ST AN442 Application note
AN442
APPLICATION NOTE
TRIAC & MICROCONTROLLERS: THE EASY CONNECTION
INTRODUCTION
The aim of this note is to show how to connect an ST triac and an ST microcontroller.
CONVENTIONAL SOLUTION
For many years the triac has been used to switch load on the AC mains and thanks to the low cost of microcontrollers (µC) this solution is widely used in the appliance market.
All the system use a buffer transistor between the output port of the microcontroller and the triac as shown in the Figure 1.
Figure 1. Drive in the 1st and 4th quadrants
+VDD
LINE
µC
IG
0V
Because of the low sensivity of the triac in the 4th quadrant this type of drive is often unpractical, and is replaced by the topology of the Figure 2.
Figure 2. Conventional drive in the 2nd and 3rd quadrants
+VDD |
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IG |
G |
A1 |
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µC |
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LINE |
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A2 |
0V |
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To save cost, manufacturers want to use fewer and fewer components and of course want to remove the buffer transistor, but a problem arises.
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REV. 2 |
April 2004 |
1/5 |
AN442 APPLICATION NOTE
Due to the low output current of the microcontroller, the triac had to be very sensitive and consequently was not able to withstand for example the static dv/dt, and the commutation.
NEW ST SOLUTION
Two parameters have been improved:
–The sensitivity of the triacs.
–The output capability of the microcontrollers in terms of sunk current.
A microcontroller is now able to drive one standard triac or several sensitive triacs, without buffer transistors (see Figure 3).
Figure 3. An easy connection!
+VDD
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IG |
VG |
A1 |
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RG |
G |
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ST |
VOL |
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LINE |
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ST |
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µC |
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A2 |
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TRIAC |
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0V
Table 1 shows the output capability of a range of controllers and the sensitivity of the triacs.
Table 1. Triac and microcontroller characteristics
MICROCONTROLLERS & |
TRIAC |
SENSITIVITY |
GATE |
CONNECTION |
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OUTPUT CAPABILITIES |
PARAMETERS |
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T & TW SERIES |
IGT = 5mA |
VG =1.5V |
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at |
1 PORT/TRIAC |
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Tx05 SERIES |
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IG = 10mA |
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ST621x SERIES |
S & SW SERIES |
IGT = 10mA |
VG =1.5V |
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at |
1 PORT/TRIAC |
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Tx10 SERIES |
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IG = 20mA |
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ST622x SERIES |
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VG =1.5V |
2 PORTS |
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IOL = 20mA |
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IGT = 25mA |
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C SERIES |
at |
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IN PARALLEL/TRIAC |
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at |
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IG = 50mA |
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VOL = 1.3V |
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IGT = 35mA |
VG = 2V |
3 PORTS |
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IVSS=100mA |
CW SERIES |
at |
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IN PARALLEL/TRIAC |
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IG = 70mA |
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IGT = 50mA |
VG = 2V |
4 PORTS |
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B & BW SERIES |
at |
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IN PARALLEL/TRIAC |
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IG = 100mA |
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