What is the reason for this voltage drop?

elec32156

What is the reason for this voltage drop? [Copy link]

 

I would like to ask you, as shown in the picture, this is the schematic diagram of a four-phase stepper motor. When testing the output terminals a and b, it is found that when Q1 is disconnected, that is, when point a becomes a high level, the voltage at point b will drop. Similarly, when the level at point b changes from low to high, the voltage at point a will also drop. What is the reason? Thank you!

newdrive

Look at the schematic diagram, is the power output insufficient?

elec32156

newdrive posted on 2018-9-25 10:37 Look at the schematic diagram. Is the power output not enough?

The power output is sufficient. The current is only over 100 mA. The adapter is of 2A specification. The schematic diagram is the part I drew. Switches Q1 and Q2 are actually driven by MOS tubes.

huaiqiao

elec32156 posted on 2018-9-25 20:20 The power output is enough, the current is only more than 100 mA, the adapter is 2A specification, the schematic diagram is the part I drew, the switches Q1 and Q2 are actually MOS tubes...

It may be when the motor rotates, the reverse rotation. For example, when the stepper motor rotates clockwise, it will rotate slightly in the reverse direction when it stops, and the effect may not be captured by the naked eye. We also use stepper motors, but we directly use stepper motor drivers without MOS pushers. It’s hard to say because you can’t see the schematic diagram.

qwqwqw2088

The drop is related to load control. In principle, if the power supply is not enough, the drop will be large. If the starting current is large, the large current will increase the loss of impedance current-carrying components such as lines and transformers, and increase the voltage drop.

xujian2000

The motor windings show inductance characteristics. When the inductor suddenly changes the direction of the current applied to it, it will generate a reverse electromotive force. This reverse electromotive force completes the circuit through the internal resistance of the power supply and affects the level of your test point. Solution: Connect a capacitor in parallel to the ground at the a and b test points (Q1 and Q2) respectively (reduce the inductance value, the capacity is to be verified by you). Give it a try!

xujian2000

The motor windings show inductance characteristics. When the inductor suddenly changes the direction of the current applied to it, it will generate a reverse electromotive force. This reverse electromotive force completes the circuit through the internal resistance of the power supply and affects the level of your test point. Solution: Connect a capacitor in parallel to the ground at the a and b test points (Q1 and Q2) respectively (reduce the inductance value, the capacity is to be verified by you). Give it a try!

xujian2000

Supplement: Reducing the inductance value does not mean replacing the motor, it is the function of L and C.

elec32156

xujian2000 posted on 2018-9-27 11:01 The motor winding presents an inductance characteristic. When the inductor suddenly changes the direction of the current applied to it, it will generate a reverse electromotive force. This reverse electromotive force is passed through...

I still don't understand why this reverse electromotive force can instantly pull the voltage level at the other end to 0V. Can you explain it? Thank you.

tianshuihu

The two windings A\B can be regarded as a common core "transformer" with a center tap; Q1 is disconnected, the magnetic flux of the A winding decreases; both windings A\B will generate reverse induced electromotive force, which will increase the voltage when superimposed on the A winding point a, and decrease the voltage when superimposed on the B winding point b; theoretically, the reverse electromotive force is equal to the induced electromotive force; the B winding is equivalent to a circuit breaker, so its voltage drop is obvious; the a point of the A winding can be discharged through the protection diode, so the voltage increase is not so obvious. The principle is similar when Q2 is disconnected. . .