MC33035 Datasheet, PDF (19/28 Pages) ON Semiconductor – BRUSHLESS DC MOTOR CONTROLLER

MC33035, NCV33035
Figure 38 shows a three phase, three step, half wave motor
controller. This configuration is ideally suited for
automotive and other low voltage applications since there is
only one power switch voltage drop in series with a given
stator winding. Current flow is unidirectional or half wave
because only one end of each winding is switched.
Continuous braking with the typical half wave arrangement
presents a motor overheating problem since stator current is
limited only by the winding resistance. This is due to the lack
of upper power switch transistors, as in the full wave circuit,
used to disconnect the windings from the supply voltage
V_M. A unique solution is to provide braking until the motor
stops and then turn off the bottom drives. This can be
accomplished by using the Fault Output in conjunction with
the Output Enable as an over current timer. Components
R_DLY and C_DLY are selected to give the motor sufficient time
to stop before latching the Output Enable and the top drive
AND gates low. When enabling the motor, the brake switch
is closed and the PNP transistor (along with resistors R₁ and
R_DLY) are used to reset the latch by discharging C_DLY. The
stator flyback voltage is clamped by a single zener and three
diodes.
Motor
Fwd/Rev
60°/120°
V_M
4
5
6
Rotor
Position
Decoder
3
22
7
25 µA
17
Undervoltage
Lockout
18
C_DLY
14
R₂
R₁
R_DLY
2
V_M
1
24
Speed
Set
Faster
R_T
Reference
Regulator
8
11 ^{Error Amp}
12
PWM
13
10
Oscillator
C_T
Thermal
Shutdown
R
Q
S
S
Q
R
21
20
19
I_Limit
9
15
Gnd 16
23
Brake
Figure 38. Three Phase, Three Step, Half Wave Motor Controller
http://onsemi.com
19
N
S
S
N