Motore di ricerca datesheet componenti elettronici |
|
LM3404 Scheda tecnica(PDF) 2 Page - National Semiconductor (TI) |
|
|
LM3404 Scheda tecnica(HTML) 2 Page - National Semiconductor (TI) |
2 / 4 page isolation and/or power factor correction, the LM3402 or LM3404 buck regulator could be paired with an existing AC- DC regulator to provide the 24V, resulting in a high-quality universal current source. 30064502 FIGURE 2. Ripple Current vs. Output Voltage 30064503 FIGURE 3. Switching Frequency vs. Output Voltage Design Procedure Designing for constant ripple in a COT converter requires a change in the selection of the on-time setting resistor R ON: 1. Start with the typical input voltage, V IN-TYP, and an output voltage that is at the center between the minimum and maximum expected value, V O-CTR. Use the maximum permissible switching frequency, f SW-MAX, and the desired peak-to-peak inductor ripple current, ΔiL. The required inductance is then: 2. Select the closest standard inductor value to L and call it L STD. RON can then be calculated with the following expression: 3. Use the closest 1% resistor value for R ON. 4. Design for the remaining components (input capacitor, Schottky diode, etc.) remains the same, and is outlined in the LM3402 and LM3404 datasheets. Switching Frequency Changes When using the LM3402 and LM3404 buck regulators in the constant-ripple configuration, the switching frequency will change with V IN and VO. Careful attention to PCB layout and proper filtering must be employed will all switching converters, and particular care is needed for systems where f SW changes. The following steps can be used to predict the switching fre- quency: 1. Calculate the on-time at the minimum and maximum values of V IN and VO using the actual 1% resistor value of R ON and the following equation: 2. The switching frequency can then be determined using t ON and the following expression: Conclusion A pure DC LED drive current would be ideal for LEDs, but in practice the majority of LED lighting is powered from the AC mains and includes at least one switching regulator between the wall and the LEDs. Even battery or solar-powered sys- tems are likely to employ a switching regulator in the interest of power efficiency. Therefore, some amount of ripple current will be present in almost every LED driver design. Allowing higher ripple current reduces the size and cost of the drive circuit, but comes at the expense of light output and reliability. Armed with the ability to control both LED ripple current and switching frequency, the LED lighting designer can make his/ her own trade-offs between solution size, cost, and quality based on the needs of the application. www.national.com 2 |
Codice articolo simile - LM3404 |
|
Descrizione simile - LM3404 |
|
|
Link URL |
Privacy Policy |
ALLDATASHEETIT.COM |
Lei ha avuto il aiuto da alldatasheet? [ DONATE ] |
Di alldatasheet | Richest di pubblicita | contatti | Privacy Policy | scambio Link | Ricerca produttore 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 |