Diodes AP8800A Manuel d'utilisateur télécharger pdf (Page 7)

AP8800A

Document number: DS35100 Rev. 3 - 2

7 of 13

www.diodes.com

August 2012

P8800A

Application Information (cont.) (@T

= +25°C, V

= 12V, unless otherwise specified.)

Inductor Selection

A 68μH inductor or higher, is recommended for most AP8800A applications with input voltage at 12V.

Figure 3 displays the resulting switching frequency with various main circuit parameters: Supply voltage, Inductor value and number of LEDs to

be driven.

Switching Frequency

100

470

100

150

470

150

220

100

200

300

400

500

600

700

0 50 100 150 200 250 300 350 400 450 500

Inductor Value [uH]

Frequency [kHz]

12V - 1LED

24V - 3 LEDs

28V - 4LEDs

Figure 3 Switching Frequency vs. Supply Voltage, Inductor, and Number of LEDs

Capacitor Selection

A low ESR capacitor should be used for input decoupling, as the ESR of this capacitor appears in series with the supply source impedance and

lowers overall efficiency. This capacitor has to supply the relatively high peak current to the coil and smooth the current ripple on the input

supply. A minimum value of 1μF is acceptable if the DC input source is close to the device, but higher values will improve performance at lower

input voltages, especially when the source impedance is high. The input capacitor should be placed as close as possible to the IC.

For AC input sources a bigger capacitor ( 300uF in the case of 12C AC) to guarantee the accuracy of the LED current.

For maximum stability over temperature and voltage, capacitors with X7R, X5R, or better dielectric are recommended.

Capacitors with Y5V dielectric are not suitable for decoupling in this application and should NOT be used.

Diode Selection

For maximum efficiency and performance, the rectifier (D1) should be a fast low capacitance SBR diode with low reverse leakage at the

maximum operating voltage and temperature. The recommended diode for use with this part is the SBR1A40, with a current rating above the

peak coil current and a continuous current rating higher than the maximum output load current. It is very important to consider the reverse

leakage of the diode when operating above 85°C. Excess leakage will increase the power dissipation in the device.

1 2 3 4 5 6 7 8 9 10 11 12 13

Commentaires sur ces manuels

Pas de commentaire

Diodes AP8800A Manuel d'utilisateur Page 7

Commentaires sur ces manuels

Produits connexes et manuels pour Matériel Diodes AP8800A