Circuit arrangement
View Patent ↗In an up-converter feed forward control of the output current is effected by rendering the conduction time of the switching element proportional to V out /V in 2 . This control is fast and avoids interference and loss of efficiency.
1. A circuit arrangement for supplying an LED array comprising:
input terminals for connection to a voltage supply source;
output terminals for connection to the LED array;
a DC—DC-converter coupled between the input terminals and the output terminals, the DC—DC-converter comprising:
an inductive element L;
a unidirectional element;
a switching element coupled to the inductive element and the unidirectional element; and
a control circuit coupled to a control electrode of the switching element for generating a high frequency control signal for rendering the switching element conductive and non-conductive at a high frequency to thereby operate the DC—DC-converter in the critical discontinuous mode and equipped with circuitry for controlling the current through the output terminals at a predetermined value, the circuitry for controlling the current through the output terminals comprising:
a circuit coupled to the input terminals and the output terminals for controlling a time lapse T on , during which the switching element is maintained in a conductive state during each high frequency period of the control signal, proportional to a mathematical expression that is a function of V in and V out , wherein V in is the voltage present between the input terminals and V out is the voltage present between the output terminals;
wherein the DC—DC-converter is an up-converter and the circuit comprises a circuit for controlling T on proportional to V out /V in 2 .
2. A circuit arrangement for supplying an LED array comprising:
input terminals for connection to a voltage supply source;
output terminals for connection to the LED array;
a DC—DC-converter coupled between the input terminals and the output terminals, the DC—DC-converter comprising:
an inductive element L;
a unidirectional element;
a switching element coupled to the inductive element and the unidirectional element; and
a control circuit coupled to a control electrode of the switching element for generating a high frequency control signal for rendering the switching element conductive and non-conductive at a high frequency to thereby operate the DC—DC-converter in the critical discontinuous mode and equipped with circuitry for controlling the current through the output terminals at a predetermined value, the circuitry for controlling the current through the output terminals comprising:
a circuit coupled to the input terminals and the output terminals for controlling a time lapse T on , during which the switching element is maintained in a conductive state during each high frequency period of the control signal, proportional to a mathematical expression that is a function of V in and V out , wherein V in is the voltage present between the input terminals and V out , is the voltage present between the output terminals;
wherein the DC—DC-converter is a down-converter and the circuit comprises a circuit for controlling T on proportional to V out /((V out −V in ) 2 .
3. A circuit arrangement for supplying an LED array comprising:
input terminals for connection to a voltage supply source;
output terminals for connection to the LED array;
a DC—DC-converter coupled between the input terminals and the output terminals, the DC—DC-converter comprising:
an inductive element L;
a unidirectional element;
a switching element coupled to the inductive element and the unidirectional element; and
a control circuit coupled to a control electrode of the switching element for generating a high frequency control signal for rendering the switching element conductive and non-conductive at a high frequency to thereby operate the DC—DC-converter in the critical discontinuous mode and equipped with circuitry for controlling the current through the output terminals at a predetermined value, the circuitry for controlling the current through the output terminals comprising:
a circuit coupled to the input terminals and the output terminals for controlling a time lapse T on , during which the switching element is maintained in a conductive state during each high frequency period of the control signal, proportional to a mathematical expression that is a function of V in and V out , wherein V in is the voltage present between the input terminals and V out is the voltage present between the output terminals;
wherein the DC—DC-converter is a flyback-converter comprising a transformer with a transformation ratio N and the circuit comprises a circuit for controlling T on proportional to (V in +V out /N)/V in 2 .
4. A circuit arrangement for supplying an LED array comprising:
input terminals for connection to a voltage supply source;
output terminals for connection to the LED array;
a DC—DC-converter coupled between the input terminals and the output terminals, the DC—DC-converter comprising:
an inductive element L;
a unidirectional element;
a switching element coupled to the inductive element and the unidirectional element; and
a control circuit coupled to a control electrode of the switching element for generating a high frequency control signal for rendering the switching element conductive and non-conductive at a high frequency to thereby operate the DC—DC-converter in the critical discontinuous mode and equipped with circuitry for controlling the current through the output terminals at a predetermined value, the circuitry for controlling the current through the output terminals comprising:
a circuit coupled to the input terminals and the output terminals for controlling a time lapse T on , during which the switching element is maintained in a conductive state during each high frequency period of the control signal, proportional to a mathematical expression that is a function of V in and V out , wherein V in is the voltage present between the input terminals and V out is the voltage present between the output terminals;
wherein the circuit comprises a current source that generates a current that is proportional to V in 2 .
5. A circuit arrangement as claimed in claim 4 , wherein the current source comprises a first voltage divider coupled to the input terminals, a first zener diode coupled to the first voltage divider and a switching element coupled to the first zener diode.
6. A circuit arrangement as claimed in claim 5 , wherein the current source comprises a second zener diode.
7. A circuit arrangement as claimed in claim 4 , wherein the circuit further comprises:
a capacitor coupled to the current source; and
a comparator, comprising:
a first comparator input terminal coupled to the capacitor,
a second comparator input terminal coupled to an output terminal of a second voltage divider coupled to the output terminals of the circuit arrangement, and
a comparator output terminal coupled to the control electrode of the switching element.
8. A circuit arrangement as claimed in claim 4 , wherein the control circuit is equipped with circuitry for substantially square wave modulating the amplitude of the current through the output terminals.
9. A Liquid Crystal Display unit equipped with a backlight formed by a LED array and with a circuit arrangement as claimed in claim 4 .