NCP1653_09 datasheet(14/19 Pages) ONSEMI

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NCP1653, NCP1653A

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calculation to always be the peak of the sinusoidal voltage

due to very little current consumption (i.e., Vin = √2 Vac and

Ivac ≈ 0). This Ivac current represents the RMS input voltage

Vac and will be used in overpower limitation (OPL) and the

PFC duty modulation.

Figure 37. Input Voltage Sensing

Current

Mirror

12 k

Cvac

Rvac

Ivac

4 V

Vin

9 V

There is an internal 9 V ESD Zener Diode on the pin.

Hence, the value of Rvac is recommended to be at least

938 k

W for possibly up to 400 V instantaneous input voltage.

Rvac

400 V * 9V

12 kW

9V * 4V

(eq.19)

Rvac u 938 kW

Overpower Limitation (OPL)

Sense current IS represents the inductor current IL and

hence represents the input current approximately.

Input−voltage current Ivac represents the RMS input

voltage Vac and hence represents the input voltage. Their

product (IS × Ivac) represents an approximated input power

(IL × Vac).

Figure 38. Overpower Limitation Reduces Vcontrol

ref

reg

300 k

Vcontrol

96% I

Limitation

Overpower

Regulation Block

When the product (IS × Ivac) is greater than a permissible

level 3 nA2, the output Vreg of the regulation block is pulled

to 0 V. It makes Vcontrol to be 0 V indirectly and VM is

pulled to be its maximum. It generates the minimum duty

ratio or no duty ratio eventually so that the input power is

limited. The OPL is automatically deactivated when the

product (IS × Ivac) becomes lower than the 3 nA2 level. This

3 nA2 level corresponds to the approximated input power

(IL × Vac) to be smaller than the particular expression in

(eq.20).

IS Ivac t 3nA2

IL @

RCS

Vac @

Rvac ) 12 kW

t 3nA2

IL @ Vac t

RCS

Rvac ) 12 kW

3nA2

(eq.20)

Biasing the Controller

It is recommended to add a typical 1 nF to 100 nF

decoupling capacitor next to the VCC pin for proper operation.

When the NCP1653 operates in follower boost mode, the PFC

output voltage is not always regulated at a particular level

under all application range of input voltage and load power.

It is not recommended to make a low−voltage bias supply

voltage by adding an auxiliary winding on the PFC boost

inductor. Alternatively, it is recommended to get the VCC

biasing supply from the second−stage power conversion stage

as shown in Figure 39.

Figure 39. Recommended Biasing Scheme in

Follower Boost Mode

Input

Output

EMI

Filter

NCP1653

bulk

Second−stage

Power Converter

Voltage

When the NCP1653 operates in constant output voltage

mode, it is possible to make a low−voltage bias supply by

adding an auxiliary winding on the PFC boost inductor in

Figure 40. In PFC boost circuit, the input is the rectified AC

voltage and it is non−constant versus time that makes the

auxiliary winding voltage also non−constant. Hence, the

configuration in Figure 40 charges the voltages in

capacitors C1 and C2 to n

×(Vout − Vin) and n×Vin and n is

the turn ratio. As a result, the stack of the voltages is n

×Vout

that is constant and can be used as a biasing voltage.

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