H-bridge drive circuit working in two quadrants

The safe reversal program should be as follows: first
change the PWM signal to zero level, delay it for a period of time to stop the motor, or detect and monitor the back
electromotive force After it reaches zero, change Fwd, and then start the motor. . For
loads such as fans and pumps, two-quadrant operation is more appropriate, as the acceleration performance and efficiency
are higher than four-quadrant operation.
    The H-bridge structure shown in Figure 2-4
consists of four power switches and four freewheeling diodes. The characteristic of the bipolar mode is that two sets of switches on the diagonal line of the four bridge arms are respectively controlled,
VF, and VF, and one group is turned on or off at the same time, VF, and VF. As a group, they are also
turned on and off at the same time. At most one group is allowed to be turned on at any time. The simplest
control is that within a switching cycle, first the first group (VF, and VF.) is turned on, a forward voltage
is applied to both ends A and B of the motor , and then it changes to the second group (VF, and VFa) conduction, a reverse voltage is applied across the motor. From this, the time share occupied by the two states determines whether the average voltage is positive or negative, and whether the average current is forward or reverse. When the two states are equal (1; 1), it is equivalent to the average voltage being zero and the motor stalling. In the bipolar mode, there may be a problem of direct connection between the upper and lower bridge arms. For this reason, a "dead zone" state is inserted between the two states , that is, a state in which all four bridge arms are turned off for a short period of time. Like the PWM control of the MC33030 , a dual-comparator window comparator is used to generate four-bridge arm control to achieve bipolar PWM switching control with dead zone. Bipolar PWM control is most commonly used in DC motor application-specific integrated circuits, such as the late UC3637, L292, TAL955, etc.