I need to generate 3-30VDC (controlled digitally with at least 12bit resolution, e.g. using a DAC)) from a 12VDC power supply. What would be the best way to achieve this? (sorry in case this is a common type of question, but I lack the terminology to search for it efficiently).

TIA, Beat

 

I need to generate 3-30VDC (controlled digitally with at least 12bit resolution, e.g. using a DAC)) from a 12VDC power supply. What would be the best way to achieve this? (sorry in case this is a common type of question, but I lack the terminology to search for it efficiently).

TIA, Beat

What you need is a buck-boost converter with a digitally controlled VCO. Question: How will the DAC know what voltage to select?
https://en.wikipedia.org/wiki/Buck–boost_converter
http://www.learnabout-electronics.org/PSU/psu33.php

 

Another approach is to separate the buck from the boost. First, boost the 12 V to a fixed 30 V. Then regulate the 30 V with the DAC output with either a buck or linear regulator. More overall parts, but it might lend itself to DAC control over a 10:1 range better than an integrated buck-boost controller.

ak

 

Thanks for your answers.

How will the DAC know what voltage to select?

I just want to control the voltage from a microcontroller in whatever way is most efficient. Since I don't need high modulation speed, a DAC with an I2C interface might be good (I usually end up with too few PWM channels, but in principle, PWM could be used, too).

 

Look LTC3115-2.

 

There are two basic types of voltage regulators: fixed reference/variable gain, and fixed gain/variable input voltage. For DAC control, life is much easier with the latter topology. The part mentioned above is of the former type, and has consequences:

1. This part has a fixed voltage reference and relies on a divided output voltage for adjustment. A DAC with a low impedance output voltage will need some kind of circuit to interact with the control loop.

2. The voltage-setting resistor divider is part of the frequency compensation loop. This makes making this regulator adjustable more difficult.

3. The frequency compensation changes as a function of the output voltage.

ak

 

Thanks for your answers.



I just want to control the voltage from a microcontroller in whatever way is most efficient. Since I don't need high modulation speed, a DAC with an I2C interface might be good (I usually end up with too few PWM channels, but in principle, PWM could be used, too).

With all due respect -- this is not an answer. I know you want to use a microcontroller to control the DAC, and efficiency has nothing to do with how you intend to decide what voltage to set the DAC at.

 

With all due respect -- this is not an answer. I know you want to use a microcontroller to control the DAC, and efficiency has nothing to do with how you intend to decide what voltage to set the DAC at.

Ok, I guess I didn't understand your question then, sorry about that.
The power supply will drive an array of piezoelectric blowers (via individual resonant driving circuits), the combined flow will be measured by a mass flow meter. It'll be a closed-loop PID system. Thus a perfectly linear response is not that important. Is that what your question aimed at?

 

Ok, I guess I didn't understand your question then, sorry about that.
The power supply will drive an array of piezoelectric blowers (via individual resonant driving circuits), the combined flow will be measured by a mass flow meter. It'll be a closed-loop PID system. Thus a perfectly linear response is not that important. Is that what your question aimed at?

Not quite. If I understand correctly the mass flow meter will indicate how much air the fans are moving, and that value will determine the output voltage of the supply. So last(hopefully) question how is the information from the mass flow meter given to the processor? If the response is not linear you will have other problems, but that is a discussion for another time.

 

So last(hopefully) question how is the information from the mass flow meter given to the processor?

I plan to use a sensor, e.g a Honeywell Zephyr, with an I2C interface.

 

I plan to use a sensor, e.g a Honeywell Zephyr, with an I2C interface.

OK, so the processor uses the I2C interface to take samples of the mass flow rate on a periodic basis. What happens in the case of an inability to obtain a sample?

 

OK, so the processor uses the I2C interface to take samples of the mass flow rate on a periodic basis. What happens in the case of an inability to obtain a sample?

It will increment an error counter for the sensor by a, retry, and decrement the counter by b in the case of success. If the counter hits a defined threshold c, the device cancels operation safely, giving an appropriate error message.

 

It will increment an error counter for the sensor by a, retry, and decrement the counter by b in the case of success. If the counter hits a defined threshold c, the device cancels operation safely, giving an appropriate error message.

That answers the questions about the method of closing the loop. You mentioned in an earlier post that you were not concerned about linear behavior. I want to caution you about some of the problems you may encounter with non-linear behavior. The two most important ones are:

1. Divergent output from unexpected input conditions
2. Limit Cycling, which is a characteristic of some non-linear systems.

https://en.wikipedia.org/wiki/Limit_cycle

 

Thanks for the hint, @Papabravo . I'll keep that in mind.