How can I increase current output for my computer controlled DAC?

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Discussion Overview

The discussion revolves around increasing the current output for a computer-controlled Digital-to-Analog Converter (DAC) project. Participants explore methods to achieve a desired output current of 500mA while maintaining the required voltage levels, focusing on the use of operational amplifiers (op-amps) and power supply considerations.

Discussion Character

  • Technical explanation
  • Exploratory
  • Homework-related

Main Points Raised

  • The original poster seeks advice on how to boost the output current of an 8-bit DAC to 500mA, noting that available IC chips only support currents below 20mA.
  • One participant suggests using an op-amp with a 500mA output drive capability in a voltage-follower configuration to achieve the desired current output.
  • The original poster asks for clarification on the power supply requirements for the op-amp, specifically regarding the Vcc current and its relationship to the output current needed for the load.
  • Another participant clarifies that the power supply should be able to source the current required by the load and suggests using a 1 amp power supply for safety, noting that current is drawn as needed by the load.

Areas of Agreement / Disagreement

Participants generally agree on the use of an op-amp to boost current output and the necessity of a power supply that can meet the load's current demands. However, there are still questions regarding specific wiring and power supply configurations that remain unresolved.

Contextual Notes

There are unresolved questions regarding the appropriate Vcc current for the op-amp and how the load will interact with the power supply, including the implications of starting current versus running current for the fan.

Who May Find This Useful

This discussion may be useful for individuals working on electronics projects involving DACs, those interested in operational amplifier applications, and learners seeking to understand current and voltage relationships in circuit design.

KayMan2k
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I have taken a few college courses in EE and am putting together a pet project for a computer controlled DAC. I am using the parallel port to drive an 8-bit DAC for voltages 0 to 12V and I want an ouput current of 500mA. I have found several IC chips that allow me to do this, but only below 20mA. How can I pump up the current while mainting voltage after the DAC process? I am confused about this and any help would be greatly appreciated.

Thnx
 
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Connect the DAC output to any op-amp that has a 500 mA output drive capability wired in voltage-follower configuration.

There are probably hundreds available from all your favorite semiconductor manufacturers, such as National, ADI, Maxim, Linear, and so on.

Here are a bunch of high-power op-amps from National: http://www.national.com/parametric/0,1850,695,00.html

The LM675 looks like it would fit your needs, for example.

Let me know if you have any more questions.

- Warren
 
Last edited by a moderator:
Thank you VERY much. It looks like this will perfectly solve my problem. Just 2 quick follow up questions to fully understand exactly how to wire this up (I know how to wire a voltage-follower... just questions about Vcc for op amp).

1) It looks like the op amp you suggested needs 16V Vcc, which is the power supply voltage I am using anyway. Should the current of Vcc be the 500mA that I am trying to boost the signal to or keep it at 18mA and the op amp will convert the volts to current as needed?

2) I see that the maximum output of the op amp is 4A. If I put a Vcc of 800mA.. will the fan I am trying to power just draw 500mA or overload pulling 800mA?

Again, thank you. Some of my questions may seem basic but I am trying to better understand these concepts. It is very kind of you to answer my questons in such depth.
 
Yes the supply needs to be able to source the current that the load requires. You would be smart with a 1 amp power supply.

Current is drawn as it is needed. When the fan starts it will draw more current than when it runs at full speed.
 

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