ADT14

–15–

REV. 0

Figure 30 illustrates the system described in the previous para-

graph, where each trip-point output corresponds to a 25% re-

duction in power when tripped. This is accomplished by the

dual rail-to-rail precision OP284 op amp configured as an in-

verting summer in the first stage, and as a V/I converter in the

second stage.

Suppose, however, that the heating element at a reduced power

level is unable to raise the ambient temperature to the desired

setting. This issue can be addressed by using a microcontroller

as shown in Figure 28. The microcontroller allows the time for

the given volume of material to heat up from a low trip-point

temperature to the next highest temperature trip-point to be

measured. If this time is too long, the microcontroller could add

additional power to the heater by altering a setpoint level.

1/2 OP284

1/2 OP284

10k

Ω

10k

Ω

10k

Ω

10k

Ω

2.49k

Ω

ADT14

TRIP4 (0%)

TRIP3 (25%)

TRIP2 (50%)

TRIP1 (75%)

+5V

+5V

+5V

HEATING

ELEMENT

Q1

Figure 30. Combination Trip-Point Output