# How can I use an LM310 as a voltage follower?

I'm trying to take an input from a signal source and split that input into multiple outputs using voltage followers.

My chip of choice is the LM310 voltage follower.

I plan on using it with a +15V/-15V linear power supply to generate a -10V to 10V output that follows a -10V to 10V input. The source signal comes from a device with 30 ohms output impedance. The output of each voltage follower should have an output impedance that does not exceed 50 ohms.

My secondary "bonus points" question is whether or not through-hole resistors and capacitors (power) will significantly affect the capabilities of the system.

Edit: Corrected input / output discrepancy, should be -10 to +10, not 0-10.

Edit2: Forgot to update the power supply, should have been -15V/+15V, not -12V/+12V

• I can not see any question except the title. Please help us in finding out what you want to know?! Mar 12 at 15:28
• Why have you chosen a device that is no longer produced and very expensive? Do you know that any random opamp can be configured as a voltage follower?
– CL.
Mar 12 at 15:33
• @CL. I'm trying to keep the circuit as simple as possible because of my limited experience in electrical engineering. The LM310 is surprisingly convenient for this. I already have plenty of the chips on-hand. Mar 12 at 15:59
• Please tell me it's a metal can version of the 310 Mar 12 at 16:01
• @SimonFitch It's a ceramic 16 pin (LM310J) Mar 12 at 17:05

I refer to this datasheet.

This is how you do it, if your input source has an impedance of less than 10kΩ:

simulate this circuit – Schematic created using CircuitLab

If the signal source at IN has an output impedance exceeding 10kΩ, then you may omit R2, but if in doubt, don't. This op-amp has no frequency compensation, and R1 and R2 are necessary to prevent oscillation. Most modern op-amps do not have this requirement.

It has a very high input impedance, in the gigohms, and an output impedance of close to zero ohms, due to negative feedback.

That doesn't mean you can draw any amount of current from the output. I suspect if you sink or source more than about 10mA there, you will find that the output can't reach +10V or -10V.

However, if your load is small, with a resistance greater than 1kΩ (or the input impedance of the next stage exceeds that), you will have the relationship:

$$V_{OUT}=V_{IN} + V_{OFS}$$

Input offset voltage $$\V_{OFS}\$$ can be anything up to 10mV, but can be mitigated by employing the offset-balancing circuit on page 5 (section 2-43).

While there's no mention of slew rate in the datasheet, or bandwidth, from the graphs "Large signal pulse response" on page 4 (section 2-42), and "Large signal frequency response", I estimate this device, as a voltage follower, can handle a 10V amplitude sinusoid up to about 300kHz without much distortion, and small signals up to slightly over 1MHz without attenuation.

Regarding your question about through-hole components, at these frequencies (up to a few hundred kilohertz) I doubt that there would be any appreciable difference whether they are through hole or SMD. That's not to say you shouldn't pay attention to layout, you should always aim to keep paths short, and current loops small.

I don't know where you intend to attach a capacitance (do you mean a bypass/decoupling capacitor across the power supply?), but I doubt that the fact that it's a through-hole device will make any difference. If you are referring to power supply decoupling, then your biggest concern is proximity to the op-amp's power supply pins. Make it close, through-hole or otherwise.

• It's looking like I should just use a more modern op-amp. Any recommendations to make a decently high-performance voltage follower? The application is taking a single input and splitting it into 5 outputs. Simply put I'm trying to measure a signal across 5 different devices without them interfering with the overall input impedance seen by the source. Mar 13 at 21:35
• Here are some of the OP-Amps I'm looking at, I could be way off here but they seem correct: digikey.ca/short/b3w2c4d4 Mar 13 at 21:55

The LM310 is a voltage follower. It has no other function. The +12,-12supply voltage is in range. But heed the advice in the datasheet shown in the image. To get a 10 volt output you need a 15 volt supply voltage. Also reading Note 5 indicates that a higher output voltage can be obtained by using the booster pin. This may allow you to get 10V out for a 12V supply. You will have to experiment.

The output current must be less than about 20mA.

Be certain to put a 10K resistor in series withe the input as indicated in the application hint. A low source resistance can cause instability.

The short answer is maybe if the external booster can reduce the 5V headroom required.

This is not a good choice for your application. There are many, many modern choices that are better suited.

Based on the improvement to the OP, the LM310 should function at low frequecies on $$\\pm 15V\$$ supplies. However, the large signal frequency response at 600KHz is down to $$\\pm 4V\$$.

So may original stance that this is a poor choice still stands.

A selection of alternatives can be found here.

• What modern choice would be better suited? Mar 12 at 18:22
• @DiskBiskit Here are 42 possibilities. Mar 12 at 19:09
• I messed up the question as you correctly called out the issue I had. I do have a -15V and +15V supply, I was mistaken, also my input and output are -10V to +10V. I just want to use this device as a voltage follower. I am unsure how to set up the circuit. Do I need to have a resistor on the input/output pulling it towards 0V? How do I set this up so I can not fry these things when I do the breadboard layout? Mar 12 at 21:38
• Is indicated in the answer, put a 10k resistor in series with the input. Not to ground. Don't expect more than 20mA from the output. The load resistance should be greater than 1000 ohm depending on the booster resistor. Mar 12 at 22:01
• Thankfully it's only a signal I care about, so the low current won't matter much. Ultimately you've convinced me I need something better, so I'm now taking a step back to determine how to take a modern op-amp and use it as a relatively precise voltage follower with the same input/output requirements. From what I can see, these are fairly close to what I'm looking for: digikey.ca/short/b3w2c4d4 Mar 13 at 21:54