DRIVING METHODS AND DRIVING CIRCUITS Eu -contlnued £v
FOR BRUSHLESS DC MOTORS WITHOUT r"('3 r4) = I- + Ew = Vs - — + £« = ^
ROTOR POSITION SENSORS
5 FIG. 2 shows a conventional brushless DC motor
BACKGROUND OF THE INVENTION driving circuit applied to the driving method of FIG. 1.
-r, . . 4. i * . j ■ • r As shown in FIG. 2, it is constructed by coils la, lv,
The present invention relates to driving circuits for a , , . , „ ■ e. c .'
. ... , . ., ° . . 1h> correspondent with phases (hereinafter, referred to
rotor position sensorless, i.e. not having a rotor position , r -i \ „• » m T>-> <
u i.i T-.^ ■ i , J • as phase-corresponding coils), resistors Rl, R2 for exsensor, brushless DC motor, more particularly to dnv- * • r • i. i i
', I . i. . f, „^ 10 trading a rotor position information by using back elec
vng methods and driving circuits for a brushless DC tromotive forces of the ... coils la,
motor which enable high speed functions of the DC ly> y CQm K ^ 3 3w for determimn which of
motor to be attained rn a DC motor-used headphone- the phase.correSponding coils la, lv, lw is selected,
type stereophonic product, by enhancing the maximum power transistors Q1> Q2; Q3 for making a current flow
speed of a rotor position sensorless brushless DC motor. 15 through the one of the phase-corresponding
In general, a rotor position sensorless brushless three- coils lu> lv> lw> ^ transist0rs Q4, Q5, Q6 for turning
phase DC motor can be minimized m its size because it off by means of the turnKJn signal of a next ^ one of
has no rotor position sensor. Accordmg to this, its appli- ^ phase-corresponding coils lu, lv, lw which is active,
cation to a light, thin and simplified product such as a operation of the conventional circuit will be
headphone-type stereophonic product or the like is 2o described below with reference to the waveforms of
very useful. FIG. 1.
In the meantime, since it is a general trend to use a Referring to FIG. 1, a high potential signal output
single dry cell of 1.5 voltages as a power supply in a from the comparator 3u at time tl makes the transistor
product such as a headphone-type stereophonic prod- Qi turn on so that an electric current flows through a
uct or the like, the driving method for the rotor position 25 coil la for the u phase (hereinafter, referred to as a
sensorless brushless three-phase DC motor used in the u-phase coil). That is, at this time, the transistor Q4 is
product should be also active under a low voltage. forced to be turned off because the transistor Q2 is
Thus, the unipolar driving method which allows only turned off and the transistor Q7 is turned on. a one-directional current flow in the motor coils can not Accordingly, at this time, since the power supply Vs be employed because of the problems caused by the 30 is applied to the non-inverting input terminal of a cornintegration of PNP power transistors and a voltage parator 3u and a bit lower voltage than the power supdrop between the collector and emitter of the power ply Vs is applied to the inverting input terminal of the transistor. comparator 3a, the output of the comparator 3u be
FIG. 1 is waveforms showing the relationship be- comes high potential. This high potential signal causes a
tween induced voltages which are back electromotive 35 transistor Ql to be turned on so that an electric current
forces in accordance with phases of the brushless DC flows through the u-phase coil lu. And also, at this time,
motor and turn-on time periods, having laid open in since the turn-on of the transistor Ql makes a transistor
Japanese laid-open patent publication No. 58-172994. Q9 turn off and thus a transistor Q6 is turned on, the low
As shown in FIG. 1, a phase difference of an electric potential signal applied to the non-inverting input termi
angle §77 exists among the induced voltages Eu, Ev, Ew 40 nal of the comparator 3w makes its output low potential,
in accordance with the respective phases. Since the low potential signal turns the transistor Q3
That is, a 120° phase difference exists as shown below off so that no electric current flows through a coil lw
in equations (1), (2) and (3). f°r tne w phase (hereinafter, referred to as a w-phase
coil) and also the turn-off of said transistor Q3 makes a
Ev - Sin 6 45 trans'stor Q8 tum on 80 ^at a transistor Q5 is turned
"~~ off, the power supply Vs is applied to the non-inverting
(2) input terminal of the comparator 3v.
Ev = Sin [ e - — Tt | However^at this time, since the voltage of a connec
\ 3 / tion point (v) applied to the non-inverting input terminal
50 of the comparator 3v becomes higher than the power
/ \ (3) supply Vs and thus the output of the comparator 3v
Ew = Sin I e - -j. v J appears low potential, a transistor Q2 is turned off.
According to such operations as mentioned above,
. , when the time t2 of FIG. 1 is met with a 120* rotation
When the motor rotates in a sequential order of u v „ of {he ... since tfae yol a{ ^ ^mt 0
and w phases, 60 before and 60 after the moment that a bk Jower than the , Vs ^ tmjs^
each of the phases generates the maximum torque, i.e. the output of the comparator 3v becomes high potential,
120 , become one of the turn-on time periods Tu, Tv, the transistor Q2 is turned on so that an electric current
Tw of the respective phases. flows through a 1v for the v phase (hereinafter,
The turn-on time periods Tu, Tv, Tw of the respec- ^ referred to as v-phase coU). At this time, the turn-on of
tive phases can be expressed as m equations (4), (5) and the transistor Q2 makes the transistor Q7 turn off so that
the transistor Q4 is turned on, causing the output of the comparator 3a to be low potential.
Tu(i\-a) = Er + Eu m Vs — Ew + Ev = Vs (4) Since the low potential signal makes the transistor Ql
2 2 65 turn off, no electric current flows through the u-phase
Ew Eu (51 CO''
Tu(a-a) = -j- + £" = ^ — ~y~ + Ew= vs And also, at this time, since the turn-off of the transistor Ql leads a transistor Q9 to a turn-on state, the tran
