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UC2854B: CT pin Max voltage

Steve Widener
Genius 9575 points
Part Number: UC2854B
Other Parts Discussed in Thread: UCC2818

What is the ABS max voltage allowed on the CT pin (for cases where there is an external sync pulse injection)

  • 0
    TI__Mastermind 34465 points

    Hello Steve,

    The CT voltage has an operating range up to 5.9V and the internal bias power to the UC2854B is 7.5V
    The actual ABS max voltage for CT is not specified in the data sheet and I cannot give you a definitive figure for this parameter since it is not measured.
    However it is reasonable to assume that any voltage higher than 5.9V on CT will damage the oscillator.

    That is about as much information that is available and hopefully it is of use to your application.

    Regards

    John

  • 0 in reply to John Griffin1
    TI__Genius 9575 points

    Thanks John.

    Do you have guidance on how to synchronize the devices switching frequency (such as ~ 300kHz)

    I did see the schematic here showing a SYNC input but it is not clear what the characteristics of that signal should be...

    https://www.ti.com/lit/an/slua177a/slua177a.pdf 

    Is there a circuit you are aware of that could take 5V logic (or perhaps 12V logic) and synchronize the operation of the UC2854B?

  • 0 in reply to Steve Widener
    TI__Mastermind 34465 points

    Hi Steve,

    The UC2854B has an oscilllator similiar to the UCC2818 and it can be synchronised as in this configuration:

    This drawing shows the pfc being sync'd to a downstream pwm. In your design you will probably  not require C1,D1 and D2 .

    The free running frequency is et at 10% lower than the sync frequency and a narrow pulse from the external oscillator will synchronise the pfc to the external  frequency source. I do not have the circuit for an external digital logic type oscillator source.

    Regards

    John

  • 0 in reply to John Griffin1
    TI__Mastermind 34465 points

    Since there has been no response to my most recent response for over 15 days now I assume you have made some progress on this issue. I am going to close this post, please open a new post if you have more questions