Multiple LED driver power can actually do this
As a new energy-saving and pollution-free light source, the lamp plays a revolutionary role in modern lighting applications due to its unique illuminating lighting characteristics. As one of the most important components in the lighting industry chain, the typical problems of low reliability and high cost of drive control technology for drive power have always restricted the development of lighting. The development and reliability research of multi-drive power technology is an important issue in the industry.
1. Analysis of driving status
A remarkable feature of general-purpose lighting at home and abroad is that the light source is usually composed of a large number of chips. The characteristics of the LED itself determine that the LED is suitable for constant current driving, which has been recognized by experts and scholars at home and abroad. The LED driving method is mainly a single-channel constant-voltage output (light source built-in constant current source), a single-channel constant current output, and a single-channel constant voltage source configuration multi-channel DC/DC constant current output.
1. 1 single output constant current drive
Driving the LED light source as a single set of loads from a single output power supply is the simplest way to control the LED drive. There are many ways to connect the multiple light sources. Figure 1 below shows the connection of all LED loads in series. The single output power supply is a constant current source characteristic drive lamp. Since the light sources are connected in series, there is no current sharing problem, but when the number of LEDs connected in series is large, the light source voltage will increase, and the excessively high light source voltage requires the insulation cost of the whole lamp to meet the safety standard, and the higher the heat sink and insulation requirements of the lamp, The greater the thermal resistance, the worse the heat dissipation effect will affect the lamp life.
As an improvement, the LED lamp shown in FIG. 2 is a grid-like arrangement structure, which can prevent the voltage of the light source from being too high. When the number of parallel LEDs is large, the single lamp is open, which has less influence on the entire LED lamp. However, this single LED is directly connected in parallel, and the current balance of the LED is poor, which causes the reliability of the LED light source to be reduced; at the same time, one of the short circuits and the parallel connection thereof will be extinguished.
As shown in Figure 3 below, the LEDs are connected in series and then connected in parallel. In the absence of LED failure, the current sharing characteristics of the structure are better than the grid structure shown in Figure 2, but if some LEDs have a short-circuit fault, Causes severe current imbalance between multiple strings.
The above analysis shows that the single output constant current drive has certain limitations in the application, especially the connection mode of the light source in parallel will have a greater impact on the service life and reliability of the light source.
1. 2 multi-output constant current drive
As shown in Figure 4 below, the drive control mode of each group of loads with independent constant current source characteristics is an ideal solution. This aspect solves the problem of current imbalance between multiple outputs, and on the other hand overcomes The aforementioned shortcoming of single output constant current driving, but the driving efficiency of this scheme is relatively low.
At present, the more commonly used multi-channel driving scheme is as shown in Fig. 5. At the output port of the single-output constant voltage source, several stages of non-isolated DC/DC converters are arranged, and each LED load is realized by a separate DC/DC converter. Stream drive control. The shortcoming of this scheme is that the DC/DC converter circuit is relatively complicated, the cost is relatively high, and the reliability is low; for each additional DC/DC converter, the driving efficiency is correspondingly reduced, and the electromagnetic interference (EMI) is easily accompanied; The voltage, current and power of each load of different types of light sources are different, and the design of the universal DC/DC converter is difficult to standardize, which brings great inconvenience to the industrialization.
2. Research on key technologies of new multi-channel drive power
It is considered that in the case of using a capacitor to realize multi-channel constant current driving, it is easier to achieve overall stability and reliability while participating in circuit resonance and changing the characteristics of the converter, and at the same time, the cost can be greatly reduced. Three new technical solutions are proposed:
2. 1 two-stage transformation to achieve multi-drive
As shown in Figure 6 below, the main circuit adopts two-stage transformation to realize multi-channel driving of LED. The circuit includes high-frequency pulse AC source, impedance network Z1 and high-frequency transformer T0, high-frequency resonant capacitor Cb1, dual rectifier filter circuit and load. . The input of the impedance network Z1 is a high-frequency pulse AC source, the output is connected to the primary side of the high-frequency transformer T0, one end of the transformer secondary side is connected in series with the resonant capacitor Cb1, and the other end is connected in parallel with two rectifier filter circuits; the diodes D1, D4 and the diodes D2 and D3 are respectively The two independent half-wave rectification circuits and the filter capacitors Co1 and Co2 form a two-way rectification and filtering circuit; the filter capacitors Co1 and Co2 are respectively connected in parallel at the two ends of the load, and two independent half-wave rectification circuits are respectively given to The road load provides power. On the one hand, the resonant capacitor Cb1 forms a high-frequency resonant network with the impedance network Z1, which participates in the resonance of the main circuit. On the other hand, when the voltage drop of the two loads is unbalanced, the pressure difference between the two channels can be balanced by Cb1, so that The average value of the road load operating current is equal.
The circuit shown in Figure 7 below is an implementation of a high frequency resonant network. The impedance network includes a resonant inductor Lr, Lm and a high-frequency transformer primary resonant capacitor C0. The resonant inductor Lm is connected in parallel with the primary side of the high-frequency transformer T0. The parallel link is connected in series with the resonant inductor Lr and the resonant capacitor C0, and Cb1 is the secondary resonant capacitor of the transformer. . The resonant inductors Lr and Lm can be external independent inductors, Lr can also be the leakage inductance of the high frequency transformer T0, and Lm can also be the magnetizing inductance of T0. Since the resonant capacitor Cb1 participates in the resonance transformation of the main circuit, the gain curve is changed, and the equivalent conversion to the primary side of the transformer is comparable to the primary resonant capacitor C0, which speeds up the response speed of the converter and avoids the large capacitance. Output overshoot under dynamic conditions such as starting.
2. 2 new positive flyback circuit to achieve multi-drive
In the foregoing technical solution, the high-frequency pulse AC source must be a positive-negative symmetrical square-wave voltage pulse to ensure that the resonant capacitor Cb1 performs a better current sharing effect when the two loads are unbalanced, so that the front-end circuit must be double Bridge circuit of the switch tube. As a further breakthrough in technology, a new type of forward-excited circuit multi-output drive topology has been developed. As shown in Figure 8, the transformer has a single-switch S1 and a high-frequency series in a rectifier circuit on the secondary side of the transformer. Inductance L1. When the primary side switch S1 is turned on, the transformer Ta1 stores energy, the secondary side passes through the capacitor Cb1, the diode D3, the inductor L1, the load A1, and the diode D2 constitute a current loop, and the transformer operates in a forward state; when the primary side switch S1 is closed When it is off, the transformer Ta1 releases energy, the secondary side passes through the diode D1, the load A2, the diode D4, and the capacitor Cb1 constitute another current loop, and the transformer operates in a flyback state. In the forward loop, the resonant capacitor Cb1 and the high-frequency inductor L1 resonate, so that the diodes D2 and D3 operate in a zero current switching state, reducing the reverse recovery loss of the diode and improving efficiency. When the voltage drop of the two loads is unbalanced, the capacitor Cb1 can still balance the load current.
2. 3 PFC circuit backup
In medium to high power applications, as a pre-active PFC circuit, the BOOST boost circuit is the most common topology.
Since the PFC circuit is directly connected to the power grid through the rectifier circuit, factors such as surges or lightning strikes in the power grid are likely to cause malfunction of the PFC circuit. When the PFC circuit is faulty, it is easy to cause the rear load to fail to work normally. It can be divided into the following two cases: In the first case, the rear load cannot be operated due to the power failure of the PFC circuit; the second case, although PFC When the circuit is faulty but the current path can still be provided, the output voltage is no longer stable due to the fault of the PFC circuit, but changes with the fluctuation of the power grid, causing the voltage ripple on the load to be too large, resulting in poor performance of the load, such as efficiency. reduce.
How to ensure the normal operation of the rear-end circuit after the PFC circuit is damaged is the main problem solved by this technology. As shown in Figure 9 below, a PFC backup circuit is connected in series with the output of the PFC circuit. When the PFC circuit works normally, the PFC circuit is used to implement the power factor correction function. The PFC backup circuit is only used to provide the current path. When the PFC circuit fails, the PFC circuit Used only to provide current path, the PFC backup circuit is used to stabilize the output voltage. In this way, the PFC circuit and the PFC backup circuit can be alternately operated to ensure the reliability of the drive system.
3. Key technological innovations
From the perspective of lighting reliability and cost, multi-drive modular luminaires will become the trend of future lighting. At present, various research institutes and production enterprises at home and abroad carry out multi-channel LED drive power supply technology development, mainly based on the research of new positive and negative flyback combined converter drive power, using voltage-type variable frequency control, and the three-stage converter circuits all work in critical mode. Technology can improve the reliability of the drive power, but the circuit is complicated and the cost is high. The main innovations of the key technologies of this research project are:
(1) Breaking through the multi-path driving idea realized by the traditional three-level transformation, using two-stage transformation to realize the multi-channel driving. The resonant capacitor participates in the resonant conversion characteristic of the main circuit, improves the dynamic response speed of the converter, reduces the inrush current to the load under dynamic conditions such as the start of the converter, and improves the reliability of the drive. At the same time, the resonance capacitor is used to balance the multi-output load current, and the high-precision current sharing characteristic between the multiple outputs is realized, which has the characteristics of low cost, small volume and high efficiency. The new circuit topology solves the problem of open circuit and short circuit protection of multiple drive circuits. Any one of the roads ensures normal output of other circuits and maximizes the reliability of the circuit. At the same time, the protection circuit does not have any inrush current to the load, further improving the reliability of the circuit and reducing the cost.
(2) Proposed a new single-switch forward-reverse multi-output circuit. The main circuit has only one switch tube to realize the current sharing control of the multi-output of the secondary side of the transformer, which further reduces the circuit cost; Reduce the volume of the transformer and improve the efficiency; the current sharing capacitor of the secondary side not only realizes the current sharing control of the multiple outputs, but also forms a resonant circuit with the current sharing inductor, thereby realizing the zero current switching state of the secondary side rectifier diode and reducing the diode reverse Recover loss, reduce electromagnetic interference, and further improve efficiency.
(3) Proposing the backup idea of ​​the PFC circuit, the PFC circuit of the pre-stage PFC circuit has made a PFC backup circuit, which effectively solves the problem that the subsequent circuit can not work normally when the PFC circuit is faulty in the prior art, and ensures the work of the post-stage load. Performance is not affected by PFC circuit failure, further ensuring the reliability of the drive system.
4, the conclusion
The key technology of multi-channel driving power source studied in this paper adopts two-stage conversion to realize multi-channel driving. Through single-switch positive and negative-excitation multi-output circuits, only one switching tube is used to realize multi-output current sharing. PFC circuit backup is used, and patent application has been completed. Main technical indicators of the product: 1. Multi-channel output efficiency: >0. 92 (at room temperature); 2. Multi-output uniformity: ≤5% (at room temperature); 3. Power factor: >0. 98 (room temperature Next, when the input voltage is 110Vac) 4. Waterproof rating: IP67; 5. Ambient temperature: -30 ~ 70 °C.
1. Analysis of driving status
A remarkable feature of general-purpose lighting at home and abroad is that the light source is usually composed of a large number of chips. The characteristics of the LED itself determine that the LED is suitable for constant current driving, which has been recognized by experts and scholars at home and abroad. The LED driving method is mainly a single-channel constant-voltage output (light source built-in constant current source), a single-channel constant current output, and a single-channel constant voltage source configuration multi-channel DC/DC constant current output.
1. 1 single output constant current drive
Driving the LED light source as a single set of loads from a single output power supply is the simplest way to control the LED drive. There are many ways to connect the multiple light sources. Figure 1 below shows the connection of all LED loads in series. The single output power supply is a constant current source characteristic drive lamp. Since the light sources are connected in series, there is no current sharing problem, but when the number of LEDs connected in series is large, the light source voltage will increase, and the excessively high light source voltage requires the insulation cost of the whole lamp to meet the safety standard, and the higher the heat sink and insulation requirements of the lamp, The greater the thermal resistance, the worse the heat dissipation effect will affect the lamp life.
As an improvement, the LED lamp shown in FIG. 2 is a grid-like arrangement structure, which can prevent the voltage of the light source from being too high. When the number of parallel LEDs is large, the single lamp is open, which has less influence on the entire LED lamp. However, this single LED is directly connected in parallel, and the current balance of the LED is poor, which causes the reliability of the LED light source to be reduced; at the same time, one of the short circuits and the parallel connection thereof will be extinguished.
As shown in Figure 3 below, the LEDs are connected in series and then connected in parallel. In the absence of LED failure, the current sharing characteristics of the structure are better than the grid structure shown in Figure 2, but if some LEDs have a short-circuit fault, Causes severe current imbalance between multiple strings.
The above analysis shows that the single output constant current drive has certain limitations in the application, especially the connection mode of the light source in parallel will have a greater impact on the service life and reliability of the light source.
1. 2 multi-output constant current drive
As shown in Figure 4 below, the drive control mode of each group of loads with independent constant current source characteristics is an ideal solution. This aspect solves the problem of current imbalance between multiple outputs, and on the other hand overcomes The aforementioned shortcoming of single output constant current driving, but the driving efficiency of this scheme is relatively low.
At present, the more commonly used multi-channel driving scheme is as shown in Fig. 5. At the output port of the single-output constant voltage source, several stages of non-isolated DC/DC converters are arranged, and each LED load is realized by a separate DC/DC converter. Stream drive control. The shortcoming of this scheme is that the DC/DC converter circuit is relatively complicated, the cost is relatively high, and the reliability is low; for each additional DC/DC converter, the driving efficiency is correspondingly reduced, and the electromagnetic interference (EMI) is easily accompanied; The voltage, current and power of each load of different types of light sources are different, and the design of the universal DC/DC converter is difficult to standardize, which brings great inconvenience to the industrialization.
2. Research on key technologies of new multi-channel drive power
It is considered that in the case of using a capacitor to realize multi-channel constant current driving, it is easier to achieve overall stability and reliability while participating in circuit resonance and changing the characteristics of the converter, and at the same time, the cost can be greatly reduced. Three new technical solutions are proposed:
2. 1 two-stage transformation to achieve multi-drive
As shown in Figure 6 below, the main circuit adopts two-stage transformation to realize multi-channel driving of LED. The circuit includes high-frequency pulse AC source, impedance network Z1 and high-frequency transformer T0, high-frequency resonant capacitor Cb1, dual rectifier filter circuit and load. . The input of the impedance network Z1 is a high-frequency pulse AC source, the output is connected to the primary side of the high-frequency transformer T0, one end of the transformer secondary side is connected in series with the resonant capacitor Cb1, and the other end is connected in parallel with two rectifier filter circuits; the diodes D1, D4 and the diodes D2 and D3 are respectively The two independent half-wave rectification circuits and the filter capacitors Co1 and Co2 form a two-way rectification and filtering circuit; the filter capacitors Co1 and Co2 are respectively connected in parallel at the two ends of the load, and two independent half-wave rectification circuits are respectively given to The road load provides power. On the one hand, the resonant capacitor Cb1 forms a high-frequency resonant network with the impedance network Z1, which participates in the resonance of the main circuit. On the other hand, when the voltage drop of the two loads is unbalanced, the pressure difference between the two channels can be balanced by Cb1, so that The average value of the road load operating current is equal.
The circuit shown in Figure 7 below is an implementation of a high frequency resonant network. The impedance network includes a resonant inductor Lr, Lm and a high-frequency transformer primary resonant capacitor C0. The resonant inductor Lm is connected in parallel with the primary side of the high-frequency transformer T0. The parallel link is connected in series with the resonant inductor Lr and the resonant capacitor C0, and Cb1 is the secondary resonant capacitor of the transformer. . The resonant inductors Lr and Lm can be external independent inductors, Lr can also be the leakage inductance of the high frequency transformer T0, and Lm can also be the magnetizing inductance of T0. Since the resonant capacitor Cb1 participates in the resonance transformation of the main circuit, the gain curve is changed, and the equivalent conversion to the primary side of the transformer is comparable to the primary resonant capacitor C0, which speeds up the response speed of the converter and avoids the large capacitance. Output overshoot under dynamic conditions such as starting.
2. 2 new positive flyback circuit to achieve multi-drive
In the foregoing technical solution, the high-frequency pulse AC source must be a positive-negative symmetrical square-wave voltage pulse to ensure that the resonant capacitor Cb1 performs a better current sharing effect when the two loads are unbalanced, so that the front-end circuit must be double Bridge circuit of the switch tube. As a further breakthrough in technology, a new type of forward-excited circuit multi-output drive topology has been developed. As shown in Figure 8, the transformer has a single-switch S1 and a high-frequency series in a rectifier circuit on the secondary side of the transformer. Inductance L1. When the primary side switch S1 is turned on, the transformer Ta1 stores energy, the secondary side passes through the capacitor Cb1, the diode D3, the inductor L1, the load A1, and the diode D2 constitute a current loop, and the transformer operates in a forward state; when the primary side switch S1 is closed When it is off, the transformer Ta1 releases energy, the secondary side passes through the diode D1, the load A2, the diode D4, and the capacitor Cb1 constitute another current loop, and the transformer operates in a flyback state. In the forward loop, the resonant capacitor Cb1 and the high-frequency inductor L1 resonate, so that the diodes D2 and D3 operate in a zero current switching state, reducing the reverse recovery loss of the diode and improving efficiency. When the voltage drop of the two loads is unbalanced, the capacitor Cb1 can still balance the load current.
2. 3 PFC circuit backup
In medium to high power applications, as a pre-active PFC circuit, the BOOST boost circuit is the most common topology.
Since the PFC circuit is directly connected to the power grid through the rectifier circuit, factors such as surges or lightning strikes in the power grid are likely to cause malfunction of the PFC circuit. When the PFC circuit is faulty, it is easy to cause the rear load to fail to work normally. It can be divided into the following two cases: In the first case, the rear load cannot be operated due to the power failure of the PFC circuit; the second case, although PFC When the circuit is faulty but the current path can still be provided, the output voltage is no longer stable due to the fault of the PFC circuit, but changes with the fluctuation of the power grid, causing the voltage ripple on the load to be too large, resulting in poor performance of the load, such as efficiency. reduce.
How to ensure the normal operation of the rear-end circuit after the PFC circuit is damaged is the main problem solved by this technology. As shown in Figure 9 below, a PFC backup circuit is connected in series with the output of the PFC circuit. When the PFC circuit works normally, the PFC circuit is used to implement the power factor correction function. The PFC backup circuit is only used to provide the current path. When the PFC circuit fails, the PFC circuit Used only to provide current path, the PFC backup circuit is used to stabilize the output voltage. In this way, the PFC circuit and the PFC backup circuit can be alternately operated to ensure the reliability of the drive system.
3. Key technological innovations
From the perspective of lighting reliability and cost, multi-drive modular luminaires will become the trend of future lighting. At present, various research institutes and production enterprises at home and abroad carry out multi-channel LED drive power supply technology development, mainly based on the research of new positive and negative flyback combined converter drive power, using voltage-type variable frequency control, and the three-stage converter circuits all work in critical mode. Technology can improve the reliability of the drive power, but the circuit is complicated and the cost is high. The main innovations of the key technologies of this research project are:
(1) Breaking through the multi-path driving idea realized by the traditional three-level transformation, using two-stage transformation to realize the multi-channel driving. The resonant capacitor participates in the resonant conversion characteristic of the main circuit, improves the dynamic response speed of the converter, reduces the inrush current to the load under dynamic conditions such as the start of the converter, and improves the reliability of the drive. At the same time, the resonance capacitor is used to balance the multi-output load current, and the high-precision current sharing characteristic between the multiple outputs is realized, which has the characteristics of low cost, small volume and high efficiency. The new circuit topology solves the problem of open circuit and short circuit protection of multiple drive circuits. Any one of the roads ensures normal output of other circuits and maximizes the reliability of the circuit. At the same time, the protection circuit does not have any inrush current to the load, further improving the reliability of the circuit and reducing the cost.
(2) Proposed a new single-switch forward-reverse multi-output circuit. The main circuit has only one switch tube to realize the current sharing control of the multi-output of the secondary side of the transformer, which further reduces the circuit cost; Reduce the volume of the transformer and improve the efficiency; the current sharing capacitor of the secondary side not only realizes the current sharing control of the multiple outputs, but also forms a resonant circuit with the current sharing inductor, thereby realizing the zero current switching state of the secondary side rectifier diode and reducing the diode reverse Recover loss, reduce electromagnetic interference, and further improve efficiency.
(3) Proposing the backup idea of ​​the PFC circuit, the PFC circuit of the pre-stage PFC circuit has made a PFC backup circuit, which effectively solves the problem that the subsequent circuit can not work normally when the PFC circuit is faulty in the prior art, and ensures the work of the post-stage load. Performance is not affected by PFC circuit failure, further ensuring the reliability of the drive system.
4, the conclusion
The key technology of multi-channel driving power source studied in this paper adopts two-stage conversion to realize multi-channel driving. Through single-switch positive and negative-excitation multi-output circuits, only one switching tube is used to realize multi-output current sharing. PFC circuit backup is used, and patent application has been completed. Main technical indicators of the product: 1. Multi-channel output efficiency: >0. 92 (at room temperature); 2. Multi-output uniformity: ≤5% (at room temperature); 3. Power factor: >0. 98 (room temperature Next, when the input voltage is 110Vac) 4. Waterproof rating: IP67; 5. Ambient temperature: -30 ~ 70 °C.
38120HP 8Ah 3.2V Lithium Ion Battery
Lithium Car Battery,Lithium Titanate Battery,Lithium Ion Battery Charging,Hw38120Hp 8Ah Lifepo4 Battery
Zhejiang Xinghai Energy Technology Co.,Ltd , https://www.headwayli-battery.com