mcp4725 DAC driver circuit

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Dieter007
 
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Joined: Thu May 01, 2014 7:26 pm

mcp4725 DAC driver circuit

Post by Dieter007 »

Hi Guys,

I need to design a circuit using the MCP4725 DAC output to drive some sort of linear voltage follower op-amp or just a simple transistor, is this possible?

Why i need a secondary( Driver ) circuit is because of the current drain (500mA, 0-5V).
Vin = Vout

Thanks in advance
DAC.jpg
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adafruit_support_mike
 
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Re: mcp4725 DAC driver circuit

Post by adafruit_support_mike »

You'll definitely need some kind of power stage.. most DACs only deliver a few milliamps, and even high-power op amps tend to stop at around 100mA per channel.

It's hard to get 0v-5v output from 0v-5v supply rails at 500mA though. The most stable power stages are made from BJTs configured as emitter followers (the class AB push-pull amplifier), but at 500mA the output from those can only get within about 1v of the positive and negative supply rails.

Common-emitter power stages get closer to the supply rails, but they're harder to control (you need an op amp), you have to be careful about fast-moving signals ringing or causing oscillation, and you'll still have an offset of about 200mV from either rail.

Power stages made from mosfets can get very close to the supply rails, but it's hard to find well-matched P and N power mosfets. The push-pull version needs significantly more headroom than a BJT power amplifier (to get the really low ON-resistances you need about 5v between gate and source), and the common-source version is even more twitchy than the kind made with BJTs.

What kind of load are you driving, and what frequency range will be normal for the signals?

Dieter007
 
Posts: 5
Joined: Thu May 01, 2014 7:26 pm

Re: mcp4725 DAC driver circuit

Post by Dieter007 »

Thanks for the reply,

Its not really going to be running at a frequency but more a set voltage.
i'm using this setup as an adjustable power supply for powering little loads (< 500mA) for testing things
the load type is more resistive.

I'm not just limited to a 5v rail voltage but have 12v too.

just as an example I might have buttons/rotary switch connected to the arduino and have preconfigured voltages that ill write to the dac, knowing the dac wont be able to handle the current, I'd rather go with the mosfet's then...

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