I designed a 3 phase H bridge to be supplied with 8V from a LM7808 voltage regulator while the origin voltage source is supplying the MOSFET (IRF540) gates with 12V. I noticed that the voltage coming from the regulator towards the drain of the high side MOSFETs are choppy like the PWM signals that I feed through the gates.
How can the regulator give the high side MOSFETs constant voltage instead? The picture below shows the high side gate signal pwm1_h (at the time the voltage level for VDD was 18V but the same issue occurs when the voltage is lowered):
[Complete picture] The PWMs are generated with 555 timers together with a sine reference for 50 Hz and a 2 kHz switching wave. The PWMs are then sent to a TSC428 driver to increase the voltage level to be higher than the threshold voltage of the IRF540 (4V). The TSC428 has one inverted and one non-inverted output. These are then sent to the H bridge as pwmX_l or pwmX_h.