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Motorola Sensor Device Data
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POWER OPTO ISOLATOR MOC2A60 DESCRIPTION
The MOC2A60 is a new Motorola POWER OPTO
isolator
and consists of a gallium arsenide, infrared emitting diode,
which is optically coupled to a zero–cross triac driver and a
power triac. It is capable of driving a load of up to 2 A (rms)
directly from a line voltage of 220 V (50/60 Hz).
ZVA
*
Device Schematic
1, 4, 5, 6, 8. No Pin
1, 4, 5, 6,
2. LED Cathode
1, 4, 5, 6,
3. LED Anode
1, 4, 5, 6,
7. Main Termnal
1, 4, 5, 6,
9. Main Termnal
* Zero Voltage Activate Circuit
9
7
3
2
CASE 417
PLASTIC
PACKAGE
Figure 2. MOC2A60 POWER OPTO Isolator
SIGNAL CONDITIONING
When a full range pressure is applied to the MPXM2010GS,
it will provide an output of about 20 mV (at an 8 V supply).
Therefore, for an application using only a few percent of the
pressure range, the available signal may be as low as a few
hundred microvolts. To be useful, the sensor signal must be
amplified. This is achieved via a true differential amplifier (A1
and A2) as shown in Figure 4. The GAIN ADJ (500 ohm)
resistor, RG, sets the gain to about 200.
The differential output of this stage is amplified by a second
stage (A3) with a variable OFFSET resistor. This stage
performs a differential to single–ended output conversion and
references this output to the adjustable offset voltage. This
output is then compared to a voltage (VREF = 4 V at TP2) at
the input of the third stage (A4).
This last amplifier is used as an inverted comparator
amplifier with hysteresis (Schmitt trigger) which provides a
logic signal (TP3) within a preset range variation of about 10%
of the input (selected by the ratio R9/(R9 + R7).
If the pressure sensor delivers a voltage to the input of the
Schmitt trigger (pin 13) lower than the reference voltage (pin
12), then the output voltage (pin 14) is high and the drive
current for the power stage MOC2A60 is provided. When the
sensor output increases above the reference voltage, the
output at pin 14 goes low and no drive current is available.
The amplifier used is a Motorola MC33179. This is a quad
amplifier with large current output drive capability (more than
80 mA).
OUTPUT POWER STAGE
For safety reasons, it is important to prevent any direct
contact between the ac main power line and the liquid
environment or the tank. In order to maintain full isolation
between the sensor circuitry and the main power, the
solid–state relay is placed between the low voltage circuit
(sensor and amplifier) and the ac power line used by the pump
and compressor.
The output of the last stage of the MC33179 is used as a
current source to drive the LED (light emitting diode). The
series resistor, R8, limits the current into the LED to
approximately 15 mA and guarantees an optimum drive for the
power opto–triac. The LD1 (MFOE76), which is an infrared
light emitting diode, is used as an indicator to detect when the
load is under power.
The MOC2A60 works like a switch to turn ON or OFF the
pump’s power source. This device can drive up to 2 A for an
ac load and is perfectly suited for the medium power motors
(less than 500 watts) used in many applications. It consists of
an opto–triac driving a power triac and has a zero–crossing
detection to limit the power line disturbance problems when
fast switching selfic loads. An RC network, placed in parallel
with the output of the solid–state relay is not required, but it is
good design practice for managing large voltage spikes
coming from the inductive load commutation. The load itself
(motor or solenoid valve) is connected in series with the
solid–state relay to the main power line.
EXAMPLE OF APPLICATION:
ACCURATE LIQUID LEVEL MONITORING
The purpose of the described application is to provide an
electronic system which maintains a constant liquid level in a
tank (within
±
5 mm H2O). The liquid level is kept constant in
the tank by an ac electric pump and a pressure sensor which
provides the feedback information. The tank may be of any
size. The application is not affected by the volume of the tank
but only by the difference in the liquid level. Of course, the
maximum level in the tank must correspond to a pressure
within the operating range of the pressure sensor.
LIQUID LEVEL SENSORS
Motorola has developed a piezoresistive pressure sensor
family which is very well adapted for level sensing, especially
when using an air pipe sensing method. These devices may
also be used with a bubbling method or equivalent.
F
Freescale Semiconductor, Inc.
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