> Quick answer: In solar lamps, the LED driver regulates a steady current to SMD LEDs using switched-mode power supplies despite sagging battery voltage [1][14]. This ensures that the light remains bright throughout the night by dynamically adjusting output to maintain stable current.
How Does an LED Driver Keep Solar Lamps Bright All Night?
Solar lamps are increasingly popular for their eco-friendly and cost-effective illumination. However, one critical factor in ensuring consistent brightness is the LED driver’s ability to regulate a constant current despite battery voltage fluctuations through the night [1][2]. Let’s dive into how these drivers maintain steady light output.
How Constant Current Drivers Work
The heart of any solar lamp lies in its LED driver, which uses active regulation mechanisms like switched-mode power supplies (SMPS) such as buck, boost, or buck-boost converters to adjust their output dynamically [1][14]. These circuits ensure that the current flowing through the SMD LEDs remains constant even when battery voltage drops significantly.
For example, a buck-boost converter can operate in either mode depending on whether the battery voltage is below or above the required output voltage, ensuring consistent current delivery across a wide input range [14]. This adaptability allows the driver to sustain current regulation from 4.2 V down to as low as 3.0 V [12].
Feedback Mechanisms and PWM
The core mechanism involves switching elements—typically power MOSFETs—controlled by a pulse-width modulation (PWM) signal generated by a microcontroller or integrated circuit [5][8]. The driver continuously monitors the actual current flowing through the LEDs and adjusts its switching behavior to compensate for voltage drops. When the battery voltage sags, the driver increases the duty cycle of the switching signal to maintain the same average current through the LEDs [17][19].
Comparing Constant Current vs. Constant Voltage Drivers
| Type | Brightness Stability | Energy Efficiency |
|–––––––-|–––––––––––-|––––––––––––––-|
| Constant Current (CC) | Maintains stable brightness over a wide range of input voltages [1] | Higher efficiency as it adapts to battery voltage drops [17][19] |
| Constant Voltage (CV) | Brightness fades with dropping battery voltage [13]|[8] Typically less efficient due to constant power draw |
Intelligent Energy Scaling
Some advanced systems incorporate intelligence to dynamically adjust brightness based on available energy. For instance, one patent describes a system that divides the night into segments and scales the LED current based on the battery’s stored energy, ensuring LEDs operate at a constant current level throughout [12][15].
When the battery voltage drops below critical levels, such as 3.0 V or 2.8 V, the driver reduces current consumption to extend operating time and prevent over-discharge [12][13]. This dynamic adjustment prevents abrupt failure at dawn and preserves battery life.
Limitations and Variability in Market Products
However, not all solar lamps are equipped with these advanced features. Many low-cost systems rely on simple resistive or non-regulated drivers that do not maintain constant brightness as the battery discharges [13]. These less sophisticated designs often result in a linear decrease in brightness as voltage drops, contrary to the goal of consistent illumination.
Key Takeaways
- Active Regulation: Switched-mode power supplies (SMPS) ensure stable current and light output.
- Feedback and PWM Control: Continuous monitoring and adaptive switching maintain constant current despite battery sag.
- Intelligent Energy Use: Advanced systems dynamically adjust brightness based on available energy, extending runtime.
Frequently Asked Questions
[{„q”: „Why does the LED driver need to regulate current?”, „a”: „The LED driver regulates current to maintain consistent brightness as the battery voltage drops through the night. Without regulation, the light would fade [13][8].”},
{„q”: „How do constant current drivers work in solar lamps?”, „a”: „Constant current (CC) drivers use feedback mechanisms and PWM signals to dynamically adjust output, ensuring that the current remains steady even as battery voltage decreases [5][17].”},
{„q”: „What are some advanced features of solar lamp LED drivers?”, „a”: „Advanced systems divide the night into segments and scale LED current based on available energy. They also reduce current or turn off LEDs at low voltages to prevent over-discharge [12][13].” }]
References
- [1] LED_circuit_-_Wikipedia__19b164d2 — wikipedia
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flow. Drivers may be constant current (CC) or constant voltage (CV). In CC drivers, the voltage changes while the current stays the same. CC drivers are used when the electrical load of the LED circuit is either unknown or fluctuates, for example, a lighting circuit where a variable number of LED lamp fixtures may be installed. As an LED heats up, its voltage drop decreases (band gap decrease[1]). This can encourage the current to increase. An active constant current source is commonly used for high power LEDs, stabilizing light output over a wide range of input voltages which might increase the useful life of batteries. Active constant current is typically regulated using a depletion-mode MOSFET (metal–oxide–semiconductor field-effect transistor), which is the simplest current limiter.[2] Low drop-out (LDO) constant current regulators also allow the total LED voltage to be a higher fraction of the power supply voltage. Switched-mode power supplies (e.g. buck, boost, and buck-boost converters) are used in LED flashlights and household LED lamps. Power MOSFETs are typically used for switching LED drivers, which is an efficient solution to drive high-brightness LEDs. Power integrated circuit (IC) chips are widely used to drive the MOSFETs directly, without the need for additional circuitry.[2] Series resistors are a simple way to stabilize the LED current, but energy is wasted in the resistor. Miniature indicator LEDs are normally driven from low voltage DC via a current-limiti
- [2] DiodeGoneWild__Ultra_efficient_Dubai_LEDs__5csGL6sdQiY — youtube
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this keeps the current through the LEDs roughly constant. The capacitor parallel to the LEDs is just a ceramic capacitor with quite a low capacitance. This way you could see a high frequency ripple in the light measured by the solar panel. You will have to disconnect something to measure this capacitor. And when the transistor is on, the current flows from the positive rail through the LEDs, the inductor, the transistor and this current sensing resistor to the negative rail. And the voltage on this inductor is in this polarity. Of course, the voltage drop of the LEDs is lower than the total voltage on this rail so the inductor drops some portion of the voltage. But unlike a resistor which would have dissipated its voltage drop times the current, the inductor doesn't dissipate it. It stores the energy as a magnetic field in its core and its air gap. And when the transistor turns off, the current still goes through the inductor in the same direction but the polarity on it changes. The current goes here through this diode and through the LEDs in a circle like this. It is basically not connected to the supply rails. It then uses the energy stored in the inductor. That's how a buck regulator can reduce the voltage without dissipating much. It does not have to dissipate the difference. And when the energy runs out in the inductor, the transistor can turn back on and the cycle can repeat. Of course, the voltage on the LEDs is always this polarity. It's quite difficult to see on the
- [5] CN101626652A_-_Dimmable_LED_constant_current_source_driver_with__acd3cd20 — patent
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driver in the illuminating field. The driver comprises a voltage identification circuit, a light compensation circuit, an MCU control circuit, a temperature compensation circuit and a dimmable constant current source circuit, wherein the output ends of the voltage identification circuit, the light compensation circuit and the temperature compensation circuit are all connected with the input end of the MCU control circuit, the PWM output end of the MCU control circuit is connected with the input end of the dimmable constant current source circuit, the voltage identification circuit and the dimmable constant current source circuit are both connected into direct-current or alternating-current input voltage, the light compensation circuit is connected with a photosensitive device, the temperature compensation circuit is connected with a thermistor, and the output end of the dimmable constant current source circuit is connected with an LED light source. The invention has low cost, small volume, stable and reliable working of a system and prolongs the service life of an LED. Description Technical field The present invention relates to a kind of led light source driver in the lighting field, relate in particular to a kind of Dimmable LED constant current source driver with wide voltage range. Background technology Current, in short supply and national the vigorously advocating under the energy-saving and cost-reducing background in global energy, along with science and technology de
- [8] An_Illuminating_Look_at_LED_Driving_Electronic_Design__3d16287f — magazine
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Other arrangements use an external MOSFET to speed up the dimming response and minimize nonlinear brightness response. Figure 4 shows one arrangement. 4. LED dimming is accomplished with a switching current regulator using a variable duty-cycle PWM input from a microcontroller or other source. The external components enable faster switching at higher frequencies. Backlighting LEDs are widely used to backlight liquid crystal displays (LCDs), such as those used for typical laptops. One common arrangement is an array of 60 white LEDs made up of six strings of 10 series-connected LEDs. Each string needs a driver that can be utilized for dimming. Light guides and diffusers are used to spread the light uniformly across the screen. Backlights must be super bright to give sufficient brightness to an LCD. As a result, they generally consume a considerable amount of power. When selecting a driver, efficiency is an important factor. The two basic ways to control dimming are linear current variation and PWM. The linear version works well, but it’s limited because of the difficulty in delivering very small currents. The nonlinearity of the LEDs limits the minimum brightness level. A widely used driver is the dc-dc converter with PWM. The PWM approach varies the duty cycle of applied pulses to control the average LED current and the brightness. Though this method can achieve very small duty cycles and good low brightness resolution, it suffers from inefficiency and high switching noise at
- [12] US20110252678A1_-_Method_apparatus_and_system_-_Google_Patents__66ffc305 — patent
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correct level of current consumption during all the night time hours. The exemplary circuit ofFIG. 14 can evenly divide the night time hours required for LED operation and scale the output signal to match with the available battery energy that has previously been stored during the daytime hours and provided to the scaler divider circuit in the form of the analog charge level input signal provided from the circuit ofFIG. 12 . – FIG. 15 is the exemplary LED driver circuit, which adjusts the voltage output signal from the energy scaler circuit so that none of the LEDs operate at more than approximately 20 mA or alternatively 25 mA per LED, which could overdrive the LEDs and cause early failure. All during the night time hours, the LED driver circuit continues to provide battery power to operate the LEDs at a constant level of current consumption. The LEDs are connected to the LED driver circuit through jumpers J10 and J11 located at the lower right hand corner ofFIG. 15 . If the battery voltage decreases down to 3.0 VDC due to power consumption by the LEDs, then the LED driver circuit turns down the current consumption by the LEDs regardless the input from the scaler energy circuit to extend the LED operating time. If the battery voltage continues to decrease down to below about 2.8 VDC, the transistor Q2 turns off the LEDs to conserve some of the battery energy and avoid over-discharging the battery. – FIG. 16 further illustrates the battery protection features of the control c
- [13] LED_circuit_-_Wikipedia__19b164d2 — wikipedia
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# LED circuit – Wikipedia Source: Blog/Web URL: https://en.wikipedia.org/wiki/LED_circuit Author: Date: 2006-06-12 In electronics, an LED circuit or LED driver is an electrical circuit used to power a light-emitting diode (LED). The circuit must provide sufficient current to light the LED at the required brightness, but must limit the current to prevent damaging the LED. The voltage drop across a lit LED is approximately constant over a wide range of operating current; therefore, a small increase in applied voltage greatly increases the current. Datasheets may specify this drop as a "forward voltage" () at a particular operating current. Very simple circuits are used for low-power indicator LEDs. More complex, current source circuits are required when driving high-power LEDs for illumination to achieve correct current regulation. The simplest circuit to drive an LED is through a series resistor. It is commonly used for indicators and digital displays in many consumer appliances. However, this circuit is not energy-efficient, because energy is dissipated in the resistor as heat. The LED's depends on its material. Ohm's law and Kirchhoff's circuit laws are used to calculate the appropriate resistor value, by subtracting the LED's from the supply voltage and dividing by the desired operating current. With a sufficiently high supply voltage, multiple LEDs in series can be powered with one resistor. If the supply voltage is close or equal to the LED's , then no reasonable value fo
- [14] US9992826B1_-_Dual_mode_constant_current_LED_driver__71bc120a — patent
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the output voltage of the driver using a DC voltage signal provided by the DC power source, a current flowing through the first inductor, a switching frequency of the first switch, and a duty ratio of the first switch. – the device may further include an electro-magnetic interference (EMI) filter operatively connected between the DC power source and the converter, and configured to eliminate high frequency components of a DC voltage signal from the DC power source. – EMI electro-magnetic interference Landscapes – Circuit Arrangement For Electric Light Sources In General (AREA) Abstract A dual mode constant output current LED driver is capable of operating with a very wide range of input direct current (DC) voltage. This provides an effective topology for a wide range of constant output current LED drivers, and allows for changing the number of connected LEDs without negatively impacting the output current. The LED driver includes a converter and a mode selection circuit that control the modes of the circuit based on the voltage. The converter and mode selection circuit operate in a buck-boost mode when the output voltage of the LED driver is less than the DC input voltage plus a first threshold amount, and in a boost mode when the output voltage of the LED driver is greater than the DC input voltage plus a second threshold amount. Description The present disclosure relates to power supplies suitable for driving light emitting diode (LED) lighting systems as well as other elec
- [15] US20110252678A1_-_Method_apparatus_and_system_-_Google_Patents__66ffc305 — patent
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operated simply by supplying a fixed DC voltage. – the DC current supplied to one or more LEDs may have to be properly controlled to avoid burning out the LEDs if the current is too high, but also to provide adequate current to the LEDs (to assure adequate light output from the LEDs) over a reasonably wide range of power supply voltages. – the battery system includes a rechargeable battery connected to a solar photovoltaic panel, which recharges the battery during the daytime when there is adequate ambient light intensity. – the battery system is then used to operate one or more LEDs as determined by the Control Circuit used as an integral part of the present invention. – the Control Circuit used as an integral part of the present invention. – the voltage output from the photovoltaic solar panel system drops to a level near zero, this then signals the onset of the night hours and the control circuit then subsequently turns on the one or more LEDs. – Other types of sensor signals could optionally be used to provide on-off control of the LEDs, such as photocell sensors, photodiodes, phototransistors, photothyristors and light-activated silicon-controlled rectifiers (LASCRs). – an enhanced visibility street name sign having one or more LEDs which are operated from a battery-powered control circuit, wherein the battery receives electrical power from a solar photovoltaic panel system during the daytime, and wherein the control circuit monitors the total amount of solar energy supp
- [17] US9699844B2_-_Multichannel_constant_current_LED_driving_circuit__e42a6a3f — patent
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accordance with current feedback signal VFB and the reference current signal, such that the output current of the power stage circuit is consistent with driving current requirements of LED strings LED1 and LED2. In accordance with certain requirements, such as warm-and-cold lamp applications, the luminance of LED strings LED1 and LED2 may be different. Also, the duty cycle of each PWM dimming signal can be regulated in accordance with associated luminance requirements. In addition, each of the switching transistors corresponding to the LED strings can be controlled by current control unit 301 in accordance with a corresponding PWM dimming signal. In this way, the average current of each LED string can be regulated to be consistent with the luminance requirements. Referring now to FIG. 3D , shown is a waveform diagram showing example operation of the multichannel constant current LED driving circuit shown in FIG. 3A , in accordance with embodiments of the present invention. In one switching period T, the output current can flow through LED string LED1 in time interval T1, during which PWM dimming signal PWM1 is active, and the output current may flow through LED string LED2 in time interval T2, during which PWM dimming signal PWM2 is active. Therefore, the luminance of LED strings LED1 and LED2 can be regulated to be different in view that the average current of LED strings LED1 and LED2 is different in order to achieve color and/or dimming control. In this fashion, the lumina
- [19] US9408265B2_-_Multichannel_constant_current_LED_driving_circuit__0c494fbd — patent
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the multichannel constant current LED driving circuit shown in FIG. 3A , in accordance with embodiments of the present invention. In one switching period T, the output current can flow through LED string LED1 in time interval T1, during which PWM dimming signal PWM1 is active, and the output current may flow through LED string LED2 in time interval T2, during which PWM dimming signal PWM2 is active. Therefore, the luminance of LED strings LED1 and LED2 can be regulated to be different in view that the average current of LED strings LED1 and LED2 is different in order to achieve color and/or dimming control. In this fashion, the luminance of a cold-and-warm lamp that includes two LED strings can be regulated. In particular embodiments, only one driving circuit may be utilized in driving a plurality of LED strings that are connected in series. For example, the driving circuit can include a buck configuration with power switching transistor QM, inductor L1, and the rectifier diode. The luminance of each of the LED strings may be controlled by a corresponding PWM dimming signal in order to meet different luminance requirements. Further, both constant driving current to drive the LED strings, and luminance regulation can be achieved in certain embodiments with a simplified circuit structure, fewer elements, and lower costs/volume, as compared to other approaches. Referring now to FIG. 3C , shown is a schematic block diagram of a second example multichannel constant current LED dri
flow. Drivers may be constant current (CC) or constant voltage (CV). In CC drivers, the voltage changes while the current stays the same. CC drivers are used when the electrical load of the LED circuit is either unknown or fluctuates, for example, a lighting circuit where a variable number of LED lamp fixtures may be installed. As an LED heats up, its voltage drop decreases (band gap decrease[1]). This can encourage the current to increase. An active constant current source is commonly used for high power LEDs, stabilizing light output over a wide range of input voltages which might increase the useful life of batteries. Active constant current is typically regulated using a depletion-mode MOSFET (metal–oxide–semiconductor field-effect transistor), which is the simplest current limiter.[2] Low drop-out (LDO) constant current regulators also allow the total LED voltage to be a higher fraction of the power supply voltage. Switched-mode power supplies (e.g. buck, boost, and buck-boost converters) are used in LED flashlights and household LED lamps. Power MOSFETs are typically used for switching LED drivers, which is an efficient solution to drive high-brightness LEDs. Power integrated circuit (IC) chips are widely used to drive the MOSFETs directly, without the need for additional circuitry.[2] Series resistors are a simple way to stabilize the LED current, but energy is wasted in the resistor. Miniature indicator LEDs are normally driven from low voltage DC via a current-limiti
this keeps the current through the LEDs roughly constant. The capacitor parallel to the LEDs is just a ceramic capacitor with quite a low capacitance. This way you could see a high frequency ripple in the light measured by the solar panel. You will have to disconnect something to measure this capacitor. And when the transistor is on, the current flows from the positive rail through the LEDs, the inductor, the transistor and this current sensing resistor to the negative rail. And the voltage on this inductor is in this polarity. Of course, the voltage drop of the LEDs is lower than the total voltage on this rail so the inductor drops some portion of the voltage. But unlike a resistor which would have dissipated its voltage drop times the current, the inductor doesn't dissipate it. It stores the energy as a magnetic field in its core and its air gap. And when the transistor turns off, the current still goes through the inductor in the same direction but the polarity on it changes. The current goes here through this diode and through the LEDs in a circle like this. It is basically not connected to the supply rails. It then uses the energy stored in the inductor. That's how a buck regulator can reduce the voltage without dissipating much. It does not have to dissipate the difference. And when the energy runs out in the inductor, the transistor can turn back on and the cycle can repeat. Of course, the voltage on the LEDs is always this polarity. It's quite difficult to see on the
driver in the illuminating field. The driver comprises a voltage identification circuit, a light compensation circuit, an MCU control circuit, a temperature compensation circuit and a dimmable constant current source circuit, wherein the output ends of the voltage identification circuit, the light compensation circuit and the temperature compensation circuit are all connected with the input end of the MCU control circuit, the PWM output end of the MCU control circuit is connected with the input end of the dimmable constant current source circuit, the voltage identification circuit and the dimmable constant current source circuit are both connected into direct-current or alternating-current input voltage, the light compensation circuit is connected with a photosensitive device, the temperature compensation circuit is connected with a thermistor, and the output end of the dimmable constant current source circuit is connected with an LED light source. The invention has low cost, small volume, stable and reliable working of a system and prolongs the service life of an LED. Description Technical field The present invention relates to a kind of led light source driver in the lighting field, relate in particular to a kind of Dimmable LED constant current source driver with wide voltage range. Background technology Current, in short supply and national the vigorously advocating under the energy-saving and cost-reducing background in global energy, along with science and technology de
Other arrangements use an external MOSFET to speed up the dimming response and minimize nonlinear brightness response. Figure 4 shows one arrangement. 4. LED dimming is accomplished with a switching current regulator using a variable duty-cycle PWM input from a microcontroller or other source. The external components enable faster switching at higher frequencies. Backlighting LEDs are widely used to backlight liquid crystal displays (LCDs), such as those used for typical laptops. One common arrangement is an array of 60 white LEDs made up of six strings of 10 series-connected LEDs. Each string needs a driver that can be utilized for dimming. Light guides and diffusers are used to spread the light uniformly across the screen. Backlights must be super bright to give sufficient brightness to an LCD. As a result, they generally consume a considerable amount of power. When selecting a driver, efficiency is an important factor. The two basic ways to control dimming are linear current variation and PWM. The linear version works well, but it’s limited because of the difficulty in delivering very small currents. The nonlinearity of the LEDs limits the minimum brightness level. A widely used driver is the dc-dc converter with PWM. The PWM approach varies the duty cycle of applied pulses to control the average LED current and the brightness. Though this method can achieve very small duty cycles and good low brightness resolution, it suffers from inefficiency and high switching noise at
correct level of current consumption during all the night time hours. The exemplary circuit ofFIG. 14 can evenly divide the night time hours required for LED operation and scale the output signal to match with the available battery energy that has previously been stored during the daytime hours and provided to the scaler divider circuit in the form of the analog charge level input signal provided from the circuit ofFIG. 12 . – FIG. 15 is the exemplary LED driver circuit, which adjusts the voltage output signal from the energy scaler circuit so that none of the LEDs operate at more than approximately 20 mA or alternatively 25 mA per LED, which could overdrive the LEDs and cause early failure. All during the night time hours, the LED driver circuit continues to provide battery power to operate the LEDs at a constant level of current consumption. The LEDs are connected to the LED driver circuit through jumpers J10 and J11 located at the lower right hand corner ofFIG. 15 . If the battery voltage decreases down to 3.0 VDC due to power consumption by the LEDs, then the LED driver circuit turns down the current consumption by the LEDs regardless the input from the scaler energy circuit to extend the LED operating time. If the battery voltage continues to decrease down to below about 2.8 VDC, the transistor Q2 turns off the LEDs to conserve some of the battery energy and avoid over-discharging the battery. – FIG. 16 further illustrates the battery protection features of the control c
# LED circuit – Wikipedia Source: Blog/Web URL: https://en.wikipedia.org/wiki/LED_circuit Author: Date: 2006-06-12 In electronics, an LED circuit or LED driver is an electrical circuit used to power a light-emitting diode (LED). The circuit must provide sufficient current to light the LED at the required brightness, but must limit the current to prevent damaging the LED. The voltage drop across a lit LED is approximately constant over a wide range of operating current; therefore, a small increase in applied voltage greatly increases the current. Datasheets may specify this drop as a "forward voltage" () at a particular operating current. Very simple circuits are used for low-power indicator LEDs. More complex, current source circuits are required when driving high-power LEDs for illumination to achieve correct current regulation. The simplest circuit to drive an LED is through a series resistor. It is commonly used for indicators and digital displays in many consumer appliances. However, this circuit is not energy-efficient, because energy is dissipated in the resistor as heat. The LED's depends on its material. Ohm's law and Kirchhoff's circuit laws are used to calculate the appropriate resistor value, by subtracting the LED's from the supply voltage and dividing by the desired operating current. With a sufficiently high supply voltage, multiple LEDs in series can be powered with one resistor. If the supply voltage is close or equal to the LED's , then no reasonable value fo
the output voltage of the driver using a DC voltage signal provided by the DC power source, a current flowing through the first inductor, a switching frequency of the first switch, and a duty ratio of the first switch. – the device may further include an electro-magnetic interference (EMI) filter operatively connected between the DC power source and the converter, and configured to eliminate high frequency components of a DC voltage signal from the DC power source. – EMI electro-magnetic interference Landscapes – Circuit Arrangement For Electric Light Sources In General (AREA) Abstract A dual mode constant output current LED driver is capable of operating with a very wide range of input direct current (DC) voltage. This provides an effective topology for a wide range of constant output current LED drivers, and allows for changing the number of connected LEDs without negatively impacting the output current. The LED driver includes a converter and a mode selection circuit that control the modes of the circuit based on the voltage. The converter and mode selection circuit operate in a buck-boost mode when the output voltage of the LED driver is less than the DC input voltage plus a first threshold amount, and in a boost mode when the output voltage of the LED driver is greater than the DC input voltage plus a second threshold amount. Description The present disclosure relates to power supplies suitable for driving light emitting diode (LED) lighting systems as well as other elec
operated simply by supplying a fixed DC voltage. – the DC current supplied to one or more LEDs may have to be properly controlled to avoid burning out the LEDs if the current is too high, but also to provide adequate current to the LEDs (to assure adequate light output from the LEDs) over a reasonably wide range of power supply voltages. – the battery system includes a rechargeable battery connected to a solar photovoltaic panel, which recharges the battery during the daytime when there is adequate ambient light intensity. – the battery system is then used to operate one or more LEDs as determined by the Control Circuit used as an integral part of the present invention. – the Control Circuit used as an integral part of the present invention. – the voltage output from the photovoltaic solar panel system drops to a level near zero, this then signals the onset of the night hours and the control circuit then subsequently turns on the one or more LEDs. – Other types of sensor signals could optionally be used to provide on-off control of the LEDs, such as photocell sensors, photodiodes, phototransistors, photothyristors and light-activated silicon-controlled rectifiers (LASCRs). – an enhanced visibility street name sign having one or more LEDs which are operated from a battery-powered control circuit, wherein the battery receives electrical power from a solar photovoltaic panel system during the daytime, and wherein the control circuit monitors the total amount of solar energy supp
accordance with current feedback signal VFB and the reference current signal, such that the output current of the power stage circuit is consistent with driving current requirements of LED strings LED1 and LED2. In accordance with certain requirements, such as warm-and-cold lamp applications, the luminance of LED strings LED1 and LED2 may be different. Also, the duty cycle of each PWM dimming signal can be regulated in accordance with associated luminance requirements. In addition, each of the switching transistors corresponding to the LED strings can be controlled by current control unit 301 in accordance with a corresponding PWM dimming signal. In this way, the average current of each LED string can be regulated to be consistent with the luminance requirements. Referring now to FIG. 3D , shown is a waveform diagram showing example operation of the multichannel constant current LED driving circuit shown in FIG. 3A , in accordance with embodiments of the present invention. In one switching period T, the output current can flow through LED string LED1 in time interval T1, during which PWM dimming signal PWM1 is active, and the output current may flow through LED string LED2 in time interval T2, during which PWM dimming signal PWM2 is active. Therefore, the luminance of LED strings LED1 and LED2 can be regulated to be different in view that the average current of LED strings LED1 and LED2 is different in order to achieve color and/or dimming control. In this fashion, the lumina
the multichannel constant current LED driving circuit shown in FIG. 3A , in accordance with embodiments of the present invention. In one switching period T, the output current can flow through LED string LED1 in time interval T1, during which PWM dimming signal PWM1 is active, and the output current may flow through LED string LED2 in time interval T2, during which PWM dimming signal PWM2 is active. Therefore, the luminance of LED strings LED1 and LED2 can be regulated to be different in view that the average current of LED strings LED1 and LED2 is different in order to achieve color and/or dimming control. In this fashion, the luminance of a cold-and-warm lamp that includes two LED strings can be regulated. In particular embodiments, only one driving circuit may be utilized in driving a plurality of LED strings that are connected in series. For example, the driving circuit can include a buck configuration with power switching transistor QM, inductor L1, and the rectifier diode. The luminance of each of the LED strings may be controlled by a corresponding PWM dimming signal in order to meet different luminance requirements. Further, both constant driving current to drive the LED strings, and luminance regulation can be achieved in certain embodiments with a simplified circuit structure, fewer elements, and lower costs/volume, as compared to other approaches. Referring now to FIG. 3C , shown is a schematic block diagram of a second example multichannel constant current LED dri