Under Over Voltage Detector
The function of this circuit is to detect and report Under/Over Voltage per phase. Three of these circuits are
used to monitor individual phase lines. The circuitry provides two outputs namely UVOUT and OVOUT which are
at CMOS levels and is fed to the MCU. The MCU further monitors these six different inputs and protects the
motor from damage. The input to circuit is provided from individual phase lines from the phase detector’s DC
voltage outputs named XOUT (where X denotes R/Y/B phase).
Circuit Design
The circuit is designed using a CMOS comparator type LM393AD from National Semiconductor. The chip
contains two comparators in a single 8 pin package and 3 identical circuits are used to detect Under/Over
Voltage per phase. The circuitry compares input voltage divided down by the 10K potentiometer with a
reference voltage of 5VDC applied at non inverting input of comparator A and inverting input of comparator B
for detecting Over and Under voltages. The Comparator A compares applied input voltage at the inverting
terminal with reference voltage of 5VDC applied at the non inverting input and if the voltage at applied input is
greater the comparator will output an active low at its output pin indicating an Over Voltage state. Now similarly
if the input voltage is less than 5VDC the B comparator will output an active low output voltage at its output
terminal indicating an Under Voltage state. Normally when the input voltage remains at 5VDC levels both the
comparator outputs will remain at CMOS compatible high levels (2-3.7VDC).
VDD
5V
PHASE-VIN
8
U1A
3
R1
1k
R2
1k
1
R7
OVOUT
2
10k
4
LM393AD
8
U1B
5
7
UVOUT
6
4
LM393AD
Complete Schematic of the Under/Over Voltage Detector
LM393 Comparator
General Description
The LM193 series consists of two independent precision voltage comparators with an offset voltage specification
as low as 2.0 mV max for two comparators which were designed specifically to operate from a single power
supply over a wide range of voltages. Operation from split power supplies is also possible and the low power
supply current drain is independent of the magnitude of the power supply voltage. These comparators also have
a unique characteristic in that the input common-mode voltage range includes ground, even though operated
from a single power supply voltage.
Internal Device Circuit & Package Dimensions
Simulation
The simulation of complete circuit was carried out in Multisim 11 before it was fabricated and tested. The
simulation results are shown below using logic probes at the phase detector outputs. An input voltage of 10VDC
was provided in the simulation using a DC voltage source. The voltage divider potentiometer was kept at 50%
and the input voltage was varied to test under and over voltage conditions.
VDD
5V
X1
8
U1A
3
R1
1kΩ
2V
1
V: 5.00 V
I: -25.0 nA
2
Probe3
4
LM393AD
X2
8
U1B
5
R2
1kΩ
7
V1
10 V R3
50%
1kΩ
Key=A
6
4
LM393AD
UV/OV detector outputs with 10VDC input (Normal Condition)
2V
VDD
5V
X1
8
U1A
3
R1
1kΩ
2V
1
V: 4.50 V
I: -50.0 nA
2
Probe3
4
LM393AD
X2
8
R2
1kΩ
U1B
5
2V
7
V1
9V
R3
50%
1kΩ
Key=A
6
4
LM393AD
UV/OV detector outputs with 9VDC input (Under Voltage Condition)
VDD
5V
X1
8
U1A
3
R1
1kΩ
2V
1
V: 5.50 V
I: 17.8 pA
2
Probe3
4
LM393AD
X2
8
U1B
5
R2
1kΩ
7
V1
11 V R3
50%
1kΩ
Key=A
6
4
LM393AD
UV/OV detector outputs with 11VDC input (Over Voltage Condition)
2V
Fabrication
The fabrication of complete circuit was done on a general purpose Printed Circuit Board.
Following is a component placement layout of the PCB with the track routing. The tracks were routed using bare
copper wire soldered to the 0.1” grid pads on the General Purpose PCB.
Component Placement and track layout for the General purpose PCB
Testing
Testing was carried out using a single phase 230VAC line. And the output from the 15VDC phase power supply
was given to another voltage divider potentiometer for simulating UV/OV conditions.
Test Results with different phase availabilities