# Thread: I found the contradiction of the PWM method constant current circuit.

1. ## I found the contradiction of the PWM method constant current circuit.

Hi　All.
About constant current drive of Stepper Motor.
I found the contradiction of a constant current control system known for some experiments generally.
It is seen in "Stepper Motor Control Using" as "AN906".
I rediscovered a method to realize a constant current drive type.
The problem of this method was known in some limited makers, and what was done understood measures in its own way.
I want to challenge a constant current method by another method that does not move to the method that a maker carries out.
I help me how about an engineer more detailed than me and am worse by a plan together and will develop a circuit and the program jointly?

Kyoji

2. ## About a PWM wave pattern and estrangement of the true electric current control

Opening).
I examined current control by PWM wave, but a theory value and a true electric current have a gulf.
This is not almost problem in the bipolar winding and appears in uni-Paula winding and four substance aspect drive said to conspicuously.

Coil form difference).
When it used an exclusive electric current return IC for a drive element in uni-Paula, MCU nominates direct PWM wave, and it is a difference when it supposed that it imitates the just what.

General remarks).
The contents which investigated by Class coil and the combinations such as a switching wave pattern, the dead time,

Current element).
"An electric current damps residual voltage - inertia with "time constant drive - increase electric current" to a coil for a short time", and, besides, there is "time straight - generation rapid current decrement" in an electric current increase - punch through electric current of time constant - inertia electric current way home passage - invalidity - short circuit and the process when I said at drive time.

Detection 1).
Furthermore, as for the case by the general addition current mirror conversion by the coil common line, driving current, an inertia electric current, a time can detect a life electric current without distinction as a detection method of the current return, but it is the thing which does not contribute to flow drive as the original opposite direction, but both aspects can detect the punch through electric current of the short circuit as synthesis value.

Detection 2).
Or the electric current which drifted to either of both directions when I turn on drive (with one μ S) for the period when the back pole that completely intercepted an inertia electric current circuit is short, and A/D converts a passage electric current at that time and detects it is replaced as driving current and can measure it because it is an electric current of the substance.
（The fault of this method cannot but expect the electric current of the section that I do not drive）

Measures).
Dead time control to wait for the electricity end of the switch element is necessary even if it cuts a signal of neither more without becoming it when I drive a drive circuit, an inertia electric current circuit by these things at the same time.

Element division).
When is longer than this period, the energy in the coil cannot flow out than a normal element, but it is an electric current of the student generation in parasitism or a time to draw up from a line common throughout GND by the diode which endowed with distinction; and of the power supply is returned.
The interception side coil voltage rises to the power supply double voltage theoretically then.

Excess substance).
（It is supposed, and these are ABBA orchid Xie characteristics added to a drive element, and an excess wave pattern of around 600V seems to be taken in substantially, but is connected for destruction for a radiation of heat element in element in itself when I repeat it and occur if there is not the tolerance）

Movement change).
The consideration in the case a drive circuit goes to the GND from a power supply, and to send an electric current to a coil.

An inertia electric current circuit is already driven; and of the electricity possibility when was in a state or when an inertia electric current circuit was driven later, and became the state of the electricity possibility,

When these happen to (a drive circuit, an inertia electric current circuit) simultaneously, it is gone down toward the GND, and the coil drive edge drains a "source" electric current.
The coil drive reverse edge is connected to a power supply by a comparatively low voltage descent through an inertia electric current circuit and drains a "source" electric current.

At this point I produce the increase of a sudden electric current without an inertia electric current circuit becomes equivalent as for the important thing if a short circuit is in a state as for the coil because impedance is low, and inductance working effectively because there are few elements limiting an electric current.
A direction is reverse, and the flowing electric current of this coil is the almost same, and it is size.
（It depends on grade of the magnetism of both coils being high）On a coil common terminal, a double electric current by what both were added to is called off.

Drive matter) which is in a state.
It seems to be the issue of chicken egg, but does which phase of the drive I speak it from with the thing which at first begin it from a drive circuit to think from the point in time in a device start.

Summary) of the device.
The whole driving means assumes it coil A with two sets of middle point, ACOM, /A and B, BCOM, /B.
I attach a common side, current monitor sensing device to ACOM, BCOM each. （Two）I attach an inertia electric current rectification collector (a diode) to A, /A and B, /B each. （Four）I attach an inertia electric current control circuit to the inertia electric current rectification collector of Class A and the Class B each. （Two）I attach a driving current control circuit (a diode) to A, /A and B, /B each. （Four）I attach a current monitor current sense resistor to the driving current control circuit of Class A and the Class B each. （Two）I am in a condition not to drift to whether a straight electric current drifts in turn in driving current and a time for this resistance.
When I replace a current monitor current sense resistor with current monitor sensing device, include a direction, and a coil can analyze a drifting electric current when I add them generally and subtract it from.

Drive phase 1).
I make a drive circuit an electricity state.
The electric currents increase according to the time constant of the inductance resistance circuit of the coil.
When a current monitor current sense resistor or current instructions value with the current monitor sensing device was set, I stop the electricity of the drive circuit.
Drive Motoko passes through changes such as the gate accumulation, and an electric current completely stops decrease afterwards.
（I assume it dead time 1）

Drive phase 2).
Including dead time 1 of drive phase 1
It is shut out that I continue being going to drift by the electromotive force of a direction disturbing the change of the magnetic flux, and it is it with the voltage so that there is not it, and the energy of magnetism saved after this by a coil occurs to a coil and rises to the direction that is higher than GND in a coil terminal voltage.
The coil middle point leads to a power supply (through current monitor sensing device) then and lowers the coil other side terminal toward the GND by the inversion action.
When this voltage falls ahead of the voltage of the GND side voltage descent element, I draw up an electric current from GND than drive element parasitism diode or opposite direction diode done in parallel, and fixation clamps coil other side terminal in the GND voltage neighborhood.
I fix the voltage of the drive side coil by inversion action in the double power supply voltage neighborhood, and this movement clamps it.
It is a straight electric current decrease period in as for this namely a time.
This movement is derived to take in a transitional phenomenon before the next inertia electric current circuit beginning to work.

Drive phase 3).
I drain driving current from the power supply into the coil after the electricity electric current of the driving current circuit completely stopped by I drive an inertia electric current circuit, and carrying away the remainder of the energy of saved magnetism to the coil by little voltage descents without supplying energy.
When it is it in lower than set point which a current monitor current sense resistor or current instructions value with the current monitor sensing device was fixed at, I stop the electricity of the drive circuit.
Drive Motoko passes through changes such as the gate accumulation, and an electric current completely stops decrease afterwards.
（I assume it dead time 2）

Drive phase 4).
The energy saved to the coil which was suddenly intercepted is handled in the same way as drive phase 2.

Drive phase 5).
I drive a driving current circuit and begin electricity after the electricity electric current of the inertia electric current circuit completely stopped.
This is the same movement to lead to drive phase 1.

Drive phase 6).
The drive element stopping the electricity of the inertia electric current circuit pass by changes such as the gate accumulation, and an electric current completely stops decrease afterwards if I sent an electric current by an inertia electric current circuit when I detect the state because this is an electric current value bigger than the electric current which was set in the movement of drive phase 3 when the set point which is newer than a former current set point was changed by few electric currents.
（I assume it dead time 2）

Drive phase 7).
Including dead time 2 of drive phase 6
It is a straight electric current decrease period by movement same as drive phase 2 in a time and decreases a current value rapidly.

These modes are methods to be able to approach the electric current of the setting as much as possible by doing the ratio appropriately in time.

AN906 Stepper Motor Control Using the PIC16F684 not uni-Paula
http://www.microchip.com/stellent/id...pnote=en012150

AN907 Stepping Motors Fundamentals
http://www.microchip.com/stellent/id...pnote=en012151