What is Digital Power Supply? Sanken MCU for Digital Power Supply “MD660x Series”

Contents

A Movement of Switching Power Supply; ”Analog Control to Digital Control”

Demand for minimizing the energy loss of switching power supply

Switching power supply (AC/DC or DC/DC) is an essential requirement in various fields such as industry, consumer, or automotive.
One of the requirements of switching power supply is how to convert the supplied power to the power required by load with minimized loss and stable output. Global warming and energy issues are urgent concerns recently, so technology to minimize energy loss in power supply to the extent possible has been sought.

Conventional “Analog Control” ==> New Approach “Digital Control”

Analog control was generally used for conventional switching power supply in order to stabilize output voltage. For the analog control power supply, response to load change and power supply efficiencies have been improved by adopting various methods such as the characteristics of error amplifiers to compensate phases or optimal selection of operating modes in low-load conditions.
On the other hand, as energy issues become more serious, a power supply utilizing digital control technology is being newly incorporated as a method to achieve new high efficiency.
Digital power supply can control the converter using new topology which was hard to be achieved by conventional analog control. It is also a great advantage that the operating method or control method can be switched optimally depending on the situation by communicating with the host side or load side.
However, control of digital power supply requires a very quick response because control targets are electric circuits, so a powerful and expensive DSP (Digital Signal Processor) was necessary in the past.

Sanken MCU for Digital Power Supply, “MD660x Series”
Sanken Electric has released the MD660x Series, 8-bit MCU (Micro Controller Unit) optimum for digital power supply control, which are already in production.
MD660x Series are compact and low-power MCUs equipped with indispensable and optimized functions and performance required to control the power supply. You can easily design a digital power supply by using MD660x Series.

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MCUs for Digital Power Supply

What is Digital Power Supply?

Conventional Analog Control Power Supply

The conventional analog control power supply realizes feedback control by, for example, compensating the phase characteristics in feedback loop using an error amplifier and adjusting the duty ratio of the PWM waveform indicating ON/OFF of the power MOSFET built in the converter (The diagram, left half).


This method is inexpensive but has the following problems

  • If multiple error detections are to be implemented, the hardware size will be increased.
  • There are limitations on variegating the converter topology to improve efficiency.
  • It is difficult to lower output voltage because of the limitations of the reference voltage on the error amplifier.
  • It is necessary to replace passive components to support various specifications.
  • To add the communication capability or operation logging function, additional micro-controller device is required.

On the other hand, it is a main feature of the digital control power supply to compensate phases using arithmetic operations by a DSP (digital filter), which was performed by an error amplifier by the analog control method (The diagram, right half).


Digital Power Supply

How does digital power supply compensate phases using arithmetic operations by a DSP? This section introduces the flow of digital control.

Flow of Digital Control

①The output voltage fed back is read by the A/D converter and converted to a digital numerical number.

②Perform phase compensation by arithmetic operations in the DSP to determine the necessary PWM duty ratio.

③Output the PWM waveform in accordance with the duty ratio determined in step ②.

The PWM waveform of step ③ is generated by a digital logic circuit. If the resolution of duty ratio or cycle which can be specified is not high, the output voltage is rippled. So, high-resolution PWM generating smooth and precise duty ratio or cycle period should be used.

These processes are performed repeatedly in a certain control cycle. Control is provided in synchronization with the cycle of the PWM carrier in many cases.
Digital control can realize flexible active processing in every cycle, which cannot be performed by analog control, so that more advanced control can be introduced.


Devices Required to Control Digital Power Supply

To control digital power supply, the following devices are required:

Devices required for feedback control

  • A high-speed high-precision A/D converter
  • A DSP capable of high-speed calculation
  • A high-resolution PWM capable of setting up duty ratio or cycle smoothly
  • A comparator or an operating amplifier to detect overcurrent etc.

Various intelligent processing and communications processing

  • CPU
  • Communications function
  • A flash memory which can be rewritten freely as a memory to store CPU programs

Sanken MD660x Series are equipped with all these elements required for digital power supply.


Advantages Obtained by Digital Power Supply Control

There are many advantages obtained by digital power supply control.
It is necessary to consider digitalization of the power supply which can derive the most appropriate advantages according to the application out of the various advantageous trade-offs.


1, High Efficiency
  • - The most appropriate operating mode and operating frequency are
      selectable according to the load.
  • - Dead time can be changed optimally depending on the load.
  • - Duty ratio control to reduce the circulating current
  • - Intermittent operation in the condition of light load
  • - Switching between linear control and non-linear control
  • - Changing the priority order between efficiency and power factor, or
      suspending PFC under light load

2, High-speed Response
  • - Phase compensation that analog control cannot realize
  • - Modern discrete control based on an advanced theory
  • - Optimal non-linear control

3, Supporting various converter topologies

  • - Support for converter topologies which are difficult to be achieved with
      analog control.
  • - Synchronous rectification and bridgeless configuration, which achieve
      higher efficiency
  • - Support for special topologies by which the number of components can be
      minimized.

4, High Reliability


  • - Phase compensation by which chemical capacitors can be eliminated
  • - Elimination of analog circuits’ aging degradation
  • - Reduction of EMI noise realized by frequency modulation

5, Supporting Various Device Types

  • - It is able to define the specifications and set the parameters by software,
      which were set by passive components in the past.
  • - The specifications of a custom power supply are supported by writing
      corresponding parameters in the flash memory directly before shipment.

6, Downsizing

  • -To be higher switching frequency
  • -To incorporate the multifunctional hardware achieved by analog control into
      software
  • -To incorporate the error detecting external hardware such as OCP/OVP into
      software


7, Low Voltage and High Current


  • - High-precision low-voltage sensing by the A/D converter, which cannot be
      achieved by analog control
  • - Supporting SoC/FPGA, whose current consumption varies greatly and
      sharply, by utilizing high-speed response

8, Intelligent (such as the communication
    function)
  • - The startup/shutdown sequence of the power supply can be set freely.
  • - Storage of the operation status log
  • - Setup of the power supply state using external commands
  • - Collaborated operation with other power supply devices

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