
Application Notes
AN1003
2002 Teccor Electronics
Thyristor Product Catalog
AN1003 - 9
http://www.teccor.com
+1 972-580-7777
Figure AN1003.24
Microcontroller Heater Control
Summary
The load currents chosen for the examples in this application 
note were strictly arbitrary, and the component values will be the 
same regardless of load current except for the power triac or 
SCR. The voltage rating of the power thyristor devices must be a 
minimum of 200 V for 120 V input voltage and 400 V for 240 V 
input voltage.
The use of alternistors instead of triacs may be much more 
acceptable in higher current applications and may eliminate the 
need for any dv/dt snubber network.
For many electrical products in the consumer market, competitive 
thyristor prices and simplified circuits make automatic control a 
possibility. These simple circuits give the designer a good feel for 
the nature of thyristor circuits and their design. More sophistica-
tion, such as speed and temperature feedback, can be devel-
oped as the control techniques become more familiar. A 
remarkable phenomenon is the degree of control obtainable with 
very simple circuits using thyristors. As a result, industrial and 
consumer products will greatly benefit both in usability and mar-
ketability.
120VAC 
(HIGH)
AC 
(RETURN)
WHITE
RV1
VARISTOR
R1
47
  C3
.1μF
+5V
R2
1M
2000 W
D1
1N4001
D1
1N4001
R3
20M
D3
1N5231
C1
220μF
  C2
.01μF
VDD
GP5
GP4
GP3
VSS
GP0
GP1
GP2
R6
470
R70
100
Q1
L4X8E5
Q2
Q4025L6
R4
470
R5
470
S2
S1
INCREASE HEAT
DECREASE HEAT
VDD
U1
12C508