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UC2843A: TL494IDR UC2843AD8TR

Rogers Chen
Intellectual 825 points
Part Number: UC2843A
Other Parts Discussed in Thread: UC3845, UC3843, UC3842, UC3844, TL494

Dear TI experts,

The following are the circuits on our new product, please help to review whether there is any problem with the design, thanks!

  

  • 0
    TI__Expert 7900 points

    Hello Rogers,

    Comments on the '3843 circuit:

    1) Current mode control typically requires Type-II compensation.  This circuit simply has a capacitor from COMP to ground (Type-I).  Type-I compensation will have significant lag and usually overshoot and undershoot before settling.

    2) You must populate the RCD snubber (R51, R52, C28) or Q10 will be destroyed.  It presently shows NC for these components.

    3) You must populate the current sense filter capacitor, C5.  It presently shows NC.  I recommend starting with 47pF to 100pF.

    4) I recommend having the option to increase the VCC capacitor, C24, 10uF.  This capacitor must maintain the VCC voltage above UVLO OFF, 7.6V, during startup.  If this capacitor is too small the regulator will not achieve regulation and will cycle on (at VCC=8.4V) and off (at VCC=7.6V).

    5) Do you require >50% duty cycle operation?  If not, change to UC3845 and remove the slope compensation transistor, Q11/R23.

    6) The UC3843 starts at fairly low voltages (VCC=8.4/7.6V) and has minimal hysteresis.  Do you need these low voltages?  If not, consider changing to UC3842 (100% duty cycle) or UC3844 (50% duty cycle) to have a larger ON/OFF hysteresis (16V/10V).

    Comment  on the TL494 circuit:

    It's difficult to determine exactly what this circuit does.  Have you provided enough of the schematic?  Where does CE_FB1 and LIMITER_VCC_1 come from?

    Regards,

    Eric