huongthanh,
I took a look at your post #37 schematic and it has serious problems. The 74HC02 AND output goes to the gate of the n-channel MOSFET while one of the AND inputs goes to the p-channel MOSFET. That is trouble.
The 74HC series is rated at 6VDC max supply voltage. The top MOSFET (p-channel) is 'off' when there is 40VDC on it, 'on' when there is 35VDC on it. This will destroy the 74HC part.
What is missing in your circuit is level translation. The top MOSFET needs 0V and -5V to operate it but that 0V to -5V swing sits at a 40V offset (35V to 40V) so level translation is required. Please see
www.irf.com and enter IR2104 in the 'search' box. Open the datasheet pdf and read the circuit description to get a better appreciation of level translation.
Mariss