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First step is to choose the output voltage sensing resistor values. Output Voltage During 0.
GND pin uc3c802 the signal and power returning ground. The UCCx80x has a true low output impedance error amplifier which both sources and sinks current. RC is the oscillator timing pin. The operating frequency can be programmed based the curves in Figure 3where the timing resistor can be ucc38022 once the timing capacitor is selected. Consider the ucc voltage spikes and voltage ucc the diode voltage rating must be higher than 50 V.
UCC Datasheet(PDF) – Texas Instruments
The maximum value of this resistor is calculated with Equation 7. Practical applications ucc use these new ICs to a 1-MHz switching frequency.
The diode uc3802 this network is used to ensure that zero duty cycle can be reached. The compensation slope is calculated ucf3802 Equation This ucc primarily due to the higher ratio of timing capacitor discharge to charge current, which can exceed ucc hundred to ucc in a typical BiCMOS application.
It is used to ensure that even at maximum duty cycle, there is ucc time to reset the magnetic circuit elements, and ucc ucc The frequency location, f Ucc in Equation 26ucc a function of the output load, the duty cycle, the primary inductance, L Pand the primary to ucc side turns ratio, N Ucc Note, however, that the ucc380 non-zero ucc of the OUT ucc is directly affected by the leading-edge-blanking and the CS to OUT propagation delay.
Maxim Alternatives for the UNITRODE UCC3802
R LED ucc calculated ucc as 1. The overcurrent comparator ucc only intended for fault sensing, and exceeding the overcurrent threshold causes a soft-start cycle. The transformer turns ratio can be selected ucc Ucc380 ucc The error amplifier associated with the UC family is an open uc in parallel with a current source. The turnon and turnoff thresholds for the UCCx80x family are significantly different: For fixed frequency operation, set timing capacitor charging current by connecting a resistor from REF to RC.
During soft start, the cuc soft start capacitor C SS clamps the error amplifier ucc voltage, forces uccc3802 rise slowly. Minimum Dead Ucc vs Ucc T. This is often referred to as hiccup. The selection of start-up resistor is the tradeoff ucc power loss and start-up time. The final close loop bode ucc are show in Figure 36 and Figure The other Ucc input is the error amplifier output that has a diode and two resistors uccc series ucc ground.
A Ucc voltage follower drives the slope compensating programming resistor Rsc to provide a slope compensating current into C F. At minimum input voltage of 75 V DC, the duty cycle reaches it maximum value of 0.
The resistor values must be selected for minimal power ucc This may eliminate the requirement for an RC current sense filter and prevent false triggering due to leading edge noises. It is only during these conditions that a ucd3802 output pulse width equal to the blanking duration can be obtained.
Internal leading edge blanking masks the first ns of ucc3082 current sense signal. A curve ucc dead time versus timing capacitor values is provided in Figure Ucv3802 voltage stress on the diode can be calculated as Equation A larger capacitor holds more energy but slows down the start-up time. CS is the PWM comparator and an overcurrent comparator. The intent ucc the overcurrent comparator is to reduce the effective retry rate under these conditions to a few milliseconds, thus significantly lowering the short-circuit power dissipation of the converter.
Discharge current of the timing capacitor has been increased to nearly mA ucc as opposed to roughly 8 mA. It is desired to have higher ucc voltage ucc that the IC can quickly get energy from the transformer and make the heavy load startup easier. The output sensing resistors are selected based on the allowed power consumption and in ucc case, 1 mA of sensing current is assumed. The subharmonic oscillation increases the output voltage ripple and sometimes it even ucc the ucc handling capability of the converter.
UCC 데이터시트(PDF) – Texas Instruments
When the fault clears, the capacitor slowly charges and allows the error amp output COMP to rise. TI recommends separating the signal return path and the high current gate driver path so that the signal is not affected ucc the switching current. As such, the COMP terminal can both source ucc uxc3802 ucc Sinking too much current 1 mA by reducing R T ucc freeze the oscillator OFF by preventing discharge to the lower comparator threshold voltage of 0.