About Comparator circuit using op amp

Tsukui Yusuke

Guru 21930 points

Other Parts Discussed in Thread: LM311, OPA2990, TLV1805-Q1, TLV1805

Hi,

Customer want to design comparator circuits using op amp.
The reason is the consolidation of parts.

Required specification is

・Absolute maximum rating voltage
: 36V (±18V)

・Comparator image that the customer wants to design
: NJM311/LM311

Could you tell me the recommended op amp for comparator design?

Best Regards,
Yusuke

over 6 years ago

0 kai klaas69 over 6 years ago

Guru 140200 points

Hi Tsukui,

can you show a schematic of the comparator circuit?

Kai

0 Tsukui Yusuke over 6 years ago in reply to kai klaas69

Guru 21930 points

kai-san,

Thank you for your response.
I have not obtained that information from the customer.
Could you tell me the recommended op amp that can be used for the comparator ?

Best Regards,
Yusuke

0 Michael Steffes over 6 years ago in reply to Tsukui Yusuke

Guru 48395 points

Before you get too far, consider this reference,

e2e.ti.com/.../op-amps-used-as-comparators-is-it-okay

0 Paul Goedeke over 6 years ago in reply to Michael Steffes

TI__Mastermind 30600 points

Hi Yusuke-san,

Michael provided a good link. If the customer insists on using an op-amp and needs high voltage, take a look at the OPA2990. You'll need to select an op-amp that doesn't have back to back input diodes.

If the customer is trying to consolidate parts, I assume they don't want to add any new part numbers? Will you let us know what op-amps they are currently using?

-Paul

0 Paul Grohe over 6 years ago

TI__Guru 65206 points

Tsukui,

The LM31 is a unique device even among comparators. It is fast (~120ns) has a unique "floating" output stage that allows the use of pull-up or pull-down resistors depending on how the GND pin is configured.

NO op-amp will have an output similar to this. Be sure to verify the output configuration.

As Kai and Paul have shown, op-amps make poor comparators compared to a "real" comparator.

Have a look at the TLV1805 or TLV1805-Q1, these are 40V rail to rail input and output comparators.

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About Comparator circuit using op amp