In most designs that use current-mode operation to control led flood light, the sine
reference is obtained by using a resistive divider to sense the input voltage.
An internally generated sine reference, produced using digital mapping, makes
the LED current of the buck-boost topology more stable. Internal generation of
the sine reference also makes it possible to eliminate the resistive divider,
for lower component count and a more compact design. Figure 1 gives the block
diagram of the circuit.
In converters that use a boost topology, input current is configured by the inductor current. This optimizes PFC in critical-conduction mode (CRM) operation, since there is a constant on-time with variable off-time. With the buck-boost topology, on the other hand, input current is proportional to switch current. As a result, PFC is degraded in CRM operation, and the line peak voltage is flatter. Input current is determined by the inductor current associated with MOSFET turn-on. Equation 1 shows how to calculate the input current in the buck-boost converter.
This means that the best method is discontinuous conduction mode (DCM) operation with fixed turn-on time.As described above, to improve LED current fluctuation and line-voltage distortion, our design uses led high bay light operation and the fixed internal sine reference in a buck-boost converter. This approach does an excellent job of regulating the LED current, without visible flicker, even if there is a line voltage transient between 90Vac and 265Vac. Figure 2 shows the current slope for the inductor current.In general, line regulation is used to regulate output current in response to variations in input voltage. Load regulation is used to maintain output power independent of changes in the LED forward voltage. As forward voltage goes down in response to system temperature or LED derating, constant-current load regulation is used to reduce LED power with a luminous decrease.
you can read more:http://yahamflood.blogspot.com/2013/09/how-to-change-or-tune-lighting-color-in.html
In converters that use a boost topology, input current is configured by the inductor current. This optimizes PFC in critical-conduction mode (CRM) operation, since there is a constant on-time with variable off-time. With the buck-boost topology, on the other hand, input current is proportional to switch current. As a result, PFC is degraded in CRM operation, and the line peak voltage is flatter. Input current is determined by the inductor current associated with MOSFET turn-on. Equation 1 shows how to calculate the input current in the buck-boost converter.
This means that the best method is discontinuous conduction mode (DCM) operation with fixed turn-on time.As described above, to improve LED current fluctuation and line-voltage distortion, our design uses led high bay light operation and the fixed internal sine reference in a buck-boost converter. This approach does an excellent job of regulating the LED current, without visible flicker, even if there is a line voltage transient between 90Vac and 265Vac. Figure 2 shows the current slope for the inductor current.In general, line regulation is used to regulate output current in response to variations in input voltage. Load regulation is used to maintain output power independent of changes in the LED forward voltage. As forward voltage goes down in response to system temperature or LED derating, constant-current load regulation is used to reduce LED power with a luminous decrease.
you can read more:http://yahamflood.blogspot.com/2013/09/how-to-change-or-tune-lighting-color-in.html
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