On the L298 datasheet (http://www.sparkfun.com/datasheets/Robotics/L298_H_Bridge.pdf), the Bidirectional motor control application example (Fig 6) shows that the need to be two diodes connecting the ground. I understand that you connect a flyback diode to the V_supply for EMF protection by allowing the current to flow back into the motor itself. However, why is there a need for a diode connecting to ground? I don't see how the diode can be made forward biased.
Asked
Active
Viewed 1,739 times
1 Answers
2
If you pull an inductance to ground (with a low side driver, the inductor's other terminal being connected to VCC) and then turn off the driver, the inductor will generate a positive spike - this forward biases the diodes (D1 or D3 in figure 6 on this datasheet) and conducts the spike into the positive supply.
But if you pull the inductor high (with a high side driver) and then turn off the driver, the inductor will generate a negative spike - this will forward bias diodes D2 or D4 and conduct the spike into the negative supply (ground).
In a bridge driver, both of these are happening (one at each terminal of the motor) so both pairs of diodes are necessary.