Dimmer circuit

Claim 2

In a dimmer circuit of the type wherein the light intensity from a lamp is adjusted by controlling the firing angle of one or more series-control elements supplying ac power to said lamp, the improvement consisting of: a firing angle function generator for producing during each ac half cycle a signal f( Alpha ) monotonically related in amplitude to control element firing angle, comparator means for triggering said control elements when said signal f( Alpha ) crosses an adjustable, light intensity setting level linearly related to the position of an operator actuated dimmer control handle, said function generator comprising: a. a capacitor, b. means for discharging said capacitor at the beginning of each ac half cycle, and c. means for charging said capacitor at selectable rates during said half cycle, said signal f( Alpha ) being represented by the voltage across said capacitor.

Claim 3

A dimmer circuit as defined in claim 1 wherein said means for charging comprises: a first transistor connected between a source of voltage and said capacitor, a base bias resistor establishing the magnitude of current supplied to said capacitor by said first transistor, a second transistor, the voltage across said capacitor being supplied to the base of said second transistor, at least one resistor effectively shunted across said base bias resistor by conduction of said second transistor when the voltage across said capacitor exceeds a preselected value, shunting of said resistors causing an increase in the charging rate of said capacitor, a programmable unijunction transistor and a series resistor connected in shunt with said capacitor, and means for biasing said unijunction transistor to initiate conduction thereof when the voltage across said capacitor exceeds a preset value established by the bias on said unijunction transistor, conduction through said transistor and series resistor causing a decrease in the charging rate of said capacitor.

Claim 4

A dimmer circuit as defined in claim 1 wherein the amplitude of said signal f( Alpha ) increases between a minimum value at the ac zero crossing initiating said half cycle and a maximum value at the end of said half cycle, and wherein said light intensity setting level is inversely proportionate to a linear control voltage.

Claim 5

A dimmer circuit as defined in claim 3 further comprising: operational amplifier means, receiving said linear control voltage, for establishing said light intensity setting level.

Claim 6

A dimmer circuit for controlling the light intensity from a lamp in response to a control voltage ec LINEARLY related to the position of a dimmer control handle, comprising: at least one silicon controlled rectifier series connected between a source of ac power and said lamp, a firing angle function generator producing during each ac half cycle a signal f( Alpha ) monotonically related in amplitude to SCR firing angle, and comparator means for triggering said silicon controlled rectifiers each time said signal f( Alpha ) crosses an amplitude level established by said control voltage ec, and wherein said firing angle function generator comprises: a capacitor, discharge means for discharging said capacitor in synchronism with the zero crossings of said ac power, and waveshape control circuit means for charging said capacitor at preselectable rates during each ac half cycle, the voltage across said capacitor corresponding to said signal f( Alpha ), said signal f( Alpha ) thereby comprising a piecewise linear approximation of a selected dimmer response curve.

Claim 7

A dimmer circuit for controlling the light intensity from a lamp in response to a control voltage ec LINEARLY related to the position of a dimmer control handle, comprising: at least one silicon controlled rectifier series connected between a source of ac power and said lamp, a firing angle function generator producing during each ac half cycle a signal f( Alpha ) monotonically related in amplitude to SCR firing angle, and comparator means for triggering said silicon controlled rectifiers each time said signal f( Alpha ) crosses an amplitude level established by said control voltage ec, and wherein said firing angle function generator comprises: a capacitor, discharge means for discharging said capacitor in synchronism with the zero crossings of said ac power, and waveshape control circuit means for charging said capacitor at preselectable rates during each ac half cycle, the voltage across said capacitor corresponding to said signal f( Alpha ), said signal f( Alpha ) thereby comprising a piecewise linear approximation of a selected dimmer response curve.

Claim 8

A dimmer circuit as defined in claim 5 wherein said discharge means comprises: a transistor and a current limiting resistor shunting said capacitor, and sync pulse means for pulsing on said transistor in synchronism with said zero crossings.

Claim 9

A dimmer circuit as defined in claim 5 wherein said comparator means comprises: a programmable unijunction transistor, said signal f( Alpha ) establishing the anode voltage of said transistor, and means for providing at the gate of said transistor a voltage Vc linearly proportionate to said control voltage ec.

Claim 10

A dimmer circuit as defined in claim 5 wherein said circuit means further comprises: a first transistor supplying current to said capacitor, a base bias resistor establishing the magnitude of current supplied by said first transistor, a second transistor, the voltage across said capacitor being supplied to the base of said second transistor, at least one resistor shunted across said base bias resistor by conduction of said second transistor when the voltage across said capacitor exceeds a selector value, thereby increasing current to said capacitor.

Claim 11

A dimmer circuit as defined in claim 5 wherein said waveshape control circuit means comprises: means for providing current to said capacitor, at least one means for increasing the amount of current provided to said capacitor when the voltage across said capacitor exceeds corresponding selected levels, and at least one means for decreasing the amount of current provided to said capacitor when the voltage across said capacitor exceeds other corresponding selected levels.

Claim 12

A dimmer circuit as defined in claim 5 wherein said circuit means comprises: means for providing current to said capacitor, means responsive to the voltage level across said capacitor for reducing the current supplied to said capacitor when said voltage level exceeds a preset value.

Claim 13

A dimmer circuit as defined in claim 10 wherein said means responsive comprises: a programmable unijunction transistor and a series resistor connected in shunt with said capacitor, and means for biasing said unijunction transistor to initiate conduction thereof when the voltage across said capacitor exceeds a preset value established by the bias on said unijunction transistor, conduction through said transistor and series resistor thereby decreasing the charging rate of said capacitor.