Ballast design

AN3040

10/27

Doc ID 16181 Rev 2

Supposing there is a 240 µA current flowing into the divider, the value of the lower resistor

Equation 8

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

minimum line voltage of 0.59 V and at maximum line voltage of 1.85 V. As a result, the

multiplier operates correctly within its linear region.

●

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

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

Equation 9

●

Pin10 INV: to implement the voltage control loop, a resistive divider (Figure 4) must be

Equation 10

●

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

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.

Ω

=

+

⇒

Ω

=

⋅

ε

ε

−

=

+

Ω

=

⇒

Ω

=

μ

=

M

5

.

1

R

R

M

52

.

1

R

1

R

R

k

5

.

7

R

k

79

.

7

A

240

V

R

9

5

17

9

5

17

max

MULT

17

()

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

=

⋅

−

≤