Rev. C 05/15

4

SEN012-013

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Application Example

SENZero in PFC Bus Voltage Feedback Network

Commercial PFC IC’s typically has a pin dedicated for sensing the

output voltage of the PFC Stage. The information on this pin is

typically used by the PFC IC for various major functions.

1. Output regulation – input to the non-inverting input of the error

amplifier.

2. OVP detection – input to the OVP comparator.

3. Open-loop protection – used to detect open-loop conditions.

The last 2 functions were used for protecting the bus from overvolt-

age condition.

Figure 11. PFC Bus Voltage Sense Network.

The SENZero objective is to eliminate the losses associated with the

sense resistors without affecting the functionality of the circuit. To

keep the operation of the PFC IC unaffected, SENZero and PFC on

and off event must follow the required timing sequence during power-

up, power-down, remote-on, and remote-off event.

PI-6203-102510

Error Amplifier

OLP

R1

R2

R3

RFB

CBULK

PFC VOUT

OVP

FB

PFC IC

SENZero

Switch

ON

ON

OFF

OFF

OFF

OFF

VCC

SENZero

PFC

PI-6205-102510

ON

ON

ON

OFF

OFF

OFF

OFF

OFF

OFF

PS(ON)

SENZero

PFC

PI-6206-102510

Figure 12. Timing between PFC IC and SENZero during Power-Up and

Power-Down.

In case of shared VCC Connection, it must be ensure that SENZero

have a lower turn-on and turn-off threshold voltage compared to the

PFC IC.

Figure 13. Timing between PFC IC and SENZero with PS

(ON) Signal.

From off-state to on-state, SENZero must turn-on ahead of the PFC.

From on-state to off-state, PFC must shutdown ahead of the

SENZero. This is to ensure that whenever PFC is operating (switch-

ing), SENZero is invincible to the PFC. SENZero only disconnects the

sense resistors when PFC is in off-condition and thus eliminates its

associated losses during standby condition.