Home > Circuits > 10 Channel Light Controller



Modified:22:15, 22 October 2013
A 10 channel light controller that uses PWM to dim 10 individual light bulbs from 0-100%. Can be easily expanded or reduced in channels as required. Each channel can run up to 24 volts at 1 Amp, but this can be increased by changing the drivers. Also drive other devices such as LEDs and motors with added diode protection.

Please note I have not built and tested this yet but it works in theory and simulation.

CIRCUIT DESCRIPTION
This is based on a very common circuit used for generating Pulse Width Modulation control over output devices, such as the Drill Speed Controller, with extra comparators and drivers added all running from the same Ramp astable.

A variable mark space ratio between on/off times effectively delivers an average voltage. By altering the duty cycle, the amount of voltage can be varied easily. For more explanation see the Drill Speed Controller page.

The circuit can be broken down into 3 sections.

Ramp Astable
This produces a ramp wave output at about 16KHz. The minimum and maximum voltages are about 3.2v to 6v. This is just outside the voltage references.

Voltage References
This section generates a 9 volt supply for the ICs and two reference voltages (VRH = 6.2v, VRL = 3.1v) for the input potentiometers.

Channel Drivers
The input potentiometers provide an input voltage between VRH and VRL. The comparator compares this against the ramp waveform. When the input voltage is higher than the ramp voltage, the output switches on, thus by changing the input voltage, a fully adjustable duty cycle from 0-100% is achieved. Note if the ramp output levels exceed that of the reference voltages, the outputs will not achieve the full range of duty-cycles.

BLOCK DIAGRAM

CIRCUIT DIAGRAMS
RAMP GENERATOR ASTABLE

This is the astable which is the beating heart of the system. IC1b forms a ramp generator who's output will ramp the opposite direction of the voltage at the output of IC1a. This forms a non-inverting Schmitt trigger which will saturate high (due to positive feedback) when the ramp exceeds its Upper Threshold voltage. This high input to the ramp generator causes the output to ramp low unitl it reaches the Lower Threshold voltage where the output of the Schmitt Trigger saturates low. This cause the ramp generator to ramp high once more and so the cycle repeats.

Adjusting R3 will alter the output amplitude of the ramp should it ramp outside of the reference voltages.


REFERENCE VOLTAGE GENERATOR
RG1 generates the 9v stabalised supply for the ICs.

IC4d uses D2 to produce a steady 6.2 volts. IC4b is used to buffer this vootage and generate VRH.

IC4c generates half this voltage using the potential divider formed by R8/9 and buffers it to produce VRL.


CHANNEL DRIVER

Each channel driver has a potentiometer who's limits are connected to VRH and VRL. The output is fed to the comparator and compared against the Ramp output. When the ramp rises above the input voltage, the output switches off. By increasing the input voltage, the output stays on for more of the time.

Q1 is a Darlington transistor driver and can sink up to 3A but will need a heatsink on anything over 1A. This can be uprated to several Amps using a TIP127 but the copper track supplying power to the transistor drivers would need to be reinforced - if not redesigned - to carry such high currents.

Extra outputs can be created using more Channel Drivers as needed.

CIRCUIT BOARD
The circuit board measures 210mm x 85mm. (8.25" x 3.325")

Terminal blocks provide connection to the outputs and inputs. TB6 has connections for VRH and VRl which connect to all potentiometers.

DOWNLOADS NOTES:

Circuit Simulation - (LiveWire)

PCB Layout - (PCB Wizard)

The potential divider in each driver R10/20, may need altering. Toff voltage will depend on the saturation voltage of the op-amp.

R3 could be make a variable to alter the amplitude of the triangle wave if the output does not switch fully on or off.

If built, use an oscilloscope on the output of the op-amp in each channel driver to ensure outputs switch fully on and off.

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Designed and Written by Phil Townshend 2011

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