in power supply there are voltage mode and current mode and some has power mode ,my question is in power mode how the servo loop control the power,is he control the voltage and current in the same time or how ?

 

I assume it adjusts the voltage so that the product of the output voltage and current (power) stay constant (within the current and voltage limits of the supply). So it would have some type of multiplier to perform the multiplication of the output voltage and current.

 

Are you referring to the two methods of servo control?
Either the older method of voltage (velocity) control or the current common method of Torque (current) mode?
Dr Jacob Tal has many video tutorials on servo's, see the one on servo amp basics velocity or current control.
http://www.galilmc.com/learning/tutorial-display.php?tutorial=servo-amplifier-basics
Max.

 

I assume it adjusts the voltage so that the product of the output voltage and current (power) stay constant (within the current and voltage limits of the supply). So it would have some type of multiplier to perform the multiplication of the output voltage and current.

SO WHAT IS THE DIFFERENCE BETWEEN VOLTAGE MODE AND POWER MODE

 

You still specifically need to define if it is the servo loop/drive you are referring to as you mention servo loop in your OP, or some other part of the equipment?
Max.

 

SO WHAT IS THE DIFFERENCE BETWEEN VOLTAGE MODE AND POWER MODE

"power mode" is when you use both current limit AND voltage limit at the same time on a power supply. It is not a fair/accurate description. I don't think good quality suppliers like Agilent, Tektronix use this term but I have seen it in the manuals of low-end power supplies.

It is essentially voltage control until you apply a load, then current limit if your load hits that. There is no constant power feature on the supply that called it POWER MODE - I think it was B&K.

 

SO WHAT IS THE DIFFERENCE BETWEEN VOLTAGE MODE AND POWER MODE

If there is a true "Power Mode" in a supply it would adjust the voltage to keep the output power constant independent of load. The Voltage Mode keeps the output voltage constant independent of load.

WHY ARE YOU SHOUTING?