N Channel MOSFET H Bridge

mosfet h bridge

I'm stumped. I can't seem to get this thing working. I only get a humming noise. No motor movement. My o-scope displays a lot of noise when connected to the motor terminals.

n channel mosfet h bridge

Your problem lies in how you are driving your high side mosfets. A N-channel mosfet requires a positive voltage at the gate with respect to the source in order to turn on. I am assuming your logic gates are using 5V. Since your supply is 12V, when you turn on one of the high side mosfets the voltage at the source of the mosfet rises to something a little less than 12V. And since your logic can only drive 5V the Vgs is essentially negative, thus shutting off the Mosfet.

You need to use a high side mosfet driver to drive the gate voltage in reference to the Mosfet source. These typically use a bootstrap type circuit. Just do a google search for high side mosfet driver and you will get tons of results.

mosfet bridge

Plese also verify the current capability of the logic you use...
at least you need a gate resistor to limit the gate current.

With the use of a a gate driver you will obtain better results

mosfet h-bridge schematic

First, these are power mosfets that have large gate capacitance, and TTL logic are not going to provide a fast, sharp rising edge to the mosfet inputs. If you have slow rise times on the gate, you will begin to dissipate a lot of power in the power MOSFETS, resulting in smoke and pops!

Second, the motor drive voltage is 12V, and I imagine your TTL logic voltage is 5V. So, you will not be able to drive the mosfet gates strongly enough. You should aim to drive the mosfet gates with 12V square waves unless you have a good reason not to. Check with your scope to see that the waveforms have rise times well under 100 ns.

Third, if you want to use all NMOS power MOSFETS you will need to drive the upper two mosfets differently, using a floating bootstrapped power supply. The solution would be to buy a common IC called a Half-bridge Driver or a Synchronous N-Channel MOSFET Driver. Linear Tech makes the LTC4447, but there are many others available. This will give you an idea what you are looking for. A simpler approach would be to substitute PMOS for the upper power MOSFETS. Your choice comes down to cost.

Off the top of my head, I'd recommend power mosfets with a max VDS voltage of 30V, any more than that is overkill, but the motor inductance can ring and you might see greater than 12V because of it, so you want more than 12V. You have 1.1A flowing through the motor. You don't want to have to heatsink your MOSFETS so keep the power dissipation lower than 100mW. Therefore 100mW/((1.1A)^2)=0.08Ohm rDSon, with a 12V gate drive (rDSon gets higher with lower gate drives). Use some kind of MOSFET driver chip between your control logic and the MOSFET gates. If you choose the pmos/nmos solution, use something like Intersil EL7202, if you choose the dual nmos solution, use the slightly more complex half bridge driver LTC4447

Also you will need good power supply decoupling capacitors very near the power mosfets and gate driver chips. Ceramic caps of 1uF will cut down the ringing. The datasheets explain this.

mosfet h-bridge

Ok, I think I might have a solution for the top MOSFETS. I hope to use op amps to drive a 17 volt signal into them. This circuit works fine in the simulator, so I hope that it will work empirically. Please let me know if something does not seem feasible with my design.

h-bridge n channel fet drive

Hello,

I have one sugestion, you can use two Ir2184 half driver and 4 irf 1405 or similar.

I post the schematics soon.

Regards

n channel mosfet

I hope this helps. You need to also be concerned about turning both left or right mostfets on at the same time, even briefly, because there will be a large shoot-through current. These mosfet drivers have that safety feature built in.

I design floating power mosfet drivers at work. Believe me when I say this is going to simplify your life tremendously.

n-channel mosfet

Is there an IC like the LTC4447 that is not so hard to find and that comes in both PDIP and SOIC packages? The LTC4447 also seems to be an obsolete.

ir2184 schematic

Hello,

You can Use the IR2112, IR 2184 for example.

Regards

h-bridge n channel fet driver

Your Mosfets are very old with poor performance.
Your TTL logic gates are very old.
Your quad opamp is very old.
Why?

The IRF620 Mosfet needs a gate voltage of 10V to fully turn on.
But the output of the old 74LS08 is only 3.5V when it is high.
So your low side Mosfets also might not turn on.

EDIT:
The output of an opamp is never at a voltage that is higher than its power supply voltage.

n channel fet

I also recommend you to use any drivers like IR2104. Look at www.irf.com. There are many drivers and MOSFETS there. You can find some examples there.
This topic may be useful for you.

Re: n channel mosfet

snafflekid said:

I hope this helps. You need to also be concerned about turning both left or right mostfets on at the same time, even briefly, because there will be a large shoot-through current. These mosfet drivers have that safety feature built in.

I design floating power mosfet drivers at work. Believe me when I say this is going to simplify your life tremendously.

Click to expand...

It will certainly help me. THANKS!
I have a small bagful of MOSFETs rescued from landfill that are now going to drive some bipolar steppers. (Also from landfill!)
Martin

which IC can i use ?????????????????????????????

which IC can i use ?????????????????????????????
please i want to know which MOSFET driver IC can i use
there are a lot of ICs such as LTC4447 , IR2184 , IR2112 , .............
according to what can i choose??????????
i will use N channel MOSFET H bridge

If you have some P-Channel MOSFETs you might consider using them for the high side switches. You could drive the FETs with 4000 series logic from 12 volts then.

Just remember for the boot strap H-bridge drivers you need to keep PWM going all the time to refresh the 0.1 uF floating supply cap. You can go from 2% to 98% duty cycle but never let is go to 0% or 100% duty cycle.

---------- Post added at 23:02 ---------- Previous post was at 22:51 ----------

ronv said:

If you have some P-Channel MOSFETs you might consider using them for the high side switches. You could drive the FETs with 4000 series logic from 12 volts then.

Click to expand...

The issue with using a P-ch in the upper device is you have to manage the cross over delays so you don't get shoot through current spikes due to turn-off delays.

The boot strap IC's have this delay within the driver IC.

than you for replay

Yesterday my friend bought a driver for me
it is ICL7667
i want to know how to use it
i want a schematic of the driver with 2 N channel MOSFETs

ICL7667 is an inverting driver, an input high will create output low. Please ensure that all inputs are pulled high before driving any MOSFET. To enable output drive pull input low. You may use pull up resistor to VCC and use PWM controllers like 3527 or TL 494 or 3524 to pull down the input as these chips have open collector pins.
Else you may use a simple transistor to pull the input low from a high signal of a µ-controller too. Refer intersil data sheet for more info.
Thanks
hari

thank you for replay
i want to make H bridge with 4 IRF740 N channel MOSFETs and the ICL7667 driver IC
please i want a schematic of the circuit
thank you

The ICL7667 is a low side driver. You will also need a high side driver for your H Bridge. If your bridge is to drive a motor you will need a high side driver with a charge pump.

thank you for replay
1) OK, i want to know a number of high side driver that i can use with ICL7667 low side driver to make the H bridge

2) If i use the high side transistors as P channel MOSFEts like IRF9520 can i use only the low side driver to drive the high side and low side MOSFETs ??

thank you