Electronic Components Datasheet Search |
|
NCP1217AD65R2G Datasheet(PDF) 9 Page - ON Semiconductor |
|
NCP1217AD65R2G Datasheet(HTML) 9 Page - ON Semiconductor |
9 / 19 page NCP1217, NCP1217A www.onsemi.com 9 Startup Sequence When the power supply is first powered from the mains outlet, the internal current source (typically 7.0 mA) is biased and charges up the VCC capacitor. When the voltage on this VCC capacitor reaches the VCCON level (typically 12.8 V), the current source turns off and no longer wastes any power. At this time, the VCC capacitor only supplies the controller and the auxiliary supply is supposed to take over before VCC collapses below VCCmin. Figure 16 shows the internal arrangement of this structure. Figure 16. The Current Source Brings VCC Above 12.8 V and then Turns Off - + 8 6 4 6 mA or 0 CVCC Aux HV 12.8 V/5.6 V Once the power supply has started, the VCC shall be constrained below 16 V, which is the maximum rating on Pin 6. Figure 17 portrays a typical startup sequence with a VCC regulated at 12.5 V. Figure 17. A Typical Startup Sequence for the NCP1217 t, TIME (sec) 3.00 M 8.00 M 13.0 M 18.0 M 23.0 M 13.5 12.5 11.5 10.5 9.5 REGULATION 12.8 V Overload Operation In applications where the output current is purposely not controlled (e.g. wall adapters delivering raw DC level), it is interesting to implement a true short−circuit protection. A short−circuit actually forces the output voltage to be at a low level, preventing a bias current to circulate in the optocoupler LED. As a result, the auxiliary voltage also decreases because it also operates in Flyback and thus duplicates the output voltage, providing the leakage inductance between windings is kept low. To account for this situation and properly protect the power supply, NCP1217 hosts a dedicated overload detection circuitry. Once activated, this circuitry imposes to deliver pulses in a burst manner with a low duty−cycle. The system auto−recovers when the fault condition disappears. During the startup phase, the peak current is pushed to the maximum until the output voltage reaches its target and the feedback loop takes over. The auxiliary voltage takes place after a few switching cycles and self−supplies the IC. In presence of a short circuit on the output, the auxiliary voltage will go down until it crosses the undervoltage lockout level of typically 7.6 V. When this happens, NCP1217 immediately stops the switching pulses and unbiases all unnecessary logical blocks. The overall consumption drops, while keeping the gate grounded, and the VCC slowly falls down. As soon as VCC reaches typically 5.6 V, the startup source turns−on again and a new startup sequence occurs, bringing VCC toward 12.8 V as an attempt to restart. If the default has gone, then the power supply normally restarts. If not, a new protective burst is initiated, shielding the SMPS from any runaway. Figure 18 portrays the typical operating signals in short circuit. |
Similar Part No. - NCP1217AD65R2G |
|
Similar Description - NCP1217AD65R2G |
|
|
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 |