Solid state light AC line voltage interface with current and voltage limiting
An analog electronic circuit for driving a string of LEDs including input terminals for accepting connection to AC voltage, a current regulation circuit operatively coupled to receive an AC voltage from the input terminals and to provide an output for connection to drive the string of LEDs. Included is a current regulation circuit configured to limit the current flow through the string of LEDs on a half-cycle basis to a predetermined value. Also disclosed is an over voltage circuit configured to switch off electrical connection between the AC voltage and the string of LEDs upon the AC reaching a predetermined high voltage value on a half-cycle basis.
1. An analog electronic circuit for driving a string of LEDs comprising:
a) input terminals for accepting connection to AC mains voltage; and
b) a constant current regulation circuit operatively coupled to receive an AC voltage from the input terminals and to provide an output for connection to drive the string of LEDs; the current regulation circuit configured to regulate current flow through the string of LEDs on a half-cycle basis, to a predetermined value;
c) a voltage sensing circuit configured to detect that the AC voltage coupled to the current regulation circuit exceeds a predetermined level, the voltage sensing circuit controlling the current regulation circuit such as to force the current regulation circuit to a non-conduction state when the predetermined level is exceeded; and
the analog electronic circuit requiring no power storage capacitor.
2. The circuit of claim 1 further comprising a rectifier operatively coupled between the input terminals and the current regulator.
3. The circuit of claim 2 further comprising two or more distinct current regulating portions with two or more, respective, output connections for driving two or more distinct strings of LEDs, and having a common rectification stage.
4. The circuit of claim 1 having no rectification of the AC mains and comprising distinct, functionally mirror image circuitry for regulating current of positive and negative AC phases, respectively, and where the LEDs to be driven are so-called AC LEDs.
5. The circuit of claim 1 further comprising a compatible string of LEDs.
6. The circuit of claim 1 where the predetermined voltage level and controlling of the current regulation by the voltage sensing circuit is such that the current regulating circuit enters the non-conducting state at a voltage level below a level that would cause the power dissipation of at least one component in the current regulation circuit to exceed a predetermined level.
7. A circuit for powering LEDs from an AC source comprising:
a controllable constant current regulator arranged to be coupled to an AC source and configured to drive an LED string where the controllability of the current regulator is at least between a driving state where a constant current is provided during a phase angle providing a voltage above a minimum voltage, and an off state where substantially no current is provided;
a voltage sensing circuit arranged to sense voltage applied to the controllable current regulator where a voltage above a predetermined level causes the current regulator to assume the off state, whereby the power dissipation of the current regulator is limited; and the circuit operable on a half-cycle basis and without requirement for filtered AC.
8. The circuit of claim 7 further comprising a rectifier interposed between the coupling for an AC source and the current regulator.
9. The circuit of claim 8 where the rectifier is a full-wave rectifier.
10. The circuit of claim 7 where the current regulator comprises a three terminal shunt voltage regulator component.
11. The circuit of claim 7 with two or more distinct constant current regulators in parallel providing for a respective two or more LED strings to be powered.
12. The circuit of claim 11 where at least one constant current regulator operates on a positive phase of the AC source and at least another of the constant current regulators operates on a negative phase of the AC source.
13. A method for powering a string of LEDs from unfiltered AC, the method comprising:
applying an AC voltage to a circuit powering LEDs;
regulating an AC flow of current to the string of LEDs to a predetermined, constant level on a phase-by-phase basis during phases of the AC voltage that meet a minimum diode-drop level;
switching a circuit when a sense voltage related to the applied voltage exceeds a predetermined voltage level;
ceasing the flow of current, the ceasing engendered by the switching; and
where the predetermined voltage level and sense voltage is such as to cease the current flow at a point to prevent one or more regulating components from exceeding a chosen power rating.