NE555: VCC supply by resistor divider

user4979989

Part Number: NE555
Other Parts Discussed in Thread: TL783, TPS7A4001, LMC555, TLC555

Hi team,

My customer would like to use NE555, but the board voltage they have only 48V.

Do you think use a resistor divider to scale down from 48V to 12V is a good way for NE555 VCC pin?

I check the datasheet of NE555 VCC, the maximum supply current of VCC is 15mA, which is high if want to use resistor divider.

Or you will suggest us to use one more buck IC to converter the power?

Thanks.

Regards,

Allen

over 6 years ago

0 Ron Michallick over 6 years ago

TI__Guru**** 174126 points

Allen,

The TPS54061 is an efficient choice. Is the NE555 the only thing on the 12V supply bus? How much 12V current is expected?

If efficiency doesn't matter there is also TL783 or a NPN/NMOS transistor plus a zener diode and bias resistor could do the job. A series zener to drop input voltage then using a uA78L12 is yet another option.

0 user4979989 over 6 years ago in reply to Ron Michallick

TI__Intellectual 2800 points

Hi Ron,

Thanks for the suggestion.

Do you think TPS7A4001 is also a suitable solution? (100V/50mA LDO)

The maximum VCC supply current should be up to 15mA, right? if not, what's the maximum VCC supply current?

Regards,

Allen

0 Ron Michallick over 6 years ago in reply to user4979989

TI__Guru**** 174126 points

Allen,

NE555 current will be less than 15mA. The current for the load on NE555 output and the timing capacitor charge current will be extra current.

TPS7A4001 looks good. If total current was 16mA, power loss in TPS7A4001 would be 16mA * (48V-12V) = 0.576 watts. Per data sheet Tja is 66.7C/W, so expected temperature rise is 38.4C which is reasonable.

NE555 could be replaced with TLC555 or LMC555 to lower the supply current needed.

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NE555: VCC supply by resistor divider