NCP1397A データシートの表示（PDF） - ON Semiconductor

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NCP1397A

High Performance Resonant Mode Controller with Integrated High-Voltage Drivers

ON Semiconductor 

NCP1397A, NCP1397B

450 16.0

351 V

350 12.0

Vin

250 8.0

250 V

150 4.0

50

0

BO

20 m

60 m

100 m

140 m

180 m

time in seconds

Figure 41. Simulation Results for 350 / 250 ON / OFF Levels

To the contrary, when the internal BO signal is high

(Mlower and Mupper pulse), the IBO source is activated and

creates a hysteresis. As a result, it becomes possible to select

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

IBO is off

V()) + Vbulk1

Rlower

Rlower ) Rupper

(eq. 1)

IBO is on

V()) + Vbulk2

) IBO

Rlower

Rlower ) Rupper

ǒ Ǔ Rlower Rupper

Rlower ) Rupper

(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

Rlowerer + VBO

Vbulk1 * Vbulk2

IBO ǒVbulk1 * VBOǓ

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:

Rupper = 3.57 MW

Rlower = 10.64 kW

The bridge power dissipation is 4002 / 3.781 MW =

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

Figure 41 simulation result confirms our calculations.

Latchoff 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 over temperature is detected. Thanks to the addition

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

lift up this pin above Vlatch (4 V typical) and permanently

disable pulses. The VCC needs to be cycled down below

6.5 V typically to reset the controller.

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