Class D amplifier using NE555 Timer


2012-11-29 1:32 pm
Hey everyone,

I designed a H-Bridge Class D Amplifier to only amplifier some specific single , meaning it won't be used to amplify audio signal . the target signals are : voltage sags, voltage swell ..... etc ,

well i generated the PWM for my class D amplifier using NE555 , the Frequency of the PWM is 14KHZ then send it to gate drive which is IR2109 with 540ns dead time then to the first half bridge which consists of two MOSFET "IRF840" , i took the same PWM signal generated from the NE555 Time and invert it using 4049 then send it to the second gate driver which is also IR2109 then send it to the second half bridge ,

The two half bridge form i H-bridge .the bridge is fed with 10V for testing.
, finally i used butterworth filter of 1.4KHZ as cutt-off frequency here come the problem :

The output signal is small and does not seem to be sine wave in its low part also whenever i want to increase the bridge DC source the output signal will have a dc off-set and satueate at its top also to have a good PWM wave i was forced to add DC off-set to input sine
here are the circuit design using proteus and the output signal after the implimetation of the circuit:

the output signal :

please not that is i increase the DC off-set of the input signal the output signal amplitude will increase but saturate in its bottom meaning the bottom of this sine wave will be square wave
i would like to note that the DC offset of the input sine is mandatory to have a PWM generated from the NE555 timer
secon, i increase the input sine wave amplitude the output signal amplitude increases but the problem of saturation appears .
Please help me because i ve no idea what the problem is !!!???
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