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AN701

Designing High-Frequency DC-to-DC Converters With the Si9114A Switchmode Controller

Vishay Semiconductors 

AN701

Vishay Siliconix

Integrated high-voltage start circuit:

the depletion transistor circuit allows fast turn-on and

eliminates the need for extra components. At lower

frequencies and power levels, it is possible to omit the bias

winding completely, since circuit consumption is low, and the

depletion circuit behaves as a linear regulator.

Synchronization in phase and frequency:

is a necessary benefit for distributed power systems where

multiple converters are operated.

CONCLUSIONS

Operation at 500 kHz is possible using BiC/DMOS PWM

control circuits. Significant power savings are possible,

yielding high efficiencies and lower parts count due to the

integrated high-voltage start circuitry. Operation at high

frequencies allows the use of small, efficient, low-profile

energy storage components, with higher reliability and

calculated MTBFs. Surface mounted power MOSFETs are

easily assembled using conventional assembly techniques.

REFERENCES

1. Murakami, Noaki and Yamasaki, Mikio. “Analysis of a

Resonant Rest Condition for a Single Ended Forward

Converter.” PESC88 Record (April 1988) CH

2523-9/88/0000-1018 $1.00 1988 IEEE.

2. Chryssis, George C. High Frequency Switching Power

Supplies: Theory and Design. 2nd. ed. New York: McGraw Hill.

3. “Designing DC/DC converters with the Si9110 Switched

Controller.” AN703. Vishay Siliconix Power Integrated Circuits

Data Book, 1999.

4. “Efficient ISDN Power Converters Using the Si9100.”

AN702. Vishay Siliconix Power Integrated Circuits Data Book,

1999.

1 The strange shape of the ripple needs to be further analyzed but could be explained as follows:

S The step voltage that appears at the same time as the voltage switching edges is caused entirely by the ESR, as it is the only possible cause

for a rapid step voltage across a capacitor. In this case, the measured value is on the order of 8 mV, thus predicting an ESR value of 6/0.3 = 20 mW

for both devices. This is slightly higher than predicted, but of the same order of magnitude.

S The sinusoidal waveform must be caused by the equivalent capacitance that appears across the inductor, causing a capacitive coupling directly

into the output.

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Document Number: 70575

16-Jan-01

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