CN104202862A - Single-stage type LED drive power supply without electrolytic capacitor - Google Patents

Abstract

A single-stage non-electrolytic capacitor LED drive power supply, which is essentially an AC/DC converter, consists of an input filter rectifier circuit, a flyback primary switch circuit, an auxiliary winding full-bridge bidirectional circuit, and a secondary rectifier filter circuit. It realizes power factor correction by fixing the duty cycle of the main switch MOS transistor _Q1 ; it works in the current discontinuous mode to avoid the reverse recovery of the secondary diode _QR ; its main circuit is a flyback conversion composed of 1, 2, and 4 parts In the flyback converter, a winding is added to the isolation transformer of the flyback converter, and a full-bridge converter with bidirectional power flow is used on the auxiliary winding side to balance the difference between input and output power instantaneous fluctuations, and the average voltage and voltage fluctuations of the auxiliary energy storage capacitor are increased. Reduce the capacitance of the auxiliary energy storage capacitor; remove twice the power frequency AC component of the output current, reduce the capacitance of the output filter capacitor, and replace the electrolytic capacitor with a film capacitor to achieve small size and long life; the output current of the LED drive power supply For constant current.

Description

A single-stage non-electrolytic capacitor LED drive power supply

Technical field:

The invention relates to a single-stage non-electrolytic capacitor LED drive power supply, which belongs to the application field of switching power supplies, especially LED drive power supplies. the

Background technique:

With the rapid development of human society, the demand for energy consumption is increasing rapidly, and the energy crisis is becoming more and more serious. There are two main ways to solve the energy crisis. One way is to develop renewable energy and reduce dependence on traditional fossil energy; the other way is to seek new energy-saving technologies to reduce energy consumption and improve energy utilization efficiency. Among them, lighting is an important aspect of human energy consumption. Traditional lighting products such as incandescent lamps, fluorescent lamps, and high-pressure sodium lamps have serious problems of high power consumption and low efficiency. Therefore, reducing the power required for lighting will help reduce global energy consumption. In recent years, green and energy-saving lighting has become an important issue of concern to all countries in the world, and the demand for new light sources is becoming more and more urgent. the

LED (Light Emitting Diode) light-emitting diodes have developed rapidly in recent years and are widely used in various occasions due to their advantages of cleanliness, high efficiency, high luminous efficiency, long life, and natural light simulation. One of the most important advantages of LED is its long service life, about 30,000 to 100,000 hours. When the input power factor of a traditional LED driver is 1, its input current is a sine wave with the same phase as its input voltage, so its input power is in the form of the square of the sine. And because of its constant voltage load characteristics and the need for constant current drive, its output power is flat. Therefore, the driving power supply needs a large-capacity energy storage capacitor to balance the input power and output power, and the energy storage capacitor is mostly an electrolytic capacitor. The life of electrolytic capacitors is generally only 5,000 hours, and the life of LED body is 100,000 hours. The working life of the two is very different. Therefore, electrolytic capacitors are the key factors that limit the life of LED drive power supplies. Moreover, the volume of the electrolytic capacitor is large, which affects further improvement of the power density of the driving power supply. For this reason, it is necessary to remove the electrolytic capacitor in the LED driving power supply. the

Invention content:

The purpose of the present invention is to provide a single-stage non-electrolytic capacitor LED drive power supply. Since the power of the LED drive power supply is small and the output voltage is low, a flyback converter with a simple structure is used as the main circuit for power factor correction. An auxiliary winding is added to the isolation transformer of the flyback converter, and a power bidirectional flow full-bridge converter is used on the auxiliary winding side to balance the difference between input and output power instantaneous fluctuations, so that the output filter capacitor can use a film capacitor with a small value. the

The present invention adopts the following technical solutions: a single-stage electrolytic capacitor-free LED drive power supply, which includes an input filter rectifier circuit, a flyback primary switch circuit, an auxiliary winding full-bridge bidirectional circuit, a secondary rectifier filter circuit and an isolation transformer. the

Further, the isolation transformer _T1 is composed of a primary winding and two secondary windings, including the primary inductance L _m and leakage inductance of the isolation transformer _T1 ;

The filter circuit of input filter rectifier circuit 1 is composed of input filter inductor L ₁ and input filter capacitor C ₁ connected in parallel at both ends of the grid input, and the rectification part of input filter rectifier circuit 1 uses four diodes D ₁ , D ₂ , D ₃ , D The full-bridge uncontrolled rectification circuit composed of ₄ is connected in parallel at both ends of the filter circuit;

The flyback primary side switch circuit 2 is composed of the opposite end of the primary side winding of the isolation transformer _T1 connected to the drain of the main switch MOS transistor _Q1 , and the main switch MOS transistor _Q1 includes its parasitic diode and parasitic capacitance;

Auxiliary winding full bridge bidirectional circuit 3 consists of first and second auxiliary IGBT transistors Q _s1 and Q _s2 and first and second auxiliary MOS transistors Q _s3 and Q _s4 , first and second auxiliary diodes D _s1 and D _s2 and auxiliary The energy storage capacitor C _b is composed of the first auxiliary IGBT tube Q _s1 , the first auxiliary diode D _s1 and the first auxiliary MOS transistor Q _s3 in series, the second auxiliary IGBT tube Q _s2 and the second auxiliary diode D _s2 and the second Auxiliary MOS transistor Q _s4 is connected in series to form two bridge arms in parallel, and connected in parallel to both ends of the second secondary winding of isolation transformer T ₁ , and the opposite end of the second secondary winding of isolation transformer T ₁ is connected to the first and second secondary windings. The collectors of the two auxiliary IGBT tubes Q _s1 and Q _s2 are connected, the terminals with the same name are connected to the source stages of the first and second auxiliary MOS tubes Q _s3 and Q _s4 , and one end of the auxiliary energy storage capacitor C _b is connected to the first auxiliary IGBT tube The midpoint of Q _s1 and the first auxiliary diode D _s1 , the other end is connected to the midpoint of the second auxiliary IGBT transistor Q _s2 and the second auxiliary diode D _s2 , the first and second auxiliary IGBT transistors Q _s1 and Q _s2 respectively contain Its parasitic capacitance, the first and second auxiliary MOS transistors Q _s3 and Q _s4 respectively include their parasitic diodes and parasitic capacitances;

The secondary side rectification filter circuit 4 is composed of a rectification diode D _R , a rectification MOS transistor Q _R , an output filter capacitor C ₂ and an output filter inductor L ₂ , and the opposite end of the first secondary winding of the isolation transformer T ₁ is connected to the rectification diode D The anode of _R , the rectifier diode _DR , the rectifier MOS transistor _QR , and the output filter inductor _L2 are connected in series to the positive output terminal of the LED load, and the terminal with the same name of the first secondary winding of the isolation transformer _T1 is connected to the negative output of the LED load. The output filter capacitor _C2 is connected in parallel between the source of the rectifier MOS transistor _QR and the negative output terminal of the LED load, and the rectifier MOS transistor _QR includes its parasitic diode and parasitic capacitance.

The present invention has the following beneficial effects:

(1) Realize power factor correction by fixing the main switch MOS transistor _Q1 ;

(2) The converter works in discontinuous mode, which avoids the reverse recovery of the secondary side diode; the isolation transformer of the flyback converter adds a winding, and the auxiliary winding side uses a power bidirectional flow full-bridge converter to balance the input and output power pulsation The difference is to reduce the capacitance of the auxiliary capacitor by increasing the average voltage and voltage ripple of the auxiliary energy storage capacitor, remove twice the power frequency AC component of the driving current in the LED drive power supply, and reduce the capacitance of the output filter capacitor, so that It can replace electrolytic capacitors with film capacitors to achieve small size and long life;

(3) The added auxiliary circuit does not affect the work of the main circuit, and the auxiliary circuit only handles the difference between input and output instantaneous power fluctuations;

(4) The output current of the LED drive power supply is constant current, which is suitable for the application of LED drive power supply requiring constant current output. the

Description of drawings:

FIG. 1 is a schematic structural diagram of a single-stage electrolytic capacitor-less LED driving power supply of the present invention. the

Fig. 2 is a schematic diagram of main waveforms of a single-stage electrolytic capacitor-free LED drive power supply. the

3-7 are schematic diagrams of equivalent circuit structures of each switching mode. the

Names of main symbols in the above drawings: v _in —grid voltage; L ₁ —input filter inductance; C ₁ —input filter capacitor; D ₁ , D ₂ , D ₃ , D ₄ —diodes; Q ₁ —main switch MOS tube ; Q _s1 — the first auxiliary IGBT tube; Q _s2 — the second auxiliary IGBT tube; Q _s3 — the first auxiliary MOS tube; Q _s4 — the second auxiliary MOS tube; D _s1 — the first auxiliary diode; D _s2 — the second Auxiliary diode; C _b —auxiliary energy storage capacitor; T ₁ —isolation transformer; D _R —rectifier diode; Q _R —rectifier MOS tube; C ₂ —output filter capacitor; L ₂ —output filter inductor; V _o —output voltage; I _o — output current; C _b — auxiliary energy storage capacitor; p _in — input power; p _o — output power; p _rip — difference between input power and output power instantaneous power ripple; T _line — power frequency cycle; L _m — Primary inductance; i _s2 — current on the second secondary winding; i _s1 — current on the first secondary winding; i _in — grid input current; i _p — primary current of transformer T ₁ ; v _cb — The voltage across the auxiliary energy storage capacitor; v _AB —the voltage between point A and point B.

Detailed ways:

Please refer to Figure 1, the single-stage electrolytic capacitor LED drive power supply of the present invention is composed of an input filter rectifier circuit 1, a flyback primary switch circuit 2, an auxiliary winding full-bridge bidirectional circuit 3, and a secondary rectifier filter circuit 4. Its main circuit is a flyback converter composed of 1, 2, and 4 parts. the

The isolation transformer _T1 consists of a primary winding and two secondary windings, including primary inductance (generated by self-inductance) and leakage inductance. The filter circuit of input filter rectifier circuit 1 is composed of input filter inductor L ₁ and input filter capacitor C ₁ connected in parallel at both ends of the grid input, and the rectification part adopts a full bridge composed of four diodes D ₁ , D ₂ , D ₃ , and D ₄ . The controlled rectification circuit is connected in parallel at both ends of the filter circuit. The flyback primary switch circuit 2 is composed of the opposite terminal of the primary winding of the isolation transformer _T1 connected to the drain of the main switch MOS transistor _Q1 . The main switch MOS transistor _Q1 includes its parasitic diode and parasitic capacitance. The composition of the auxiliary winding full-bridge bidirectional circuit 3 is that the first auxiliary IGBT transistor Q _s1 , the first auxiliary diode D _s1 and the first auxiliary MOS transistor Q _s3 are connected in series in sequence, and the second auxiliary IGBT transistor Q _s2 and the second auxiliary diode D _s2 and the second auxiliary MOS transistor Q _s4 are sequentially connected in series to form two bridge arms connected in parallel, and connected in parallel to both ends of the second secondary winding of the isolation transformer _T1 . The opposite end of the second secondary winding of the isolation transformer _T1 is connected to the collectors of the first and second auxiliary IGBT tubes Q _s1 and Q _s2 , and the end of the same name is connected to the first and second auxiliary MOS transistors Q _s3 and Q _s4 connected at the source level. One end of the auxiliary energy storage capacitor C _b is connected to the midpoint of the first auxiliary IGBT transistor Q _s1 and the first auxiliary diode D _s1 , and the other end is connected to the midpoint of the second auxiliary IGBT transistor Q _s2 and the second auxiliary diode D _s2 . The first and second auxiliary IGBT transistors Q _s1 and Q _s2 each include their parasitic capacitances, and the first and second auxiliary MOS transistors Q _s3 and Q _s4 each include their parasitic diodes and parasitic capacitances.

The secondary side rectification and filtering circuit 4 is composed of a rectification diode _DR , a rectification MOS transistor Q _R , an output filter capacitor C ₂ and an output filter inductance L ₂ . The opposite end of the first secondary winding of the isolation transformer _T1 is connected to the anode of the rectifier diode _DR . The rectifier diode _DR is connected in series with the rectifier MOS transistor _QR and the output filter inductor _L2 , and then connected to the positive output terminal of the LED load. The terminal with the same name of the first secondary winding of the isolation transformer _T1 is connected to the negative output terminal of the LED load. The output filter capacitor C ₂ is connected in parallel between the source stage of the rectifier MOS transistor Q _R and the negative output terminal of the LED load. The rectifier MOS transistor Q _R includes its parasitic diode and parasitic capacitance.

The AC mains is connected to the rectifier bridge composed of diodes D ₁ , D ₂ , D ₃ , and D ₄ through a filter circuit composed of input filter inductor L ₁ and input filter capacitor C ₁ , and its anode is connected to the primary winding of isolation transformer T ₁ The end of the same name is connected. The opposite end of the primary winding of the isolation transformer _T1 is connected to the drain of the main switch MOS transistor _Q1 , and the source of the main switch MOS transistor _Q1 is connected to the negative pole of the rectifier bridge.

The auxiliary winding full-bridge bidirectional circuit 3 is composed of two auxiliary IGBT transistors Q _s1 , Q _s2 , two auxiliary MOS transistors Q _s3 , Q _s4 , two auxiliary diodes D _s1 , D _s2 and an auxiliary energy storage capacitor C _b . The role of the auxiliary energy storage capacitor C _b is to balance the difference between input power and output power ripple.

The secondary side of the isolation transformer _T1 is rectified by the rectifier diode _DR and the rectifier MOS transistor _QR , and filtered by the output filter capacitor _C2 and the output filter inductor _L2 .

Combining the structure of the single-stage electrolytic capacitor LED drive power supply in Figure 1 and the main waveform schematic diagram of the single-stage electrolytic capacitor LED drive power supply in Figure 2, the basic method of the single-stage electrolytic capacitor LED drive power supply to realize the electrolytic capacitor is described below. It can be seen from Figure 2 that when the power factor is 1, the input voltage and the input current have the same phase, so the input power is

${\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&omega;t</span>}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&omega;t</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&omega;t</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 2</span>}}$

In the formula, V _m is the effective value of the grid input voltage, and I _m is the effective value of the input current.

Due to the constant voltage load characteristics of the LED and the need for constant current drive, the output power is flat, denoted as P _o . Assuming the efficiency of the converter is 100%, the average input power and output power should be equal. From this, the difference between the input power and the output power instantaneous power ripple can be obtained

p _rip ＝p _in (t)-P _o ＝-P _o cos2ωt (2)

The difference between the instantaneous power on the auxiliary energy storage capacitor and the instantaneous pulsation of the input power and output power is equal, so that the difference between the input power and the output power pulsation can be balanced. Within [T _line /8, 3T _line /8], the energy absorbed by the auxiliary energy storage capacitor C _b is

$\mathrm{<span\; class="notranslate">\; \&Delta;E</span>}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; \&Integral;</span>}_{\frac{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; line</span>}}}{\mathrm{<span\; class="notranslate">\; 8</span>}}}^{\frac{{\mathrm{<span\; class="notranslate">\; 3</span>}\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; line</span>}}}{\mathrm{<span\; class="notranslate">\; 8</span>}}}<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}<span\; class="notranslate">\; ]</span>\mathrm{<span\; class="notranslate">\; dt</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

At the same time, the energy absorbed by the auxiliary energy storage capacitor during this period can also be expressed as

$\mathrm{<span\; class="notranslate">\; \&Delta;E</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; max</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; min</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

The above two formulas are equal to get the capacitance value of the auxiliary energy storage capacitor, which is

${\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; max</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; min</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; \&Delta;V</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; av</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

Where ω is the angular frequency of the power frequency, ΔV _c is the voltage ripple value of the auxiliary energy storage capacitor, and V _{c_av} is the average value of the voltage of the auxiliary energy storage capacitor. It can be seen from the above formula that the capacitance of the auxiliary energy storage capacitor can be greatly reduced by increasing ΔV _c and V _{c_av} . In the present invention, ΔV _c and V _{c_av} can be increased by adjusting the turn ratio of the second secondary winding and the primary winding to further reduce the size of the auxiliary energy storage capacitor, so that it can be replaced by a film capacitor with a smaller capacitance electrolytic capacitor.

The driving mode of the single-stage electrolytic capacitor-free LED drive power supply and the specific working principle of each mode will be described below in combination with the main waveform diagram in Figure 2 and the equivalent circuit structure diagram of each switch mode in Figure 3-7. It can be seen from Figure 2 that this converter mainly has two operating modes. When the input instantaneous power is greater than the output instantaneous power, it is recorded as Mode1, and when the output instantaneous power is greater than the input instantaneous power, it is recorded as Mode2. In Mode1, there are four switching modes in each switching cycle, namely [t ₀ , t ₁ ], [t ₁ , t ₂ ], [t ₂ , t ₃ ], [t ₃ , t ₄ ]. The working conditions of each switch mode are analyzed in detail below.

Before the analysis, the following assumptions are made: ①All switches and diodes are ideal devices; ②All inductors, capacitors and isolation transformers are ideal components; ③The output inductance is large enough to approximate the output as a DC current source I _o , I _o is the output current; ④Because the power frequency cycle is much longer than the switching cycle, in a switching cycle, the input voltage v _in is approximately regarded as constant, which is V _m sinωt; the voltage v _cb at both ends of the auxiliary energy storage inductor C _b is also approximately as unchanged.

1. Switch mode 1[t ₀ ,t ₁ ] (corresponding to Figure 3)

At time t ₀ , the main switch MOS transistor Q ₁ is turned on, the opposite terminal of the first secondary winding of the isolation transformer T ₁ is a negative voltage, the secondary rectifier diode _DR is reverse-biased and cut off, and the primary current of the isolation transformer T ₁ is i _p Rising linearly with the slope v _in /L _m , the AC mains supplies energy to the primary side inductance. L _m is the size of the primary side inductance. Power is supplied to the load by the output filter capacitor and output filter inductor. After D _y T _s time, the main switch MOS transistor Q ₁ is turned off at time t ₁ . Among them, D _y is the duty cycle of the main switch MOS transistor _Q1 , and T _s is the switching period. The peak value of the primary side current of the isolation transformer _T1 is

${\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; pk</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&omega;t</span>}<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}}{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

The average value of the primary current in one switching cycle is

${\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; av</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; pk</span>}}{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&omega;t</span>}<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

In the formula: f _s is the switching frequency; it can be seen from this that within half the power frequency cycle, if the duty cycle D _y remains unchanged, the average value of the input current is proportional to the input voltage, so the duty cycle of the main switch MOS tube is fixed , Working in current discontinuous mode can automatically realize power factor correction.

2. Switch mode 2[t ₁ ,t ₂ ] (corresponding to Figure 4)

After the main switch MOS transistor _Q1 is turned off at time _t1 , the first auxiliary IGBT transistor Q _s1 and the second auxiliary MOS transistor Q _s4 are turned on, the second auxiliary IGBT transistor D _s2 is also turned on, and the secondary side rectifier MOS transistor Q _R is turned off , the energy of the primary inductor L _m charges the auxiliary energy storage capacitor C _b , and the current i _s2 of the second secondary winding decreases linearly. Power is supplied to the load by the output filter capacitor and output filter inductor. When the energy on the primary side inductance L _m decreases to exactly equal to the energy required for output in one switching cycle, that is, at time _t2 , the first auxiliary IGBT transistor Q _s1 and the second auxiliary MOS transistor Q _s4 are turned off.

3. Switch mode 3[t ₂ ,t ₃ ][corresponding to Figure 5]

Turn off the first auxiliary IGBT transistor Q _s1 and the second auxiliary MOS transistor Q _s4 at time _t2 and then turn on the secondary side rectification MOS transistor Q _R , the opposite end of the first secondary winding of the isolation transformer _T1 is positive voltage, and the rectifier diode D _R is turned on, the energy on the primary inductance L _m is converted into electric field energy and discharged to the load and the output capacitor C _o , the current i _s1 on the first secondary winding of the isolation transformer T ₁ decreases linearly until it drops to 0, That is, at _t3 , this mode ends.

4. Switch mode 4[t ₃ ,t ₄ ][corresponding to Figure 6]

In this mode, the current on the winding of the isolation transformer _T1 is zero, which is a discontinuous mode, and all switches and diodes are cut off. The load is supplied with energy by the output filter capacitor and output filter inductor.

In Mode2, there are also four switching modes in each switching cycle, namely [t ₀ , t ₁ ], [t ₁ , t ₂ ], [t ₂ , t ₃ ], [t ₃ , t ₄ ] . Where [t ₀ , t ₁ ], [t ₁ , t ₂ ], [t ₃ , t ₄ ] in Mode2 and [t ₀ , t ₁ ], [t ₁ , t ₂ ], [t ₃ ] in Mode1 , t ₄ ] mode works in a similar way and will not be repeated here.

The working principle of the converter at the switching mode 2 [t ₁ , t ₂ ] [corresponding to Fig. 7 ] in Mode2 will be specifically analyzed below.

After the main switch MOS transistor _Q1 is turned off at time _t1 , the second auxiliary IGBT transistor Q _s2 and the first auxiliary MOS transistor Q _s3 are turned on, the first auxiliary diode D _s1 is also turned on, and the secondary side rectifier MOS transistor Q _R is turned off. The auxiliary energy storage capacitor C _b charges the primary inductance L _m of the isolation transformer T ₁ , and the current i _s2 of the second secondary winding rises linearly. The LED load is powered by the output filter capacitor and output filter inductor. When the energy on the primary side inductance L _m rises to exactly equal to the required output energy in one switching cycle, that is, at time _t2 , the second auxiliary IGBT transistor Q _s2 and the first auxiliary MOS transistor Q _s3 are turned off.

It can be seen that the current i _s1 on the first secondary winding of the isolation transformer _T1 does not contain twice the power frequency component, but only contains the switching frequency and high-order harmonic components, and the high-frequency The component is filtered out to obtain a flat output current.

A specific example of the present invention is as follows: effective value of input grid voltage: V _m =220V; grid power frequency frequency: f _line =50Hz; output DC voltage: V _o =48V; output current: I _o =0.7A; isolation transformer T ₁ Transformation ratio of the primary side to the first secondary winding: 4; Isolation transformer T ₁ Transformation ratio of the primary side to the second secondary winding: 1; Primary inductance: L _m = 200uH; Main switch MOS tube Q ₁ , the second One auxiliary MOS transistor Q _s3 , the second auxiliary MOS transistor Q _s4 : IXTP4N80P; the first auxiliary IGBT transistor Q _s1 , the second auxiliary IGBT transistor Q _s2 : SGP02N60; the secondary side rectification MOS transistor Q _R : IRF630; the first auxiliary diode D _s1 , second auxiliary diode D _s2 : US5J; secondary rectifier diode D _R : MBRS3200; auxiliary energy storage capacitor C _b : 4.7uF/400V; input filter capacitor C ₁ : 0.47uF/400V; input filter inductance L ₁ : 50uH ; Output filter capacitor C ₂ : 10uF/100V; Output filter inductance L ₂ : 50uH; Switching frequency: f _s =200kHz.

The above is only a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, some improvements can also be made without departing from the principle of the present invention, and these improvements should also be regarded as the invention. protected range. the

Claims (2)

1. a single stage type no electrolytic capacitor LED driving power, is characterized in that: comprise input filter rectification circuit (1), the former limit of flyback switching circuit (2), auxiliary winding full-bridge two-way circuit (3), secondary current rectifying and wave filtering circuit (4) and isolating transformer (T ₁).

2. single stage type no electrolytic capacitor LED driving power as claimed in claim 1, is characterized in that: isolating transformer (T ₁) formed by a former limit winding and two secondary windings, comprise isolating transformer (T ₁) former limit inductance (L _m) and leakage inductance;

The filter circuit of input filter rectification circuit (1) is by input filter inductance (L ₁) and input filter capacitor (C ₁) being connected in parallel on electrical network input two ends composition, the rectifying part of input filter rectification circuit (1) adopts four diode (D ₁, D ₂, D ₃, D ₄) composition full-bridge not control rectifying circuit be connected in parallel on filter circuit two ends;

The former limit of flyback switching circuit (2) is by isolating transformer (T ₁) different name end and the main switch metal-oxide-semiconductor (Q of former limit winding ₁) drain electrode be connected to form, main switch metal-oxide-semiconductor (Q ₁) comprise its parasitic diode and parasitic capacitance;

Auxiliary winding full-bridge two-way circuit (3) is by first, second auxiliary IGBT pipe (Q _s1, Q _s2) and first, second auxiliary MOS transistor (Q _s3, Q _s4), first, second booster diode (D _s1, D _s2) and auxiliary energy storage electric capacity (C _b) composition, wherein the first auxiliary IGBT pipe (Q _s1) and the first booster diode (D _s1) and the first auxiliary MOS transistor (Q _s3) series connection successively, the second auxiliary IGBT pipe (Q _s2) and the second booster diode (D _s2) and the second auxiliary MOS transistor (Q _s4) after series connection, form two brachium pontis parallel connections successively, and be connected in parallel on isolating transformer (T ₁) second secondary winding two ends, isolating transformer (T ₁) different name end and first, second auxiliary IGBT pipe (Q of second secondary winding _s1), (Q _s2) collector electrode be connected, Same Name of Ends and first, second auxiliary MOS transistor (Q _s3, Q _s4) source class be connected, auxiliary energy storage electric capacity (C _b) one end be connected in the first auxiliary IGBT pipe (Q _s1) and the first booster diode (D _s1) mid point, the other end is connected in the second auxiliary IGBT pipe (Q _s2) and the second booster diode (D _s2) mid point, first, second auxiliary IGBT pipe (Q _s1, Q _s2) each self-contained its parasitic capacitance, first, second auxiliary MOS transistor (Q _s3, Q _s4) each self-contained its parasitic diode and parasitic capacitance;

Secondary current rectifying and wave filtering circuit (4) is by rectifier diode (D _r), rectification metal-oxide-semiconductor (Q _r) and output filter capacitor (C ₂) and output inductor (L ₂) composition, isolating transformer (T ₁) the different name end of first secondary winding is connected in rectifier diode (D _r) anode, rectifier diode (D _r) and rectification metal-oxide-semiconductor (Q _r), output inductor (L ₂) be connected in the positive output end of LED load, isolating transformer (T after series connection ₁) Same Name of Ends of first secondary winding is connected with the negative output terminal of LED load, output filter capacitor (C ₂) be parallel to rectification metal-oxide-semiconductor (Q _r) source class and the negative output terminal of LED load between, rectification metal-oxide-semiconductor (Q _r) comprise its parasitic diode and parasitic capacitance.