Under Voltage and Over Voltage monitoring


The TPS3702 family of devices combines two comparators and a precision reference for overvoltage and undervoltage detection. The TPS3702 features a wide supply voltage range (2 V to 18 V) and highly accurate window threshold voltages (0.9% over temperature). The TPS3702 is designed for systems that require an active low signal if the voltage from the monitored power supply exits the accuracy band. The outputs can be pulled up to 18 V and can sink up to 10 mA. Unlike many other window comparators, the TPS3702 includes the resistors used to set the overvoltage and undervoltage thresholds internal to the device. These internal resistors allow for lower component counts and greatly simplifies the design because no additional margins are needed to account for the accuracy of external resistors.
The TPS3702 is designed to assert active low output signals when the monitored voltage is outside the window band.

Download PDF: Under Voltage and Over Voltage monitoring using TPS3702

Also there is one other IC from same manufacturer.

The TPS2400 has fixed turn-on and turn-off thresholds of 3 V and 6.9 V, respectively, making it an ideal overvoltage protector for 3.3 V and 5 V loads that are 6.9 V tolerant. However, many loads have an operating voltage that is greater than 6.9 V. To be compatible with these loads, the overvoltage threshold of the protector circuit can be
raised above 6.9 V.

Download PDF: Under Voltage and Over Voltage monitoring using TPS2400

Source: Texas Instrument

Types of Relays

An electrical relay is a switch that is used for controlling circuits. Today you’ll learn about different types of electrical relays.

Electromagnetic attraction type

The magnetic force produced by undesired current attracts the armature of the relay. Electromagnetic attraction type relays can operate on either a.c or d.c quantities. They are further divided into three types:

  1. Attracted armature type
  2. Solenoid type
  3. Balance beam type
Induction type relay

The working of Induction type relays relies on the electromagnetic induction phenomenon. They are only used for a.c quantities. They are further classified into two groups:

  1. Induction cup relay
  2. Induction disc relay
Directional type relay

Directional type relays operate on the direction of current and power. They are classified into two groups:

  1. Reverse current
  2. Reverse power
Time relays

The tripping instant in time-based relays can be controlled. Such relays are classified into three classes:

  1. Instantaneous type relays
  2. Definite time lag type
  3. Inverse time lag type
  4. Capacitor type
  5. Electronic type
Distance type relay

Distance type relays contain two coils. One of which is energized using current and another one with voltage. The voltage to current ratio is measured and working of distance relays is based on this voltage to current ratio. They are further classified into three distinctive groups:

  1. Admittance
  2. Impedance
  3. Reactance
Differential relay

A differential relay compares the difference of quantity entering and leaving the system. They are also classified into two groups:

  1. Differential current
  2. Differential voltage
Thermal Relay

The relay operates when the temperature rises above certain limit due to current.

Rectifier relay

The sensed quantities are first rectified and then provided to relay coil.

PMMC Relay

It is a permanent magnet d.c relay in which he coil is free to rotate.

Gas actuated relay

In such relays, the gas pressure is adjusted in a manner so as to trip the relay coils.

Numerical/Microprocessor based relay

Microprocessor based relays are the most advanced type of programmable relays.

Reed switch relays

These are simple and compact relays. The basic reed relay is simple reed switch which has a winding wrapped around the relay. They are manufactured in many DIP and SIP packages as well as winding free reeds are also available.

Static relays – Solid State Relays

Static relays are composed of electronic components. Such relays are composed of transistors, diodes, integrated circuits, resistors and other electronic components. An essential part of such relays is a comparator which takes two or more current/voltages as input and provides an output.

Frequency Monitoring relays

The frequency of voltage plays key role in electrical power networks. The working of various electrical machines, generators, and mechanisms heavily relies on frequency. Frequency relays continuously monitor the operating frequency of system and trip on the variations.

Thermal relays

As the name indicates, the working of thermal relays depends on the temperature of the equipment. They can either directly detect the temperature or can detect the current overloading conditions.

Motor load monitoring relays

Such relays monitor the load condition and operate under specified conditions. These relays can be based on current measurement or on cosφ based.

Insulation monitoring relays

Insulation monitoring relays continuously monitor the insulator. Whenever insulation fault occurs it immediately trips when the voltage drops behind specified threshold value.

Liquid monitoring relays

They are used to monitor regulator and control of liquid fluids.

Hybrid Relays

One part of such relays in electro-mechanical while another part is solid state electronics.

General purpose relays

These are different types of relays whose working principle is based on either of above types.

MAX44211 Output Protection


Unwanted transients emanating from the power line back to the line-driver’s output and back-EMF generated by the coupling circuit when the load is disconnected and connected, and vice versa, create undesirable over-voltage conditions. Back-EMF is also generated when the line driver outputs are toggled from high to low impedance state, if significant current was flowing at the disconnect time. The MAX44211 power line communications driver most often is placed facing the power line with an isolating stage between them. In case of such over-stress conditions, external protection is required to protect the MAX44211 and downstream circuits.

The internal ESD clamping structure is present inside MAX44211 (see Figure) to protect the part from ESD or sub-microsecond events. When the application has hazards where these events can occur frequently and for comparatively longer time, it is recommended to have external protection circuitry. Failure to accommodate an output protection can result in over-stressing the outputs (OUT+/ OUT-) and eventually damage the part.

This application note provides insights and information on how to add external protection circuitry at the outputs of the MAX44211. A circuit using VAVDD = 15V is used in this application note.

The figure shows the internal ESD clamping protection structure.

Download PDF: MAX44211-Output-Protection

Source: Maxim Integrated

High-Speed Over-current Detection


This high-speed, low-side over-current detection solution is implemented with a single zero-drift fast-settling amplifier (OPA388) and one high-speed comparator (TLV3201). This circuit is designed for applications that monitor fast current signals and over-current events, such as current detection in motors and power supply units.

The OPA388 is selected for its widest bandwidth with ultra-low offset and fast slew rate. These parameters allow the circuit to be a well-balanced, high-speed solution in order to accurately detect high frequency current components. In applications that only require average current detection, devices with less bandwidth can be used like the LPV821. In applications that require faster response time, devices with larger bandwidth can be used like the THS4521.

The TLV3201 is selected for its fast response due to its small propagation delay of 40 ns and rise time of 4.8 ns. This allows the comparator to quickly respond and alert the system of an over-current event all within the transient response time requirement. The push-pull output stage also allows the comparator to directly interface with the logic levels of the micro-controller. The TLV3201 also has low power consumption with a quiescent current of 40 µA.

Typically for low-side current detection, the amplifier across the sense resistor can be used in a non-inverting configuration. The application circuit shown, however, uses the OPA388 as a differential amplifier across the sense resistor. This provides a true differential measurement across the shunt resistor and can be beneficial in cases where the supply ground and load ground are not necessarily the same.

Dedicated current sense amplifiers can also be an option for high-speed current detection. The trade-offs for each option should be taken into account when deciding on a current sense solution. Integrated solutions can provide larger bandwidth and savings on board space, but can be more costly and offer limited customization. Discrete solutions can be lower cost and easily customizable, but could require precision resistors to increase measurement precision.

Download PDF: High-Speed-Overcurrent-Detection

Source: Texas Instrument