DC motor drive circuit

The bridge drive circuit in the figure below has the following features: first, it triggers the motor to run at a low level; second, the control terminals A and B have a trigger lock function; third, it has multiple protections, such as the trigger lock of D1 and D2, and the power tube collector protection of D3~D6. Therefore, this circuit has only three input states valid, and the motor still has five working states. The function of D1-D2 is: if A is at a low level, BG1, BG2, and BG5 are turned on. The high level of the collector of BG2 will block the input of the B terminal through D2 to ensure that BG6 is turned off. If this circuit is triggered by a TTL circuit, an open collector gate circuit must be selected.