Hi everyone. I am a beginner in circuits.
I try to make a circuit that contains the inverting and non-inverting op-amps. Namely, I use AD797 op-amps. I looked in the Data Sheet for AD797 (find in the attachment), and on the diagram for recommended inverting amplifier connection it has grounded 600 Ohm load after the output. What is the purpose of this grounded load and do I need to insert this load in my circuit? Thanks in advance!

 

600 Ohm not required. Its a test condition to show the fact the part
can deliver a lot of current and still swing large signal levels.

Regards, Dana.

 

See the “L” subscript on R(L)? That’s to represent whatever load you place on the output. It’s not a required component.

 

See the “L” subscript on R(L)? That’s to represent whatever load you place on the output. It’s not a required component.

Thanks for the answer. The thing is they also recommend to use ``load'' capacitance C(L) in some connections. In this case, it is a required component. Look, for instance, at the recommended connection for the non-inverting configuration. They add C(L) in parallel intentionally.

So, I was confused by this. C_L is a required component, but R_L is not required, am I right?

 

Thanks for the answer. The thing is they also recommend to use ``load'' capacitance C(L) in some connections. In this case, it is a required component. Look, for instance, at the recommended connection for the non-inverting configuration. They add C(L) in parallel intentionally.

So, I was confused by this. C_L is a required component, but R_L is not required, am I right?

Well some load may be required but the exact value shouldn’t matter much between some max and min value.

 

Well some load may be required but the exact value shouldn’t matter much between some max and min value.

So, do I actually have to insert some load between the output and ``0'' for each op-amp in my circuit?

 

So, do I actually have to insert some load between the output and ``0'' for each op-amp in my circuit?

No.

 

Thank you!

 

It's "difficult" for an OP-amp to drive capacitance loads therefor a max CL is usually specified. It may oscillate and do wierd things

The capacitors on the power supply are called "Bypass Capacitors". Usually you follow the manufacturer's advice and usually they are between 0.1 and 1 uF ceramic caps. They should be placed as close to the power pins as possible.

There are a few other newbie things to worry about. Some OP-amps are not unity gain stable. e.g. Use when gain is > 5.

You need to find a place for Ib (the input bias current to go). At the OP amp there is Ib and Vos. Vos is referred to the input.
So an effective R in parallel with the input needs to be < Ros/Ib

Input protection MAY have to be provided. An inherent diode forms at the inputs when the power supply is zero. A typical number is 10 mA not to exceed. So an input may have to have the current into the (+) (-) terminals limited IF a signal can be applied with the OP amp off. "Over the top(TM)" op amps circumvent this.

Remember the GBW or gain multiplied by bandwidth is a constant.

You can current limit an output with a series resistor in a buffer configuration, but take the feedback after the resistor.

You can get yourself in trouble when connecting the output of one OP amp to another with out a place for Ib to go. Even if Vos is tiny, it's still significant when the wire resistance is near zero and so is the output Z.

 

So, do I actually have to insert some load between the output and ``0'' for each op-amp in my circuit?

No. Presumably you're doing something with the output though? That's your load, your RL. You don't need an extra load. And the op-amp will work just fine without any load, but it's like a tree falling in the forest with no one to hear it.