 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
CS51221EDR16 Datasheet(PDF) 7 Page - Cherry Semiconductor Corporation |
|
||||||||||||||||||||||||||||||
CS51221EDR16 Datasheet(HTML) 7 Page - Cherry Semiconductor Corporation |
|
|
7 / 12 page  Typical Performance Characteristics 7 Application Information Feed Forward Voltage Mode Control In conventional voltage mode control, the ramp signal has fixed rising and falling slope. The feedback signal is derived solely from the output voltage. Consequently, voltage mode control has inferior line regulation and audio susceptibility. Feed forward voltage mode control derives the ramp sig- nal from the input line, as shown in Fig.1. Therefore, the ramp of the slope varies with the input voltage. At the start of each switch cycle, the capacitor connected to the FF pin is charged through a resistor connected to the input volt- age. Meanwhile, the Gate output is turned on to drive an external power switching device. When the FF pin voltage reaches the error amplifier output VCOMP, the PWM com- parator turns off the Gate, which in turn opens the external switch. Simultaneously, the FF capacitor is quickly dis- charged to 0.3V. Overall, the dynamics of the duty cycle are controlled by both input and output voltages. As illustrated in Fig. 2, with a fixed input voltage the output voltage is regulated solely by the error amplifier. For example, an elevated output voltage reduces VCOMP which in turn causes duty cycle to decrease. However, if the input voltage varies, the slope of the ramp signal will react immediately which pro- vides a much improved line transient response. As an example shown in Fig.3, when the input voltage goes up, the rising edge of the ramp signal increases which reduces duty cycle to counteract the change. Figure 1: Feed Forward Voltage Mode Control. The feed forward feature can also be employed to provide a volt-second clamp, which limits the maximum product of input voltage and turn on time. This clamp is used in circuits, such as Forward and Flyback converter, to prevent the transformer from saturating. Calculations used in the design of the volt-second clamp are presented in the Design Guidelines section. Figure 2: Pulse Width Modulated by Output Current with Constant Input Voltage. Figure 3: Pulse Width modulated by Input Voltage with constant Output Current. Powering the IC & UVL The Under Voltage Lockout (UVL) comparator has two voltage references; the start and stop thresholds. During power-up, the UVL comparator disables VREF (which in- turn disables the entire IC) until the controller reaches its VCC start threshold. During power-down, the UVL com- parator allows the controller to operate until the VCC stop threshold is reached. The CS51221 requires only 50µA dur- ing startup. The output stage is held at a low impedance state in lock out mode. During power up and fault conditions, the soft-start clamps the Comp pin voltage and limits the duty cycle. The power up transition tends to generate temporary duty cycles much greater than the steady state value due to the low output voltage. Consequently, excessive current stresses often take place in the system. Soft Start technique alleviates this problem by gradually releasing the clamp on the duty cycle to eliminate the in-rush current. The dura- tion of the Soft Start can be programmed through a capaci- tance connected to the SS pin. The constant charging cur- rent to the SS pin is 50µA (typ). VIN VCOMP FF RTCT GATE IOUT VOUT VCOMP FF VIN RTCT GATE VIN COMP FF FB VOUT Error Amplifier C R Latch & Driver PWM Feedback Network Power Stage GATE Theory of Operation |
Similar Part No. - CS51221EDR16 |
|
Similar Description - CS51221EDR16 |
|
|
|
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 |
English ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
