RT9591 Просмотр технического описания (PDF) - Richtek Technology

Номер в каталоге

Компоненты Описание

Список матч

RT9591

Smart Photoflash Capacitor Charger with IGBT Driver

Richtek Technology 

RT9591

Preliminary

Spike Voltage @Switching

Spike

voltage

VSW

(10V/Div)

The peak reverse voltage of the diode is approximately:

VPK-R ≈ VOUT + (N x VBAT)

The peak current of the diode equals primary peak current

divide transformer turn ratio as the following equation:

IPK-SEC = IPK-PRI/N

Note: N is transformer turns ratio.

IPRI

(1A/Div)

VSW

(20V/Div)

Time (250ns/Div)

Figure 4

Swing Current @Switching

Swing Current

NMOS

The NMOS is the switching component of the flyback

converter. Select adequate drain to source voltage and

NMOS turn ON drain current is very important. For the

RT9591 typical application circuit,

If VOUT = 300V, VBAT = 6.5V, transformer turn ratio N = 15.

VDS(MIN) = 300/15 + 6.5 = 26.5V.

The NMOS minimum drain to source voltage should be

greater than 26.5V.

In addition, make sure that VDD is higher than VGS(th) (Gate

threshold voltage) so as to sufficiently turn on the

MOSFET.

IPRI

(1A/Div)

Time (1us/Div)

Figure 5

4. Transformer Secondary Capacitance

Any capacitance on the secondary can severely affect the

efficiency. A small secondary capacitance is multiplied by

N2 when reflected to the primary side. This capacitance

forms a resonant circuit with the primary leakage

inductance of the transformer. Therefore, both the primary

leakage inductance and secondary side capacitance

should be minimized.

Capacitor

X5R ceramic capacitor ≥ 10uF/10V is recommended for

input capacitor to well decouple the switching current.

Figure 6 and Figure 7 compare the input current waveforms

with different input capacitors.

Input Average Current & Output Voltage

VBAT = 3.3V

CIN = 4.7uF

Rectifying Diode

The rectifying diode should be with short reverse recovery

time (small parasitic capacitance). Large parasitic

capacitance increases switching loss and lowers charging

efficiency. In addition, the peak reverse voltage and peak

current of the diode should be sufficient.

www.richtek.com

10

Patent Pending

Time (1s/Div)

Figuer 6

DS9591-07 August 2007

Share Link: