Lamp driver with overvoltage protection

Abstract

The lamp driver provides an output voltage and an output current to a lamp load. A current regulation circuit on the secondary side provides a feedback signal for use by the driver when in current regulation mode. An overvoltage protection circuit detects an overvoltage condition of the output voltage and modulates the feedback signal during detection of the overvoltage condition. The overvoltage condition can then be more easily recognized based on the resulting modulation of the output voltage.

Description

[Technical Field]

[0001] The present invention relates to a lamp driver with overvoltage protection, for example for use when a regulated current is supplied to the lamp. [Background technology]

[0002] LEDs are increasingly becoming the dominant lighting technology in residential and commercial applications.

[0003] LEDs are current-driven devices, and therefore LED drivers are often designed to provide a regulated output current. However, if the driver attempts to provide a regulated current into an open circuit (e.g., no LED device connected or with an open circuit failure mode), the voltage will rise to an unacceptable level.

[0004] It is therefore known to implement an overvoltage protection function, for example, if the output voltage rises above a maximum level, the driver can switch to a voltage regulation mode and / or implement a safety shut-down function.

[0005] It is desirable to detect this overvoltage mode at the lamp side and provide a feedback signal to report this condition. In fact, for DALI drivers, it is necessary to detect an open load condition for lamp failure.

[0006] With a tolerance, the overvoltage level and the maximum LED voltage level can be very close to each other. For example, 58V is an example of a maximum output voltage above which overvoltage protection is activated. The voltage may be required not to exceed 60V. However, 54V may be the maximum specified output voltage, which may reach 56V under normal conditions. This means that only a small voltage headroom of approximately 4V remains to distinguish between one operating mode and another based on output voltage detection.

[0007] This makes it very difficult to detect the activation of overvoltage protection on the primary side of an LED driver by voltage sensing alone, especially if only a simple output voltage measurement is implemented.

[0008] LED drivers are often isolated drivers with a primary side and a secondary side, and therefore feedback of a signal representing the output state from the primary side to the secondary side is performed using an isolated feedback element such as an optical isolator.

[0009] One option to address the above problem is to make a sufficiently accurate voltage measurement on the primary side or to add another feedback interface across the isolation, however these are relatively expensive options. Summary of the Invention [Problem to be solved by the invention]

[0010] Therefore, there is a need for primary side detection of the difference between voltage regulation, also known as overvoltage protection, and current regulation without significantly increasing the cost or complexity of the driver. [Means for solving the problem]

[0011] The invention is defined by the claims.

[0012] According to an example according to an aspect of the present invention, a primary side circuit; a secondary side circuit isolated from the primary side circuit for supplying an output voltage and an output current to a lamp load; an isolation feedback unit for providing a feedback signal from the secondary side circuit to the primary side circuit; an isolation driver circuit having a current regulation mode and a voltage regulation mode, The secondary side circuit is a current regulation circuit for providing the feedback signal based on a sensed output current for use by the isolation driver when in the current regulation mode; an overvoltage protection circuit for detecting an overvoltage condition of the output voltage; a modulator for modulating the feedback signal during detection of the overvoltage condition; The primary side circuit is A lamp driver is provided having a controller adapted to recognize the overvoltage condition based on modulation of the output voltage during an overvoltage protection mode.

[0013] This lamp driver generates a single feedback signal that can be used for normal current regulation or for voltage control when there is an overvoltage condition, thereby implementing voltage regulation mode. Modulation is applied to the feedback signal to allow the driver to more clearly distinguish between the normal current control and the overvoltage protection at the primary side (even though similar voltages may be present at the output). This modulation occurs during the voltage control, thereby resulting in a modulated output voltage. This modulation can be more easily detected at the primary side.

[0014] The modulator may, for example, comprise an oscillator circuit, which provides a low-cost circuit that can be used to generate a periodically varying output signal.

[0015] The oscillator circuit includes, for example, an operational amplifier oscillator circuit.

[0016] The overvoltage protection circuit may include a resistive divider connected to the output voltage, and an overvoltage comparison circuit for comparing the output of the resistive divider with a reference voltage representative of a maximum output voltage.

[0017] Therefore, a scaled version of the output voltage is compared to a reference voltage to determine if the output voltage has reached a maximum voltage level.

[0018] In that case, the overvoltage protection circuit may have a shorting switch for selectively shorting resistors of the resistive divider, thereby changing the input to the overvoltage comparison circuit, the shorting switch being controlled by the modulator. By shorting resistors in the resistive divider, the output voltage of the resistive divider is changed, and therefore the feedback signal is changed so that the voltage regulation results in a different output voltage.

[0019] The current regulation circuit may comprise a current sensor, for example in the form of a sense resistor for connection in series with the lamp load, and a current regulation comparison circuit for comparing a voltage derived from the voltage across the current sense resistor with a reference voltage representative of a target current, such that deviation from the target current is provided as a feedback signal and no overvoltage protection signal is required.

[0020] In that case, the overvoltage protection circuit may be configured to adapt the feedback signal by providing a bias signal to the input of the current regulation comparison circuit, which bias signal therefore interrupts the normal operation of the current feedback signal so that voltage regulation is performed.

[0021] The isolation driver circuit may, for example, comprise a DALI driver. The overvoltage protection circuit may, for example, be for detecting an open circuit lamp load.

[0022] The present invention provides a lamp driver as defined above; and an LED device including the lamp load.

[0023] This lighting system is, for example, incorporated into a lighting fixture.

[0024] The present invention provides providing an output voltage and an output current to a lamp load using a secondary side circuit; providing a feedback signal from the secondary side circuit to a primary side circuit; performing current regulation by providing a feedback signal from the secondary side circuit to the primary side circuit based on sensed output current; detecting whether there is an overvoltage condition on the output voltage, and if there is an overvoltage condition, modulating the feedback signal during detection of the overvoltage condition; and recognizing the overvoltage condition on the primary side based on modulation of the output voltage during an overvoltage protection mode.

[0025] This method allows for the overvoltage condition to be recognized on the primary side using a single feedback signal, even with low accuracy voltage sensing components.

[0026] The step of detecting the overvoltage condition may, for example, comprise comparing the output of a resistive divider connected to the output voltage with a reference voltage representing a maximum output voltage, and the step of modulating may comprise selectively shorting resistors of the resistive divider.

[0027] The step of performing current regulation may, for example, comprise comparing a voltage representative of the output current with a reference voltage representative of a target current, and the step of adapting the feedback signal may comprise providing a bias signal when comparing the voltage representative of the output current.

[0028] These and other aspects of the invention will be elucidated and elucidated with reference to the following embodiments. [Brief explanation of the drawings]

[0029] For a better understanding of the present invention, and to show more clearly how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which: [Figure 1A] 1 illustrates a lighting circuit according to an example of the present invention. [Figure 1B]1 illustrates a lighting circuit according to an example of the present invention. [Figure 2] 1 shows an example of modulation applied to the output voltage. [Figure 3] The lamp driving method is shown. DETAILED DESCRIPTION OF THE INVENTION

[0030] The present invention will be described with reference to the drawings.

[0031] It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the devices, systems, and methods, are for purposes of illustration only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the devices, systems, and methods of the present invention will become better understood from the following description, appended claims, and accompanying drawings. It should be understood that the figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the figures to indicate the same or similar parts.

[0032] The present invention provides a lamp driver that provides an output voltage and an output current to a lamp load. A current regulation circuit on the secondary side provides a feedback signal for use by the driver when in current regulation mode. An overvoltage protection circuit detects an overvoltage condition of the output voltage and modulates the feedback signal during detection of the overvoltage condition, which performs voltage regulation. In this case, the overvoltage condition can be more easily recognized based on the resulting modulation of the output voltage.

[0033] 1A and 1B show a lighting circuit according to an example of the present invention, connected by a node X and also by an LED voltage V_LED+.

[0034] 1A shows a lamp load LED and a first part of a lamp driver including a primary side circuit PSC shown on the left side of the isolation and a secondary side circuit SSC shown on the right side of the isolation and therefore isolated from the primary side circuit. The primary side circuit has a ground connection GND, which is connected to the luminaire, for example via a safety capacitor, and the secondary side circuit has a virtual secondary side ground SGND.

[0035] The isolated driver circuit has a primary side DP and a secondary side DS. Any suitable driver topology can be used. Isolation is provided by a transformer.

[0036] As used herein, the term "isolation," and by extension, "insulator" or "electrical isolator," refers to any means of preventing direct electrical power-level transfer. An electrical isolator is, for example, a transformer where power is transferred at the transitions between electric and magnetic fields and between magnetic and electric fields. An isolated driver is a transformer-based converter, such as a flyback converter, a boost-integrated flyback (BiFRED) converter, an LLC or LCC converter, etc., where the driver output does not have direct access to the input power. Instead, the input is connected to a primary winding of a transformer, and the output is connected to a secondary winding of the transformer, with the two windings only magnetically coupled for electrical coupling of power levels.

[0037] The driver has a current regulation mode in which switching is controlled to provide a desired output current (eg, corresponding to a desired lamp brightness), and a voltage regulation mode (eg, as a safety mode).

[0038] The driver also has a primary-side means for measuring the output voltage on the secondary side. The secondary voltage is measured, for example, by an auxiliary winding that provides a reflected voltage on the secondary side to the primary. Another approach is to measure the switching frequency in the case of an LLC converter. If not only the frequency but also the current setting is known, the secondary voltage can be calculated using software and a microcontroller. These methods are not very accurate and therefore not suitable for accurate measurement of the secondary voltage.

[0039] The driver provides an output voltage V_LED+ and an output current I_LED to the lamp load LED. The isolation feedback unit OP_ISOL is for providing a feedback signal from the secondary side circuit to the primary side circuit.

[0040] FIG. 1A shows a current regulation circuit in the secondary side circuit for generating a feedback signal based on the sensed output current I_LED for use by the isolation driver when in current regulation mode.

[0041] The current regulation circuit has a current sensor in the form of a sense resistor Rsense connected in series with the lamp load LED, so that the voltage across the sense resistor is representative of the output current.

[0042] The measurement voltage is fed through a low pass filter R1, C1 to a comparator U1, which has an input resistor R2 and a negative feedback resistor R3, which define the gain of the comparator.

[0043] A measurement voltage representing the current is fed to the inverting terminal of comparator U1, and a reference voltage V(I_LEDtarget) representing the target current is fed to the non-inverting terminal through a resistor and capacitor scaling and filtering network and through input resistor R4.

[0044] Therefore, deviation from target current is provided as a feedback signal and no overvoltage protection signal is required.

[0045] The output of comparator U1 defines the feedback signal. Node X plays no role during normal current regulation. Therefore, normal operation of the circuit can be understood from FIG. 1A.

[0046] FIG. 1B shows further components of the secondary circuit.

[0047] An overvoltage protection circuit is provided to detect an overvoltage condition on the output voltage V_LED+ and adapt a feedback signal to provide voltage regulation during the overvoltage condition.

[0048] The overvoltage protection circuit includes a resistor divider R5, R6, and R7 connected to the output voltage V_LED+. The voltage at the first tap between R5 and R6 is fed to an overvoltage comparator U2, which compares this output of the resistor divider to a reference voltage representing the maximum output voltage. This reference voltage is shown as a 5V voltage source, VSEC_5V. The scaling of the resistor divider means that the 5V reference voltage is an appropriate value to represent the maximum output voltage. Therefore, a scaled version of the output voltage is compared to the reference voltage to determine if the output voltage has reached the maximum voltage level.

[0049] If the reference voltage at the non-inverting input of comparator U2 is not reached, the output connected to node X remains low, and node X plays no role in the operation of the circuit of Figure 1A, as explained above. For example, diodes D1 and D2 prevent the injection of any bias current.

[0050] When the reference voltage is reached at the non-inverting input of comparator U2, the output connected to node X goes high. A bias current is then injected into the inverting terminal of comparator U1 through diodes D1 and D2. The driver interprets the decrease in voltage at the output of comparator U1 as a request to decrease the current.

[0051] Specifically, an increase in the signal at node X causes a decrease in the voltage drop across resistors R1 and R2, which decreases the voltage across the sense resistor and decreases the LED current. With a total open load, the signal at node X increases until the LED current reaches zero.

[0052] During this period, the output voltage is regulated to a level that depends on the comparison result of the overvoltage protection circuit. Specifically, the voltage is regulated so that the voltage sensed by the resistor divider R5, R6, R7 matches the reference voltage. Thus, the voltage limiting function is implemented using the same feedback control on the primary side.

[0053] The DALI standard requires that the driver indicate that it is in overvoltage protection mode. Sometimes this is also dictated by the driver's requirements.

[0054] Since the DALI microcontroller is located on the primary side of the driver, the overvoltage protection indication must also be on the primary side of the driver. The current and voltage regulation is located on the secondary side of the driver, so there is no direct input to the microcontroller to indicate overvoltage protection mode.

[0055] In accordance with the present invention, modulation of the feedback signal during an overvoltage condition is used to modulate the resulting output voltage so that the overvoltage condition can be more easily detected on the primary side.

[0056] The overvoltage protection circuit further includes a shorting switch T3 for selectively shorting resistor R7 of the resistive divider, thereby changing the input to the overvoltage comparator circuit U2.

[0057] During normal current regulation mode, T3 is turned on by a 5V voltage source VSEC_5V, two resistors R8 and R9, and diode D3.

[0058] 1B also shows a modulator circuit based on op amp U3 for modulating the feedback signal during detection of an overvoltage condition. The modulator circuit in this example includes a standard resistor-and-capacitor-based oscillator circuit that defines the positive and negative feedback paths.

[0059] During normal current regulation mode with node X low, T1 is turned off and T2 is turned on by the 5V voltage source VSEC_5V and two resistors R8 and R9. This pulls the non-inverting input of op-amp U3 to ground, thus suppressing oscillation of the oscillator circuit. The output of op-amp U3 remains low, and the voltage at the gate of T3 is sufficient to keep T3 turned on.

[0060] When the driver is in voltage regulation mode with node X at a high voltage, transistor T1 conducts. This pulls the gate of T2 to ground, turning it off. Diode D3 isolates transistor T3 from all circuitry except the oscillator output.

[0061] The modulator, i.e., the oscillator circuit, is then turned on since it is no longer inhibited by transistor T2. The shorting switch T3 is then controlled by the modulator. By shorting the resistors in the resistor divider, the output voltage of the resistor divider is changed, and therefore the feedback signal is altered.

[0062] Thus, the voltage regulation function provides different control values ​​for the output voltage V_LED+.

[0063] When T3 is on, the voltage supplied to comparator U2 is high, and when T3 is off, the voltage supplied to the comparator is low. Thus, the voltage at node X has a modulation. This modulation causes the voltage regulation function to modulate the output voltage V_LED+. In particular, the modulation signal provides a modulated bias signal to the input of current regulation comparator U1. This results in a modulated output voltage that corresponds to changes in the resistor divider configuration.

[0064] The modulated output voltage is then recognized on the primary side as indicative of an overvoltage mode.

[0065] The lamp driver therefore generates a single feedback signal that can be used for normal current regulation or that can be used to modulate the output voltage during voltage regulation to indicate an overvoltage condition, thus allowing the primary side circuitry to more clearly distinguish between normal current regulation and overvoltage protection.

[0066] The isolation driver circuit may, for example, comprise a DALI driver, and the overvoltage protection circuit may, for example, be for detecting an open circuit lamp load.

[0067] 2 shows first the output voltage V_LED+ during normal current regulation, and then the output voltage when a modulated feedback signal is provided during overvoltage protection. The output voltage V_LED+ oscillates between OVP low, e.g., 40 V, and OVP high, e.g., 60 V, as a result of, for example, different feedback control signals provided to the voltage regulation function.

[0068] The oscillation period is adapted to be greater than the discharge time constant formed by the output buffer capacitor and the power consumption of the small signal circuitry, so that the modulated output voltage can settle at two levels before switching between them.

[0069] This modulation can be easily verified on the non-isolated / primary side by min and max detection in the microcontroller to process this information for the DALI interface.

[0070] The present invention addresses the problem that on the primary side of an isolated LED driver, the output voltage cannot be detected accurately enough to distinguish between an open load (e.g., lamp failure) and rated operation with high LED voltage. Voltage modulation of the output voltage can be easily detected by the primary side output voltage measurement means and can be easily evaluated as a lamp failure mode, for example, by the primary side microcontroller.

[0071] The two levels can be significantly different, allowing the relatively inaccurate primary output voltage measurement to distinguish between rated operation and failure modes.

[0072] Figure 3 shows In step 30, using a secondary side circuit to provide an output voltage V_LED+ and an output current I_LED to a lamp load; In step 32, providing a feedback signal from the secondary side circuit to the primary side circuit; and At step 34, the method for driving a lamp is shown to include providing current regulation by providing a feedback signal from the secondary side circuit to the primary side circuit based on the sensed output current.

[0073] At step 36, there is detection of whether there is an overvoltage condition of the output voltage. If there is an overvoltage condition, at step 38, the feedback signal is modulated during detection of the overvoltage condition.

[0074] Modulation of this feedback signal results in a modulated output voltage due to the voltage regulation function of the driver. At step 40, an overvoltage condition is recognized on the primary side based on the modulation of the output voltage during overvoltage protection mode.

[0075] Those skilled in the art can understand and effect variations to the disclosed embodiments in practicing the claimed invention, from a study of the drawings, the specification and the appended claims. In the claims, the word "comprises" does not exclude other elements or steps, and the singular does not exclude a plurality.

[0076] The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0077] It should be noted that when the term "adapted to" is used in the claims or specification, the term "adapted to" is intended to be equivalent to the term "configured to."

[0078] Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. a primary side circuit; a secondary side circuit isolated from the primary side circuit for supplying an output voltage and an output current to an LED lamp load; an isolation feedback unit for providing a feedback signal from the secondary side circuit to the primary side circuit; 1. A lamp driver comprising: an isolated driver circuit in the form of a transformer-based switched mode power converter having a primary side in the primary side circuit and a secondary side in the secondary side circuit, the isolated driver circuit having a current regulation mode and a voltage regulation mode, The secondary side circuit is a current regulation circuit including a current sensor for sensing the output current, the current regulation circuit for providing the feedback signal based on the sensed output current; an overvoltage protection circuit for detecting an overvoltage condition of the output voltage, the overvoltage protection circuit being configured to adapt the feedback signal to provide voltage control during the overvoltage condition; a modulator for modulating the feedback signal during detection of the overvoltage condition; The primary side circuit is an output voltage measuring means for measuring the output voltage; a controller adapted to recognize the overvoltage condition based on a modulation of the output voltage during an overvoltage protection mode.

2. 2. The lamp driver of claim 1, wherein the modulator comprises an oscillator circuit.

3. 3. The lamp driver of claim 2, wherein the oscillator circuit comprises an operational amplifier oscillator circuit.

4. 4. A lamp driver as claimed in any one of claims 1 to 3, wherein the overvoltage protection circuit comprises a resistive divider connected to the output voltage and an overvoltage comparison circuit for comparing the output of the resistive divider with a reference voltage representative of the maximum output voltage.

5. 5. The lamp driver according to claim 4, wherein the overvoltage protection circuit comprises a shorting switch for selectively shorting resistors of the resistive divider, thereby changing the input to the overvoltage comparison circuit, and the shorting switch is controlled by the modulator.

6. 6. A lamp driver as claimed in any one of claims 1 to 5, wherein the current regulation circuit comprises a current sensing resistor for connecting in series with the LED lamp load, and a current regulation comparison circuit for comparing a voltage derived from the voltage across the current sensing resistor with a reference voltage representing a target current.

7. 7. A lamp driver according to claim 6, wherein the overvoltage protection circuit is configured to adapt the feedback signal by providing a bias signal to the input of the current regulation comparison circuit.

8. 8. The lamp driver of claim 7, wherein the bias signal is modulated by the modulator.

9. 9. A lamp driver according to any one of the preceding claims, wherein the isolated driver circuit comprises a DALI driver.

10. 10. A lamp driver according to any one of claims 1 to 9, wherein the overvoltage protection circuit is for detecting an open circuit LED lamp load.

11. A lamp driver according to any one of claims 1 to 10; and an LED device including the LED lamp load.

12. 12. The lighting system of claim 11, incorporated into a lighting fixture.

13. providing an output voltage and an output current to an LED lamp load using a secondary side circuit; providing a feedback signal from the secondary side circuit to a primary side circuit; performing current regulation by providing a feedback signal from the secondary side circuit to the primary side circuit based on sensed output current; detecting whether there is an overvoltage condition on the output voltage, and if there is an overvoltage condition, modulating the feedback signal during detection of the overvoltage condition; measuring the output voltage at the primary side; and recognizing the overvoltage condition on the primary side based on modulation of the output voltage during an overvoltage protection mode.

14. 14. The method of claim 13, wherein the step of detecting an overvoltage condition comprises comparing an output of a resistive divider coupled to the output voltage to a reference voltage representative of a maximum output voltage, and wherein the step of modulating comprises selectively shorting resistors of the resistive divider.

15. 15. The method of claim 13 or 14, wherein performing current regulation comprises comparing a voltage representative of the output current to a reference voltage representative of a target current, and adapting the feedback signal comprises providing a bias signal when comparing the voltage representative of the output current.

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