Key words:
LED driver, dimming, power factor, correction
First, circuit characteristics description
The RD-251 can provide 350 mA single constant current output at 12 V and 18 V LED string voltages. The use of standard AC electricity controllable silicon modulus can reduce the output current to 1% (3 mA), which will not cause the LED load performance to unstable or flash. This circuit can simultaneously compatibility with low-cost front elevators and more complex rear elevators.
This circuit is used to operate within a general AC input voltage range (85 VAC to 265 VAC, 47 Hz), but it does not cause damage within the input voltage range of 0 VAC to 300 VAC. This can improve the service reliability, extend the service life underline voltage drop and surge conditions. Linkswitch-PL design provides high power factor (>0.9) to help meet all current international standards, allowing a single design to globally.
The shape of the power source can meet the requirements of the standard pear shaped (A19) LED replacement lamp. The output is non-separated, requiring the mechanical design of the outer casing to isolate the power output and LED load from the user.
Second, the circuit schematic
LED driver circuit schematic
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Circuit diagram (removing structures that highlight the display) can be used for non-tuning applications)
Note: C1, R22 and C12 are not assembled.
For non-tuned applications, active attenuation circuits and bleed circuits can be removed to detect the following elements: Q3, R20, R3, R4, R10, R11, C6, and C3. Replace R7, R8, and R20 to 0 Euro resistors.
For only high pressure applications, you must match the high-leaking dimmer such as REV 300 W, which is fine-tuned to BUSCH 2250 (600 W) or the following similar components. Replace F1 with a 47/2W melting resistor, replace R7 and R8 with 20 NF, replace the C6 to replace R10 and R11 to minimum 510/0.5 W, replace C3 with 150nf, and replace R16 to 1k / 0.25 W.
Third, circuit principle analysis
The circuit is a non-separator, a discontinuous conductive mode flyback converter circuit, provides driving by an output current of 350 mA to 12V to 18 V to 18 V. The drive is fully capable of operating within the wide input voltage range and provides high power factor. This circuit can simultaneously meet the input surges and EMI requirements, with fewer number of components, which enables the board size to meet the requirements of LED bulb replacement applications.
3.1 Dimming Performance Circuit Design Guide
We need to have a comprehensive trade-off when designing the output dimmer in front of the phase-controlled dimmer, and we need to perform comprehensive trade-offs during design. Since the power consumption of LED lighting is very low, the current absorbed by the whole lamp is often less than the maintenance current of thyristor in the dimmer. This produces a poorly-dimming range limited and / or flashing. Since the impedance of the LED driver is relatively large, it produces a very serious oscillation when the controllable silicon is transported. At a moment of controllable silicon, a very large surge current flows into the input capacitance of the driver to excite the line inductance and cause current oscillation. This also causes similar adverse situations because oscillations reduce the controllable silicon current to zero and shutdown while causing LED lights flashing.
To overcome these issues, two circuit function blocks are used in the circuit - an active attenuation circuit and a bleed circuit. The disadvantage of these circuit function blocks is to increase power, thereby reducing the efficiency of the power supply.
The value of the attenuation circuit and the bleed circuit in this design can make the vast majority of dimmeters (600 W)
The lower dimmer and includes a low-cost front-edge controllable silicon-operated normal operation throughout the input voltage range. This design enables a light to connect a dimmer when the high voltage input is enabled to achieve no blinking lighting.
A lamp will result in minimum output current and maximum surge current (time-controlled silicon), which is the worst case. Therefore, the active attenuation circuit and the bleed circuit are very obvious: the bleed circuit can reduce the impedance, and the attenuation circuit can improve the impedance. But this will increase power consumption, thereby reducing the efficiency of the drive and the performance of the entire system.
The plurality of lamps are required to connect to a dimmer to reduce the current required for the bleed circuit, at which point the value of R10 and R11 can be increased and the value of C6 is reduced.
If the lamp is operated only at low pressure (85 VAC to 132 Vac), the peak current that occurs when the front-edge controllable silicon is turned on, and the value of R7 and R8 is reduced.
Both changes will reduce the distribution and improve efficiency.
For non-tunitive applications, these components can be omitted, replacing R7 and R8 with jumper, thereby increasing efficiency, but does not change other performance characteristics.
3.2 Enter EMI filtering and input rectification
The EMI filter is optimized to reduce the impact on dimming performance. The resistor R20 is a melting resistance. If a component failure causes an input current, you should select the cash resistance to make the open circuit. Thin film resistance (relative to the wire resistance) is acceptable compared to non-PFC design or passive PFC design. This reduces the instantaneous power dissipation when the input capacitor is charged, but the rating of 2 W is recommended for the design of the work under high pressure. In addition, they can limit the inrope current generated when the phase super-active silicon light is turned on and when the capacitance C4 and C5 are charged. When the thyristor is turned on at a 90 degree or 270 degree angle (the surge current reaches the maximum), it corresponds to the peak of the AC waveform. Finally, they can attenuate any current oscillation caused by the surge current between the AC input impedance and the power input stage when the front-edge controllable silicon is transmitted.
The two π-type diameter filter EMI stages together with C1, R2, L1, and C2 form a second level, C4, L2, R9, and C5 form a second level. At the time of the test, it was found that there was no request to meet the transmission EMI limit, so there was no assembly.
The AC input is rectified by BR1, filtered by C4 and C5. The total equivalent input capacitance (C4, C5 and C6 and C6) can ensure that the LinkSwitch-PL device performs the correct zero-zero point detection on the AC input, which is necessary for normal operation and optimal performance during dimming. .
3.3 active attenuation circuit
Active attenuated circuit is used to limit the surge current, associated voltage spikes and oscillations generated during the controlled silicon in the dimmer. The circuit is connected to the impedance (R7 and R8) connected in series with the input rectifier in a transient time of each AC half cycle, and bypassing the remaining AC cycle by one bypassing the SCR (Q3). Resistors R3, R4, and C3 determine the delay time before the Q3 is turned on.
3.4 Break Circuit
Resistors R10, R11 and C6 form a bleed circuit to ensure that the initial input current is sufficient to meet the maintenance current requirements of the thyristor, especially when the controllable silicon conductors is not large enough.
For non-tuning applications, the active attenuation circuit and the bleed circuit can be removed simultaneously. To this end, the following elements can be deleted: Q3, R20, R3, R4, R10, R11, C6, and C3. Replace R7, R8, and R20 to 0 Euro resistors.
3.5 LinkSwitch-PL primary
The LNK457DG device (U1) integrates power switching devices, oscillators, output constant current control, start, and protection. The integrated 725 V MOSFET provides a wider voltage margin, and high reliability can be ensured even in the event of an input surge. The device receives power from the bypass pin through the decoupling capacitor C9. After startup, C9 is charged from the internal current source and via the drain pin, and then powered by the output via R15 and D4 during normal operation.
The input voltage of the rectified and filter is added to one end of the T1 primary winding. The integrated MOSFET drives the other side of the primary winding of the transformer in U1. D2, R13, R12 and C7 form an RCD-R clamp circuit, which is limited to the drain voltage spike caused by the leak.
The diode D6 is used to prevent the IC from generating negative oscillation (the drain voltage oscillation below the source voltage) when the power MOSFET exceeds the DC bus voltage, ensures a higher power factor with the minimum input capacitor.
3.6 Output rectification
The secondary transformer is rectified by D5, filtered by C11. The Schottky barrier diode is selected to improve efficiency. Since C11 provides energy storage during the AC cross-zero point, its value determines the magnitude of the line voltage output ripple (due to full wave rectification and 2 x fl). Therefore, this value can be adjusted according to the desired output ripple. For the displayed 680 micro F value, the output ripple is 50% of the positive and negative IO. Resistors R17 and C10 are used to attenuate high frequency oscillation, improve conductivity and radiation EMI.
3.7 Output Feedback
The constant current mode setting point is determined by the voltage drop in R18, and then fed into the feedback pin of U1. Output overvoltage protection is provided by VR2 and R14 (R14 has slightly negligible influence on current detection signals, negligible).
Fourth, printed circuit board layout
2011-9-28 13:39:26 Upload
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