Communication circuit for a digital electronic dimming ballast
First Claim
1. A communication circuit for a load control device, the load control device operable to be coupled to a communication link having two conductors, the load control device operable to transmit a digital message by alternating the communication link between an idle state in which a link voltage is developed across the conductors on the communication link and an active state in which the conductors of the communication link are substantially the same electrical potential, the communication circuit comprising:
- a receiving circuit coupled between the conductors of the communication link, the receiving circuit operable to conduct an idle current when the communication link is in the idle state; and
a transmitting circuit coupled between the conductors of the communication link, the transmitting circuit comprising;
an optocoupler having an input and an output, the output comprising a phototransistor and operable to become conductive when the input is driven with an input current, the output operable to conduct the idle current immediately after becoming conductive;
a voltage clamp coupled across the output of the optocoupler, the voltage clamp operable to clamp the voltage across the output of the optocoupler in the idle state, wherein the voltage clamp limits the voltage across the output of the optocoupler to approximately two diode drops;
a controllably conductive device responsive to the output of the optocoupler to electrically couple the conductors of the communication link together when the output of the optocoupler is conductive and to stop electrically connecting the conductors of the communication link when the output is non-conductive; and
a current source coupled to the phototransistor of the optocoupler, the current source operable to generate a source current when the controllably conductive device is electrically coupling the conductors of the communication link together;
wherein the output of the optocoupler is operable to conduct a first portion of the source current and the voltage clamp is operable to conduct a second portion of the source current in the active state, such that the phototransistor of the optocoupler is maintained in an active region of operation.
2 Assignments
0 Petitions
Accused Products
Abstract
A communication circuit for an electronic dimming ballast provides high-voltage miswire protection and improved rise and fall times of a transmitted digital signal. The electronic dimming ballast comprises a control circuit, which is coupled to a digital communication link, for example, a DALI communication link, via the communication circuit. The communication circuit comprises a receiving circuit for detecting when the digital ballast communication link is shorted and for providing a received digital message to the control circuit. The communication circuit also comprises a transmitting circuit for shorting the communication link in response to the control circuit. The communication circuit also includes a high-voltage fault protection circuit for protecting the circuitry of the communication circuit if the communication circuit high-voltage mains voltages. The communication circuit is operable to reliably transmit digital messages having improved rise and fall times. The communication circuit draws acceptable amounts of current when the communication link is alternatively in idle and active states.
16 Citations
25 Claims
-
1. A communication circuit for a load control device, the load control device operable to be coupled to a communication link having two conductors, the load control device operable to transmit a digital message by alternating the communication link between an idle state in which a link voltage is developed across the conductors on the communication link and an active state in which the conductors of the communication link are substantially the same electrical potential, the communication circuit comprising:
-
a receiving circuit coupled between the conductors of the communication link, the receiving circuit operable to conduct an idle current when the communication link is in the idle state; and a transmitting circuit coupled between the conductors of the communication link, the transmitting circuit comprising; an optocoupler having an input and an output, the output comprising a phototransistor and operable to become conductive when the input is driven with an input current, the output operable to conduct the idle current immediately after becoming conductive; a voltage clamp coupled across the output of the optocoupler, the voltage clamp operable to clamp the voltage across the output of the optocoupler in the idle state, wherein the voltage clamp limits the voltage across the output of the optocoupler to approximately two diode drops; a controllably conductive device responsive to the output of the optocoupler to electrically couple the conductors of the communication link together when the output of the optocoupler is conductive and to stop electrically connecting the conductors of the communication link when the output is non-conductive; and a current source coupled to the phototransistor of the optocoupler, the current source operable to generate a source current when the controllably conductive device is electrically coupling the conductors of the communication link together; wherein the output of the optocoupler is operable to conduct a first portion of the source current and the voltage clamp is operable to conduct a second portion of the source current in the active state, such that the phototransistor of the optocoupler is maintained in an active region of operation. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
-
-
15. A high-voltage fault protection circuit for protecting a communication circuit of a load control device coupled to a digital communication link via first and second terminals, the fault protection circuit operatively coupled to the first and second terminals of the load control device, the fault protection circuit comprising:
-
a controllably conductive device having two main load terminals and a control input, the main load terminals coupled in series electrical connection between the communication circuit and the second terminal of the load control device, the controllably conductive device rendered conductive when a first voltage having a magnitude less than a predetermined threshold is provided across the first and second terminals, the controllably conductive device operable to become non-conductive and to disconnect the communication circuit and the second terminal when a second voltage having a magnitude greater than the predetermined threshold is provided across the first and second terminals; and a turn-on circuit coupled between the first terminal and the control input of the controllably conductive device, the turn-on circuit operable to provide a drive voltage to the control input of the controllably conductive device when the first voltage is provided across the first and second terminals, wherein the turn-on circuit comprises a resistor, a capacitor, and a zener diode, the capacitor coupled to the control input of the controllably conductive device such that the drive voltage develops across the capacitor, the zener diode coupled in parallel electrical connection with the capacitor to limit the magnitude of the drive voltage. - View Dependent Claims (16, 17, 18, 19)
-
-
20. A communication circuit for a load control device, the load control device operable to be coupled to a communication link having two conductors, the load control device operable to transmit a digital message by changing the communication link between an idle state in which a first voltage is developed across the conductors on the communication link and an active state in which the conductors of the communication link are at substantially the same electrical potential, the communication circuit comprising:
-
a receiving circuit coupled between the conductors of the communication link, the receiving circuit operable to conduct an idle current; a transmitting circuit coupled between the conductors of the communication link, the transmitting circuit comprising an optocoupler having a phototransistor for providing an output, a voltage clamp operable to clamp the voltage across the output of the optocoupler in the idle state, wherein the voltage clamp limits the voltage across the output of the optocoupler to approximately two diode drops, a controllably conductive device responsive to the output of the optocoupler to electrically couple the conductors of the communication link together when the output of the optocoupler is conductive, and a current source operable to provide the phototransistor of the optocoupler with excess current such that the phototransistor is maintained in the active region when the phototransistor is conductive; and a fault protection circuit operatively coupled between the conductors of the communication link and operable to protect the receiving and transmitting circuits, the fault protection circuit comprising a controllably conductive device coupled between the receiving and transmitting circuits and a second one of conductors of the communication link, the controllably conductive device rendered conductive when the first voltage is provided across the conductors of the communication link, the controllably conductive device rendered non-conductive when a second voltage is provided across the first and second terminals, the first voltage having a magnitude less than a predetermined threshold, the second voltage having a magnitude greater than the predetermined threshold. - View Dependent Claims (21, 22)
-
-
23. A method of transmitting a digital message from a communication circuit via a communication link having two conductors, the method comprising the steps of:
-
drawing an idle current when the communication link is in an idle state; providing an optocoupler having an input and an output comprising a phototransistor; limiting the voltage produced across the output of the optocoupler to approximately two diode drops; driving the input of the optocoupler, such that the output of the optocoupler is operable to conduct a drive current; electrically connecting the two conductors of the communication link to change the communication link from an idle state to a shorted state in response to the step of driving the input of the optocoupler; providing a source current to the phototransistor to maintain the phototransistor in the active region of operation when the phototransistor is conducting the drive current; and ceasing driving the input of the optocoupler, such that the output of the optocoupler ceases to conduct the drive current. - View Dependent Claims (24, 25)
-
Specification