During frequency foldback uccs, as the load decreases, the MOSFET peak current is kept uccd datasheet datasneet the switching frequency is reduced foldback to reduce the output power. Operation Mode Switching Frequencies. The transformer magnetizing inductor value has to be uccd datasheet accordingly so that the converter can deliver the maximum required power while maintaining a switching frequency that is greater than the f QR min over uccd datasheet entire input operating range. Depending upon the line and load conditions, the UCC controls the converter using different modes of operation, which are defined as quasi-resonant QR modediscontinuous conduction mode DCMfrequency foldback mode FFM and green mode GMdetermined by the voltage on the FB pin, as shown in Figure When uccd datasheet bias winding is positive, during demagnetization or portions of the resonant ring, the OVP pin voltage is positive. It also uccd datasheet a minimum frequency clamp of 40 kHz. The proper amount of additional voltage has the effect of limiting the power uccd datasheet a cycle-by-cycle basis.
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Nazahn The details of the functional boxes also conceptualize the various fault detections and responses that are included in the UCC When the bias winding uccd datasheet positive, during demagnetization or portions of the resonant ucdd, the OVP pin voltage is positive.
In this mode, uccd datasheet flyback converter will always operate in discontinuous conduction mode. During frequency foldback mode, as the load decreases, the MOSFET peak current is kept constant and the switching frequency is reduced foldback to reduce the output power.
In QRM, the switching frequency will decrease as the load increases; DCM uccd datasheet is at the uccd datasheet maximum switching uccd datasheet kHz.
During all modes of operation, this controller operates in current mode control. When the primary current exceeds maximum current level which is indicated by a voltage of 1.
It datasgeet operation when the internal reference is below 4. To uccd datasheet lesser degree uccd significantthe boundaries are affected by the MOSFET output capacitance and transformer leakage inductance. At this maximum switching frequency, the converter enters Uccd datasheet control. The transformer magnetizing inductor value has to be designed accordingly so that the converter can deliver the maximum required power while maintaining a switching frequency that is greater than the f QR uccd over the entire input operating range.
UCCD from Texas Instruments The proper amount of additional voltage has the effect of limiting the power on a cycle-by-cycle basis. Uccd datasheet the device will initiate cycle-by-cycle power limit first, uccd datasheet side current protection is not intended to protect against output short circuit conditions.
Voltage uccd datasheet in FFM is achieved by varying the switching frequency in the range from kHz to 40 kHz. These figures conceptualize how the UCC executes uccd datasheet command of the FB voltage to have the responses that are shown in Figure 11 uccd datasheet, Figure 5 and Figure The UCC has many protection features that are found only on larger, full featured controllers. Refer to the Functional Block DiagramTypical Application DiagramFigure 6Figure 7Figure 8Figure uccd datasheetFigure uccd datasheetand Figure 12 for detailed block descriptions that show how uccd datasheet features are integrated into the normal control functions.
Operation Mode Switching Frequencies. When the FB voltage is between 1. Thus during cycle-by-cycle power limit, the peak CS voltage is typically 0. Under normal uccd datasheet conditions, the FB pin commands the operating mode of the UCC at uccd datasheet voltage uccd shown in the control flow chart, Figure Uccd datasheet logic control coordinates the fault detections to provide proper power supply recovery.
CS 3 I Equation 1. As the load increases, the kHz switching will become consistent and the controller will transition to frequency fold-back mode Datashedtwhere the peak primary current is held constant and the switching frequency is modulated from 40 kHz up to kHz, in order to uccd datasheet regulation.
Resonant valley switching is an integral part of QR operation. At higher loads, the UCC will operate in either DCM, where the peak primary current is modulated but the switching frequency is maintained at its maximum value, or quasi-resonant mode QRMwhere the switching frequency and the peak primary current are both modulated in order to maintain regulation.
When the load increases, the peak current increases and the switching frequency decreases. Resistor Uccd datasheet PL results in the addition of a voltage to the current sense signal that is proportional to the line voltage. Please do not use this site with Internet Explorer Depending upon the line and load conditions, the UCC controls the converter using datasjeet modes of operation, which are defined as quasi-resonant QR modediscontinuous conduction mode DCMfrequency foldback mode FFM and green mode GMdetermined by uccd datasheet voltage on the FB pin, as shown datashest Figure Uccd datasheet oscillator, shown in Uccd datasheet 8uccd datasheet internally datasheeet and trimmed so it is clamped by the circuit in Figure 8 to a nominal kHz maximum operating frequency.
Protection is provided to guard against operation during unfavorable bias uccd datasheet. The use of the UCC design calculator, SLVCis highly recommended in order to achieve the desired results with a careful balance between the transformer parameters and the programming resistors.
This current source adds a proportional step offset power limit offset to the CS signal and is part of the cycle-by-cycle power limit function that is discussed in the Protection Features section.
As the load decreases from its designed maximum output power, the UCC will daatasheet a higher switching frequency and decreased peak current.
It also has a minimum frequency clamp of 40 kHz. If the OVP voltage is greater than 3. Related Articles.
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