Drive circuit for brushless DC motors

A drive circuit for brushless DC motors comprising a rotor and a stator with at least one stator coil includes a commutation device which supplies commutation pulses of drive current to the stator coil(s). The commutation device senses the rotor position and calculates current rotor speed therefrom. The rotor speed is then used to shift the commutation currents according to predetermined functions. The shifting of commutation currents is occasioned by shifting either or both of the ignition part of a commutation pulse and the extinction part of such pulses.

The invention pertains to a drive circuit for brushless dc motors according 
to the preamble of claim 1. 
Drive circuits of this kind are known from DE-OS 35 37 403 A1. These 
circuits exhibit a number of properties that are advantageous for the 
operation of a commutatorless dc motor. 
Sample functions include: 
low loss speed control of the motor, 
temperature governed speed control of the motor, 
signal output in case of excess temperature, 
reduction of acoustic and EMI radiation. 
One particular advantage of these circuits consists in the fact that they 
can be fully integrated onto a relatively small silicon module (chip). 
There, these circuits on their allocated silicon module, represent a very 
high functional density. It is therefore difficult and complicated to 
implement additional module functions of this type since signal functions 
and performance control functions will have to be present side-by-side on 
the same silicon chip. 
For greater power or higher speed motors, however, more extensive speed 
control functions and control functions are required. 
In addition, it is an advantage to achieve a yet higher efficiency for the 
motor and associated drive circuit. 
Therefore, it is the task of the invention to describe an electronic 
circuit that will ensure an improved overall efficiency for the drive 
circuit and motor by means of a wider speed range and to include an 
expanded level of functions. 
This problem is be solved by the features of the characterizing portion of 
claim 1 or by the secondary claim 2. 
The invention is suitable both for single phase motors with permanent 
magnetic auxiliary torque according to DE-OS 23 46 380, and also for 
multiphase motors or commutatorless motors without permanent magnets 
(reluctance motors). 
The invention is based on the fact that for purposes of additional energy 
savings through increasing the overall efficiency of the motor and drive 
circuit, the following activities are be combined: 
First, according to this invention it is an advantage specifically to shift 
in time the rising and/or falling edges of motor current pulses by means 
of a suitable circuit, and, of course, especially as a function of the 
speed of the motor. This will achieve both reliable start-up behavior and 
also good efficiency for the motor. 
For all motors in the range of high and maximum speed, it is an advantage 
to shift forward the moment of connection of a motor current pulse in 
order to provide the necessary current maximum in a timely manner due to 
the finite rate of rise of a motor current pulse. Depending on the motor 
and speed range, shifts of the commutation timing by several ten degrees 
(electric) is an advantage. 
In the case of motors with permanent magnetic auxiliary torque, it is 
particularly useful to shift the turn-off edge of a motor current pulse 
forward in time within the range of minimum speed (increase of the 
extinction angle), where the stated extinction angle can amount to as much 
as about 90.degree. (electric). 
After start-up of the motor (ramp phase) within an average speed range, 
normally no essential shift in the moments of commutation is needed, 
whether for the ignition angle at the beginning of current flow or for the 
extinction angle at the end of a motor current pulse. 
In this range, therefore, we can succeed, even without specific measures, 
in bringing the time rise of a stator current pulse into approximate 
coincidence with the shape of the induced counter-EMF of an (unconnected) 
stator coil, in a generally known manner. 
Secondly, the first activity according to this invention, is combined with 
a circuited (clocked) current flow to the motor (i.e., usually the 
stator), and, of course, with a clock frequency preferably outside of the 
range of human hearing. 
This measure has the advantage that by means of differing individual pulse 
widths in the clocked method of current flow, the effective motor current 
can be preset and adjusted in a simple manner without any large losses in 
performance due to this adjustment process, as is already generally known. 
In addition, in a similarly known manner, the advantage results that the 
effective, maximum rate of rise of the motor current can be increased 
through simultaneous increase in the supply voltage. 
It is understood that the supply voltage cannot be increased indefinitely, 
so that also the effective maximum rate of rise of the motor current 
remains limited to a finite value. 
For high motor speeds it is therefore an advantage to effect a preshifting 
of the ignition timing, even in the case of circuited or clocked motor 
current. 
In this case, one decisive parameter, in addition to the motor speed, is 
the electric time constant of the motor coils: the ratio of inductivity to 
resistance, L/R. 
In addition, according to the invention it is an advantage to modify the 
high frequency timing of the motor current during one commutation phase in 
the direction of smaller pulse duty factors, and, of course, toward the 
end of one commutation phase. It has proven advantageous to reduce the 
percentage of the pulse duty factor in two steps each of about 5% after 
passage of 50% and 75%, respectively, of one commutation phase. This will 
also avoid additional expense as is necessary in a continuous reduction of 
the pulse duty factor during one current flow phase, and, furthermore, the 
latter method has the same or better power reduction effect. 
In a third aspect of the invention actions are illustrated that will ensure 
the provision of differing ignition or extinction angles and thus cause a 
preignition or advanced extinction of a motor current pulse. 
Proceeding from a standard ignition with an ignition angle of zero, it is 
initially not possible in the range of high and maximum speed of the motor 
to implement in advance any commutations without a knowledge of future 
moments of commutation, as this is actually necessary for preignition 
(according to definition). 
According to this invention, in order to solve this problem, the signal 
output for a commutation is undertaken by means of a galvanomagnetic 
sensor. However, in this case the sensor is intentionally placed at a 
location, e.g., between stator and rotor, that will cause a forwardly 
shifted signal output of, e.g., 5.degree. (electric), as compared to 
normal signal output. By means of a delay feature in the drive circuit, a 
delay in these commutation signals will also be possible. Thus it is 
possible to generate advance ignition angles up to a specified angular 
value. A delay feature that can delay the commutation signals in a 
variable manner is a particular advantage, so that the actual start of a 
commutation process can take on any value between the stated value and 
later phase angles or moments. 
At greater speeds that can necessitate a more prominent forward shift of 
the ignition angle, the problem again arises of the absence of knowledge 
of the phase position of the rotor at the desired moment of ignition, at 
which the commutation process of the stator current is to begin. In 
addition, the problem exists that the optimum moment of commutation is 
being shifted constantly, i.e., depending on the speed of the rotor, it 
consists of another phase position or speed setting of the rotor. 
However, according to the invention, in this case, a solution is possible 
according to the following logic: 
The additionally necessary phase preshifting of the moment of ignition 
occurs practically only at high speeds. At these speeds, the rotational 
motion due to the mechanical inertia of the rotor, i.e., of the stored 
mechanical energy, is determined practically for several future rotations 
of the rotor. 
Accordingly, it is possible, with a knowledge of the current rotational 
speed of the rotor and of the last moment of signal output of the 
rotational position sensor, to calculate a moment that corresponds to a 
desired or necessary, future moment of ignition at the current rotational 
speed (angular velocity) of the rotor. 
In this case, according to the invention, a generally known device will be 
used that determines the rotational velocity of the rotor from the 
progress of the last determined sensor signals. 
In this case, the following mathematic relation will be used: 
EQU Z=K(n)+(K(n)-K(n-1))*(1+.phi.(.omega.)/360.degree. (el.)) 
where 
Z is the time of the prognosticated or extrapolated, future, next moment of 
ignition, while K(n) or K(n-1) is the moment of the last or next to last 
output signal of the sensor. 
.phi.(.omega.) represents the necessary speed-dependent angle of the 
preignition which always has a negative sign with regard to a standard 
commutation with ignition offset 0. 
In a preferred circuit design it is provided that the forward shifting of 
the ignition timing increases linearly with increasing speed of the motor. 
This takes place in a range between a motor-typical reference speed and 
the maximum permissible motor speed. 
The rise in the associated characteristic curve that shows the forward 
shift as a function of the speed is also typical of the motor. Reference 
parameters of this type that are typical of the motor, will be placed in a 
simple manner as table values in the memory of the circuit configuration. 
It is a precise method to perform the forward shifting of the ignition 
timing in a nonlinear manner, for example, according to a characteristic 
curve in the form of a hyperbola. Parameters of this type can also be 
stored in the memory area of a circuit device. 
A compromise solution between linear and nonlinear forms of the 
characteristic curves according to this invention consists in approaching 
nonlinear regions by means of stepwise, linear regions. 
For particular regions it is possible according to the invention, also to 
implement unsteady transitions of the characteristic curve. 
The actions to shift the falling edge of a (stator) current pulse will also 
be carried out accordingly with a delay device to delay the rotational 
setting-sensor signal for the definition of the moment of commutation. 
One preferred solution consists in delaying the signal of the rotary 
position sensor by a comparatively long time span by means of a delay 
device of this type in order then to suspend the current flow to the motor 
temporarily at the delayed moment. 
This can occur, e.g., by specifying a pulse duty factor with value zero. 
This method will be simplified in an advantageous manner by the use of 
microprocessor functions--likewise for the design of the delay itself. 
It is also the advantage to make the stated delay of the signal of the 
rotational position sensor dependent, in a nonlinear manner, on the speed 
of the motor. 
In particular, in the case of motors with permanent magnetic auxiliary 
torque, a delay feature with the following operation will be used 
according to this invention: 
In the ramp range up to a speed of about 600 rpm, an extinction angle of 
0.degree. (electric) will be retained; that is, no preshifting of the 
shut-off timepoint will take place. Above this speed value, an extinction 
angle of about 40.degree. (electric) will be specified which will be 
reduced up to a rated speed of about 3000 rpm in a continuous, preferably 
linear manner to the value zero. 
In every case it is an advantage to place values belonging to the curve 
profile into a memory or in an electronically readable table. 
Therefore, it is a benefit to provide a circuit design in the device for 
the above stated functions of the control circuit that contains a 
microprocessor or controller. 
According to this invention this, opens up the potential to provide a 
number of additional functions for the control circuit, where the 
increased hardware and software effort in comparison to the attainable, 
additional benefit is small or is to be judged favorably. 
If an expansion of this kind of drive circuit is to be undertaken at a 
later time, so that yet more functions will be added, then, as a rule, 
this is not particularly difficult. 
Now the additional functions pertain primarily to checking and control or 
regulation functions that are supplied both with regard to external 
physical parameters, and also with regard to internal motor parameters. 
For the stated external physical parameters, we are dealing, for example, 
with temperatures. This will be measured, e.g., by means of a 
temperature-dependent resistor and fed to a microprocessor that converts 
the different levels of resistance values into temperature values. The 
resistance values will be checked for plausibility. Deviations from a 
permissible value range will be recognized by the microprocessor and cause 
an alarm signal. 
According to a computed temperature or another physical parameter, the 
microprocessor or the drive circuit determines what speed the motor is to 
use by means of a predefined table or by means of a specified function. 
This desired speed will be compared with the actually occurring speed. 
Deviations between the desired and actual speed will be minimized or 
eliminated through an appropriate change in motor current. 
In this case, the drive circuit has a device, as discussed above, with 
which the motor current can be fed at high frequency in differing wide, 
individual pulses. By means of this current setting feature, therefore, a 
speed control is possible for the motor. Furthermore, it is also possible 
to limit the motor current with this device. 
When the rotor of the motor is blocked, a speed control device usually 
tries to bring the motor back into rotation by means of maximum current. 
However, this can lead to excessive motor temperature and possibly to 
damage to the motor. 
Therefore, according to the invention, a device is provided that will 
determine the motor current punctually at specified times, and limit the 
motor current to a specified value. 
For the case of a blocked rotor, a device is also provided that will cause 
a short-term, super-elevated motor current, whereupon rated current will 
be fed to the motor for a time and a check run will be initiated to 
determine whether this kind of start attempt has set the rotor in motion. 
If this is the case, then a normal motor power feed will take place as 
described above. 
Otherwise, a current interrupt will occur, so that the motor can cool off. 
After a preadjustable time, a renewed start attempt will be performed in 
the same manner. 
In addition, it is possible to perform improved alarm functions for motor 
operation. These functions consist, for example, in maintaining a constant 
coordination of motors when several motors are operating in parallel. 
For this purpose, of course, communications or alarm signal features can be 
provided that are performed according to this invention by means of the 
mentioned microprocessor. Another improvement for an alarm function 
consists in the fact that the output alarm signals can contain 
supplemental information so that an easier and more reliable validation of 
a registered alarm is possible. 
This will be set up according to the invention so that a valid alarm signal 
may have only one prespecified minimum or maximum size. Another solution 
consists in an alarm signal having at least one ac voltage signal 
component of predefined frequency and amplitude characteristics.

FIG. 1 illustrates how the shift in the extinction angle per this invention 
will be undertaken for a motor with permanent magnetic auxiliary torque as 
a function of the speed of the motor. 
The speed of the motor is plotted on the abscissa; depending on the 
particular application, it can also take on greater values than shown. 
The value of the preliminary shift of the moment of commutation (extinction 
angle) is plotted on the ordinate in degrees (electric). 
The speed range below 700 rpm is identified with symbol "A" and comprises 
the line segment 11. 
The speed range includes the start-up and an initial ramp range of the 
motor and has no preshifting of the extinction angle. 
Line segment 12 pertains to a second ramp range of the motor and exhibits 
continually falling extinction angles that amount to a maximum of about 
60.degree. (electric). 
A preshifting of the extinction angle or also of the ignition angle for a 
motor current pulse takes place according to this invention by means of a 
delay of a commutation signal that in itself is advanced by a phase angle 
of about 5.degree. (electric) with regard to a zero crossing of the 
induced voltage of a stator coil. 
A delay in the ignition signal of this type such that an effective ignition 
angle of, e.g., zero degrees (electric) will set in; it will thus be 
undertaken as follows: 
From the preceding determinations of the (advancing) ignition signal, the 
current speed of the motor will be recognized if one determines the time 
differences between sequential ignition signals, e.g. with a timing 
component. If a pulse sequence from a crystal oscillator is counted out 
between two such signals, then, in a very accurate manner it is possible 
to determine the elapsed time difference. The reciprocal value of this 
time difference is known to be a frequency that differs from the angular 
velocity by a factor of 1.times.3.1415 or n.times.3.1415, where n is a 
natural number. With the general relation .phi.=.omega..times..tau., 
according to which an angle of rotation is computed as the product of 
angular velocity multiplied by a time difference, the drive circuit delays 
the ignition signal by means of a built-in delay circuit by precisely the 
time necessary to define a desired, advanced (possible delayed) moment of 
ignition or extinction, at the current speed of the motor, at which the 
commutation process will be initiated or ended for the stator current fed. 
As we can see from FIG. 1, in a speed range of over approximately 25% of 
the rated speed, the extinction angle will be reduced with increasing 
speed, and, of course, with the above-mentioned delay techniques. 
For the delay of a previously occurring moment of ignition, it is possible 
to use the phase offset of the commutation signal as an advantage. For the 
medium to high speed range accordingly, an adaptation of the optimum, 
speed dependent preignition point can be effected by means of a delay in 
the signal of the galvanomagnetic rotational position sensor. 
This is possible up to a speed at which no more delay takes place between 
the signal output through the positional setting sensor and the initiation 
of the commutation process. This means that the preignition has the same 
electrical phase offset as will correspond to the geometric offset of the 
signal generator. 
An additional preliminary shift of the ignition angle in a high to very 
high speed range for the motor is thus possible according to the invention 
only when a preceding signal from the rotational position sensor is 
delayed in phase by the difference between the electrical angle for a 
commutation phase, e.g., 180.degree. or 360.degree. (electric) and the 
desired, advanced ignition angle, and effects the beginning of a 
corresponding commutation process. 
Therefore, by calculation and moderate sequencing of the delay of the 
equivalent commutation or ignition signal, this corresponds to a 
relatively large angle that is smaller than 180.degree., 360.degree. 
(electric), etc. For three-phase and higher-phase motors, therefore, a 
delay of somewhat less than 120.degree. (electric), 90.degree. (electric) 
etc., will be needed, and it must be taken into account whether the 
particular motor is to be designed as single pulse or double pulse. 
For this method as well, the above referenced method for delay by the drive 
circuit will be used to advantage; this drive circuit will be prepared in 
a particularly economical manner by digital means. 
As is evident from the foregoing, this type of moment of ignition 
definition is not strictly causal, since the commutation process takes 
place at a time that has to be extrapolated or prognosticated. 
FIG. 2a shows a function with reference number 21 that reproduced the 
speed-dependent improvement of the overall efficiency for a motor and its 
drive circuit. 
This function is different from one type of motor to the next. 
FIG. 2b explains how the extrapolation of a desired moment of ignition at 
high speeds can be carried out with a predictor segment 26 of the drive 
circuit. 
On the time axis denoted by the letter "t," the previous moments of 
ignition Z1, Z2, Z3, Z4 and Z5 are plotted. They differ by advancing, 
individual time or phase angle components from the moments of the 
commutation signal output K1 . . . K5 which have been delivered by the 
rotational position sensor of the motor. 
From the last recorded time difference K5-K4, the speed of the motor is 
known, and the future commutation process at time Z will be undertaken in 
the range of about 300.degree. . . . 360.degree. (electric) later, 
depending on this known speed; see the formula stated above for time Z. 
FIG. 3 shows the relation between a time or angle value of a commutation 
phase of a motor and associated specified values of the pulse duty factor 
ED. A low cost profile of the pulse duty factor of specific, high 
frequency motor current pulses with a frequency of more than 5000 Hz will 
be represented by the line that emanates from point "a" on the ordinate 
and then connects points 31, 32, 33, 34 and 35. Up to a time that 
corresponds to about 50% of a commutation phase of the motor, a pulse duty 
factor with a percentage "a" will be used. Then, up to a value of about 
75% of a commutation phase, this percentage will be reduced by a factor 
f1. For the remainder of the commutation phase, an even smaller factor f2 
will be specified. 
With a somewhat more complicated drive circuit it is also possible to 
implement a prespecified or preprogrammed profile of the pulse duty factor 
in continuous form. 
Functions b) (reference number 37) and c) (reference number 38) show this. 
The general pulse shape of an associated stator current average value will 
be symbolized by function 36. It is important that the current not rise 
toward the end of the commutation phase, as is otherwise the case, 
provided no corresponding current limitation activities are undertaken. 
Activities of this type with circuit features from analog technology are 
already known and have the advantage as in the case described here, of 
reducing the operating noise of a motor. 
A comparable power curve is shown in FIG. 4. A commutation phase extends 
from the origin of the coordinate intersection up to the time T. Within 
this time, power is applied with single pulses of the specified pulse duty 
factor ED, where the single pulses exhibit a repetition frequency of 
1/42.5 .mu.sec, and in the specific case of FIG. 4, they begin with a 
pulse duty factor of 100%. 
FIG. 5 explains the relation between a determined temperature, e.g., an air 
temperature, and an allocated, preprogrammed desired rpm. Function 53 
consists of several linear segments that have a linearly rising transition 
53 between the onset point 51 and end point 52. For temperature values 
below about 35.degree. C., a lower speed for the motor will be specified, 
while above about 70.degree. C., a maximum motor speed n(max) should be 
reached. 
A continuous run with lower onset point 55 is represented by function 54. 
The motor should then be shut off below a temperature of 10.degree. C. At 
a temperature of about 25.degree. C., the motor should already be running 
at 50% of the maximum motor rpm. 
FIG. 6 shows how a speed n(nominal) of the motor can be fixed to the 
desired, e.g., temperature-dependent, value 62, by means of a control 
process. If the operating point 63 is abandoned at lowered rpm, then the 
motor current I will be increased by increasing the pulse duty factor for 
the individual pulses. A maximum current I(max) (reference no. 60) will 
not be exceeded however, since the actually flowing motor current will be 
converted into a measured voltage by means of measurement resistors 18 and 
19, which will be converted into a digital value by the A/D converter ADC2 
of microprocessor 1104. 
In case of excessive current, the drive circuit will then reduce the total 
motor current. To do this, it will use the microprocessor 1104 that 
produces single stator current pulses with reduced pulse duty factor (see 
FIGS. 11a and 11b). 
The named speed control with the goal of providing a reliable 
temperature-independent speed value of the motor, for example, takes place 
according to standard methodology, inasmuch as the so-called PID control 
will be designed with digital features in the control circuit. An 
attendant control level in the drive circuit will then adjust the motor 
current, depending of the deviation of the actual speed of the motor from 
a desired speed, and this will continue until the required, desired speed 
is reached. 
This takes place according to the known state of the art inasmuch as the 
power will be supplied proportional to the deviation (P component for the 
control, characterized by the factor k(p)), but also as a function of the 
size of the preceding or following number of motor revolutions (I 
component of the control), or also depending on how fast the desired and 
actual speeds are moving apart (D component of the control). 
Normally, the procedure is such that the speed will be determined at 
equidistant time points. By using control factors held constant that are 
allocated to the referenced P, I and D components of the speed deviation, 
a motor power feed will then be implemented that will effect the desired 
speed of the motor within, usually, a short time. 
But in the case of the invention it is more advantageous not to determine 
the speed as equidistant time points, but rather to carry out the speed 
determination within the cycle of the output of the commutation signal. 
But this means that an application of constant control factors will not 
lead to a satisfactory speed control. Since the drive circuit is equipped 
with a microprocessor anyway, according to the invention, it is 
advantageous to adjust the control coefficients to the different length 
sensing interval (determinative interval) for the rpm. This applies, in 
particular, for the control coefficient k(p) for the proportional 
component. 
FIG. 7 shows how this kind of adjustment can be effected by simple means, 
as a function of the motor speed. 
In the range of about 60% to 100% of the maximum speed n(max) the 
characteristic curve range 72 exhibits a nominal weight of 100% for the 
control coefficient k(p). 
If the motor has only a speed of about 40% to 60% of the maximum speed, 
then due to the then lengthened sensing time interval, a weight of 50% 
will be used for the control coefficient k(p) (characteristic curve range 
71). Beneath this speed range, a characteristic curve range 70 will be 
used that has a weight of only 12.5% for k(p). With the stated weights of 
100%, 50% and 12.5%, the necessary time for the calculation step for the 
speed control will be favorably reduced since these weights will allow a 
simple division. 
FIG. 8 shows a block diagram for motor 80 and controller 1104. 
The motor 80 will be powered via the supply line 81 with high frequency, 
single pulses of the correct polarity and the resulting motor current will 
be converted into a digital signal with precision resistor 18 and analog 
digital converter (ADC) 84, which is fed to the power measuring stage 85. 
At the same time, by means of position sensor 82, a position signal will be 
produced for the rotor, which has a phase offset (precession) in 
comparison to the run of stator voltages induced by the rotor. This signal 
will be fed to a time and speed measuring stage 83 whose output signals 
are switched to the shifting stage 93. Their output signals will be sent 
to the controller 1104. Likewise, via temperature sensor 96, a temperature 
will be measured and sent to a temperature control stage 95. At the same 
time, additional control signals that are applied to junction points 98 
and 99 will be sent to this stage. 
The output signal of the temperature control stage will be fed to a speed 
setting unit 87. Another component of controller 1104 is an alarm signal 
generator 86 that outputs an alarm signal to junction point 97 in case of 
incorrect motor rpm or if an over-temperature is registered; this alarm 
signal may also have an overlapped ac voltage component. 
Furthermore, the controller 1104 has an input 93 for a cooperation signal 
that is sent to a compensation unit 88. 
A power stage 89 will be driven by the pulse width adjuster 94 and is 
located either outside of the controller or inside it as an integral unit. 
It is used for direct power feeding to motor 80. 
When the rotor of the motor is blocked, a speed control device usually 
tries to bring the motor back into rotation by means of maximum current. 
However, this can lead to excessive motor temperature and possible to 
damage to the motor. Therefore, according to the invention, a device is 
provided that will determine the motor current punctually at specified 
times, and limit the motor current to a specified value. 
For the case of a blocked rotor, a device is also provided that will cause 
a short-term, super-elevated motor current, whereupon rated current will 
be fed to the motor for a time and a check run will be initiated to 
determine whether this kind of start attempt has set the rotor in motion. 
Such a power sequence is applied to safely free a blocked rotor as long as 
the predefined power sequence is applied to the stator, until the motor 
starts up again. 
FIG. 9 is a timing chart for a motor current specification with the motor 
blocked. For the partial interval 90 with a length of several thousandths 
of a second, a current in the amount of about 120% of rated current is 
used. In the following partial interval 91, the rated current will be 
supplied for about 2 seconds. Next comes a currentless partial interval of 
several seconds duration. This interplay is repeated with the subsequent 
partial interval 90' which corresponds to the partial interval 90, until 
the motor starts turning again. This will be ascertained by a speed check 
toward the end of partial interval 91. 
FIG. 10 explains how the self-secured temperature measurement is 
implemented by means of NTC resistor 101. It is powered via the series 
resistor 100 by a constant supply voltage. At the junction site of the two 
resistors, a temperature-related voltage is picked off that is present at 
the level of the supply voltage in case of fracture of the NTC resistor 
101, or in case of short circuiting of the NTC resistor 101, its value 
will be registered as zero. The temperature-related voltage will be sent 
to an analog digital converter 102 that is an integral constituent of the 
temperature control stage 95. 
A voltage outside of a predefined region leads to an alarm signal, or, 
optionally, to motor shut down, or--provided the motor is driving, e.g., a 
fan--to maximum motor speed. 
The output alarm signal may be provided optionally with additional 
information that will allow a safe or simple validation of the alarm 
signal by an overhead control device. 
One suitable method of the stated kind consists, e.g., in that a valid 
alarm signal will have a suitable signal level that must rest above a 
minimal value and below a maximum value. 
Another method consists in applying at least one supplemental ac voltage 
fraction to the alarm signal. This supplement will be predefined with 
regard to frequency and amplitude, and in case of several ac voltage 
components, it will also be characterized by the mutual phase relation. 
FIGS. 11a, 11b and 11c--which are to be taken together and which are 
provided with associated connecting line symbols--represent an actual 
design of the invention for a commutatorless dc motor with auxiliary 
torque generated by permanent magnet. 
A start-up circuit consisting of relay 1108 and drive transistor 1150, and 
also resistors 1126 and 1128 will prevent power-on current surges and 
cause a smooth start-up of the motor. After passage of a safety period, 
shortly after turn-on of the drive circuit, the motor can be powered at 
maximum permissible current. 
A microprocessor 1104, model B7C752, will be clocked by a crystal 
oscillator 1178, 1179 and 1180 and has a number of digital input and 
output lines, and also a number of input lines for analog signals. 
The output stages 1156, 1157, 1158 and 1159 are driven with pulse generator 
stages 1105 and 1106 via allocated driver stages 1153 and 1154, or they 
are driven directly. 
In the illustrated example, in a known manner, by means of a full bridge 
circuit of transistors 1153, 1154, 1156 and 1157, an alternating current 
is set through the individual motor coils 1170. 
As explained above, the power or commutation takes place according to a 
sensor 1110 that determines the rotor position and its output signal is 
used to determine the rotor speed, where its output signal will be 
modified as a function of the rotor speed in another part of the drive 
circuit for the purpose of motor commutation. 
To implement a large number of the above stated functions, it is possible 
per this invention to use the single controller 1104 as control and 
regulation unit; as we see, it can make do with a minimum of external 
circuit features but will have to be provided with suitable, internally 
stored software. 
Finally, FIG. 11A show a 5 V power supply for the existing logic circuits. 
This power supply is fed by the motor power supply via a prevoltage 
regulator that consists essentially of Zener diode 1149 and regulating 
transistor 1155. At its node with the collector a dc voltage of about 12 V 
is available to power a downstream voltage regulator 1107, model 7805. A 
stabilized dc voltage of 5 V is available at its output.