Design Idea DI-128
PeakSwitch
35 W (75 W Peak) Variable-speed
DC Motor Drive
Application
Device
Power Output
Input Voltage
Output Voltage
Topology
DC Motor Drive
PKS606Y
35 W (75 W Pk)
90-265 VAC
12 V
Flyback
Design Highlights
supplied3.6Vto10VDCvoltagesource(connectedtoJ4). The
motor speed controls vary the output voltage of the supply.
•
•
•
Replaces a two-stage, linear power supply and chopper
circuit with a simple, single-stage design
Eliminates the chopper circuits normally used to
achieve variable-speed control of DC motors
Motor speed is controllable by a small potentiometer or
a 3.6 V to 10 V variable DC voltage
The controller in U1 receives feedback from the output and
enables or disables the switching of its integrated MOSFET.
Regulation is maintained by disabling or skipping MOSFET
switching cycles. The output voltage is sensed across the
series string of R12, Zener diode VR2 and the LED in U2
(in parallel with R13). As the output voltage rises above the
VR2 conduction threshold, the current that flows through the
U2 LED turns on transistor Q3. As Q3 pulls current out of
the EN/UV pin of U1 switching cycles are skipped and less
energy is transferred to the output. Once the output voltage
falls, switching cycles are enabled again.
•
•
•
•
Low component count: only 47 parts
Efficiency: ≥77% (at a load of 35 W)
Meets EN55022 B conducted EMI limits
ON/OFF control scheme is stable over the entire motor
speed (output voltage) range
Operation
The flyback converter shown in Figure 1 uses a member of
the PeakSwitch family (U1, a PKS606Y) to drive a 35 W
motor, while delivering startup and load transition peaks of
up to 75 W. The motorʼs speed is variable by two methods:
1) potentiometer R20 (connected to J3), or 2) an externally
Abiaswinding(T1,pins4and5)onthetransformerisrectified
and filtered by D7 and C6, and supplies operating current to
U1, through R7. AsmartAC sense circuit–comprised of D5,
C7, R5 and R6–enables the under-voltage lockout (UVLO)
and latching shutdown functions of U1. The frequency jitter
C10
1 nF
250 VAC
C11
330 pF
1 kV
R8
68 Ω
1/2 W
9,10
7,8
R20
5 kΩ
J3-1
J3-2
D8
MBR1060
C15
100 nF
50 V
1
3
2
R12
4.99 kΩ
1%
C4
180 µF
400 V
D1-D4
1N4007
VR1
P6KE200A
200 V
C17
4700 pF
1 kV
C5
470 pF
1 kV
C20
680 µF
25 V
+12 V
JP3
C12
680 µF
25 V
R15
2.2 Ω
1/8 W
R3
150 Ω
1/2 W
J2-1
J2-2
D12
1N4148
MOTOR
D6
FR106
5
C6
47 µF
35 V
4
R19
2 kΩ
RTN
D5
1N4007
L1
5.3 mH
1 A
VR2
1N5222B
2.5 V
R1 & R2
1.3 MΩ
R5
2.2 MΩ
R7
4.7 kΩ
PeakSwitch
U1
PKS606Y
J4-1
J4-2
D7
1N4148
RT1
10 Ω
C3
680 nF
+
O
C7
100 nF
400 V
R6
2.4 MΩ
t
C19
1 nF
250 VAC
R13
1 kΩ
D
S
JP1
EN/UV
BP
U2B
PC817X4
275 VAC
GND
U2A
C21
PI-4519-110606
PC817X4 1.0 µF
Q3
2N3904
50 V
F1
3.15 A
C8
220 nF
50 V
C2,C1
100 pF
275 VAC
R18
20 Ω
1/8 W
JP2
H
PE
L
CON3
Figure 1. Circuit Diagram of 35 W Continuous, 75 W Peak, Motor Drive Power Supply with Dual Speed Control Inputs.
November 2006
DI-128