FA5502P 데이터 시트보기 (PDF) - Fuji Electric

부품명

상세내역

제조사

FA5502P

Power Supply Control IC

Fuji Electric 

FA5502P/M

(3) Designing a boost converter

Fig.19 shows a basic circuit of boost converter used

as an PFC converter. The following describes how to

determine each values of the circuit.

L

D

Vin

Q

Co

Vo

Rs

Fig.19 Boost converter circuit

(3-1) Output voltage

Set the output voltage of boost converter at least

10V higher than the peak value of maximum input

voltage to ensure a stable operation. When it is used

as PFC converter, the input voltage has a sinusoidal

waveform. Therefore, set the output voltage Vo by:

Vo ≥ 2 × Vin(max) + 10 [V]

• • (12)

Vin(max) : Maximu AC input voltage [Vrms]

(3-2) Inductor

When PFC converter operates in the continuous

current mode, select an approximate inductance

considering the ratio of inductor ripple current to the

peak input current by:

( ) L

≥

Vin2 Vo − 2 × Vin

γ × fs × Pin × Vo

• • • • • (13)

Where,

Vin: AC input voltage [Vrms]

γ: Ratio of ripple content to peak input current.

(Set to approx. 0.2, see Fig.20)

fs: Switching frequency [Hz]

Pin: Maximum input power [W]

Inductor current γ = Ir / Iac(peak)

Ir

Iac(peak)

line current

Quality is our message

So that the voltage inputted to IDET pin will not be

beyond -1V, whereby the overcurrent limiting circuit

will not operate at a normal operation, calculate Rs by:

RS ≤

Vin(min) [Ω] • • • • • (15)

2 × Pin(max)

Where,

Vin (min): Minimum AC input voltage [Vrms]

Pin (max): Maximum input position [W]

As a matter of fact, the peak current changes with

switching ripple current contained in the inductor

current, circuit efficiency, etc. Definitely determine it by

evaluation on a actual circuit.

(3-4) Smoothing capacitor

PFC converter output contains ripple voltage of

twice the line frequency as shown in Fig.21.

Instantaneous value Vo(t) of output voltage is

approximated by:

Vo(t)

=

Vo

−

Io

2ω0 ×

Co

×

sin(2ω0

×

t)

• • • • • (16)

Where,

Io: Output current [A]

ω0 = 2πf0 (f0: AC line frequency [Hz])

Co: Output smoothing capacitance [F]

Therefore, output ripple voltage Vrp (p-p) is:

Vrp

=

Io

ω0 × Co

• • • • • (17)

Using formula (17), determine the necessary value.

The overvoltage limiting circuit of FA5502 monitors the

instantaneous output voltage. Therefore, determine

the capacitance of smoothing capacitor Co so that the

instantaneous output voltage including the ripple at a

normal operation will not reach the overvoltage limit.

Vrp

Vo

2xfac

Fig.21 Output ripple voltage

t

Fig.20 Outline of inductor and AC line current

(3-3) Current detecting resistance Rs

Rs is a resistor which allows to detect an inductor

current to control the line current into sinusoidal.

Because the threshold voltage for overcurrent limiting

circuit is -1.1V (typ.), peak inductor current limit Ip is

calculated by:

Ip

=

1.1

RS

[A]

• • • • • (14)

19

Share Link: