Gentlemen,

My signal generator can't source/sink current which makes it rather useless, my question is: How can I make it source/sink current? I guess a good place to start would be with a op-amp, but is there a simpler solution?

Function generator specs:
Standard waveforms Sine, square, triangle, ramp (up/down)
Arbitrary waveform buffer 4,096 samples
DAC clock frequency 2 MHz
Maximum signal frequency using standard waveforms 100 kHz
Output impedance 600 Ω
Resolution 8 bits
Amplitude ±250 mV to ±2 V with ±1 V offset

Evilly yours
Dr. Evil

 

What are you wanting to do with your signal generator? It sounds very useful to me.
It is almost like saying a microphone is useless as it cannot source/sink current.
A signal generator is just that, not a power amplifier. That is what you feed it into if you need more output.
What current do you want to source/sink, and what voltage out?
What is the load you expect to drive?

 

What are you wanting to do with your signal generator? It sounds very useful to me.
It is almost like saying a microphone is useless as it cannot source/sink current.
A signal generator is just that, not a power amplifier. That is what you feed it into if you need more output.
What current do you want to source/sink, and what voltage out?
What is the load you expect to drive?

Dear denad,

That is exactly what I mean, e.g. if I want to drive a transistor or logic input, I would at least need 5-20 milli amps source/sink ability, so how do I do that the most simplest way?

 

I don´t think there is anything simpler than an opamp. You can increase the output swing as well as the output current with one part and a few resistors.

 

I don´t think there is anything simpler than an opamp. You can increase the output swing as well as the output current with one part and a few resistors.

Yeah, but you know then you have to mess with dual supply, unless I use an op-amp with single supply and limit my self to positive output.

 

hi,
What power supplies do you have for this project.?

 

You may want to look at a power opamp such as LM675.

 

hi,
What power supplies do you have for this project.?

Whatever I can cook up, maybe I'll just split a single source power supply, and you're Bob's nephew.

 

You may want to look at a power opamp such as LM675.

Thank you, I will look into that one.

 

Whatever I can cook up, maybe I'll just split a single source power supply, and you're Bob's nephew.

It sounds like you are thinking of making an artificial ground. That does not work well for a power amplifier. You are better off creating a negative voltage power supply using an inverting switcher.

 

It sounds like you are thinking of making an artificial ground. That does not work well for a power amplifier. You are better off creating a negative voltage power supply using an inverting switcher.

Dear Richard,

Thank you for your suggestion, but I don't really see why it wouldn't work for a power amplifier in particular.

My thinking is that if you take any point between GND and V+ in a single supply (floating GND) and call that GND and rename the original GND to V-. Then the new GND is just as much GND as the original GND, it's just a definition, the voltage potentials are what's important.

However, if you plug your "artificial" grounded circuit to another circuit that is powered by another power supply, and this second power supply is not galvanic isolated from the first circuit, then you will have some form of short circuit.

 

... Thank you for your suggestion, but I don't really see why it wouldn't work for a power amplifier in particular.

My thinking is that if you take any point between GND and V+ in a single supply (floating GND) and call that GND and rename the original GND to V-. Then the new GND is just as much GND as the original GND, it's just a definition, the voltage potentials are what's important.

The problem is the impedance of that artificial ground relative to the power rails. If you use a resistor divider, then your power amp can be as beefy as you want, but the impedance of the ground will be so high that the ground point will follow the output of the amp and you will not be able to push any significant current through it. That means you would need two power amps, one to keep the ground steady and one to amplify the actual signal.
Or you can use a transformer and easily get the +/- rails.