Hello Ti Team,
I have one question from bollowing blog of Mr Dave Wilson. It is related to Unipolar 4-Quadrant PWMs” (Form 1).
Below link states :--
e2e.ti.com/.../so-which-pwm-technique-is-best-part-3
>> Returning to our circuit example above, let’s analyze the condition where Fwd/Rev is set to 1 (forward motion). This means that Q1 will be ON continuously while Q3 and Q4 are PWMing in a complementary fashion. Let’s also assume that the PWM duty-cycle is high and the motor loading is light, which means that the motor speed will also be high and the back-EMF polarity is such that it is positive on the left side of the motor symbol.
>> In this state, the H-Bridge looks like a high impedance to the motor, and no current flows. But with this 4-quadrant topology, when Q4 is OFF, Q3 turns ON, and we effectively short the motor terminals together. >> Since the motor is spinning forward (back-EMF polarity is positive on the left side of the motor), this eventually causes current to flow in the clockwise direction in the top half of the H-Bridge.
If Q1 & Q4 are ON then current flows in motor from left to right , i.e counter clock wise.
As per above link If Q4 turns OFF & Q3 is ON then current flows in motor in clock wise direction Q1 to Q3 due to back emf.
Bun in this case when Q1 & Q3 are ON then wont you think Inductor of the motor will make current to flow in anticlock wise direction i.e same as previous from LEFT to right.
Because inductor has property to object the change in direction of current and in forward state direct of current is left to right i.e anti clockwise?
Also When Fwd/Rev is set to 1 (forward motion) and Q1 & Q3 are turned on at same time. Then will some current flow from battery to the H-Bridge ?
>> But with this 4-quadrant topology, when Q4 is OFF, Q3 turns ON, and we effectively short the motor terminals together.
Does This statement means that both end of battery is connected to Vbus ?
Please clarify these doubts ?
regards,
Dinesh
