H Bridge for vibrator coil drive

Dear All
Please see my attched circuit which is powered by 230 VAC and Mosfets are driven Atmega8 16A and some optocoupler .Load is A Coile of vibrator. I dn,t understand why circuit disigner used Two PWM output to drive two mosfet.I think One output is sufficinet for it
Please guide
Thanks

That is indeed very strange. Perhaps for an easy safety precaution. So that both must be activated. But then again, it might just be a bad design :astonished: , or they use a part of an H-bridge they already had a PCB for.

Dear Sir
One more query about this circuit.What is the use of Diode in this Bridge.can we achive same function with One Mosfet only ?Please suggest
Thanks

The diode is called a fly-back diode. It is to prevent a negative voltage peak when the inductance (from a coil or motor) is turned off. You need the mosfet to turn is on and off, and a diode parallel next to the load.

Dear Sir
Thanks for your quick reply.
Can you suggest any good PWM Driving circuit for this bridge based on atmega8 16 A and its Arduino code.
Thanks

The Arduino output to a 100 ohm resistor to a gate of a 'logic level' mosfet and sometimes a resistor from gate to ground, and a fly-back diode over the load. This schematic uses 1k instead of 100 ohm http://forum.arduino.cc/index.php?topic=12937.msg97027#msg97027

But you want to switch a high voltage. I don't know any high voltage 'logic level' mosfet. Most 'logic level' mosfets are for 60V.

If you use a normal mosfet, it turns on at about 9V. Perhaps you need an extra circuit for that.

A pwm output is done with the analogWrite() function. http://arduino.cc/en/Reference/analogWrite

Thanks For your reply
I have found One circuit in International Rectifier application note of IR2110 for for my Transformer coil driving from Arduino PWM
I have Drive this bridge circuit by Arduino 328 PWM couple by optocoupler
My problem is When I inserted Optocoupler and even though there is no PWM my bridge start with full output.But as I remove Optocoupler Then it remains OFF.
Also Mosfet Q1 goes damaged if I switch on/OFF circuit
Please suggest
Thanks

Scan 9 (1).pdf (1.05 MB)

Hi, the mosfet in the first circuit that has its drain connected to the high voltage positive supply has to be driven by a hi-side mosfet driver chip, that is the chip that is used in the IR application circuit, it incorporates low side switching as well so that one logic control is needed.
You cannot drive both of the mosfets gate from the same output, they have to be separate.

Tom… :slight_smile:

Hi Tom Can you elborate it with some sketch Thanks