Lighting system, related electronic converter and method of designing a lighting system
A lighting system includes an electronic converter, a lighting module and a switching stage. The electronic converter includes a transformer, a rectifier circuit and an output filter circuit. A capacitance is connected between the primary winding and the secondary winding. The lighting module includes a chain of LEDs and a current regulator, wherein the chain of LEDs is mounted onto a substrate of a metallic material, so that a parasitic capacitance is present between the lighting module and the substrate of a metallic material. The switching stage includes a field-effect transistor interposed in the negative line which connects the lighting module to the electronic converter, and a control unit configured to drive the gate terminal of the transistor as a function of a dimming signal. The switching stage includes a diode connected to negative output terminal of the switching stage and to positive output terminal of the switching stage.
1. A lighting system comprising: an electronic converter comprising: two input terminals configured to receive an input voltage, a positive output terminal and a negative output terminal for providing a continuous output voltage, a transformer comprising a primary winding and a secondary winding, wherein a capacitor is connected between said primary winding and said secondary winding, wherein said primary winding is coupled to said two input terminals, a rectifier circuit, wherein the input of said rectifier circuit is connected to said secondary winding of said transformer, and an output filter circuit, wherein the input of said output filter circuit is connected to the output of said rectifier circuit, wherein the output of said output filter circuit provides said continuous output voltage; a lighting module comprising a positive input terminal and a negative input terminal, and a string of LEDs or laser diodes and a current regulator connected directly in series between said positive input terminal and said negative input terminal of said lighting module, wherein said string of LEDs or laser diodes is configured to be mounted on a substrate in a metallic material, whereby a parasitic capacitance is arranged between the lighting module and said substrate in a metallic material; and a switching stage comprising: a positive input terminal and a negative input terminal connected directly to the positive and negative output terminals of said electronic converter, and a positive output terminal and a negative output terminal connected directly to the positive and negative input terminals of said lighting module, wherein said positive input terminal is connected directly to said positive output terminal; a field effect transistor, wherein the drain of said transistor is connected directly to said negative output terminal and the source of said transistor is connected directly to said negative input terminal, a control unit configured to drive the gate of said transistor as a function of a dimming signal, and a diode, wherein the anode of said diode is connected directly to the negative output terminal of said switching stage and the cathode of said diode is connected directly to the positive output terminal of said switching stage.
2. The lighting system according to claim 1 , wherein said system is configured to, when a negative transition is applied to said two input terminals, transfer said negative transition via said capacitor to the source of said transistor, wherein the drain of said transistor is maintained at a substantially constant voltage via said parasitic capacitance, such that a voltage is created between the drain and the source of said transistor, wherein, when the voltage between the drain and the source of said transistor reaches said continuous output voltage, said diode is closed impeding that a negative voltage is created between the positive terminal and the negative terminal of said lighting module.
3. The lighting system according to claim 1 , wherein said input voltage is an AC voltage, and said electronic converter comprises:
a further rectifier circuit configured to receive at input said AC input voltage and provide at output a continuous voltage,
a further switching stage configured to selectively transfer said continuous voltage to said primary winding of said transformer, and
a control unit configured to drive said further switching stage as a function of said continuous output voltage.
4. The lighting system according to claim 1 , wherein said input voltage is a DC voltage, and said electronic converter comprises:
a further switching stage configured to selectively transfer said DC input voltage to said primary winding of said transformer, and
a control unit configured to drive said further switching stage as a function of said continuous output voltage.
5. The lighting system according to claim 1 , wherein said transformer is a SELV transformer.
6. The lighting system according to claim 1 , wherein said electronic converter is a class II device, wherein at least the components between said two input terminals of said electronic converter and said primary winding of said transformer are mounted within a housing.
7. The lighting system according to claim 1 , wherein said electronic converter and said switching stage are integrated in a single device, wherein said single device comprises a positive output terminal connected to the positive output terminal of said switching stage and a negative output terminal connected to the negative output terminal of said switching stage.
8. The lighting system according to claim 7 , wherein the positive output terminal of said single device is connected through a cable to the positive input terminal of said lighting module and the negative output terminal of said single device is connected through a cable to the negative input terminal of said lighting module.
9. The lighting system according to claim 1 , wherein said switching stage is integrated in a dimmer, wherein said dimmer comprises a positive input terminal connected to the positive input terminal of said switching stage, a negative input terminal connected to the negative input terminal of said switching stage, a positive output terminal connected to the positive output terminal of said switching stage and a negative output terminal connected to the negative output terminal of said switching stage.