I have to build an analog proportional controller for a 127 V, 1 kW AC heating resistance. The power delivered to the heating element must be proportional to the difference between a set point temperature (40°C) and temperature measured with an LM35 sensor, conditioned to work between 0 and 5 VDC.
I tried to control the power delivered to the load by varying the firing angle of a TRIAC. However, I have searched online and on power electronics textbooks for ways to control the firing angle, but all the circuits I have found involve either potentiometers (such as dimmer circuits) that make then useless for automatic control, or special triggering circuits of which they provide no information whatsoever.
- Is there a way to control the firing angle of a TRIAC using a DC voltage without resorting to manual control using potentiometers?
- Or is there some other way of controlling the power delivered to an AC load using a DC voltage? Reference books or circuit diagrams would be greatly appreciated.
Also, any information regarding already existing trigger circuits for triacs (such as integrated circuits for triac firing) would be a lot of help.
NOTE: I am not allowed to use an Arduino for this circuit.