MTE1122

DS21112B-page 2

Preliminary

© 1995 Microchip Technology Inc.

FUNCTIONAL DESCRIPTION

Single-phase induction motors run most efficiently at

full load. As the applied load lessens, a greater portion

of the energy consumed by the motor is wasted, mostly

as heat.

It is estimated by the EPA that 50% of the energy pro-

duced in the US is consumed by small electric motors,

and that 20% of this energy does no useful work. There

are perhaps three major reasons for this:

1.

Over-specification -- sometimes its easier or

costs no more to specify a larger motor than

determine actual loads.

2.

Worst case design -- pumps, conveyers, fans,

and the like must be able to operate properly

with clogged filters, maximum heads, or speci-

fied loads. If filters are clean, or loads are lower,

the motor will be running only partly loaded.

3.

Idle time -- many times, systems can’t be shut

down conveniently when not in use.

Number 1 above can be corrected by proper design.

For example, in modern refrigerators, the compressor

systems have been optimized quite effectively. Num-

bers 2 and 3 can not be improved using traditional

approaches. This is where the MTE1122 provides a

new, cost-effective solution.

The MTE1122 calculates the amount of load on a motor

connected to it, and adjusts the motor’s supply voltage

to match that load. For example, if the load is lower

than the motor’s rated load, the voltage to the motor

can be reduced, thus decreasing the energy used by

the motor.

A 1/3 HP motor will typically see 85 VAC at no load

when powered through the MTE1122, for an energy

savings of as much as 58%.

A system block diagram is shown in Figure 1. A graph

of energy savings vs. motor load is shown in Figure 2.

A graph of motor efficiency with and without an

MTE1122-based energy management controller (EMC)

is shown in Figure 3.

The data for the graphs are

shown in Table 1. These figures are based on a 1/3 HP

induction motor coupled to a dynamometer.

Actual

savings may vary based on motor size, motor load and

motor construction.

PINOUT DESCRIPTIONS

P-Sense - analog input that is used by the device to

measure the load voltage.

Gate Enable - analog input that monitors the voltage

across the triac. It is used as a current feedback mech-

anism.

IND - TTL-compatible output that indicates that the sys-

tem is operating normally. It is intended to control an

LED or another indicator device.

ZC-Sense - TTL-compatible input that is used to deter-

mine the zero crossing point of the AC voltage wave-

form.

TTRIG - TTL-compatible output that is used to drive the

triac.

RESET - TTL-compatible input used to reset the device

by holding this pin low.

OSC1, OSC2 - Oscillator crystal or resonator connec-

tions.

FIGURE 3: MOTOR EFFICIENCY

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

0

1 02 0

3 04 0

5 0

6 07 0

8 09 0

1 0 0

Percent Load

With E.M.C.

Without E.M.C.