ST AN2777 APPLICATION NOTE
AN2777
Application note
New high-temperature, high-performance TRIACs for
optimized vacuum cleaner designs
Introduction
A new high-temperature TRIAC family, able to work up to a 150 °C junction temperature in
steady-state, has been introduced. This family helps to reduce the bulk of the required
heatsink. These TRIACs are particularly suitable for hot or limited environments found in
home appliances, such as vacuum cleaners.
One key parameter in the design of TRIACs operating at high temperature is the turn-off
capability. We explain here briefly how to optimize this parameter and present the
performances of a new 12 A, 600 V device.
Test results are also presented to compare these performances to other high-temperature
TRIACs available on the market today. These tests are performed in extremely severe
temperature conditions as can appear in vacuum cleaners.
April 2009 Doc ID 14748 Rev 1 1/13
www.st.com
Contents AN2777
Contents
1 TRIAC turn-off behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Improvement of turn-off capability for new high-temperature TRIACs 6
3 Vacuum cleaner requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1 Steady state thermal design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.2 Inrush current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.3 Turn-off requirement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.4 Jammed nozzle operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
6 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2/13 Doc ID 14748 Rev 1
AN2777 TRIAC turn-off behavior
N4
1 TRIAC turn-off behavior
When a TRIAC switches from on-state to off-state, the current passes through zero, and the
line voltage is rapidly reapplied across the structure. This voltage level is higher for inductive
loads with low power factor, such as pumps or motors. Indeed, for such loads, the phase
shift between current and voltage is high, and a voltage in the range of 50 to 200 V can be
applied for applications running on a 230 V rms line.
Under certain conditions, the component is not able to block this voltage, and so turns on
spontaneously [see References 1.] Indeed, a TRIAC can be compared to two thyristors
mounted in back-to-back association and coupled with a single control area. To trigger the
two thyristors, the control area overlaps the two conduction areas (see Figure 1).
During conduction, a certain quantity of charges is injected into the structure. These
charges disappear by recombination during current decrease, and by extraction with the
reverse recovery current after the turn-off. Figure 3 shows this recombination current with a
230 V, 50 Hz, 25 W pump (see Figure 2 for test schematics).
Figure 1. Simplified TRIAC silicon structure
A1 G
I
-
N1
P1
N4
P1
Gates
N2
P2
Ctrl
I
+
A2
N2
P2
N3
Figure 2. Simplified test schematic
Load
C
V
L
V
R
T
I
T
The recombination of the charges takes place particularly in the neighboring regions of the
gate. These charges can induce the triggering of the other conduction area when the mains
voltage is reapplied across the TRIAC. Figure 4 shows this kind of behavior with the same
load as given in Figure 3, but with a TRIAC with a lower turn-off capability.
Doc ID 14748 Rev 1 3/13
TRIAC turn-off behavior AN2777
Figure 3. TRIAC turn-off with pump
V
Mains
(100 V/div)
VT(100 V/div)
Recovery current
IT(10 mA/div)
Figure 4. Charge recombination induces wrong TRIAC turn-on during turn-off
dV/dt
dV/dt
OFF
OFF
VT(50 V/div)
VT(50 V/div)
dI/dt
dI/dt
To characterize the TRIAC turn-off capability, semiconductor manufacturers use a circuit
where the rate of current decrease can be adjusted. In addition, the slope of the reapplied
voltage can be controlled by using a circuit of resistors and capacitors connected across the
TRIAC [see References 1.] For a given dV/dt
increase the dI/dt
(a)
to reach TRIAC spontaneous re-triggering. This is the critical point
OFF
that the TRIAC is able to withstand. The rate levels of this point are called (dI/dt)c and
4/13 Doc ID 14748 Rev 1
(dV/dt)c in TRIAC datasheets.
a. The expressions dV/dt
the load.
OFF
and dI/dt
refer to the slopes induced by the “natural” current and voltage across
OFF
OFF
OFF
IT(10 mA/div)
IT(10 mA/div)
(a)
(see Figure 4), we progressively
OFF
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