CN203219570U - A kind of LED driving circuit without electrolytic capacitor - Google Patents

Abstract

The utility model discloses an LED driving circuit without an electrolytic capacitor, which comprises an uncontrolled rectifier bridge connected to an AC input voltage source, a power balance circuit and a DC/DC conversion circuit, and the power balance circuit is connected between the uncontrolled rectifier bridge and the DC/DC conversion circuit. Between the DC/DC conversion circuits, the power balance circuit is composed of the second switch tube, the fourth switch tube, the fifth diode, the sixth diode and the energy storage capacitor; the DC/DC conversion circuit is composed of the first A switching tube, a transformer, a third switching tube, a seventh diode, a filter capacitor and a filter inductance; the utility model can realize that when there is no large electrolytic capacitor, by controlling the working time of the switching tubes _S1 - _S4 , Provides a constant current to the LED load.

Description

A kind of LED driving circuit without electrolytic capacitor

technical field

The utility model relates to the field of LED drive circuits, in particular to an LED drive circuit without electrolytic capacitors.

Background technique

With its many advantages such as energy saving, environmental protection and long life, LED has become a new generation of green lighting source. With the continuous development and maturity of LED lighting technology, it will be widely used in various lighting fields and become the first choice for lighting tools in the future. The manufacturing process of LED itself has developed rapidly, and performance indicators such as efficiency and life have become increasingly mature, but the development of driving power has not yet matched it. Manufacture of high-efficiency, low-cost, small-size, long-life, and high-power-factor driving power supplies guarantees the quality of LED lighting and overall performance, and is the premise and driving force for promoting the widespread application of LED lighting sources in various lighting fields.

In practical applications, the LED driving circuit is connected to AC mains. Assuming that the drive circuit has a unit power factor, the input current and input voltage are sinusoidal waves with the same phase, as shown in Figure 1. At this time, the input power is in the form of a sinusoidal square. However, LEDs need constant current drive to better ensure their luminous quality. , working life and other performance indicators, so it is necessary to achieve constant current output, that is, the output power Po is constant. This causes the instantaneous value of input power and output power to be unequal, requiring additional components to achieve a balance between input and output power. Most current circuits use electrolytic capacitors with large capacitance as power balancing components. However, the life of electrolytic capacitors is far from the working life of LEDs. The life of electrolytic capacitors has become the main factor limiting the overall life of LED drive circuits. In addition, the bulky size of the electrolytic capacitor with large capacitance limits the miniaturization of the LED driving circuit and reduces the power density of the driving circuit.

Utility model content

In order to overcome the shortcomings and deficiencies of the prior art, the utility model provides an electrolytic capacitor LED drive circuit.

The technical scheme that the utility model adopts is as follows:

An LED drive circuit without electrolytic capacitors, comprising an uncontrolled rectifier bridge A connected to an AC input voltage source, a power balance circuit B and a DC/DC conversion circuit C, the power balance circuit B is connected between the uncontrolled rectifier bridge A and the Between the DC/DC conversion circuit C; the power balance circuit B consists of the second switching tube S ₂ , the fourth switching tube S ₄ , the fifth diode D ₅ , the sixth diode D ₆ and the energy storage capacitor C _p ; the DC/DC conversion circuit C is composed of a first switch tube S ₁ , a transformer T, a third switch tube S ₃ , a seventh diode D ₇ , a filter capacitor C _o and a filter inductor L _o ;

Wherein, the source stage of the second switching tube _S2 is connected to the common cathode of the uncontrolled rectifier bridge A and the same-named end of the primary side of the transformer T, and the different-named end of the primary side of the transformer T is connected to the drain of the fourth switching tube _S4 , the first The drain of a switching tube _S1 is connected, and the source of the fourth switching tube _S4 is connected to the anode of the sixth diode _D6 ;

The drain of the second switching tube _S2 is connected to the cathode of the fifth diode _D5 , the anode of the fifth diode _D5 is connected to the cathode of the sixth diode _D6 , and one end of the energy storage capacitor _Cp connect;

The other end of the energy storage capacitor _Cp is connected to the common anode of the uncontrolled rectifier bridge A and the source stage of the first switching tube S1;

The opposite end of the secondary side of the transformer T is connected to the anode of the seventh diode _D7 , the cathode of the seventh diode _D7 is connected to the drain of the third switching tube _S3 , and the third switching tube _S3 The source stage of the filter capacitor C _o is connected to one end of the filter inductor L _o , the other end of the filter inductor _L is connected to the positive pole of the LED load, and the other end of the filter capacitor C _o is connected to the secondary side of the transformer T The terminal with the same name is connected to the negative pole of the LED load.

The energy storage capacitor C _p is a polyester film capacitor or a ceramic capacitor.

The uncontrolled rectifier bridge A connected to the AC input voltage source and the DC/DC conversion circuit C form an AC/DC converter, and through proper control, the AC/DC converter works in the intermittent current mode, and obtains High power factor, realize power factor correction function. When the instantaneous input power is less than the output power, the energy storage capacitor Cp in the power balance circuit B releases energy to make up for the lack of input energy, so as to ensure constant output power and provide constant current to the LED. At this time, the third switching tube _S3 is always in the on state, the second switching tube _S2 is used to control the supply of constant current to the LED, and the voltage across the energy storage capacitor Cp drops. When the instantaneous input power is greater than the output power, the energy storage capacitor Cp in the power balance circuit B stores energy to absorb excess input energy to ensure a constant output power and provide a constant current to the LED. At this time, the second switching tube _S2 is always in the off state, the third switching tube _S3 and the fourth switching tube _S4 are used to control the supply of constant current to the LED, and the voltage across the energy storage capacitor Cp rises.

The utility model uses components with a longer life to form a power balance circuit instead of a large electrolytic capacitor with a shorter life and bulky volume, and balances the gap between the instantaneous input power and the instantaneous output power.

The beneficial effects of the utility model:

In the case of no large electrolytic capacitor in the drive circuit, the utility model provides constant current to the LED load by controlling the working sequence of the switch tubes S ₁ -S ₄ , replacing the electrolytic capacitor filter that is easy to fail at high temperature and has a limited lifespan. The LED drive circuit further improves the stability of the drive circuit, greatly prolongs the life of the drive circuit, reduces the volume of the drive circuit, and increases the power density of the drive circuit.

Description of drawings

FIG. 1 is a waveform diagram of input voltage, input current, instantaneous input power and output power of an LED drive circuit in the prior art;

Fig. 2 is the circuit diagram of a kind of non-electrolytic capacitor LED driving circuit of the specific embodiment of the present invention;

Fig. 3 is a non-electrolytic capacitor LED drive circuit shown in Fig. 2 when the instantaneous input power is less than the output power, the driving waveform diagram of each switch tube and the current waveform diagram of the primary side and secondary side of the transformer;

Figure 4a～figure 4d respectively show a kind of non-electrolytic capacitor LED drive circuit in Figure 2 when the instantaneous input power is less than the output power, in a switching cycle T _s (t ₀ ~t ₁ , t ₁ ~t ₂ , t ₂ ~t ₃ and t ₃ ~ t ₄ time period), in which Fig. 4a is the work process diagram of t ₀ ~ t ₁ time period, Fig. 4b is the work process diagram of t ₁ ~ t ₂ time period, and Fig. 4c is The working process diagram of the time period from t ₂ to t ₃ , Figure 4d is the working process diagram of the time period from t ₃ to t ₄ ;

Fig. 5 is a non-electrolytic capacitor LED drive circuit shown in Fig. 2 when the instantaneous input power is greater than the output power, the driving waveform diagram of each switching tube and the primary and secondary current waveform diagrams of the transformer;

Figures 6a to 6d are respectively a kind of non-electrolytic capacitor LED drive circuit in Figure 2, when the instantaneous input power is greater than the output power, in a switching cycle T _s (t ₀ ~ t ₁ , t ₁ ~ t ₂ , t ₂ ~ t ₃ and t ₃ ~ t ₄ time period), in which Fig. 6a is the work process diagram in the t ₀ ~ t ₁ time period, Fig. 6b is the work process diagram in the t ₁ ~ t ₂ time period, and Fig. 6c is The working process diagram of the time period from t ₂ to t ₃ , Figure 6d is the working process diagram of the time period from t ₃ to t ₄ ;

FIG. 7 is a waveform diagram of input and output voltage and current of an electrolytic capacitor LED drive circuit in FIG. 2 .

Detailed ways

The utility model will be described in further detail below in conjunction with the embodiments and accompanying drawings, but the implementation of the utility model is not limited thereto.

Example

As shown in Figure 2, an LED drive circuit without electrolytic capacitors includes an uncontrolled rectifier bridge A connected to an AC input voltage source, a power balance circuit B and a DC/DC conversion circuit C, and the power balance circuit B is connected to Between the uncontrolled rectifier bridge A and the DC/DC conversion circuit C; the power balance circuit B is composed of the second switching tube S ₂ , the fourth switching tube S ₄ , the fifth diode D ₅ , and the sixth diode D ₆ and an energy storage capacitor C _p ; the DC/DC conversion circuit C is composed of a first switching tube S ₁ , a transformer T, a third switching tube S ₃ , a seventh diode D ₇ , a filter capacitor C _o and a filter inductor L _o composition;

Wherein, the source stage of the second switching tube _S2 is connected to the common cathode of the uncontrolled rectifier bridge A and the same-named end of the primary side of the transformer T, and the different-named end of the primary side of the transformer T is connected to the drain of the fourth switching tube _S4 , the first The drain of a switching tube _S1 is connected, and the source of the fourth switching tube _S4 is connected to the anode of the sixth diode _D6 ;

The drain of the second switching tube _S2 is connected to the cathode of the fifth diode _D5 , the anode of the fifth diode _D5 is connected to the cathode of the sixth diode _D6 , and one end of the energy storage capacitor _Cp connect;

The other end of the energy storage capacitor _C is connected to the common anode of the uncontrolled rectifier bridge A and the source of the first switching tube _S1 ;

The opposite end of the secondary side of the transformer T is connected to the anode of the seventh diode _D7 , the cathode of the seventh diode _D7 is connected to the drain of the third switching tube _S3 , and the third switching tube _S3 The source stage of the filter capacitor C _o is connected to one end of the filter inductor L _o , the other end of the filter inductor L _o is connected to the positive pole of the LED load, and the other end of the filter capacitor C _o has the same name as the secondary side of the transformer T terminal, and the negative terminal of the LED load.

As shown in the accompanying drawings, terminal 1 is the terminal with the same name on the primary side of the transformer, terminal 2 is the terminal with the same name on the primary side of the transformer, terminal 3 is the terminal with the same name on the secondary side of the transformer, and terminal 4 is the terminal with the same name on the secondary side of the transformer.

The energy storage capacitor C _p is a polyester film capacitor or a ceramic capacitor.

The uncontrolled rectifier bridge A connected to the AC input voltage source and the DC/DC conversion circuit C form a flyback converter, and through proper control, the flyback converter works in the intermittent current mode to obtain high power factor to realize the power factor correction function. When the instantaneous input power is less than the output power, the energy storage capacitor Cp in the power balance circuit B releases energy to make up for the lack of input energy, so as to ensure constant output power and provide constant current to the LED. At this time, the third switching tube _S3 is always in the on state, the second switching tube _S2 is used to control the supply of constant current to the LED, and the voltage across the energy storage capacitor Cp drops. When the instantaneous input power is greater than the output power, the energy storage capacitor Cp in the power balance circuit B stores energy to absorb excess input energy to ensure a constant output power and provide a constant current to the LED. At this time, the second switching tube _S2 is always in the off state, the third switching tube _S3 and the fourth switching tube _S4 are used to control the supply of constant current to the LED, and the voltage across the energy storage capacitor Cp rises.

Therefore, the working principle of the drive circuit is different when the instantaneous input power is less than the output power and when the input power is greater than the output power. The two situations are described below:

1. The instantaneous input power is less than the output power;

As shown in Figure 3 and Figures 4a to 4d, when the input power is less than the output power, the third switching tube S3 is always on; in a switching period Ts (t ₀ ~ t ₁ , t ₁ ~ t ₂ , t ₂ ~ t ₃ and t ₃ ~ t ₄ period), the working process of the drive circuit is as follows:

During the time period from t ₀ to t ₁ , as shown in Figure 4a:

Assuming that before the time t ₀ , the primary current i _p and the secondary current i _s of the transformer are both zero, and the first switch S ₁ is turned on at the time t ₀ , assuming that the input voltage v _in remains unchanged within one switching cycle, then i _p increases linearly from zero to get:

${\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span>}{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Where _L1 is the self-inductance of the primary winding of the transformer.

During the time period from t ₁ to t ₂ , as shown in Figure 4b:

Turn on the second switch S ₂ at time t ₁ , turn on the first switch S ₁ continuously, discharge the energy storage capacitor Cp, _and continue to increase linearly, assuming that the voltage v _c at both ends of the energy storage capacitor Cp remains constant within a switching cycle change, there are:

${\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{{<span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span>}{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

In this process, if the minimum value v _{c_min} of the voltage across the energy storage capacitor Cp is less than the input voltage, the second switch tube _S2 cannot be turned on normally, and the drive circuit cannot work normally, so the minimum value v _{c_min} of the voltage across the energy storage capacitor Cp Must meet:

v _{c_min} >v _in (t) (3)

During the time period from t ₂ to t ₃ , as shown in Figure 4c:

Turn off the first switching tube S ₁ and the second switching tube S ₂ at the same time at _t2 , at this time the energy stored in the transformer begins to transfer to the secondary side of the transformer, according to formula (2), it can be obtained that the primary side of the transformer at _t2 time The current value is:

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{{<span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span>}{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

After conversion, the transformer secondary current i _s can be obtained as:

${\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>\frac{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}}{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

Among them, N _p is the number of turns of the primary winding of the transformer, N _s is the number of turns of the secondary winding of the transformer, and V _o is the output voltage.

At time _t3 , i _s drops to zero, and the time interval from _t2 to _t3 is:

$\mathrm{<span\; class="notranslate">\; \&Delta;T</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="t"\; filenames="HDA00003026382800022.png"\; state="\{\{state\}\}">t</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 6</span>}$

During the time period from t ₃ to t ₄ , as shown in Figure 4d:

During this switching cycle, no current flows through the primary and secondary windings of the transformer, the transformer is magnetically reset, and the filter capacitor Co supplies power to the LED load.

2. The instantaneous input power is greater than the output power;

As shown in FIG. 5 and FIGS. 6a-6d, when the instantaneous input power is greater than the output power, the second switching tube _S2 is always turned off. In a switching period Ts within Ts (t ₀ ~ t ₁ , t ₁ ~ t ₂ , t ₂ ~ t ₃ and t ₃ ~ t ₄ time period), the working process of the driving circuit is as follows:

During the time period from t ₀ to t ₁ , as shown in Figure 6a:

Similar to the time period from t ₀ to t ₁ when the instantaneous input power is less than the output power, the first switch tube S ₁ is turned on, and the input voltage v _in makes i _p increase linearly from zero.

${\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span>}{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

During the time period from t ₁ to t ₂ , as shown in Figure 6b:

At time t ₁ , the first switching tube S ₁ is turned off and the fourth switching tube S ₄ is turned on, the energy stored in the transformer starts to charge the energy storage capacitor Cp, and the primary current _ip of the transformer starts to decrease linearly.

The value of transformer primary current i _p at time _t1 is:

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span>}{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

Assuming that the voltage _vc across the energy storage capacitor Cp remains constant within a switching cycle, then:

${\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 9</span>}<span\; class="notranslate">\; )</span>$

During the time period from t ₂ to t ₃ , as shown in Figure 6c:

At time t ₂ , the fourth switching tube S ₄ is turned off, and at the same time, the third switching tube S ₃ is turned on, and the residual energy in the transformer starts to be transferred to the secondary side.

The value of transformer primary current i _p at time _t2 is:

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 10</span>}<span\; class="notranslate">\; )</span>$

After conversion, the transformer secondary current i _s can be obtained as:

${\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>\frac{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}}{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 11</span>}<span\; class="notranslate">\; )</span>$

At time _t3 , i _s drops to zero, and the time interval from _t2 to _t3 is:

$\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="t"\; filenames="HDA00003026382800022.png"\; state="\{\{state\}\}">t</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 12</span>}<span\; class="notranslate">\; )</span>$

During the time period from t ₃ to t ₄ , as shown in Figure 6d:

During this time period, no current flows through the primary and secondary windings of the transformer, the transformer is magnetically reset, and the filter capacitor Co supplies power to the LED load.

Figure 7 shows the waveform diagram of the input voltage, current, power, output voltage, current, power, transformer primary current and secondary current within one cycle of the input voltage of the utility model.

The utility model realizes that in the case of no large electrolytic capacitor, by controlling the working time of the switch tubes _S1 - _S4 , a constant current is provided to the LED load, and the stability of the driving circuit is further improved, so as to prolong the life of the driving circuit and reduce the The volume of the driving circuit is small, and the power density of the driving circuit is improved.

The above-mentioned embodiment is a preferred implementation mode of the present utility model, but the implementation mode of the present utility model is not limited by the described embodiment, and any other changes, modifications, modifications, Substitution, combination, and simplification should all be equivalent replacement methods, and are all included in the protection scope of the present utility model.

Claims (3)

1. An LED drive circuit without electrolytic capacitors, characterized in that it includes an uncontrolled rectifier bridge (A) connected to an AC input voltage source, a power balance circuit (B) and a DC/DC conversion circuit (C), the The power balance circuit (B) is connected between the uncontrolled rectifier bridge (A) and the DC/DC conversion circuit (C). 2. The LED drive circuit without electrolytic capacitor according to claim 1, characterized in that, the power balance circuit (B) consists of the second switch tube (S ₂ ), the fourth switch tube (S ₄ ), The fifth diode (D ₅ ), the sixth diode (D ₆ ) and the energy storage capacitor (C _p ); The DC/DC conversion circuit (C) consists of a first switching tube (S ₁ ), a transformer (T), a third switching tube (S ₃ ), a seventh diode (D ₇ ), and a filter capacitor (C _o ) and filter inductance (L _o ); Wherein, the source stage of the second switching tube (S ₂ ) is connected to the common cathode of the uncontrolled rectifier bridge (A), and the same-named terminal of the primary side of the transformer (T), and the same-named terminal of the primary side of the transformer (T) is connected to the fourth switch The drain of the tube (S ₄ ) is connected to the drain of the first switching tube (S ₁ ), and the source of the fourth switching tube (S ₄ ) is connected to the anode of the sixth diode (D ₆ ); The drain of the second switching tube (S ₂ ) is connected to the cathode of the fifth diode (D ₅ ), and the anode of the fifth diode (D ₅ ) is connected to the cathode of the sixth diode (D ₆ ). , one end of the energy storage capacitor (C _p ) is connected; The other end of the energy storage capacitor (C _p ) is connected to the common anode of the uncontrolled rectifier bridge (A) and the source of the first switching tube (S ₁ ); The opposite end of the secondary side of the transformer (T) is connected to the anode of the seventh diode (D ₇ ), and the cathode of the seventh diode (D ₇ ) is connected to the drain of the third switch tube (S ₃ ). connected, the source of the third switching tube (S ₃ ) is connected to one end of the filter capacitor (C _o ) and one end of the filter inductor (L _o ), and the other end of the filter inductor (L _o ) is connected to the positive pole of the LED load , the other end of the filter capacitor (C _o ) is connected to the same-named end of the secondary side of the transformer (T) and the negative pole of the LED load. 3 . The LED drive circuit without electrolytic capacitor according to claim 2 , wherein the energy storage capacitor ( C _p ) is a polyester film capacitor or a ceramic capacitor. 4 .

Images