Electronic Components Datasheet Search |
|
UCC3817DWTR Datasheet(PDF) 9 Page - Texas Instruments |
|
|
UCC3817DWTR Datasheet(HTML) 9 Page - Texas Instruments |
9 / 31 page UCC2817, UCC2818, UCC3817, UCC3818 BiCMOS POWER FACTOR PREREGULATOR SLUS395J - FEBRUARY 2000 - REVISED MARCH 2009 9 www.ti.com APPLICATION INFORMATION Conduction loss is calculated as the product of the RDS(on) of the switch (at the worst case junction temperature) and the square of RMS current: P COND + R DS(on) K I2 RMS where K is the temperature factor found in the manufacturer’s RDS(on) vs. junction temperature curves. Calculating these losses and plotting against frequency gives a curve that enables the designer to determine either which manufacturer’s device has the best performance at the desired switching frequency, or which switching frequency has the least total loss for a particular power switch. For this design example an IRFP450 HEXFET from International Rectifier was chosen because of its low RDS(on) and its VDSS rating. The IRFP450’s RDS(on) of 0.4 Ω and the maximum VDSS of 500 V made it an ideal choice. An excellent review of this procedure can be found in the Unitrode Power Supply Design Seminar SEM1200, Topic 6, Design Review: 140 W, [Multiple Output High Density DC/DC Converter]. softstart The softstart circuitry is used to prevent overshoot of the output voltage during start up. This is accomplished by bringing up the voltage amplifier’s output (VVAOUT) slowly which allows for the PWM duty cycle to increase slowly. Please use the following equation to select a capacitor for the softstart pin. In this example tDELAY is equal to 7.5 ms, which would yield a CSS of 10 nF. C SS + 10 mA t DELAY 7.5 V In an open-loop test circuit, shorting the softstart pin to ground does not ensure 0% duty cycle. This is due to the current amplifiers input offset voltage, which could force the current amplifier output high or low depending on the polarity of the offset voltage. However, in the typical application there is sufficient amount of inrush and bias current to overcome the current amplifier’s offset voltage. multiplier The output of the multiplier of the UCC3817 is a signal representing the desired input line current. It is an input to the current amplifier, which programs the current loop to control the input current to give high power factor operation. As such, the proper functioning of the multiplier is key to the success of the design. The inputs to the multiplier are VAOUT, the voltage amplifier error signal, IIAC, a representation of the input rectified ac line voltage, and an input voltage feedforward signal, VVFF. The output of the multiplier, IMOUT, can be expressed as: I MOUT + I IAC V VAOUT * 1 K V VFF 2 where K is a constant typically equal to 1 V . The electrical characteristics table covers all the required operating conditions for designing with the multiplier. Additionally, curves in figures 10, 11, and 12 provide typical multiplier characteristics over its entire operating range. |
Similar Part No. - UCC3817DWTR |
|
Similar Description - UCC3817DWTR |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.COM |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |