DAC with 10v output

Thread Starter

fastbike

Joined Dec 29, 2020
120
I need to control a lighting fixture with a 0-10v dimming level input.

This dimming level is set by a a micro controller which has I2C output.

I was thinking of controlling the output via a DAC with an I2C input. Either I need to find a DAC that can output 10V or use an op amp stage (following the DAC) to level shift the signal.

Are there any other circuit ideas I've overlooked ?
 

MaxHeadRoom

Joined Jul 18, 2013
28,617
Depending on the nature of light source, LED etc, the signal is often non-linear, probably a PWM of the 0-10v signal may be easier to implement.
 

Thread Starter

fastbike

Joined Dec 29, 2020
120
You only mentioned one light fixture.
How many do you want to control?
At this stage thinking of groups of 4 circuits.
I was trying to solve it genetically, then scale.

In the meantime I've been looking at MCP4728 quad channel DAC, but output level is limited. I'd then need to scale the output.

Alternatively MAX500 DAC can accept 12v supply, but it looks like an expensive line item.
 

Thread Starter

fastbike

Joined Dec 29, 2020
120
Here's a simulation of the op-amp side, I'll take a look at the Adafruit website to figure out the correct usage of the MCP4728
Screenshot from 2023-03-14 19-06-36.png

Thanks for the suggestions and pointers.
 

Thread Starter

fastbike

Joined Dec 29, 2020
120
Looking on the digikey website, I've chosen TLV4172IPWR from TI.
This is a rail to rail (so can swing to 0v), has a wide supply range rating (up to 36v) and can output a decent current.
It is also available :) and affordable.
 

Thread Starter

fastbike

Joined Dec 29, 2020
120
Supply chain issues strike again. Also I'm going to power the op amp from a 24V bus that is on the device. I've run the dimming output device (with the 0-10v control input) from my power supply and can't see it drawing an appreciable current so presume it has a high impedance buffer.

So I'm using NCV21914 which has a 4-36v supply range and can switch rail to rail.
Available now in TSSOP and SOIC
 

Thread Starter

fastbike

Joined Dec 29, 2020
120
Here's the circuit schematic for a two channel proof of concept driver. Level shifting for the 3.3v I2C signals from the mcu is included.
The production version will be quad channel and include some other features (such as current sensing, load disconnection when all off etc)
Screenshot from 2023-03-25 09-51-24.png
 

Thread Starter

fastbike

Joined Dec 29, 2020
120
Why do you want to run it from 5V? You will save all the level shifting if you run it from 3.3V.
Thats a good question. My initial thoughts were:
  • Looking for a 5v output (which is doubled by the op amp) to give 0-10v at the dimmer driver output.
  • Also I think the 3v3 supply is limited, will need to check. (using MIC5401-3.3 LDO)

So, if I could use 3v3 on the DAC (also as the DAC reference volage) I'd need to change the op amp to boost the output up to 10v: which is a gain of 3.03. So R8 and R9 become 20k (or there abouts)
 
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