Triac based Lamp Dimmer power control

This is a phase angle control of a Triac which is a evolution from an SCR. The 50 Hz or 60 Hz Sine wave of mains can be turned on at any point after the Zero Crossing.

Design Notes - Power Electronics - 03



The Voltage ramps up in the sine wave which gives a near "Linear" slope which can be used to trigger the ON at a time delay after zero crossing when the voltage is zero. This is like a PWM but works on low frequency only. Some of the early SMPS(HV for TV and Mains Inverter) by Siemens were built around SCRs. Turning off a SCR is a difficult job for a designer, MOSFETS and IGBT are now used for PWM drive stages.

High Energy Circuits

You can use it with a bulb to vary brightness of bulb, this is a live circuit it can give a shock, enclose in plastic box, the pot should have a plastic knob, use a fuse, you can also use it for temperature control of soldering irons.

The Source file in CadSoft EAGLE format is here del00004.zip

80C39 and MCS48 based Process Controller

The Early Microcontroller : 80C39 is a CMOS Version of 8048 the one that preceded 8031-8051. MCS48 is the set for that, MCS51 is the current set.

Digital to Analog Converter with uC Watchdog is the front end and an external  hardware watchdog of an early kind. These are simple but robust circuits and worked well in noisy environments.

Here is an example project for 80C39-8748-8749 microcontroller. This code was written by me, and it works. But the documentation is not complete or may have errors.

Process Controller code here 80C39 Code for MCS48 (editable spreadsheet online)

The circuit for these are on this page along with other circuits. This may be difficult to put together now. But

the code and hardware is near compatible to 8051 uC. Now there are may types of ADC and uC.

Voltage to Frequency Converter AD Interface is the analog front end of this instrument. Uses a LM331 VCO. The Signal conditioning too is integrated in this circuit.

This was supposed to have Analog in and Analog out. Some parts of the circuit may be in the 80C51 page. This has ramp-up and ramp-down settings for the Increment and Decrement buttons. This helps setting setpoint quickly. There is also debouncing for the pushbutton.

Solid State Relay - Common

This is a DC controlled Solid State Relay which can turn 230V AC equipment on and off. The output is like a NO normally open contacts of a relay and have to be in series with the Load like any other switch.


This should not be used for large inductive loads like big motors. The Q1 transistor limits the current thru the LED by providing an alternate path for more current. The DC input can be from 3V to 20V.

The Triac can be chosen depending on current in the load. Look for datasheets and applications at STMicroelectronics for BTA41600 triacs. MOC3041 zero crossover opto-diacs.

Read more at my main page - Solid State Relays - SSR I used to make them long ago.