NTE1885 查看數據表（PDF） - NTE Electronics
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NTE1885 Datasheet PDF : 4 Pages
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Description of Operation:
Constant Current Chopper Drive
a) When the phase drive input is activated, the motor winding current increases. At a predetermined
current (the rated current of the motor), the applied voltage of the winding begins to be switched
ON–OFF to maintain a constant current.
This is the constant–current chopper drive by PWM offering a higher efficiency (30% under a cer-
tain condition) than a constant–voltage drive, but causing relatively large noise due to the switch-
ing operation. The PWM method consists of self–excitation and separate excitation methods. For
the separate excitation, an oscillator is required, as PWM is externally conducted. The self excita-
tion method has a simpler circuit, not requiring an oscillator, but using the resistance and induc-
tance of the motor winding instead.
b) When a voltage several times larger than the rated voltage is applied to the motor, a change in
the winding currents occurs. The time when the currents reach 63.2% of the rated current (IO)
shows a higher–speed response with regard to the rise of the winding current and acts as a time
constant for the R–L series network with the rated applied voltage.
c) Without a constant current circuit, over current will ramp up to a constant value, so that a constant–
current chopper drive is needed. The chopping is conducted below the constant value, so that
the winding resistance and the rated current must satisfy the following equation:
VCC – Vsat
IO <
R
Where
R: Winding resistance per a phase of the motor + RE1
Vsat: Vsat–1 + Vsat–2
With an increase in winding inductance, the flyback energy is increased and, when transistors for
each–phase drive are OFF, the power loss is increased. Considering b) and c), the following motor
is recommended:
Motor specification (4–phase unipolar stepping motor)
Rated current: 1.0 ± 0.5A/phase
Winding resistance: 10Ω/phase
Inductance: 1 ∼ 10mH/phase
Chopper Operation (Note: TR’s are internal transistors used for reference purposes; D’s are inter-
nal protection diodes; and L’s represent the motor windings)
The operation for a unipolar 2–phase excitation a of 4–phase stepping motor is described as:
When a High–Level input and a Low–Level input are applied to Pin5 (phase A) and Pin6 (phase
A) respectively, TR2 is turned ON. Since one terminal of 1/2 IC1 (comparator) is at GND potential,
the comparator output (point A becomes High), turning ON TR7. This also causes TR1 to be
turned ON and the current in the winding increases as shown by the equation:
i = VCC – V(sat) (l – ε–t/τ)
R
Where
also
τ: = L/R time constant
L: Winding inductance per phase
R: Winding resistance per phase plus emitter resistance, etc.
Vsat: = Vsat–1 + Vsat–2
Vsat1: VCE(sat) of chopper transistors (TR1, 6)
Vsat2: VCE(sat) of phase–drive transistors (TR2, 3, 4, 5) and Vd (Diodes, internal)
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