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UC2823A Duty Cycle

Joe Young1
Prodigy 20 points
Other Parts Discussed in Thread: UC2823A

Hello,

The datasheet for the UC2823A part says that it can go up to less than 100% DC (first table on page 2, and figure 3 on page 6), but in the characteristics table it say the max DC is 85%. Could someone explain why there is a 85% limit listed?


Thanks

  • 0
    Genius 3295 points

    Hello Joe,

    The 85% maximum duty cycle is based on the environmental and electrical conditions printed just below the title ELECTRICAL CHARACTERISTICS. There you will see the ambient temperature spec shown as TA = -55C to 125C and so forth. Notice that the timing resistance is set to 3.65K and the timing capacitance is set to 1 nF for all the specifications listed in the table. If you look in Figure 3 on page 6, you will see the "typical value" for the duty cycle with a timing resistance of 3.65K is approximately 92%. So the minimum guaranteed maximum duty cycle is 85%. I would use this value to determine my turns ratio on the transformer.

    Hope this helps,

    Chuck Sampson