UC2845: forward controller schematic review

Fred Cheng

Expert 5910 points

Part Number: UC2845

Hi team,

please help review the schematic,

let me know if anything I have to upload

UC2845_0531 (002).pdf

over 3 years ago

0 Teng Feng over 3 years ago

TI__Genius 13660 points

Hi Fred,

R1502 should be between 5 kΩ and 100 kΩ; I suggest R1505 short to GND_CTRL.

Regards,

Teng

0 Fred Cheng over 3 years ago in reply to Teng Feng

TI__Expert 5910 points

Hi Teng,

May I know the reason?

especially why would happen if we don't short R1505

Regards,

Fred

0 Fred Cheng over 3 years ago in reply to Fred Cheng

TI__Expert 5910 points

any update?

customer is urgent

0 Teng Feng over 3 years ago in reply to Fred Cheng

TI__Genius 13660 points

Hi Fred,

R1505 parallels between GND_CTRL and Pin4 of Q1501, to prevent from PWM output signal affect the current sense.

0 Fred Cheng over 3 years ago in reply to Teng Feng

TI__Expert 5910 points

Hi Feng,

thanks for your answer, so it's a bleed resistor, right?

BTW, if we increase R1502 above 5Kohm, does this mean we have to decrease Cct cap to keep the same frequency?

Regards,

Fred

0 Teng Feng over 3 years ago in reply to Fred Cheng

TI__Genius 13660 points

Hi Fred,

Yes you are right. it should increase Cct to get the same frequency.

The recommended range of timing resistor values is between 5 kΩ and 100 kΩ; the recommended range of timing capacitor values is between 1 nF and 100 nF.

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UC2845: forward controller schematic review