110

9.2W

= 5.4

2450

+220V

+12V

R1

INPUT

R2

220:

L1

D1

D2

CATHODE

C2

C1

C3

1/2W

6.8 PH

510:

OBSOLETE

15A§LM2450

www.ti.com

SNOSAN6D – SEPTEMBER 2005 – REVISED APRIL 2013

R2 would be desirable, but this has the effect of increasing rise and fall times. Inductor L1 is critical to reduce the

initial high frequency voltage levels that the LM2450 would be subjected to before the clamp diodes have a

chance to became activated. The inductor will not only help protect the device but it will also help minimize rise

and fall times as well as minimize EMI. For proper arc protection, it is important to not omit any of the arc

protection components shown in Figure 13.

Figure 13. One Channel of the LM2450 with the Recommended Application Circuit

EFFECT OF LOAD CAPACITANCE

Figure 7 shows the effect of increased load capacitance on the speed of the device. Increasing the load

capacitance from 10 pF to 20 pF will first speed up the rise time by about 5 ns, then the rise time slows down by

about 3 ns as the capactor values come closer to 20 pF. The change of capacitor values has little affect on the

fall time. Note that the power consumption of the driver will significantly increase with the larger capacitance.

EFFECT OF OFFSET

Figure 8 shows the variation in rise and fall times when the black level of the device is varied from 180V to

decreases by about 5 ns with the same offset adjustment.

THERMAL CONSIDERATIONS

Figure 9 shows the performance of the LM2450 in the test circuit shown in Figure 3 as a function of case

temperature. The figure shows that the rise and fall times of the LM2450 increase by about 3 ns as the case

temperature increases from 30°C to 110°C. Over the same case temperature range the fall time increased by

about 9 ns.

Figure 10 shows the maximum power dissipation of the LM2450 vs. Frequency when all three channels of the

given in Figure 10 is half of the pixel frequency. The graph assumes an 80% active time (device operating at the

specified frequency), which is typical in a TV application. The other 20% of the time the device is assumed to be

sitting at the black level (190V in this case). A TV picture will not have frequency content over the whole picture

exceeding 15 MHz. It is important to establish the worst case condition under normal viewing to give a realistic

worst-case power dissipation for the LM2450. One test is a 1 to 30 MHz sine wave sweep over the active line.

This would give a slightly lower power than taking the average of the power between 1 and 30 MHz. This

average is 9.4 W. A sine wave will dissipate slightly less power, probably about 9.2 W of power dissipation. All of

this information is critical for the designer to establish the heat sink requirement for his application. The designer

should note that if the load capacitance is increased the AC component of the total power dissipation will also

increase.

The LM2450 case temperature must be maintained below 110°C given the maximum power dissipation estimate

of 9.2 W. If the maximum expected ambient temperature is 60 °C and the maximum power dissipation is 9.2 W

then a maximum heat sink thermal resistance can be calculated:

(1)

This example assumes a capacitive load of 10 pF and no resistive load. The designer should note that if the load

capacitance is increased the AC component of the total power dissipation will also increase.

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