Electroluminescent lamp driver circuit with signal tracking
AssigneeSTMicroelectronics S.r.l.
InventorsErmanno Pace, Giorgio Mariani, Alessandro Fasan
Life of this patent
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Abstract
An electroluminescent lamp is driven by a driving circuit that can supply an approximately sinusoidal signal, a bi-directional sawtooth signal or a single-ended sawtooth signal. Switches selectively transfer energy from a battery to an inductor and then from the inductor to the lamp. In one embodiment, the lamp voltage is compared to a reference waveform, such as a sinusoid. The switches are activated responsive to the error between the lamp voltage and reference waveform to minimize the error. The lamp can thus be driven with a closer approximation of the reference waveform.
Claims20
An electroluminescent driver circuit for driving an electroluminescent lamp having first and second driving terminals, comprising:
- a voltage source for providing a supply voltage relative to a reference voltage;
- an inductive circuit;
- a signal source having a signal output terminal, the signal source being operative to supply a reference signal at the signal output terminal;
- a switching circuit having a voltage terminal coupled to the voltage source, a lamp terminal coupled to the first driving terminal for coupling to the lamp and a current supply terminal coupled to the inductive circuit, the switching circuit further including a first input terminal and responsive to a first clocking signal at the first input terminal to apply the supply voltage to the inductive circuit, the switching circuit further including a second input terminal and being responsive to a second switching signal at the second input terminal to couple the inductive circuit to the lamp terminal;
- and
- a comparator having a first comparator input coupled to the first driving terminal and a second comparator input coupled to the signal output terminal, the comparator being responsive to provide the first clocking signal in response to the driving terminal voltage being greater than the reference voltage terminal.
A high voltage source responsive to a set of clocking signals and an input supply voltage to produce a periodic signal having a peak voltage greater than the supply voltage, comprising:
- a reference signal source operative to produce a target signal;
- an inductive circuit having first and second terminals and being responsive to an input voltage across the first and second terminals to store energy;
- a first switching circuit coupled to the inductive circuit, the first switching circuit having a first control terminal and a first voltage terminal adapted to receive the supply voltage, the first switching circuit being responsive to a first of the clocking signals at the first control terminal to apply the supply voltage between the first and second terminals in a first direction;
- a second switching circuit coupled to the inductive circuit, the second switching circuit having a second control terminal and a second voltage terminal adapted to receive the supply voltage, the second switching circuit being responsive to a second of the clocking signals at the second control terminal to apply the supply voltage across the first and second terminals in a second direction opposite the first direction;
- and
- a comparing circuit having a first comparator input coupled to the reference signal source and a second comparator input coupled to the first or second terminal, the comparing circuit being responsive to the relative magnitudes of the target signal and the voltage of the first or second driving terminals to produce the first or second clocking signals.
A method of driving an electroluminescent lamp with a periodic lamp voltage, comprising the steps of:
- providing a target signal corresponding to a desired lamp voltage, the target signal having a period;
- charging an inductive circuit during a first portion of the target signal period;
- comparing the lamp voltage to the target signal;
- during the first portion of the target signal period, if the magnitude of the lamp voltage is less than the magnitude of the target signal, transferring part of the stored energy from the inductive circuit to the lamp;
- and
- during the first portion of the target signal period, if the magnitude of the lamp voltage is greater than the magnitude of the target signal, blocking transfer of the stored energy from the inductive circuit to the lamp.
A method of driving an electroluminescent lamp with a lamp voltage, comprising the steps of:
- storing energy in a first circuit portion during a first interval;
- comparing the lamp voltage to a desired lamp voltage;
- producing a first error signal in response to the magnitude of the compared voltage being less than the magnitude of the desired lamp voltage;
- and
- transferring some of the stored energy from the first circuit portion to the lamp in response to the first error signal.
Dependencies are inferred from the claim text.