Integrated Circuit for Precise Pulse Power Supply to LED Lamp String Using 50Hz Alternating Current

Abstract

The present invention discloses two integrated circuits for precisely pulse-powering an LED lamp string using 50Hz alternating current. One is to perform pulse power supply to the LED lamp string at two 0.707 points (45°±1° and 135°±1°) of the maximum value of a half sine wave obtained by full-bridge rectification, and no power supply is provided at other times, which is the power-saving time. The other is to supply power within the range of the maximum value region (90°±15°) of the half sine wave, and no power supply is provided at other times, which is the power-saving time. The entire integrated circuit is extremely simple and has a low cost.

Description

Technical Field

[0001] The present invention belongs to the field of energy conservation in electronic technology, and particularly relates to an integrated circuit that can be used in LED energy-saving lamps. Technical Background

[0002] Compared with tungsten filament lamps, LED lamps can be regarded as energy-saving lamps. Most of the existing LED lamps use DC power supply, but most of them are connected in series with a lot of resistors, and these resistors consume a large amount of power, so they are not energy-saving. There are also many circuits that claim to be pulse power supplies, but they are not truly pulse power supplies. They also add PWM controllers and other components in the circuit, and the whole circuit is very complex and difficult to integrate. The circuit of our invention is very simple, with only a few components, and it is a truly precise pulse power supply. The flash on the cameras we have seen is pulse-powered. It is very bright in a short time, but the power consumption is not large, and even dry batteries can afford it. Here, the memory function of human beings for brightness or the visual persistence effect of the human eye is utilized. Summary of the Invention

[0003] The purpose of the present invention is to light an LED lamp string in a pulse power supply mode with a much smaller power than that for lighting an LED lamp with direct current, so as to achieve the purpose of energy conservation. We will explain its principle with reference to the accompanying drawings. Figure 1 a, Figure 1 b shows two solutions of the present invention.

[0004] It includes three parts. The first part is a full-bridge rectifier that outputs a half sine wave 1 to supply power to the external LED lamp string 2. The second part includes a field effect transistor 4 for controlling the lighting of the LED and a diode 4 for preventing the reverse breakdown of the LED lamp string. As long as a precise positive pulse is provided to the field effect transistor, the field effect transistor conducts and the external LED lamp string is lit. This precise pulse is provided by the third part. The third part is composed of a digital circuit and a diode voltage stabilizing circuit that provides a regulated power supply for it.

[0005] We are from Figure 1Speaking of Solution A, first of all, we must obtain the zero-crossing signal of a 50Hz sine wave. This signal is used as a synchronization signal to integrate the digital circuit and keep the digital circuit synchronized with the 50HZ alternating current. The simplest way is to utilize the slight difference between the two regulated voltage waveforms presented by the different loads of two zener diodes to obtain the 50Hz zero-crossing signal. First, look at the first 5.1V regulated voltage circuit 5, which belongs to the light-load path: there is a step-down resistor R1 on it, and there is no parallel resistor beside the zener diode. It is connected to the simplest CMOS inverter 7. The characteristic of its waveform is that it is 5.1V for most of the time, and the voltage only slightly drops near the 50Hz zero signal, but does not reach zero level. The second path belongs to the heavy load 6: there is a 20K resistor connected in parallel beside the 5.1V zener diode, and there are several CMOS circuit loads behind it. The characteristic of its waveform is that the heavy load causes the voltage of this path to deviate from 5.1V earlier than that of the light-load path, and it must reach zero volts. See specifically Figure 2 a and Figure 2 b. There are obvious differences between the waveforms of the two paths, that is, the voltage of the heavy load drops one step earlier than that of the light load. That is, when the voltage of the light-load path is still 5.1V, the voltage of the heavy load that drops first will cause the inverter to reverse. Thus, we obtain the 50Hz zero-crossing signal.

[0006] After obtaining the 50HZ zero-crossing signal, it is relatively easy to implement the content of Solution 1 and Solution 2. Description of the Drawings

[0007] Figure 1 are two solutions for pulse power supply;

[0008] Figure 2 is to obtain the 50Hz zero-crossing signal from the zener diode circuits with two different loads;

[0009] Figure 3 is the integrated circuit block diagram of two pulse power supply methods; Specific Embodiment

[0010] In Solution 1, a pair of accurately positioned narrow pulses need to be generated every half cycle. This task is completed by the Schmitt circuit (CD40106) 10. During the forward charging time τ1 = 0.69C2R4, and during the reverse discharge τ2 = 0.69C2R5. Thus, a pair of narrow pulses at the 0.707 of the sine wave are obtained. However, this oscillator is a free multivibrator and will start oscillating as long as there is power supply. Therefore, the power supply must be controlled to make it start oscillating at 0.707. We cleverly thought of using the analog switch (CD4066) 9 to control the power supply. As long as the analog switch is turned on, the Schmitt circuit has power and starts oscillating immediately. This analog switch is controlled by the monostable 8. The monostable circuit is triggered by the falling edge of the zero-crossing signal. At A negative pulse is generated at the sine wave, and the high level after the negative pulse is used to control the analog switch. The analog switch is only turned on when the high level is high. At this time, the Schmitt circuit has power and the circuit starts to oscillate immediately. The monostable circuit acts as a delay circuit here, that is, the double narrow pulses generated by the Schmitt circuit are accurately shifted to 0.707 of the sine wave. Because the full-wave rectification is half a sine wave, the Schmitt circuit can only generate a pair of half a sine wave, and another pair of half a sine wave. For the full cycle, there will be 4 narrow pulses in the full cycle to light up the LED string.

[0011] In option 2, see Figure 2 b also uses two voltage regulator diodes with different light and heavy loads to obtain a 50Hz zero-crossing signal. As in the first solution, the falling edge of the zero-crossing signal is directly used to trigger a monostable circuit 11 to generate a negative pulse, and then the rising edge of the trailing edge of the negative pulse is used to trigger the next monostable circuit 12, directly generating a slightly wider pulse width precision pulse to control the field effect tube and directly light up the LED light string.

[0012] Here, the monostable trigger still acts as a delay circuit, but here the center of the single slightly wider pulse is shifted to 90° of the half sine wave to obtain an area of ​​maximum voltage.

[0013] Let's further evaluate the pros and cons of these two options:

[0014] The first solution can achieve four equal intervals in the full 50Hz cycle, and each narrow pulse of 5ms lights up the LED light string, which meets the human eye's retention effect and does not appear to flicker.

[0015] We make the two narrow pulses with a pulse width of 0.1111ms, that is, 45°±1°, 135°±1°. Although the pulses are very narrow, the corresponding voltages still have a difference of 7.68V, that is, 311V×sin 44°=216.036V, 311V×sin46°=223.714V, which is very unfavorable for the same string of LED lights, but it cannot be narrower.

[0016] Our system is open. As long as you use the narrow pulse from 216.036V to 223.714V correctly, you can save energy. Here I want to emphasize that the brightness of our system is lower than the requirement of DC power supply. All LED lights are approaching the saturation value of brightness and cannot increase the brightness infinitely. Therefore, the pulse is too narrow (0.1111ms). Although the narrow pulse is very bright and has a visual persistence effect, the total brightness is still not as bright as the DC power supply. However, if you can use a high-power LED core, the effect will be different. Therefore, this solution is suitable for home users. It is nothing more than using a few more LED lights or using a slightly higher-power LED light to exchange quantity for total brightness.

[0017] The second solution: a slightly wider single pulse with τ = 1.666 ms, i.e., 90° ± 15°, and the voltage fluctuation range is 311V × sin 75° = 300.10V, which is in a relatively stable voltage region. Since the voltage here is relatively stable and is the maximum value, the LED string in the second solution is relatively bright, and the number of lit LED strings is also large. Therefore, this solution is suitable for street lights and square lights in occasions that require higher brightness. Because the lighting period is spaced every 10 ms, and the middle lighting time is 1.6666 ms, there is no visible flicker at high brightness, but the brightness is relatively low and there is some flicker at a relatively long distance. For harsh environments, please prepare other protection measures by yourself.

[0018] Take an example. We directly connect 92 white LED strings with a power of 0.05W to the second solution. The 92 LED strings are very bright, and the measured average current is 10 mA. Of course, it is still not as bright as lighting the LED string with direct current. But it saves electricity.

Claims

1. An integrated circuit for precisely pulse-powering an LED light string using 50Hz alternating current, comprising: A 50Hz AC full-bridge rectifier (1) provides power for the entire circuit, an external load LED light string (2), a field effect tube (3) for controlling the lighting of the LED light string, a diode (4) for preventing the LED light string from reverse breakdown, an inverter (7), a first monostable circuit (8), an analog switch (9), a multi-resonator (10), a second monostable circuit (11), and a third monostable circuit (12), characterized in that it also includes two load voltage regulator diodes, namely a light load voltage regulator diode (5) and a heavy load voltage regulator diode (6); The light load voltage stabilizing diode (5) has no parallel resistor and only has a simple CMOS inverter (7). Since the voltage stabilizing diode has a capacitor, when the external charging voltage is lower than 5.1V, the capacitor still has 5.1V for the light load to slowly discharge. At this time, the voltage drops slightly, but will not drop to zero level. After the external charging voltage passes the zero point, it will immediately rise back to 5.1V. The heavy-load voltage stabilizing diode (6) is connected to a 20k resistor and multiple CMOS circuit loads, and its discharge is very fast. The voltage waveform is separated from 5.1V earlier than the light-load one, and it must reach 0V, that is, the voltage of the heavy load drops earlier than the voltage of the light load, that is, when the voltage of the light-load one is still 5.1V, the voltage of the heavy load drops first, which will cause the inverter to reverse, thereby obtaining a 50Hz zero-crossing signal; There are two ways to implement precise pulse power supply to the LED light string with the external 50Hz AC power: one is to supply power to the LED light string only at two 0.707 points of the half sine wave, i.e., 45°±1° and 135°±1°. There are four points in the whole cycle, every 5ms, and no power is supplied for the rest of the time, which is the power saving time; the other is to supply power only at the half sine wave. The LED light string is powered within the range of 90°±15° of the sine wave, and is not powered during the rest of the time, which is the power saving time.

2. The method according to claim 1, wherein: The first monostable circuit (8) generates a monostable circuit with a width of 0-0.707 of the sine wave when triggered by a zero-crossing negative signal, i.e., the pulse trailing edge is moved to 0.707, and then the positive signal at the reverse output end of the trigger is used to control the analog switch (9), so that its output end is always open and always powered after the sine wave 0.

707.

3. The method according to claim 1, wherein: The multi-resonator (10) adopts the Schmitt circuit CD40106 to realize the generation of a pair of precisely positioned narrow pulses in half a cycle; when a positive voltage is applied to the Schmitt circuit, the Schmitt circuit immediately starts to oscillate and generates a pulse wave; the width of its forward narrow pulse is determined by the time constant C2R4; and the rest period from rising 0.707 to falling 0.707 is accurately determined by the time constant C2R5; wherein C2 is a common capacitor, and R4R5 are isolated by forward and reverse diodes respectively; in this way, the Schmitt circuit can only generate a pair of pulses in half a sine wave, and another pair in the second half of the sine wave, and there will be 4 narrow pulses in the full cycle to light up the LED light string. Since there are four pulses of power supply in a week of 50Hz (20ms), no flash phenomenon will occur, which is suitable for home applications and is particularly energy-saving.

4. The method according to claim 1, characterized in that: Still obtain the zero-crossing signal of 50 Hz by means of two-way voltage-regulator diodes with different light and heavy loads; use its falling edge to trigger the second monostable circuit (11) to generate a negative pulse, so that its trailing edge is at 75° of the sine wave secondary high point, and then use the rising edge of the trailing edge of the negative pulse to trigger the third monostable circuit (12) to generate the second monostable, and its trailing edge is at 105° of the sine wave. The pulse width spans 75° - 105° to control the field effect transistor (3) to light up the LED light string. This pulse has a relatively flat voltage with the highest value of bridge rectification and can supply high-power LEDs.

5. The method according to claim 1, wherein: The full-bridge rectifier (1) provides energy for the entire circuit; The LED light string (2) is an external load; The field effect transistor (3) controls whether to light up the LED light string; The reverse diode (4) prevents the reverse breakdown of the LED light string.

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