UC1844A / Off-Line Flyback Regulator

K.Yaita

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?

Your support would be appreciated.

Best Regards,
Yaita / Japan disty

over 8 years ago

0 John Griffin1 over 8 years ago

TI__Mastermind 34465 points

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

0 K.Yaita over 8 years ago in reply to John Griffin1

Guru 29690 points

Hi John-san,

Thank you for your comment!
>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

0 K.Yaita over 8 years ago in reply to K.Yaita

Guru 29690 points

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.
+5V: 1A to 4A load
+12V: 0.1A to 0.3A load

Best Regards,
Yaita

0 K.Yaita over 8 years ago in reply to K.Yaita

Guru 29690 points

John-san,

Could you tell me how to decide the value of R2 when input voltage range is 9.5 - 16.5V?
Your help would be appreciated.

Best Regards,
Yaita

0 John Griffin1 over 8 years ago in reply to K.Yaita

TI__Mastermind 34465 points

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

Regards,
John

0 K.Yaita over 8 years ago in reply to John Griffin1

Guru 29690 points

Hi John-san,

I appreciate for your continuous support!

Best Regards,
Yaita

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UC1844A / Off-Line Flyback Regulator