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# UC1844A / Off-Line Flyback Regulator

Other Parts Discussed in Thread: UC1844A, UC1845A, UC2845A

Hi Team,

I would like to ask 2 questions about "Off-Line Flyback Regulator" in datasheet page.8.

1)
Is it possible to operate if 9.5V DC is supplied instead of 117V AC?
My customer also assumes +12V is loaded from the following point (between D2 and D3).

2)
If the answer of 1) is yes, how should I decide the value of R2?

Best Regards,
Yaita / Japan disty

• The UC1844A has a UVLO(ON) of 16V and a UVLO(OFF) of 10V so it will not work in this application.

The UC1845A has a UVLO(ON) of 8.5V so it may work.

You do not say what the input voltage range is but if the input drops below 8.5V the power supply will not turn on.

The input voltage range also determines the value of R2. It may be that R2 can be replaced with a linear regulator.

Do you have any more information on the output power and input voltage range?

Thanks,

John

• Hi John-san,

>The UC1845A has a UVLO(ON) of 8.5V so it may work.
Yes, UC2845A is the correct device I intended. I apologize for typo..
I will confirm the output power and input voltage range from my customer and contact you again.

Best Regards,
Yaita

• Hi John-san,

I confirmed the input voltage range is 9.5 - 16.5V.
Could you tell me how to decide the value of R2 in this case?

I also confirmed the output power is the same as the specification in datasheet.

Best Regards,
Yaita

• John-san,

Could you tell me how to decide the value of R2 when input voltage range is 9.5 - 16.5V?

Best Regards,
Yaita

• Hi Yaita-san,
R2= 1kOhm should be fine
That will provide a minimum of 1mA startup current to the controller.

Regards,
John
• Hi John-san,

I appreciate for your continuous support!

Best Regards,
Yaita