MPXM2102AS datasheet(448/670 Pages) MOTOROLA

448 / 670 page

AN1516

3–302

Motorola Sensor Device Data

www.motorola.com/semiconductors

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 Terminal

1, 4, 5, 6, 9. Main Terminal

* Zero Voltage Activate Circuit

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.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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