AVR-Chat

At 01:12 AM 12/21/04 -0800, you wrote:
>sorry for poor explaination.i will try explain detail a bit. i attach a 
>schematic of my cct which i just draw using visio.so forgive me for the 
>ignore nodes which i think u are understand  as usual.i also answer your Q 
>below.tq.

The circuit looks like a reasonable start.  The charge pump capacitance 
might be a bit low (it is low for a 40Hz drive).  You have gnd1 and gnd2 
connected (that is share a common reference)?  The 2110 does not float 
completely, only the high side floats.  IR has a good app note on the 
circuit required for the 2110.

You also need some way of modifying the timing of the high and low sides to 
prevent switch through.

>my motor is not rotate machine.it is linear synchronous motor. i switching 
>Q1 & Q4 and then Q2 & Q3 continuously without stop to generate a AC = 
>40Hz(not dc) square wave through the AC LSM motor. the motor will vibrate 
>between a range which i m using for other function later.

I do understand this.  However, the switching frequency and the drive 
frequency do not need to be the same.  Remember that the motor is 
essentially acting as a low pass filter.  I'd rather see a MUCH higher 
switching frequency being used to generate the 40 Hz drive wave.

The switching frequency may be part of your problem but more information is 
needed.


>Robert Adsett <subscriptions@aeolusdevelopment.com> wrote:
>At 08:11 PM 12/20/04 -0800, you wrote:
> >i build a full hbridge cct with 4 mosfet and 2 IR2110 mosfet driver and
> >test it yesteday.
> >i supply 5V to Vcc, 12V to Vcc and give signal with 5V to Hin or Lin
> >continuously to switching the 4 mosfet continuously at 40Hz like usual.
>
>5V to Vdd I assume?
>-->yes,5V to Vdd
>
>
>
> >i connect Vb to Vs with cap 1uF, a diode FR103 from Vcc to Vb, SD and Vss
> >to GND, cap 22uF from Vdd to Vss,cap 22uF from Vcc to com. HO to gate of
> >high side mosfet through 22ohm and its Source to Vs. Lo to gate of mosfet
> >low side through 22ohm and its source to com.
> >
> >after that i supply 5V to Vdd and 12 V to Vcc and 0V to my load. i found
> >that Vbs=11.0V, and Vgate of high and low mosfet or Vho and Vlo are around
> >4.0V.
>
>11V on Vbs is about right.  4V on VHO is way too low.  You should get
>pretty close to the Vbs voltage.  How are you measuring these voltages?
>--> i measure again wif multimeter(dc range),VHO=8V and in ac range it is 
>14V.i measure at pin HO to com.
>then i measure at Vgs for Q1 again..Vgs Q1=5V (dc range) and Vgs Q1=11V 
>(ac range).of cos voltage drop coz i connect a LED and 22ohm series to the 
>gate for visual inspection.

OK, a voltmeter is not going to be very much help here.  You NEED an 
oscilloscope, it is not a luxury.  Besides the gate signal you need to 
measure the switching pattern across the mosfets and the vbs voltage during 
switching.
> >then i increase the load voltage (middle of hbridge like usual)
> >slowly.everthing looks find and the output is ok. but when i keep increase
> >the voltage, i found that the Vho or gate voltage decrease and finally
> >both high side mosfet turn off when the load voltage exceed 3.0V but both
> >low side mosfet still on.
>
>First things first.  You need to figure out why your gate voltages are so
>low.  What do the gate drive signals look like on the oscilloscope?  Also
>how do you know the hi sides turn off?
>
>-->i am thinking why Vgs (high side) decrease when i increase Vm..but cant 
>figure out.the drive signal waveform look like ac square wave.i connect a 
>LED to gate,when Vm increase exceed 6.8V, the LED off and Vgs is very low 
>so i know it is off.

Again, oscilloscope.  What does the waveform look like.  I really do 
suspect your switching frequency, but the gate resistance might be too high 
as well.

Robert

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