14/17

Figure 19: Multimotor Synchronization. Large and Small Motor. Slow Current Decay

THERMAL OPERATING CONDITIONS

In many cases the modules do not require any

additional cooling because the dimensions and the

shape of the metal box are studied to offer the

minimum possible thermal resistance case-to-am-

bient for a given volume.

It should be remembered that these modules are a

power device and, depending on ambient tempera-

ture, an additional heath-sink or forced ventilation

or both may be required to keep the unit within safe

°C during op-

eration).

The concept of maximum operating ambient tem-

perature is totally meaningless when dealing with

power components because the maximum operat-

ing ambient temperature depends on how a power

device is used.

What can be unambiguously defined is the case

temperature of the module.

To calculate the maximum case temperature of the

module in a particular applicative environment the

designer must know the following data:

– Input voltage

– Motor phase current

– Motor phase resistance

– Maximum ambient temperature

From these data it is easy to determine whether an

additional heath-sink is required or not, and the

relevant size i.e. the thermal resistance.

The step by step calculation is shown for the follow-

ing example (GS-D200).

=10

q

Calculate the power dissipated from the indexer

logic and the level shifter (see electrical charac-

teristics):

• 60 mA) + (40 V • 20 mA) = 1.1 W

q

Calculate the average voltage across the winding

resistance:

q

Calculate the required ON duty cycle (D.C.) of the

output stage to obtain the average voltage (this

D.C. is automatically adjusted by the GS-D200):

D.C.

=

=

10

40

= 0.25

q

Calculate the power dissipation of the GS-D200

output power stage. The power dissipation de-

pends on two main factors:

– the selected operating mode (FAST or SLOW

DECAY)

– the selected drive sequence (WAVE, NORMAL,

HALF STEP)

FAST DECAY. For this mode of operation, the

the ON period i.e. for 25 % of the time.

During the recirculation period (75 % of the time),

the current recirculates on two internal diodes that

resistor (0.5

Ω). For this example, by assuming

maximum values for conservative calculations, the

power dissipation during one cycle is:

(1 - D.C.) + 0.5

GS-D200/GS-D200S