The LM358 configured as an integrator introduces a gain given by Rs , a pole in Gint(s) and a zero in

Z(s) :

Vfb= ( Rs / s

Assuming :

Gint

1

s

and :

H(s) = (1 + s

⋅ Rint ⋅ Cint)

the current control loop block diagram can be considered as shown in Figure 20.

The complete block diagram of the current sharing loop is shown is figure 21.

The open loop function of the current loop is given by :

F(s) := GpwmZint(s)

⋅ Gfil(s) ⋅ A(s)

In figures 22 and 23 are shown the open loop Gain and Phase Bode plot . The capacitor C5 does not

influence the system stability but is useful only to reduce the noise. The cut off frequency and a phase

margin are: Fc = 8KHz; Angle = 40°

Current

Feedback

I-

A(s)

Compensated

E/A

PWM

Gain

Gfilt(s)

Output

Filter

I+

Gint(s)

Current

integrator

Vfb

H(s)

G(s) ( Compensated E/A, PWMGain, Output Filter )

Figure 20. Block diagram of the current loop

1/Rload

G(s)

( Compensated E/A,

PWMGain,

Output Filter )

Vref

Vfb

∆ V

Av

Vout

U1 section (Voltage Loop )

Gint(s)

I+

H(s)

∆ I

-

Iout

I+

I-

-

U2 section ( Current Loop )

G(s)

( Compensated E/A,

PWMGain,

Output Filter )

Figure 21. Complete block diagram of the current sharing loop

AN1126 APPLICATION NOTE

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