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CS1680 Scheda tecnica(PDF) 9 Page - Cirrus Logic |
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CS1680 Scheda tecnica(HTML) 9 Page - Cirrus Logic |
9 / 16 page CS1680 DS1055F1 9 voltage to reach the regulation target set by constant KMode1(target). If boost output voltage VBST is below the target regulation point or the boost output voltage is falling, the boost inductor current is increased. If the boost output voltage is above the target regulation point, the boost output voltage is rising, or the clamp has been activated recently the boost current is decreased. The LED output current is set using a third-order polynomial of the rectified RMS voltage, computed over a half-line cycle and filtered to avoid lamp flicker. Mode2 In Mode2, the CS1680 will detect if the input is a trailing edge dimmer paired with an electronic transformer or no dimmer switch paired with an electronic transformer. The detection algorithm determines its operation based on the falling edge of the input voltage waveform. To provide proper dimmer operation, the CS1680 executes the boost algorithm on the falling edge of the input line voltage, which will maintain a charge in the dimmer capacitor. To ensure maximum compatibility with dimmer components, the device boosts during this falling edge event using a peak current that must meet a minimum value. The boost output voltage VBST is measured at the trailing edge of the rectified voltage every half-line cycle and compared against the regulation point, which is set by resistor RBST (see Figure 11 on page 10). The voltage difference, the setting of LED output current IOUT, and the clamp activity are used in the control loop to modulate the boost turn-on time every half-line cycle which allows the boost output voltage to reach the regulation target set by constant KMode2(target). If boost output voltage VBST is below the target regulation point or the boost output voltage is falling, the total turn-on time over a half-line cycle is increased. If the boost output voltage is above the target regulation point, the boost output voltage is rising, or the clamp has been activated recently, the total turn-on time over a half-line cycle is decreased. The Mode2 algorithm estimates the turn-on time of the transformer by measuring the conduction angle of the rectified voltage every half-line cycle. The LED output current is set based on the output power requirements for a particular conduction angle by the regulation loop. Mode3 In Mode3, the CS1680 will detect if the input is a leading edge dimmer paired with an electronic transformer. The CS1680 regulates boost output voltage VBST while maintaining the dimmer phase angle. The device executes a CCM boost algorithm that keeps the boost peak current inversely proportional to the boost output voltage. The algorithm attempts to maintain a constant power while limiting the boost peak current to prevent saturating the boost inductor. The Mode1 and Mode2 algorithms use properties of the input waveform on a cycle-by-cycle basis to determine the output current, and then adjusts the boost control parameters to balance the input power with the requested output power. Unlike the Mode1 and Mode2 algorithms, the Mode3 algorithm leaves the boost parameters fixed and adjusts the output current to balance input power and output power. As long as boost output voltage VBST remains between the voltage thresholds set by lower regulation range constant KMode3(low) and higher regulation range constant KMode3(high), the LED output current IOUT will remain constant (see Figure 9). If the boost output voltage VBST rises above the regulation range high voltage threshold set by constant KMode3(high) (due to the phase angle of the dimmer increasing which allows for the first stage to produce additional power), LED output current IOUT is gradually increased until the boost output voltage VBST falls below the regulation range high threshold. The rate of increase continues to add larger steps as long as boost output voltage VBST stays above the regulation high threshold. If the boost output voltage continues to rise and reaches the clamp-on threshold set by constant KCLAMP(on), the clamp circuit will activate to dissipate the excess power from the boost output. While the clamp is on, the LED output current IOUT increases at an accelerated rate. If the boost output voltage VBST falls below the regulation range low voltage threshold set by constant KMode3(low), LED output current IOUT is gradually decreased. The rate of decrease continues to subtract larger steps as long as the boost output voltage stays below the regulation range low threshold. If the Regulation Range High Regulation Range Low Accelerated Decrease On Accelerated Increase On Accelerated Increase Off VBST KMode3(high) VBST KCLAMP(off) VBST KCLAMP(on) VBST KMode3(low) VBST KDEC(on) t v(t) Figure 9. Mode3 Output Regulation Algorithm |
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