NCP1395D 查看數據表（PDF） - ON Semiconductor

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NCP1395D

High Performance Resonant Mode Controller

ON Semiconductor 

NCP1395A/B

To the contrary, when the internal BO signal is high

(A and B pulse), the IBO source is activated and creates

a hysteresis. The hysteresis level actually depends

on the circuit: NCP1395A features a 28 mA whereas

the NCP1395B uses a 83 mA current. Changes are

implemented to a) reduce the standby power on the

NCP1395A b) improve the noise immunity on the

NCP1395B. Knowing these values, it becomes possible to

select the turn−on and turn−off levels via a few lines of

algebra:

IBO is off

IBO is on

V()) + Vbulk1

Rlower

Rlower ) Rupper

ǒ Ǔ V()) + Vbulk2

Rlower

Rlower ) Rupper

)

IBO

Rlower Rupper

Rlower ) Rupper

(eq. 1)

(eq. 2)

We can now extract Rlower from Equation 1 and plug it

into Equation 2, then solve for Rupper:

Rupper + Rlower

Vbulk1−VBO

VBO

Rlower + VBO

Vbulk1−Vbulk2

IBO (Vbulk1−VBO)

If we decide to turn on our converter for Vbulk1 equals

350 V, and turn it off for Vbulk2 equals 250 V, then we

obtain:

IBO = 28 mA

Rupper = 3.6 MW

Rlower = 10 kW

The bridge power dissipation is 4002/3.601 MW =

45 mW when the front−end PFC stage delivers 400 V.

IBO = 83 mA

Rupper = 1.2 MW

Rlower = 3.4 kW

The bridge power dissipation is 132 mW when the

front−end PFC stage delivers 400 V. Figure 46 simulation

result confirms our calculations.

Latch−Off Protection

There are some situations where the converter shall be

fully turned off and stay latched. This can happen in

presence of an overvoltage (the feedback loop is drifting)

or when an overtemperature is detected. Due to the addition

of a comparator on the BO pin, a simple external circuit can

lift up this pin above VLATCH (5.0 V typical) and

permanently disable pulses. The VCC needs to be cycled

down below 5.0 V typically to reset the controller.

VCC

Vbulk

20 ms

Q1

+ RC

To permanent

−

latch

Vout

+

Vlatch

Rupper

IBO

Vdd

BO

+

BO

−

NTC

Rlower

+

VBO

Figure 47. Adding a comparator on the BO pin offers a way to latch−off the controller.

In Figure 47, Q1 is blocked and does not bother the BO

measurement as long as the NTC and the optocoupler are

not activated. As soon as the secondary optocoupler senses

an OVP condition, or the NTC reacts to a high ambient

temperature, Q1 base is brought to ground and the BO pin

goes up, permanently latching off the controller.

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