Ballast design

AN3032

10/26

Doc ID 16165 Rev 2

The voltage on the multiplier pin with the selected component values is recalculated at a

minimum line voltage of 0.77 V and at a maximum line voltage of 2.41 V.

As a result, the multiplier operates correctly within its linear region. To obtain noise immunity,

●

Pin9 COMP is the output of the E/A and also one of the two inputs of the multiplier. The

feedback compensation network, placed between this pin and INV (10), is a

the voltage divider between the PFC bus and the COMP pin).

Equation 9

●

Pin10 INV: to implement the voltage control loop, a resistive divider (Figure 6) must be

Equation 10

●

Pin11 ZCD is the input to the zero current detector circuit. The ZCD pin is connected to

the auxiliary winding of the boost inductor through a limiting resistor. The ZCD circuit is

negative-going, edge-triggered: when the voltage on the pin falls below 0.7 V, the PWM

latch is set and the MOSFET is turned on. However, the circuit must first be armed:

prior to falling below 0.7 V, the voltage on pin 11 must experience a positive-going,

edge-exceeding 1.4 V (due to the MOSFET switching off). The maximum main-to-

auxiliary winding turn ratio (m) has to ensure that the voltage delivered to the pin during

the MOSFET's OFF time is sufficient to arm the ZCD circuit.

Equation 11

m has been set to 10.

Considering the upper and lower clamp voltages of the ZCD pin and its minimum sink

current capability according to the maximum and minimum voltages of the PFC bus,

()

nF

530

R

R

2

10

C

11

6

2

=

+

⋅

π

⋅

=

1

5

.

2

V

R

R

R

BUSpfc

18

11

6

−

=

+

Ω

=

+

M

3

R

R

11

6

10

.

33

4

.

1

V

2

V

m

(max)

inRMS

BUSpfc

=

⋅

−

≤