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UC3845 REFERENCE DESIGN

Dhinesh Kumar1
Prodigy 100 points
Other Parts Discussed in Thread: UC3845, LM5023, UCC28050

Hi;

I am looking for reference design for the following spec

1. 12V -2A

2. 12V 5A / 24V 2A

3. 12V 10A / 24V 5A

If there is any software tool kindly provide us.i want to design it with uc3845, because its cost effective and used widely in may smps and charges for may years.

  • 0
    Genius 3295 points

    Hello Dhinesh,

    Are the output specs you list for the same converter? Are these specs for three converters? Do you want universal input and/or PFC?

    Chuck Sampson

  • 0 in reply to Chuck Sampson
    Prodigy 100 points

    Hi;

    The specifications are for different models, Universal input is ok. PFC is required for 5A and 10A model.

  • 0
    Prodigy 70 points
    You can rework the ucc2845 for a working macromodel of uc3845.
    I was getting large negative spike from direct Ct to gnd. changing / adding Dschg through 300 ohms then gnd switch solved that.
    reference: "Modular macromodeling techniques for SPICE simulators".

    I also set the conditional tests to 2.5Vdc digital turn on. Snippet of reworked macromodel:
    *$
    ****OSCILLATOR*****
    STOF1 8 GND DISCH GND SOSC * <-add / change RtCt to Disch
    *.....P...N...CP..CN
    GBDISCH RTCT GND Value = { IF ( V(8,GND) < 2.5 & V(13,GND) > 2.5, 8.4M, 0 ) }
    RPULLUP 8 VREF 100K
    RPULLDN RTCT DISCH 300 * <-add / change 300 ohm resistor in Ct discharge path to gnd
    *$
  • 0 in reply to Robert Lavender
    Prodigy 70 points

    ah, the actual problem revealed itself. it was the revision/rework to other spice system(s) and the specific requirement to set GND to zero, otherwise GND would be floating ground. bipolar and the resulting negative spiking.

    Vgnd GND 0 DC 0V

    declared as both the global variable and declared within .subckt(s). an alternative is passing GND within ,subckt call parameters.

  • 0 in reply to Robert Lavender
    Prodigy 70 points

    further experiments with TABLU / table + u-step methodology lend to more control/shaping options, with the oscillator. some testing is required but adjusting the Params:  lends to more control and possibly automated shaping of the oscillator ramp.

    ****OSCILLATOR************************************************************
    * net 80 connects OSC output to OSC_LATCH_S input
    *.....P..N..CP..CN
    Stof 80 GND RMP1 GND VSWCH
    *............OUT..GND..............IN
    Gtablu_osc_Q RMP1 GND TABLE { U( V(80, GND)-0.5V) } = ( +0.5V, 8.4Mho) ( +0.9V, 0V )
    * + Params: VinMin VoutMin VinMax VoutMax
    *
    Rpullup VREF 80 10K
    *

  • 0 in reply to Dhinesh Kumar1
    TI__Expert 7395 points
    Dhinesh,
    Thanks for your interest in TI. There is a PSpice model and Webench model for this device: www.ti.com/.../toolssoftware. I'll look around for some reference designs for those requirements.
    Regards,
    John
  • 0 in reply to John Stevens
    TI__Expert 7395 points
    Dhinesh,
    Have you searched for reference designs at ti.com/powerlab
    I found this one for example for 12V/2A: www.ti.com/.../PMP7883
    I suggest to use LM5023 has main flyback controller for all these designs so you can get familiar with 1 controller. Then just use UCC28050 for PFC 1st stage when needed.
    Regards,
    John