Control of the DC-DC

Xiaoyan,

There are also DC/DC Converters and controllers that can be configured such that their output voltage tracks a scaled version of an analog reference voltage.  Such controllers can be configured as either voltage regulators or current regulators, allowing analog control of the output voltage or output current as desired.

Thanks for your reply. However, what does the 'FAE' represent? And my requirement is as follows.

1) the output voltage can be controlled in real time.

2) the output current can be controlled in real time.

and both of the converters input/output voltage range is as follows:

Vin(min)<=4.5V, Vin(max)>=2Vin(min)

Vout around 5V

for the output current, it is better larger than 1.5A.

Could you recommend some types?

Thank you very much.

An FAE is a Field Applications Engineer.  They are regional applications and technical support.

If you can let us know what company you are from and what part of the world you are in, we may be able to put a local FAE in touch with you.

I am working in Max-Planck-Institute  in Magdeburg, Germany now.

Thank you.

Xiaoyan,

You ask for real-time control of the output voltage - Over what range?  Via what kind of signal?  (Analog or Digital?)  If digital, using what kind of communications bus? At what speed? (Slew-rate and update rate)

Same questions for output current  What range?  Via what kind of signal?  If digital, what communications bus?  What speed?

Are these two seperate supplies (1 regulated output voltage (current set by the load) and 1 regulated output current (voltage set by the load) or are you trying to regulated both voltage and current of the same supply?  If the later, I need to know the exact characteristics to provide a recommendation.

Have you ever designed a fixed voltage regulator or fixed current regulator before?

What is the end-user application for these power supplies?

Hello Peter,

One of the converter is used between a fuel cell and a portable load whose max power is less than 10W. We want to make the output of the fuel cell change continuously when the load power steps up suddenly according to controlling the dc-dc converter. And the extra power will be supplied from a battery temporarily.

At the beginning,  we want to use the Labview to design the control system. So I think the control signal is not a big problem. And the range of the output range should be

Vout±20%. And the range of the current should change from 0 to the maximum current continuously.

They are seperate supplies.

I have just used the uncontrollable fixed voltage dc-dc  before.

The end-user application is just portable applications, such as mobile phone.

Thank you.

Xiaoyan Sun,

A fixed output DC/DC converter that uses an output voltage programmed via a resistor divider to the inverting input to an error amplifier (the vast majority of Texas Instruments adjustable DC/DC controllers or converters) can be made adjustable by the addition of a controlled current source (or high-impedance voltage source) feeding additional current into the mid-point of the resistor divider.

The most common way to achieve this control through a digital interface is the addition of a Digital Analog Converter (DAC) with a resistor in series with its output.  The DAC generates a voltage across the resistor (Vdac - Vfb) to add a current into the divider.  The controller/converter attempts to regulate the voltage at the mid-point of the divider at a fixed reference, which requires a specific output voltage to maintain.  Adding current into the mid-point of the divider reduces the current required through the upper side of the divider, which in turn reduces the required output voltage.

With a properly selected resistor, the full resolution of the DAC can be used to fill the adjustment range of the converter, providing very high resolution adjustments.

A controller or converter indended for a voltage regulator can often be configured as a current source by adding a current sense element and generating a control voltage proportional to the current to the error amplifier.  In this way, the converter regulates the voltage across the current sense element and thus the current generated by the converter.  A current shunt monitor / current shut amplifier is a good choice to both scale the current across the sense element and level-shift the sense voltage to the IC ground.

If you need a combintion Constant Current / Constant Voltage coverter, you'll need to produce 2 loops, one for current and one for voltage.  This can be done using the Tracking Amplifier method described in the TPS40100 datasheet.  By diode connecting the two loops, the outer loop can only reduce the inner loop.  In this way, the converter can follow a constant current / constant voltage profile.  By adding the DAC interface described above, both of these loops can be controlled.