LM318-N: Zero cross detector

Akshay Pathak

Prodigy 40 points

Part Number: LM318-N
Other Parts Discussed in Thread: LM318, LMV7219, LM7121

Hello friends,

I am trying to design zero cross detector with LM318

input : AC 500mv 1.2MHz

output: gate Pulse +vcc and -vcc for n and p channel mosfets

please can you suggest a circuit design or any other op amp for above mention ratings

over 7 years ago

0 Ron Michallick over 7 years ago

TI__Guru**** 155756 points

Akshay,

LM318 is an amplifier so it is not the best choice for the zero crossing detector.

To get a precisely timed zero crossing, I suggest LMV7219 as input comaparator.
The input signal will need to be shifted up a little so that the input range of LMV7219 will be met. An alternative is to use a split supply for LMV7219. This 5V device. I suspect your VCC+ and VCC- are higher than this.

Therefore an interface "driver" between LMV7219 output and VCC+ and VCC- rails will be needed.
What are the voltages for VCC+ and VCC- ?

0 Akshay Pathak over 7 years ago in reply to Ron Michallick

Prodigy 40 points

Thank you Ronald Michallick.

VCC+ & VCC- =+10 or -10

0 Ron Michallick over 7 years ago in reply to Akshay Pathak

TI__Guru**** 155756 points

Akshay,

I didn't find a negative voltage driver and FET drivers are outside my product group.

I suggest looking here for a driver for your VCC+ rail FET.
www.ti.com/.../mosfet-and-igbt-gate-drivers-products.page

Once you have a part selected (or chose one randomly) , start a new post with that part number saying you also need a FET driver for a -10V VCC- rail. The engineer who answers that post will be an expert for FET drivers.

0 Akshay Pathak over 7 years ago in reply to Ron Michallick

Prodigy 40 points

Hello Ronald Michallick,

Instead comparators,I want to design opamp schmitt trigger for zero cross detector.
can you suggest any op amp which works at high frequency 1.2MHertz with (+vcc / -vcc from +/- 5 to 10) and Vinput is 0.5v

0 Ron Michallick over 7 years ago in reply to Akshay Pathak

TI__Guru**** 155756 points

Akshay,

Here are many op amps that support 20V supply and have >50 MHz bandwidth.
www.ti.com/.../high-speed-op-amps-products.page

LM7121 is good choice.

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LM318-N: Zero cross detector