Voltage Buffer, Current Amp, Drive DC motor

[SolarPlexus]

Hello all,

I'm trying to figure out the best type of voltage buffer to use for a project I'm working on, where I am attempting to drive a DC actuator with a current of up to 300mA without frying the op amp non-inverting amplifier (simple LM741) I have for my DC signal (typical output current ~20mA). Given the many ways I could do this, I'm really not sure which would be best, nor how I would figure out the right component for the job. The way I see it, I could either get a high current output op amp or try to use a transistor as a common collector voltage buffer, but I get confused about the connections for the latter option. Any advice on what component/set up would be best for this 20mA to ~300mA jump? I don't want to accidentally do something overly complicated for a simple problem.

Thanks!

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Hmm, I thought that I posted this in the "Electronic Elementary Questions" forum... Whoops! Sorry about that

 

[goldsmith]

ng to figure out the best type of voltage buffer to use for a project I'm working on, where I am attempting to drive a DC actuator with a current of up to 300mA without frying the op amp non-inverting amplifier (simple LM741) I have for my DC signal (typical output current ~20mA). Given the many ways I could do this, I'm really not sure which would be best, nor how I would figure out the right component for the job. The way I see it, I could either get a high current output op amp or try to use a transistor as a common collector voltage buffer, but I get confused about the connections for the latter option. Any advice on what component/set up would be best for this 20mA to ~300mA jump? I don't want to accidentally do something overly complicated for a simple problem.

Thanks!

Hi SolarPlexus
That's so simple , using a simple transistor based current driver would be so reasonable and cheap , of course ! . you can use either mosfet or BJT for this aim as well .
Best Wishes
Goldsmith

 

[SolarPlexus]

I recognize that a BJT is likely my best choice for a buffer, but there are so many configurations for transistors and caveats like biasing that I always get confused when I try to learn about them. For instance, in the diagram of a common collector transistor, with Vin at the base, V+ at the collector and Vout at the emitter, I don't get what the emitter resistor that is sent to ground does or what value it needs to be. I know this is simple stuff, but I haven't worked with transistors in the past.

 

[goldsmith]

I recognize that a BJT is likely my best choice for a buffer, but there are so many configurations for transistors and caveats like biasing that I always get confused when I try to learn about them. For instance, in the diagram of a common collector transistor, with Vin at the base, V+ at the collector and Vout at the emitter, I don't get what the emitter resistor that is sent to ground does or what value it needs to be. I know this is simple stuff, but I haven't worked with transistors in the past.

You can easily go through this way :
Connect out put of your command signal into the base of an NPN transistor and then tie it's emitter into the ground and then put the load between collector and + VDC . that's all you need to do . if your load is inductive then you'll need a freewheeling diode across the motor to guarantee that your transistor won't be destructed .
Adding an LC filter ins series with your motor ( LPF ) would optimize everything in your result .
Best Wishes and Good Luck
Goldsmith

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By the way don't forget to use a series resistor between your command signal and base of your transistor .

 

[SolarPlexus]

But I thought that a unity gain transistor set-up put the load at the emitter? It's what Wikipedia suggests (https://en.wikipedia.org/wiki/Buffer_amplifier#Chart_of_Single-Transistor_Amplifiers) and what it sounds like you're describing is a common emitter transistor, which would invert my voltage. I just need a unity gain common collector set-up and wanted to be sure that the emitter resistance was just the load and not some additional resistor tied to ground. If it's just Vin at the base, V+ at the collector, and the load tied to the emitter and then to ground, I can understand that.