Remote sensing in buck converters

[joniengr081]

I have attached a circuit of un-regulated buck converter in which the PWM from MCU controls the gate of FET which is the switching element. I call it un-regulated because there is no feedback from the output voltage and no output regulation.

I am wondering how do we add remote sensing in switch mode buck converters to make them regulated buck converter.

I understand the concept of remote sensing in general. When the load is far away from power supplies and there is a voltage drop across the long cables due to large amount of current, we need to introduce the sense wires in linear power supplies to regulate the output of the power supply at the point of load. Such linear power supplies are called regulated linear power supplies.

How the regulation is done in buck converter is a question in this post.

I am wondering what changes in the attached circuit we need to do in order to make it regulated buck converter.

[boB]

The feedback would be applied to the control circuit that feeds that FET gate-source and its PWM duty cycle.

So, quite a bit more needed here.

There is a reason these circuits leave the gate-source drive for you to add.  This is just the basic buck converter and will need high side gate drive.

There should be quite a bit of examples online where the gate drive is actually connected to something.  That circuit is where the voltage feedback is connected to.

Some examples may be synchronous buck converters instead of this one which is non-synchronous.

boB

[Smokey]

https://webench.ti.com/power-designer/switching-regulator?powerSupply=0

Pick a topology.  Pick a part.  Pick performance specs.  Fully formed schematics (with real part numbers) and simulation results  for your learning pleasure.

[Someone]

make them regulated buck converter.

It is unlikely your MCU will have sufficient speed (and peripherals) to produce what is usually considered "regulation". All the theory was worked out in analog:
https://ridleyengineering.com/design-center-ridley-engineering/38-control.html
While that can be done entirely in the digital domain, the vast majority of regulators retain key functionality in analog parts.

[uer166]

make them regulated buck converter.

It is unlikely your MCU will have sufficient speed (and peripherals) to produce what is usually considered "regulation". All the theory was worked out in analog:
https://ridleyengineering.com/design-center-ridley-engineering/38-control.html
While that can be done entirely in the digital domain, the vast majority of regulators retain key functionality in analog parts.

That's a bit bs though innit?
You can easily do a current mode contol loops for 100s of kHz from modern MCUs not specifically designed for digital SMPS, and MHz range for those that are.

Last time I took apart a 4.5kW PSU, the PFC stages were controlled by a low-end STM32 clone, and the output LLC with a higher end Cortex-M4 based part.

[Someone]

make them regulated buck converter.

It is unlikely your MCU will have sufficient speed (and peripherals) to produce what is usually considered "regulation". All the theory was worked out in analog:
https://ridleyengineering.com/design-center-ridley-engineering/38-control.html
While that can be done entirely in the digital domain, the vast majority of regulators retain key functionality in analog parts.

That's a bit bs though innit?
You can easily do a current mode contol loops for 100s of kHz from modern MCUs not specifically designed for digital SMPS, and MHz range for those that are.

Last time I took apart a 4.5kW PSU, the PFC stages were controlled by a low-end STM32 clone, and the output LLC with a higher end Cortex-M4 based part.

Its an opinion. "low power" switching regulators are moving to MHz with corner frequencies in the x00KHz. What goes on inside a typical 10c-$2 switching regulator is very high speed compared to a microcontroller and much finer resolution. Analog has its place in these closed loop modulators be that voltage or current mode.

You think the OP is really talking about an industrial kW converter with xx00V and xx0A switching devices? Just the gate drive would be its own work in analog design.

The basic statement stands, people developing digital solutions start with the analog models of what works. It's not possible to confirm stability without including/analysing the power parts the OP has started with as a "given".

[uer166]

OP wants an MCU controlled buck, while that is not optimal unless it's something special, why mislead them into thinking that it's not possible at all?

[Someone]

OP wants an MCU controlled buck, while that is not optimal unless it's something special, why mislead them into thinking that it's not possible at all?

Possible, but likely a wild misunderstanding. Trying to blindly implement "remote sensing" without starting with an understanding of control theory, which is well developed for switching regulators, is foolish/shortsighted.

How do you propose to help the OP develop the skills/knowledge to implement a switching regulator with an MCU? Completely ignore the established theory?