TW201431435A - Dimmable LED with constant voltage plus constant current drive circuitry - Google Patents

Abstract

A driver circuit for an LED lamp includes a first stage that is configured to receive an AC input power and produce a regulated DC voltage. A linear current regulator is coupled to the first stage and configured to regulate a lamp current supplied to the LED lamp. A feedback circuit is coupled to the first stage and is configured to monitor the regulated DC voltage and operate the first stage to maintain the regulated DC voltage at a generally constant voltage. The driver circuit also includes voltage drop monitoring and includes a voltage drop monitoring circuit coupled to the feedback circuit. The voltage drop monitoring circuit is configured to adjust the generally constant voltage produced by the first stage. The voltage drop monitoring circuit monitors the voltage drop of the linear current regulator and reduces the generally constant voltage as the voltage drop increases.

Description

Dimmable light-emitting diode with constant voltage and constant current driving circuit

Aspects of the invention relate generally to LED light sources, and in particular the invention relates to drive circuits for LED lamps.

A light emitting diode (LED) is a light source constructed from a semiconductor material, typically gallium arsenide. Like other diodes, an LED is produced by doping a semiconductor with various impurities to create a p-n junction. When a current is applied, charge carriers flow into the junction, wherein positively charged holes combine with negatively charged electrons causing the electrons to drop to a lower energy level, thereby releasing energy into visible or infrared light. Light. As in all diodes, the current flows from the positively doped p-side of the device to the n-side of the negative doping but not in the opposite direction. Therefore, LEDs are typically driven by a direct current (DC) power supply.

A plurality of individual LEDs or LED elements are typically used in lighting applications to construct LED light assemblies or LED lights. Incorporating multiple LED elements into a single LED lamp assembly provides a number of advantages, such as increased light output and a graceful failure mode. Since individual components typically fail at different times, the light output gradually degrades over time as individual components fail to achieve a graceful fault. By connecting individual LED components in series or in series, the LED lamp assembly can be driven at higher voltages and lower current levels, providing flexibility in the driver design and allowing for greater efficiency in the driver circuit. The LED lamp assembly can be assembled by having a plurality of LED strings (sometimes referred to as a series-parallel block configuration) in which the series and parallel connections are connected The system is more fault tolerant while maintaining the other advantages of the series connection assembly.

In many LED applications, such as traffic signs or home lighting applications, the drive circuitry is powered by a locally available AC grid. Such applications typically provide dimming functionality through a phase angle dimming method in which the AC input power is modified by triggering current conduction at different angles in a sine wave, thereby reducing the amount of power contained in the input power. In such applications, the AC grid power signal (which may be a phase angle dimming power signal) is converted to DC power and adjusted by the LED driver circuit such that a stable brightness is produced by the LED fixture. However, the power conditioning included in a typical LED driver effectively removes phase control dimming and operates the LED lamp at a constant brightness regardless of any phase control dimming in the input power. Therefore, in order to maintain dimming performance, special dimming detection and power control circuits must be included in the LED driver, resulting in higher driver cost and larger driver size.

Typical drive circuits for driving LED lamps fall into two categories: single-stage and multi-stage, with two- or two-stage drivers being the most common. Each type has its own set of advantages and disadvantages. Single stage drive circuits are lower cost, smaller in size and provide high drive efficiency. However, a single-stage driver must make a trade-off between the power factor and the LED chopping current. Single-stage drivers also have poor dimming performance compared to multi-level drivers. Two-stage and other multi-level drivers provide excellent dimming performance and high power factor while still maintaining a low chopping current. However, multi-stage and dual-stage drivers have higher manufacturing costs and larger sizes and have lower overall drive efficiency than single-stage drives.

Accordingly, it is desirable to provide LED driver circuits that can address at least some of the problems identified above.

As described herein, the illustrative embodiments overcome one or more of the above or other disadvantages known in the art.

One aspect of the illustrative embodiment relates to a driver circuit for an LED lamp. In an embodiment, the driver circuit includes a first stage configured to receive an AC input function Rate and produce a regulated DC voltage. A linear current regulator is coupled to the first stage and configured to regulate a lamp current supplied to the LED lamp. A feedback circuit is coupled to the first stage and configured to monitor the regulated DC voltage and operate the first stage to maintain the regulated DC voltage at a substantially constant voltage. The driver circuit also includes voltage drop monitoring and a voltage drop monitoring circuit coupled to the feedback circuit. The voltage drop monitoring circuit is configured to adjust the substantially constant voltage generated by the first stage. The voltage drop monitoring circuit monitors the voltage drop of the linear current regulator and decreases the substantially constant voltage as the voltage drop increases.

Another aspect of the illustrative embodiment pertains to an electrical lighting device. In an embodiment, the electrical lighting circuit includes a driver circuit configured to receive an AC input power and generate a lamp current and an LED lamp coupled to the lamp current. The driver circuit includes a first stage configured to receive an AC input power and generate a regulated DC voltage. A linear current regulator is coupled to the first stage and configured to regulate a lamp current supplied to the LED lamp. A feedback circuit is coupled to the first stage and configured to monitor the regulated DC voltage and operate the first stage to maintain the regulated DC voltage at a substantially constant voltage. The driver circuit also includes voltage drop monitoring and a voltage drop monitoring circuit coupled to the feedback circuit. The voltage drop monitoring circuit is configured to adjust the substantially constant voltage generated by the first stage. The voltage drop monitoring circuit monitors the voltage drop of the linear current regulator and decreases the substantially constant voltage as the voltage drop increases.

Another aspect of the illustrative embodiment is directed to a method of operating an LED driver circuit, wherein a first power stage is used to convert an AC input power to a DC output voltage. In one embodiment, a feedback signal is generated by the DC output voltage and used to regulate the DC output voltage at a substantially constant voltage. The DC output voltage is provided to an LED lamp and a linear current source is used to regulate the lamp current. The voltage drop of the linear current source is monitored and the feedback signal is adjusted to reduce the DC output voltage when the voltage drop exceeds a threshold voltage.

From the following detailed description in conjunction with the drawings, the exemplary embodiments will be understood And other aspects and advantages. However, it is to be understood that the drawings are intended to be illustrative only and not as a limitation of the invention. The additional aspects and advantages of the invention are set forth in the description which follows, and Further, aspects and advantages of the present invention can be realized and obtained by means of the means and combinations particularly pointed out in the appended claims.

1‧‧‧needle/supply terminal pin

2‧‧‧ pin/return terminal pin

3‧‧‧ pin

4‧‧‧ pin

5‧‧‧ pin

6‧‧‧ pin

7‧‧‧ pin

8‧‧‧ pin

100‧‧‧1st half LED driver system

102‧‧‧ Input power source / input power signal

104‧‧‧ first level

106‧‧‧LED lamp assembly

108‧‧‧Linear Current Regulator / Control Circuit

110‧‧‧ dimming detection circuit

114‧‧‧Voltage regulation power

116‧‧‧Light current

118‧‧‧ voltage drop signal

120‧‧‧ dimming signal

122‧‧‧Input voltage

131‧‧‧Input terminal

132‧‧‧Output terminal

200‧‧‧Power conversion stage

220‧‧‧Input filter

222‧‧‧Reciprocating converter / flyback regulator

224‧‧‧Circuit grounding

226‧‧‧ summing node

300‧‧‧ dimming detection circuit / dimming signal detection circuit

400‧‧‧ Current Regulation Circuit

402‧‧‧Circuit grounding

406‧‧‧ base

500‧‧‧1st half LED driver circuit

502‧‧‧ Input power

504‧‧‧First Stage Voltage Regulator / First Stage

506‧‧‧LED light/LED light assembly

508‧‧‧Linear Current Regulator

510‧‧‧Regulator/Feedback Control Circuit

512‧‧‧Adder

514‧‧‧ Output

516‧‧‧Light current

518‧‧‧Linear Current Regulator

520‧‧‧ circuit

522‧‧‧Feedback signal

524‧‧‧Adjustment signal/control signal

526‧‧‧Enter

528‧‧‧Voltage drop sensing circuit / voltage drop monitoring circuit

534‧‧‧ voltage drop signal

612‧‧‧DC voltage/DC power

616‧‧‧Voltage feedback/circuit node

700‧‧‧LED driving method

702‧‧‧ Convert AC input power to DC output voltage

704‧‧‧ Generate feedback signal from DC output voltage

706‧‧‧Use feedback signal to adjust DC output voltage

708‧‧‧ Provide DC output voltage to LED lights

710‧‧‧Use a linear current source to regulate the lamp current

712‧‧‧Monitor voltage drop across a linear current source

714‧‧‧ voltage drop exceeds the threshold

716‧‧‧Use voltage drop to adjust feedback signal

800‧‧‧ method

802‧‧‧ Monitoring AC input power for dimming signals

804‧‧‧ Generate a DC dimming voltage

806‧‧‧Use dimming signal to adjust lamp current

A301‧‧‧ comparator

A601‧‧‧Operational Amplifier

BD1‧‧‧Bridge Diode/Bridge Diode Circuit

C201‧‧‧ capacitor

C202‧‧‧Filter capacitor

C203‧‧‧ capacitor

C204‧‧‧ capacitor

C205‧‧‧Filter capacitor

C206‧‧‧ capacitor

C207‧‧‧ capacitor

C208‧‧‧ capacitor

C209‧‧‧Filter capacitor

C210‧‧‧ capacitor

C301‧‧‧Charging capacitor

C601‧‧‧ capacitor

CON1‧‧‧Input connector

D201‧‧‧ diode

D202‧‧‧ diode

D203‧‧‧ diode

D401‧‧‧ diode

D402‧‧‧ diode

D600‧‧‧LED lights

F201‧‧‧Fuse

L201‧‧‧Inductors

L202‧‧‧Inductors

LA401‧‧‧LED lamp assembly

Q201‧‧‧Switching device

Q401‧‧‧Optoelectronics

Q402‧‧‧Optoelectronics

R201‧‧‧Resistors

R202‧‧‧Resistors

R203‧‧‧Resistors

R204‧‧‧Resistors

R205‧‧‧Resistors

R206‧‧‧Resistors

R207‧‧‧Resistors

R208‧‧‧current sensing resistor

R209‧‧‧Resistors

R211‧‧‧Resistors

R212‧‧‧Resistors

R213‧‧‧Drive resistor

R215‧‧‧current limiting resistor

R216‧‧‧Resistors

R301‧‧‧Resistors

R302‧‧‧Resistors

R303‧‧‧Resistors

R304‧‧‧Resistors

R305‧‧‧Resistors

R306‧‧‧Resistors

R403‧‧‧Resistors

R405‧‧‧Resistors

R406‧‧‧Resistors

R602‧‧‧Resistors

T201‧‧‧Transformer

T201-1‧‧‧ main winding

T201-2‧‧‧Secondary winding / output side

T201-3‧‧‧ three-stage winding

U201‧‧‧Integral control circuit / integrated circuit / power factor correction (PFC) controller

V201‧‧‧ constant voltage / output voltage / DC voltage / voltage source

V401‧‧‧ operating voltage

V601‧‧‧reference voltage

Z601‧‧‧Zina diode

The drawings illustrate the presently preferred embodiments of the invention, and, As shown throughout the figures, the same element symbols designate the same or corresponding parts.

1 is a functional block diagram of an exemplary LED driver circuit in accordance with an embodiment of the present technology.

2 is a schematic diagram of one exemplary power conversion stage incorporating aspects of the present invention.

3 is a schematic diagram of an exemplary dimming detection circuit incorporating aspects of the present invention.

4 is a schematic diagram of one exemplary linear constant current regulator having dimming functionality incorporating aspects of the present invention.

FIG. 5 illustrates a functional block diagram of an exemplary LED driver circuit in accordance with an embodiment of the present technology.

6 is a schematic diagram of one exemplary feedback circuit incorporating one aspect of the present invention.

7 is a flow chart of an exemplary method of driving an LED lamp that includes a voltage drop in accordance with an embodiment of the present technology.

8 is a flow chart showing one of the methods of incorporating a dimming-LED lamp in accordance with aspects of the present invention.

Referring now to Figure 1, a functional block diagram of a one-stage half LED driver system 100 in accordance with one embodiment of the present invention can be seen. Application of an LED driver including a primary half driver in one embodiment The actuator system 100 provides power to an LED lamp or lamp assembly 106 that includes one or more light emitting diode elements. The input power of the LED driver system 100 is supplied by an input power source or signal 102, such as a local power grid or other suitable AC power source. Typical grid power suitable for input power 102 may range from about 110 volts root mean square (Vrms) to about 250 Vrms at about 50 Hz to 60 Hz. The input power signal 102 can also be supplied by a dimming controller, in which case the input power signal 102 can include a phase control dimming signal (such as a forward phase control dimming signal, a reverse phase control dimming or other in need of a A suitable AC dimming signal that reduces input power during dimming). A first stage 104 is coupled to the input power signal 102 and is configured to output a voltage regulated power 114 that can be supplied to the LED light assembly 106 via output terminals 131 and 132. The first stage 104 is an active power conversion circuit that includes an AC to DC conversion circuit (such as a bridge diode) to convert the substantially sinusoidal input power signal 102 to a full or half wave rectified DC signal. In some embodiments, the first stage 104 also includes a switching converter configured to provide power factor correction and regulation voltage regulation power 114 in the form of one of the first stage DC output voltages. LED lamp 106 receives a current from voltage regulated power 114 that is returned by a linear current regulator 108.

In an embodiment, the exemplary LED driver system 100 also includes a configuration configured to monitor the input voltage 122 and produce a modulation that is proportional to the dimming level indicated by the phase angle dimming level of one of the input power signals 102. A dimming detection circuit 110 of the optical signal 120. The dimming signal 120 is received by a linear current regulator or control circuit 108 that adjusts the lamp current 116 accordingly to achieve a desired dimming output from one of the LED lamps 106. To maintain a constant light output, the lamp current 116 is maintained at a constant value, however, due to environmental and other factors, the voltage drop across the LED lamp 106 can vary. As the voltage across LED lamp 106 drops, the voltage drop across linear current regulator 108 increases proportionally. In the case of a linear regulator, the power consumed by a linear regulator is proportional to the voltage drop across the regulator and the current through the regulator as compared to a switching regulator. Therefore, as the voltage drop across the linear current regulator 108 increases, the power consumed increases proportionally. Similarly, when input power letter When the desired dimming level indicated by the number 102 is low, the voltage drop across the linear current regulator 108 will increase, further increasing the power consumed by the linear current regulator 108. Any power consumed in linear current regulator 108 is not available to generate light. Therefore, it is desirable to reduce the power consumed by the linear current regulator as much as possible.

In one embodiment, to help reduce wasted power, linear current regulator 108 produces a voltage drop signal 118 when the voltage drop across linear current regulator 108 exceeds a threshold amount. A voltage drop signal 118 is provided to the first stage 104 to reduce the voltage regulated power 114 or DC output voltage to reduce the power consumed by the linear current regulator 108.

Referring now to Figure 2, an illustration of one example of an exemplary power conversion stage 200 is provided that provides a method of converting an AC input power (such as the AC input power signal 102 described above with respect to Figure 1) to a regulated DC voltage. The power conversion stage 200 is transmitted through the input terminals 1 and 2 of the input connector CON1 (generally referred to as the supply terminal pin 1 and the return terminal pin 2) to protect the power transfer stage 200 from being caused to cause excessive current to flow into the power. One of the surges or other abnormalities in the conversion stage 200, the fuse F201 receives the input power. An input filter 220 is included to regulate the input power and to prevent harmonics and switching noise generated within the power conversion stage 200 from being transmitted back to the input power through the input connector CON1. The input filter 220 includes a capacitor C210 connected in parallel with the input terminal 1 and the input terminal 2 of the connector CON1 and followed by a pair of inductors L201 and L202, each of which is connected to the supply terminal pin 1 and input of the input connector CON1. The return terminal pin 2 of the device CON1 is connected in series. Each of the inductors L201 and L202 is connected in parallel with a resistor R201 and R202.

A bridge diode circuit BD1 is used to convert the AC power into a full-wave rectified DC power, and a capacitor C201 is connected in parallel across the DC power to provide some initial filtering to help smooth out the full generation by the bridge diode circuit BD1. Wave rectified signal. A flyback converter (indicated generally by component symbol 222) converts and regulates the rectified DC power generated by bridge diode BD1 to a substantially constant voltage V201 at one of output terminals V+ and V-. The flyback converter 222 passes through the transformer T201 having one of the main winding T201-1 and the secondary winding T201-2. The stage side transmits power to the secondary or output side. The diode D201 rectifies the output power and is connected in parallel with the output voltage V201. A filter capacitor C208 provides a filtered and smoothed output voltage V201. A series connected resistor R216 and capacitor C207 are connected in parallel with the diode D201 to provide additional adjustment to the output side T201-2 of the transformer T201. The power in the primary side T201-1 is controlled by a switching device Q201 which is modulated by an integrated control circuit U201 through a driving resistor R213. In the exemplary embodiment shown in FIG. 2, switching device Q201 is illustrated as an n-channel metal oxide semiconductor field effect transistor (MOSFET). Alternatively, other types of switching devices may be advantageously employed. The drain of the switching device Q201 is connected back to the positive output of the bridge diode BD1 through a diode D202 and a resistor R212 to prevent the switching device Q201 from having an excessive voltage and providing a current cycle when the switching device Q201 is not turned on. path. A capacitor C206 is also coupled in parallel with R212.

In the exemplary flyback regulator 222, the output voltage V201 is regulated by the integrated circuit U201, which in this embodiment includes one of a number of standard power factor correction (PFC) controller integrated circuits. The integrated circuit U201 or PFC controller adjusts the duty cycle of the switching device Q201 such that the power factor of the power conversion stage 200 approaches one and maintains the DC voltage V201 at a substantially constant value. The PFC controller U201 receives the operating power on the pin 8 through the resistors R203 and R204 and the smoothing capacitors C202 and C205. The operating power is also supplied from the tertiary winding T201-3 of the transformer T201 to the PFC controller U201 through the diode D203 and the resistor R211. The three-stage winding T201-3 of the transformer T201 (in one embodiment, a fly-back type transformer) is used to provide a zero-crossing detection signal (ZCD) through a current limiting resistor R215 and a parallel connection filter capacitor C209 to Pin 5 of PFC controller U201. A current sensing resistor R208 is coupled in series between the switching device Q201 and the circuit ground 224 and provides a current sensing signal at the pin 4 of the PFC controller U201. A high power factor is achieved by keeping the current drawn from the input power in phase with the voltage of the input power. To achieve this, the PFC controller U201 is multiplied by one of the pins 4 of the PFC controller U201. The instrument input is used to sense the voltage of the input power. In the exemplary flyback converter 222, the input voltage is sensed by the resistors R205 and R206 at the full-wave rectified DC voltage output from the bridge diode BD1, and a parallel connected resistor R207 and capacitor C204 are used. The input voltage is filtered to produce a multiplier input signal at pin 4 of PFC controller U201.

By using a resistor divider network R208, R209 to feed the output voltage V201 back to the summing node of an op amp type compensation circuit exposed at the pin 1 of the PFC controller U201 Adjustment of voltage V201. This produces a feedback control loop that regulates the output voltage V201 at a substantially constant level. The stability of the control loop is achieved by integrated control generated by a capacitor C203 connected between the summing node 226 and the compensation input pin 2 of the PFC controller U201. This feedback control loop allows the PFC controller U201 to modulate the duty cycle of the switching device Q201 such that the output voltage V201 is maintained at a substantially constant level based on the feedback signal at node 226. Therefore, when the voltage is the output voltage V201, it is adjusted by adjusting the feedback signal applied to the node 226. As will be described in more detail below, this functionality can be used to adjust the output voltage V201 as desired to reduce the power consumed in other portions of an LED driver system, such as the LED driver system 100 described above.

Referring now to Figure 3, an exemplary dimming detection circuit 300 is incorporated that incorporates a comparator circuit to generate a DC dimming signal V303 corresponding to one of the dimming levels indicated by the input voltage signal V302. The dimming signal detection circuit 300 illustrates an example of a method for generating a DC dimming signal V303 indicative of a dimming level of a phase angle dimming signal. In the exemplary dimming detection circuit 300, the input voltage signal V302 is a rectified input power signal, such as the signal generated by the bridge rectifier circuit BD1 described above with reference to FIG. In many applications, such as where an LED light is retrofitted into an earlier incandescent light fixture, input power, such as input power signal 102 of Figure 1, may include one of the phase angle dimming signals known in the art. The phase angle dimming signal can have any suitable type (such as a forward phase angle) Control or reverse phase angle control) dimming. When the input power is a phase angle dimming signal, the dimming signal V303 will be a full-wave rectified phase angle dimming signal. A comparator A301 is used to provide a charging signal to the charging capacitor C301 through the resistor R305, while the resistor R306 provides a discharging path. An operating voltage source V301 provides operational power to comparator A301 and is also used to generate a reference voltage of a non-inverting input of comparator A301 via a resistor divider network formed by resistors R304 and R303. The input voltage signal V302 is applied to the inverting input of comparator A301 via a second resistor divider network formed by resistors R301 and R302. Thus, the DC dimming signal V303 changes in anti-phase with the dimming level indicated by the input voltage signal V302, i.e., the DC dimming signal V303 is a low voltage when a bright light output is desired, and vice versa.

Referring now to Figure 4, an exemplary embodiment of a linear current regulating circuit 400 can be seen that can be used to regulate the current flowing through the LED lamp assembly LA 401 to be substantially constant by a dimming signal V303. The linear current regulation circuit 400 illustrates one example of adjusting the current through the LED lamp assembly LA 401 according to the DC dimming signal V303 to a substantially constant amount. The lamp current is supplied by a voltage source V201 such as, for example, the power conversion circuit 200 described above. Alternatively, other voltage regulating circuits can be used to provide a voltage source V201, also referred to as a regulated voltage.

In one embodiment, the current regulating circuit 400 (also referred to as a controller) includes a pair of transistors Q401 and Q402, wherein the collector of the transistor Q401 receives current from the LED lamp assembly LA401, so that the transistor Q402 controls the flow. The current of the LED lamp assembly. An operating voltage V401 is supplied through a resistor R403 to the base of the transistor Q402. A resistor R405 is coupled between the emitter of the control transistor Q402 and a circuit ground 402 such that an increase in current flowing through the control transistor Q402 increases the voltage at the emitter 404. A second transistor Q401 is coupled between the base 406 of the control transistor Q402 and the circuit ground 402, wherein the control terminal or base of the transistor Q401 is coupled through a resistor R406 to the emitter of the control transistor Q402. a DC dimming signal V303 (such as described above by an exemplary dimming detection The DC dimming signal V303 generated by the path 300 is applied to the base of the transistor Q401 through a resistor R402 and a pair of diodes D401 and D402 connected in series.

The operation of the linear current regulating circuit 400 can be understood by first assuming that the resistor R406 is shorted and removing the DC dimming signal by removing the diode D401. This simplifies the DC dimming circuit 400 into a linear circuit in which the lamp current I _LED can be calculated from I _LED = 0.7 volts / R 405 Ω, wherein 0.7 volts controls the base-to-emitter voltage drop of the transistor Q402 and the sign Ω is The unit of ohms indicates the resistance value of each resistor. Now, consider a full linear current regulation circuit 400 that includes a diode D401 and a resistor R406, and the lamp current can be calculated from I _LED = (0.7vV _R406 ) / R405Ω, where V _R406 is the voltage across resistor R406. Therefore, the lamp current I _LED decreases as the DC dimming signal V303 rises. In some embodiments, resistor R405 has a low resistance (such as several ohms) and resistor R406 and resistor R402 are relatively large (such as several kilo ohms). The voltage across resistor R406 can be approximated as: V _R406 = V303 * R406Ω / (R402Ω + R406Ω) and the lamp current can be approximated as: I _LED = (0.7-V303 * R406Ω / (R406Ω + R402Ω)) / R405Ω, resulting in a Lamp current, which is a linear function of the DC dimming signal V303. In the exemplary circuit 400, two diodes D401 and D402 are coupled in series with a DC dimming signal V303 to improve the dimming curve. Each of the diodes D401, D402 has a voltage drop of approximately 0.7 volts, so the DC dimming signal V303 does not affect the linear current regulation circuit 400 until the DC dimming signal V303 exceeds approximately 1.4 volts. For example, in the exemplary circuit illustrated in Figures 3 and 4 above, the lamp current decreases linearly when the AC dimming signal V302 has a residual angle of less than about 144 degrees. The residual angle refers to the portion of the phase angle dimming signal that transmits power to the sinusoidal period of the load.

Figure 5 illustrates one of the functional blocks of a one-stage half LED driver circuit 500 that uses voltage drop monitoring to reduce power consumption while maintaining stable LED light output and dimming functionality. The exemplary LED driver circuit 500 includes a first stage voltage regulator 504 having an input 526 and an output 514. The first stage 504 is configured to convert one of the AC input powers 502 on the input 526 to a regulated DC voltage on the output 514. In some embodiments, the first stage 504 A PFC controller is included that is configured to maintain a current from input power 502 in phase with the voltage of input power 502 such that the power factor of driver circuit 500 is maintained at or near one. An LED lamp or lamp assembly 506 receives the regulated DC voltage on output 514 from the first stage 504. A linear current controller 508 is coupled in series between the LED lamp assembly 506 and one of the return stages 520 of the first stage 504 to maintain the lamp current 516 (which is the current through the LED lamps) at a substantially constant amount. The DC voltage on output 514 is regulated by a regulator 510 (also referred to as a feedback control circuit). Regulator 510 receives a feedback signal 522 and operates first stage 504 via a control signal 524 to maintain the DC voltage on output 514. At about a certain voltage. Regulator 510 receives a feedback signal from an adder 512, which combines the DC voltage on output 514 with a voltage drop signal 534 resulting from the voltage drop of a voltage drop sensing circuit 528 from linear current regulator 518. As described above, the power consumed by linear current regulator 508 is proportional to the voltage drop 518 across regulator 508. Voltage monitoring circuit 528 generates a voltage drop signal 534 when voltage drop 518 across current regulator 508 exceeds a threshold amount. When voltage drop signal 534 is added to the DC voltage on output 514 in adder 512, it modifies the feedback signal such that the DC voltage on output 514 is adjusted to a lower value. In this manner, voltage drop monitoring or sensing circuit 528 acts in conjunction with adder 512 to reduce power consumption in linear current regulator 508. To accommodate applications requiring dimming functionality, the first stage half LED driver circuit 500 includes a dimming detection circuit 536 that receives the input power signal 532 and produces one that is proportional to the dimming level indicated by the input power signal 532. Dimming signal 530. The dimming signal 530 is received by a linear current regulator 508 that is used to adjust the lamp current 516 accordingly.

It is desirable to drive the LED lamp at a constant current to maintain a steady light output. However, due to environmental and manufacturing factors, the forward voltage drop across the LED can vary. For example, as the temperature rises, the forward voltage drop of an LED decreases. The described linear current regulator 508 operates by changing its voltage drop in anti-phase with the voltage drop of the LED. This means that as the temperature rises, the LED voltage drop will decrease and the linear current regulator 508 will increase its voltage drop to maintain a constant current. Using voltage drop monitoring, a voltage monitoring circuit 528 is used to feed back a voltage drop signal 534 to the voltage regulator 510, thereby reducing the amount of power consumed in the current regulator 508. The increased voltage drop across the linear current regulator 508 results in an increase in the power consumed. Table 1 below provides some representative values to illustrate the power consumed in a drive circuit that does not employ voltage drop monitoring as described herein to reduce the power consumed in the current regulator. Referring to Table 1, in this example, the DC voltage on output 514 is approximately 14 volts and the desired LED current is approximately 0.5 amps. As seen in Table 1, the linear current regulator 508 consumes 1.5 watts when the LED voltage drops to 11 volts. As the LED voltage increases, the power consumed by linear current regulator 508 decreases. Therefore, when the LED voltage is approximately 13 volts, the power consumed in the linear current regulator 508 is 0.5 watts.

Table 2 provides representative values of LED driver circuit 500 including one of the novel voltage drop monitoring methods described above. As seen in Table 2, when the LED voltage is at or above about 12 volts, the voltage of current regulator 508 is reduced to the threshold voltage and voltage monitoring circuit 528 does not generate any voltage drop signals. When the LED voltage drops below about 12 volts (such as 11 volts), the voltage drop of current regulator 508 exceeds the threshold voltage and voltage monitoring circuit 528 begins to generate a voltage drop signal that causes the first on output 514. The stage voltage is regulated to a lower value (such as approximately 13 volts). Reducing the first stage voltage on output 514 causes the power consumed in linear current regulator 508 to decrease proportionally, which is approximately 1 watt in this example.

Referring now to Figure 6, an exemplary feedback control circuit 510 and adder 512 can be utilized to generate one of control signals 524 that can be used to operate a first stage voltage regulator, such as first stage 504, as described above. LED lamp D600 receives a DC voltage 612 that produces a current through the lamp that is regulated by current regulating transistor Q402, such as control transistor Q402 described above with respect to FIG. A resistor divider network comprising resistors R603 and R604 connected in series between DC power 612 and circuit ground 614 generates a voltage feedback 616 coupled to feedback control circuit 510 via a resistor R602. The Zener diode Z601 is coupled between the current regulator transistor Q402 and the adder 512 such that when the voltage across the current regulator transistor Q402 drops beyond the breakdown voltage of the Zener diode Z601, a voltage drop signal is applied. To circuit node 616, it is added to voltage feedback through resistor R602. An operational amplifier A 601 receives a reference voltage V601 and produces an adjustment or control signal 524. Stabilization and optimization is provided in exemplary feedback control circuit 510 by capacitor C601 coupled in parallel with a series connected resistor R601 and capacitor C602.

7 is a flow chart of one exemplary method for driving an LED lamp incorporating one of the aspects of the voltage drop monitoring techniques described herein. In one embodiment, the method uses a first stage one-stage half driver circuit to convert an AC input power to a DC output power 702. A feedback signal 704 is generated from the DC output voltage, and the feedback signal is used to adjust the voltage of the DC output voltage to a substantially constant voltage 706 corresponding to the feedback signal. In some embodiments, the first stage includes power factor correction to maintain the current drawn by the first stage in phase with the voltage of the input power such that the power factor of the LED driver is one or nearly one. The DC output power is provided to an LED lamp such as, for example, an LED lamp 708. in In one embodiment, the LED light can include a plurality of LED elements or other suitable LED lights configured in a series-parallel block configuration. The LED lamp current (i.e., the current flowing through the LED lamp) is maintained at a substantially constant amount 710 by a linear current source (also referred to herein as a linear current regulator). The power consumed in the linear current source is proportional to the lamp current and the voltage drop across the linear current source. Since this power is not used to generate light, it is essentially a waste of energy. Therefore, it is desirable to reduce the power consumed by the linear current source as much as possible. The power in the linear current source can be reduced by monitoring the voltage drop 712 across the linear current source. When the voltage drop exceeds a threshold voltage 714, the voltage drop signal is used to adjust the feedback signal 716 generated in step 704 above. As mentioned above, increasing the feedback signal will reduce the voltage to which the DC output voltage is regulated. The adjusted output signal is then used to adjust the DC output voltage to a substantially lower voltage 706.

FIG. 8 is a flow chart showing one method 800 of including dimming functionality in the exemplary LED driving method 700 illustrated in FIG. In some embodiments, the AC input power includes a dimming signal such as, for example, a forward or reverse phase control dimming signal. To achieve dimming functionality, the AC input power 802 of a dimming signal is monitored. The dimming signal is converted to produce a dimming voltage (generally a DC dimming voltage) 806, wherein one of the dimming signals corresponds to an input dimming signal. The DC dimming voltage is used to adjust the amount of lamp current provided by the linear current source.

Accordingly, while the invention has been shown and described, it is understood that the invention may be Various omissions, substitutions and alterations of the form and details of the device and its operations. In addition, it is expressly pointed out that all compositions of such elements that perform substantially the same function to obtain the same results in substantially the same manner are within the scope of the invention. In addition, it should be appreciated that the structures and/or elements shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other form or embodiment disclosed or suggested or suggested as a design choice. generally. Therefore, the present invention is intended to be only subject to The restrictions indicated in the scope of the scope of the patent application are attached.

1‧‧‧Supply terminal pin

2‧‧‧Return terminal pin

3‧‧‧ pin

4‧‧‧ pin

5‧‧‧ pin

6‧‧‧ pin

7‧‧‧ pin

8‧‧‧ pin

200‧‧‧Power conversion stage

220‧‧‧Input filter

222‧‧‧Reciprocating converter / flyback regulator

224‧‧‧Circuit grounding

226‧‧‧ summing node

BD1‧‧‧Bridge Diode Circuit/Bridge Diode

C201‧‧‧ capacitor

C202‧‧‧Filter capacitor

C203‧‧‧ capacitor

C204‧‧‧ capacitor

C205‧‧‧Filter capacitor

C206‧‧‧ capacitor

C207‧‧‧ capacitor

C208‧‧‧ capacitor

C209‧‧‧ capacitor

C210‧‧‧ capacitor

CON1‧‧‧Input connector

D201‧‧‧ diode

D202‧‧‧ diode

D203‧‧‧ diode

F201‧‧‧Fuse

L201‧‧‧Inductors

L202‧‧‧Inductors

Q201‧‧‧Switching device

R201‧‧‧Resistors

R202‧‧‧Resistors

R203‧‧‧Resistors

R204‧‧‧Resistors

R205‧‧‧Resistors

R206‧‧‧Resistors

R207‧‧‧Resistors

R208‧‧‧Resistors

R209‧‧‧Resistors

R211‧‧‧Resistors

R212‧‧‧Resistors

R213‧‧‧Drive resistor

R215‧‧‧Resistors

R216‧‧‧Resistors

T201‧‧‧Transformer

T201-1‧‧‧ main winding

T201-2‧‧‧Secondary winding / output side

T201-3‧‧‧ three-stage winding

U201‧‧‧Integral control circuit / integrated circuit / power factor correction (PFC) controller

V201‧‧‧ constant voltage / output voltage / direct current (DC) voltage

Claims (20)

A driver circuit for an LED lamp, the driver circuit comprising: a first stage configured to receive an AC input power and generate a regulated DC voltage; a linear current regulator coupled to the first Level and configured to adjust a lamp current; a feedback circuit coupled to the first stage, wherein the feedback circuit is configured to monitor the regulated DC voltage and operate the first stage to adjust the The DC voltage is maintained at a substantially constant voltage; and a voltage drop monitoring circuit coupled to the feedback circuit and configured to adjust the substantially constant voltage, wherein the voltage drop monitoring circuit monitors a voltage of the linear current regulator Lowering and decreasing the substantially constant voltage as the voltage drop increases. The driver circuit of claim 1, wherein the voltage monitoring circuit is configured to reduce the substantially constant voltage when the voltage drop exceeds a threshold voltage, and not to decrease when the voltage is lowered to the threshold voltage Small, this is a constant voltage. The driver circuit of claim 2, wherein the voltage drop monitoring circuit comprises a Zener diode. The driver circuit of claim 1, wherein the first stage comprises a bridge diode circuit. The driver circuit of claim 1, wherein the first stage is configured to maintain a power factor of one of the driver circuits at or near one. The driver circuit of claim 1, wherein the linear current regulator comprises a first transistor and a second transistor, and wherein the first transistor controls the lamp current, and the second transistor controls the first transistor A base current, and the lamp current is coupled to the base of the second transistor via a resistor. The driver circuit of claim 1, wherein the AC input power comprises a dimming signal, and the driver circuit comprises a dimming controller, wherein the dimming controller is coupled to the AC input voltage and adapted to operate the linear current The regulator is such that the lamp current corresponds to the dimming signal. The driver circuit of claim 7, wherein one of the dimming controllers controls an output coupled to the linear current regulator, and wherein the dimming controller monitors the dimming signal and the control output includes and is indicated by the dimming signal One of the dimming levels is an inversely proportional DC voltage. The driver circuit of claim 8, wherein the dimming controller is coupled to the linear current regulator through one of a plurality of series connected diodes. An electrical lighting device comprising: a driver circuit configured to receive an AC input power and generate a lamp current; and an LED lamp coupled to the lamp current, wherein the driver circuit comprises: a first stage Connected to the AC input power and configured to generate a regulated DC voltage; a linear current regulator coupled between the first stage and the LED lamp, the linear current regulator configured to adjust The lamp current is at a substantially constant amount; a feedback circuit coupled to the first stage, wherein the feedback circuit is configured to monitor the regulated DC voltage and operate the first stage such that the regulated DC The voltage is maintained at a substantially constant voltage; and a voltage drop monitoring circuit coupled to the feedback circuit and configured to adjust the substantially constant voltage, wherein the voltage drop monitoring circuit monitors a voltage drop of the linear current regulator And the substantially constant voltage is reduced as the voltage drop increases. The electrical lighting device of claim 10, wherein the LED lamp comprises one or more LED diodes coupled in a series-parallel block configuration. The electrical lighting device of claim 10, wherein the voltage drop monitoring circuit is adapted to reduce the substantially constant voltage when the voltage drop exceeds a threshold voltage. The electrical lighting device of claim 12, wherein the voltage drop monitoring circuit comprises a Zener diode. The electrical lighting device of claim 10, wherein the first stage is configured to maintain a power factor of one of the driver circuits at or near one. The electrical lighting device of claim 10, wherein the first stage comprises a flyback type power converter. The electrical lighting device of claim 10, wherein the AC input power comprises a dimming signal, the driver circuit comprising a dimming controller, and wherein the dimming controller is coupled to the AC input voltage and adapted to operate the linear A current regulator adjusts the lamp current relative to the dimming signal. A method of operating an LED driver circuit, the method comprising: using a first power stage to convert an AC input power to a DC output voltage; generating a feedback signal from the DC output voltage; using the feedback signal to adjust the DC output Voltage; providing the DC output voltage to an LED lamp; using a linear current source to regulate a lamp current; monitoring a voltage drop of the linear current source; and adjusting the feedback signal to when the voltage drop exceeds a threshold voltage Reduce the DC output voltage. The method of claim 17, comprising: monitoring the AC input power of a dimming signal; and adjusting the lamp current based at least in part on the dimming signal. The method of claim 18, further comprising: generating a DC dimming voltage corresponding to one of the dimming levels indicated by the dimming signal; and adjusting the lamp current relative to the DC dimming voltage. The method of claim 19, wherein the magnitude of the DC dimming voltage is inversely proportional to the lamp current.