AN2316 - Application Note

STEVAL-IHM006V1 Circuit Description

7/24

In order to avoid short-circuiting the mains through switches Z1 and Z2, they must work in a

complementary manner. When Z1 is ON, Z2 must be OFF and vice-versa.

For example, if the line voltage at J1 is positive with respect to J2, and the PWM signal goes

from high-to-low, Z2 switches ON with a delay inserted by its own gate capacitance and by

resistor R3 so the load is energized. In the meantime, Z1 switches OFF instantaneously.

Note:

In this condition, if the current is positive (i.e. it goes into J1 and comes out from J2), it will

flow through D4, Z2, D7, and the load. Conversely, if the current is negative, it will be going

out from J1 and closing through the load, D3, Z2, and D8.

As is the case with the current, when the PWM goes from low-to-high, Z2 is turned OFF

instantaneously, while Z1 is switched ON with a delay. This enables a freewheeling current

to flow through Z1.

Given these relationships, if “

δ” is the duty cycle (see Figure 2 on page 8), the load voltage

is may be expressed as:

Equation 3

where,

The load current may be expressed as:

Equation 4

where,

ϕ = the angle between the current and voltage.

V

()

δ V

()

⋅δ V

MAX

ωt

()

sin

⋅⋅

=

=

I

()

1

δ

--- I

AC

⋅

t

()

1

δ

--- I

MAX

ωt ϕ

+

()

sin

⋅⋅

=

=