LM1085: negative output voltage

Barani Subbiah

Part Number: LM1085
Other Parts Discussed in Thread: TPS54302, LM337

We plan to use LM1085-ADJ to generate +7.5V and -7.5V from 12VDC input. Can we use this to generate neg output voltage? If so any ckt using LM1085-ADJ,

Attached a schematic for +7,5V out with 12VDC in

This is for a analog board so like to keep it Linear than switched buck (TPS54302)mt_power_LDO_RevA1.pdf

over 3 years ago

0 JCHK over 3 years ago

TI__Mastermind 43610 points

Hi Barani,

You need a negative regulator. This difference is that a positive regulator sources current while a negative regulator sinks current. Please look at the following thread for one possible idea: https://e2e.ti.com/support/power-management/f/196/t/911950

I hope this helps.

0 Barani Subbiah over 3 years ago in reply to JCHK

Prodigy 150 points

Thanks for the link. LM337 would work for us. Just to confirm that input is neg voltage. Is there one with +12V in to -7,5V

If not, we may look for PS with +12 and -12V and use 1085-adj for +ve and LM337 for -ve 7.5.

0 JCHK over 3 years ago in reply to Barani Subbiah

TI__Mastermind 43610 points

Hi Barani,

We do not currently have a positive in/negative out converter in the Linear regs portfolio.

You are right in that the best approach is to use a switching regulator to produce the negative voltage and then clean up the ripple with the LM337.

I hope the helps

0 Barani Subbiah over 3 years ago in reply to JCHK

Prodigy 150 points

Thanks. Attached an updated + and - 7,5 schematic. Appreciate if you can verify the values and any errors.

Any other suggestion for further clean up and low ESR.

We looked at TPS54302 - the EN pin for -ve bit more complex and switch freq. leakage on analog ckt.

Thanks for your help.

mt_power_LDO_RevA2.pdf

0 JCHK over 3 years ago in reply to Barani Subbiah

TI__Mastermind 43610 points

HI Barani,

The linear regulators look OK. If you have questions on the TPS54302, could you please post to their forum?

I hope this helps.

Power management

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LM1085: negative output voltage