The brain-burning CT power controller, circuit breaker trip device... Experts explained it in Changsha

ADI Marketing Manager Zhang Songgang

Low voltage circuit breakers include molded case circuit breakers (MCCB) and frame circuit breakers (ACB). Since their structures are very compact, they are basically impossible to repair.

The tripping device of low voltage circuit breaker is divided into two types: thermal magnetic and electromagnetic tripping device and electronic tripping device (i.e. intelligent tripping device ETU). The main overcurrent protection functions of ETU of low voltage circuit breaker include long delay, short delay, instantaneous action, grounding protection and leakage protection. In addition, it also has three auxiliary functions: voltage and current measurement function, harmonic detection and communication and remote control.

First, let's take a look at the ETU system block diagram of the molded case circuit breaker~

From the system block diagram, we can see the main application features of the ETU circuit design of the molded case circuit breaker——

• Inducing energy from current transformers to supply circuit boards

• Converting a current source into a voltage source

• At present, most ETUs of molded case circuit breakers are still single-coil type, and the power supply and signal come from the same current transformer.

• Minimum starting current - single phase 0.2 times rated current

• Start-up speed and the order of the startup of the entire circuit

• The whole board startup current needs to have a certain hysteresis control

• Compatible with single coil and dual coil signal conditioning requirements

• A current transformer under one framework needs to cope with gain requirements of different rated currents

• Two different signal conditioning topologies (single coil half/full wave rectification vs dual coil air core bipolar output)

• The analog trip circuit enables the circuit to protect against extremely large currents before the MCU is initialized.

ADP2450, is ADI has developed a dedicated CT power controller suitable for CT self-powering applications with larger output current (mA level ~ 10A level). The product integrates a 4.5V ~ 36V adjustable current source (CT output) to a voltage source, a 500mA Buck regulator, CT power hysteresis monitoring, output voltage monitoring, Actuator drive circuit, etc.

So, what are the advantages of the molded case circuit breaker ETU system after using ADP2450?

Block diagram of molded case circuit breaker ETU system using ADP2450

Obviously, the circuit board size of the molded case circuit breaker ETU system using ADP2450 is greatly reduced , and it is compatible with single-coil and double-coil... Do you want to know which functions of ADP2450 achieve these "transcendence"?

• Vboost voltage can be up to 36V

• If you need to be compatible with auxiliary power supply, you only need to add a pair of diodes to do OR logic.

• Shunt Boost controller consumes only 400uA of quiescent current

• The voltage source built in Shunt Boost is used for secondary rectification to system 5V or 3.3V for the entire circuit board to work

• The maximum current output can reach 500mA

• Fast soft start time of 400us

• High switching frequency reduces external inductance requirements. For low-power applications (if the power supply current of the next stage is only a few tens of mA), an ordinary 1206 inductor can meet the requirements.

• Internal power-on sequence logic control

• Buck output starts to start after Vboost exceeds Vpth setting voltage

• After the Buck output reaches 90% of the set value, the Analog Trip circuit, PGA output, etc. begin to be enabled, and the Reset output signal is unlocked after a delay.

• Negative voltage input => positive voltage output + amplification

• +/-8V overvoltage protection

• The signal coil has bipolar output
  

• An external RC integrator circuit can be used to interface the air-core coil

• PGA amplifies the signal and adds a DC bias of 1/2 Vref to interface with the ADC input range of a general-purpose processor.

• The output of the PGA can be quickly established within tens of microseconds, making it possible for the MCU to sample two different gains of the signal in one sampling cycle.

Features of the ETU system board built using ADP2450:

• 40mm x 30mm

• 4-channel (ABCN) LSI overcurrent protection

• System starting current (single phase) 18% (18A@100A rated current)

• Vboost is set to 9.2V

• 10 x In Power supply cold start trip time 4ms

The space is limited, so I will share it here first. Remember to like it~