AN2777

Vacuum cleaner requirements

Doc ID 14748 Rev 1

11/13

3.4

Jammed nozzle operation

For vacuum cleaners, the worst operating condition occurs when the tube is blocked. This

operation does not lead to a higher current. On the contrary, as there is no air flow anymore,

the motor torque is lower and the motor rms current can decrease down to 8 A.

In fact, the stress comes from the fact that the heatsink thermal impedance drastically

increases as there is no cooling air flow anymore. The case temperature can then reach up

to 120 or 140 °C. The TRIAC (dI/dt)c capability is then highly reduced. This can cause failed

turn-off. The motor suddenly goes from low speed to high speed with a half-cycle full

conduction mode. Such operation causes noise variation and vacuum cleaner vibration.

Appliance manufacturers try to reduce this kind of behavior as much as possible, since it

may give a poor quality image of their equipment to the end-user.

This is the reason why some closed-box tests are usually performed by vacuum cleaner

designers to check the TRIAC’s ability to withstand such a stressful operation. We have

performed such a test with the following conditions:

●

TRIAC enclosed in a 10.5 x 8 x 5 cm cardboard box

●

Plastic foam around the box to thermally insulate it

●

●

Motor rms current: 5.5 A (medium speed)

●

Line voltage: 120 V, 60 Hz

●

No heatsink

Figure 12.

TRIAC performance comparison for closed-box test

The case temperature is measured from motor start-up to spurious TRIAC turn-off.

Figure 12 gives the results with the T1235H-6I and other 12 A, 600 V, 35 mA, 150 °C TRIAC

devices in insulated packages. Device A case temperature increases faster than all other

devices. This means that its power losses are higher than the other devices. This could be

certainly due to a smaller die size. Device B heating time is the slowest. But this device is

T1235H works up to 156 °C. Device C presents the same power losses as the T1235H but

works well only up to 144 °C.

Using a T1235H device thus helps to withstand the closed-box test by more than 1 mn

beyond the other devices.

0

20

40

60

80

100

120

140

160

180

0

50

100

150

200

250

time (s)

Tcase (°C)

T1235H - ST

Device A

Device B

Device C