip has a low switch on voltage or does it mean I need 1v min to 3v max above the source voltage? The more I search on this one the more confused I get!

I've also attached the whole data sheet as a PDF.

Thanks Geoff

 

At what frequency do you want the bridge to swich? RF frequencies are likely to be a challenge!

 

Knew I'd miss something out, its 125-130khz, of RFID.
Cheers Geoff

 

I think your best bet would be to use a dedicated FET-driver IC (I can't suggest any particular one, although other members here might be able to). At those frequencies the timing will be critical if shoot-through is to be avoided.

 

Depends on how much current you want to drive into your LC circuit.

 

These are logic level MOSFETS than can be driven with a gate voltage of 4.5V.

If your PIC Vdd is 5V and you are also using 5V for the supply for the upper MOSFETS, you can drive the gates directly from the PIC with a 10 Ohm resistor in between.

Bob

 

Thanks Bob,
I would like to drive my coil with more than 5v, I assume this means I would need to use but transistors to drive the high side of the h-bridge but not the low side? I would also need to careful with timings?!
. Cheers Geoff

 

Yes, a level translator transistor would be needed for the high side if more than the PIC Vdd. Or you could use a high and low side driver IC.

Bob

 

Look at the IR2110 etc, these have level shifting built in, See Tahmid's Blog.
http://tahmidmc.blogspot.ca/2013/01/using-high-low-side-driver-ir2110-with.html
Max.

 

Thanks Guys,
Just been searching around the rs site, after reading that blog Max linked to it seems to me that my little n-p chip might not be the way to go, n channel surface mount mosfets are mega cheap , those diver chips look to be designed to drive two n channels rather than the n-p h bridge?
Cheers Geoff

 

That is true. You use two N channel MOSFETs which are cheaper and better performing than P channel MOSFETs.

Bob

 

Thanks again for the help guys, you've guessed it though, I have more questions!

I've been hunting around and reading up a bit, I found this driver on the RS site, its called ISL 83202 and drives four n channel mosfets.

Here is the schematic from the data sheet;



The data sheet is also attached .

My questions are has any one used this chip? How do I decide on the value of the bootstrap capacitor and what diodes should I use? I have some 1n4148's lying around!

Cheers Geoff

 

Hi All,
I've been messing around with this chip for a bit now, made some mostly firery exploding transistors (MOSFET) and seem to have popped a couple chips . I re read Thamids blog, in his circuits he uses resistors to the mosfets gate from the drivers. Non are shown on the data sheet for this driver chip so I didn't use them, now both my chips are driving the same high side mosfet of the bridge at 12v all the time, while the other side is pulsing nicely. Could my lack of resistors have blown the drivers on the chip? I've some more on order, is there any reason not to put gate resistors and diodes as in the blog? (Ps dead time is ample!)
Cheers Geoff