What is an Isolated AC to DC Converter?

Isolated AC to DC Converter separates the input from the output by electrically and physically dividing the circuit into two sections and hence preventing direct current flow between the input and output. An isolated AC to DC converter uses a high-frequency transformer to provide isolation or galvanic isolation (physically and electrically separate two circuits) between the AC input and DC output circuits. 

An isolated AC to DC converter usually consists of a diode bridge rectifier on the primary side, an input filter capacitor, switching devices such as power MOSFET or SCR or power transistor, a high-frequency transformer, inductor, filter capacitor in the output side, and control circuits to provide regulated DC output.

Key benefits of Isolated AC to DC Converters:

·Provides safety to humans and sensitive devices from the high and potentially hazardous AC input voltage.

Breaking ground loops.

·Avoids floating outputs and level shifting.

The isolated AC-DC converters are ideal for use in medical, industrial, instrumentation, smart home, commercial and industrial electronic equipment, IoT, telecommunication, battery charger, cell phone chargers, vehicle or aircraft batteries, military, kitchen appliances, DC motors, and other consumer electronics.

Applications

Low-power switch-mode power supplies (cell phone charger, standby power supply in PCs)

Low-cost multiple-output power supplies (e.g., main PC supplies <250 W[citation needed]) The flyback converter is commonly used at the 50 to 100 W power range, as well as in highvoltage power supplies for televisions and computer monitors - Fundamentals of Power Electronics, Erickson & Maksimovic .

High voltage supply for the CRT in TVs and monitors (the flyback converter is often combined with the horizontal deflection drive)

High voltage generation (e.g., for xenon flash lamps, lasers, copiers, etc.)

Isolated gate driver

Products & Classification

Flyback controllers

UCC28700

UCC28740

UCC28881

UCC28722

Series voltage references

REF35

REF3425

REF34-Q1

REF4132

Shunt voltage references

TLV431A

TLV431

UCC2870x Constant-Voltage, Constant-Current Controller With Primary-Side Regulation

1. Features

·< 30-mW No-Load Power for 5-Star RatingPrimary-Side Regulation (PSR) Eliminates Opto-Coupler

·+5% Voltage and Current Regulation

·130-kHz Maximum Switching Frequency EnablesHigh-Power Density Charger Designs

·Quasi-Resonant Valley-Switching Operation forHighest Overall Efficiency

·Patent-Pending Frequency-Jitter Scheme to EaseEMl Compliance

·Wide VDD Range Allows Small Bias CapacitorClamped Gate-Drive Output for MOSFETProtection Functions: Overvoltage, Low-Line, and Overcurrent

·Programmable Cable Compensation (UCC28700Only)

·NTC Resistor Interface (UCC28701, UCC28702 and UCC28703 Only) With Fixed CableCompensation Options

·SOT-23 Package

2. Applications

USB-Compliant Adapters and Chargers forConsumer Electronics (Cell Phones, Tablets andCameras)

AC and DC Power Supplies

3. Description

The UCC28700 family of flyback power supplycontrollers provides Constant-Voltage (CV)andConstant-Current(CC)output regulation without theuse of an optical coupler. The devices processinformation from the primary power switch and anauxiliary flyback winding for precise control of outputvoltage and current. Low start-up current, dynamicallycontrolled operating states and a tailored modulationprofile support very low standby power withoutsacrificing start-up time or output transient response.

Control algorithms in the UCC28700 family allowoperating efficiencies to meet or exceed applicablestandards. The output drive interfaces to a MOSFETpower switch. Discontinuous Conduction Mode(DCM) with valley switching reduces switching losses.Modulation of switching frequency and primarycurrent peak amplitude(FM and AM)keeps theconversion efficiency high across the entire load andline ranges.

The controllers have a maximum switching frequencyof 130 kHz and always maintain control of the peak-primary current in the transformer. Protection featureshelp keep primary andsecondarycomponentstresses in check. The UCC28700 allows the level ofcable compensation to be programmed. The UCC28701，UCC28702,and UcC28703 devicesallow remote temperature sensing using a NegativeTemperatureCoefficient (NTC)resistorwhileproviding fixed cable-compensation levels.

UCC28740 Constant-Voltage Constant-Current Flyback Controller

1. Features

·Less than 10-mW No-Load Power Capability

·Optocoupled Feedback for CV, andPrimary-Side Regulation (PSR) for CC

·Enables +1% Voltage Regulation and +5%Current Regulation Across Line and Load

·700-V Startup Switch

·100-kHz Maximum Switching Frequency EnablesHigh-Power-Density Charger Designs

·Resonant-Ring Valley-Switching Operation forHighest Overall Efficiency

·Frequency Dithering to Ease EMl Compliance

·Clamped Gate-Drive Output for MOSFET

·Overvoltage, Low-Line, and OvercurrentProtection Functions

·SO1C-7 Package

·Create a Custom Design Using the UCC28740 With the WEBENCH® Power Designer

2. Applications

USB-Compliant Adapters and Chargers forConsumer Electronics

-Smart Phones

-Tablet Computers

-Cameras

Standby Supply for TV and Desktop

White Goods

3. Description

UCC28740Theisolated-flybackpower-supplycontroller provides Constant-Voltage(CV)using anoptical coupler to improve transient response to large-load steps.Constant-Current(CC)regulation isaccomplished through Primary-Side Regulation (PSR)techniques. This device processes information fromopto-coupled feedback and an auxiliary flybackwinding for precise high-performance control ofoutput voltage and current.

An internal 700-Vstartup switch,dynamicallycontrolled operating states, and a tailored modulationprofile support ultra-low standby power withoutsacrificing startup time or output transient response.

Control algorithms in the UCC28740 allow operatingefficiencies to meet or exceed applicable standardsThe drive output interfaces to a MOSFET powerswitch.Discontinuous conduction mode(DC)withvalley-switching reduces switching losses. Modulationof switching frequency and primary current-peakamplitude (FM and AM)keeps the conversionefficiency high across the entire load and line ranges.

The controller has a maximum switching frequency of100 kHz and always maintains control of the peak-primary current in the transformer. Protection featureskeep primary and secondary component stresses incheck. A minimum switching frequency of 170 Hzfacilitates the achievement of less than 10-mW no-load power.

UCC28722 Constant-Voltage, Constant-Current Controller

1. Features

·< 50-mW No-Load Power

·Primary-Side Regulation (PSR) Eliminates Opto-Coupler

·Dynamic BJT Drive

·80-kHz Maximum Switching Frequency EnablesHigh-Power Density Charger Designs

·Quasi-Resonant Valley-Switching Operation forHighest Overall Efficiency

·Wide VDD Range Allows Small Bias CapacitorOutput Overvoltage, Low-Line, and OvercurrentProtection Functions

·Programmable Cable Compensation

·SOT23-6 Package

2. Applications

USB-Compliant Adapters and Chargers forConsumer Electronics

-Smart Phones

-Tablet Computers

-Cameras

·Standby Supply for TVs and Desktops

·White Goods

3. Description

The UCC28722 flyback power supply controller provides isolated-output constant-voltage(Cv) and constant-current(CC) output regulation without theuse of an optical coupler. The device processesinformation from the primary power switch and anauxiliary flyback winding for precise control of outputvoltage and current.

Dynamically-controlled operating states and a tailoredmodulation profile support high-efficiency operation atall load levels without sacrificing output transientresponse.

Control algorithms in the UCC28722 device allowoperating efficiencies to meet or exceed applicablestandards.The output drive interfaces to a bipolartransistor power switch,enabling lower-cost converterdesign.Discontinuous conduction mode(DCM)withvalley switching reduces switching losses,whilemodulation of switching frequency and primarycurrent peak amplitude(FM and AM)keeps theconversion efficiency high across the entire load andline ranges.

The controller has a maximum switching frequency of80 kHz and always maintains control of the peak-primary current in the transformer. Output overvoltageand overcurrent as well asinput undervoltageprotection features help keep primary and secondarycomponent stresses in check.The UCC28722 alsoallows compensation for voltage drop in the cable tobe programmed with an external resistor.

UCC28881 700-V, 225-mA Low Quiescent Current Off-Line Conver

1. Features

·Integrated 14-0,700-V Power MOSFET

·Integrated High-Voltage Current Source for Internal Device Bias Power

·Integrated Current Sense

·Internal Soft Start

·Self-Biased Switcher (Start Up and OperationDirectly from Rectified Mains Voltage)

·Supports Buck, Buck-Boost and Flyback Topologies

·<100-yA Device Quiescent Current

·Robust Current Protection During Load ShortCircuit

·Protection

-Current Limit

-Overload and Output Short Circuit

-Over Temperature

2. Applications

·AC-to-DC Power Supplies(Non-lsolated Buck Converter with Output Currentup to 225 mA for CCM:150 mA for DCM)

·E-Meter, Home Automation SMPS

·Bias Power for MCU, RF and loT EnabledDevices

·Appliances, White Goods and LED Drivers

3. Description

The UCC28881 integrates the controller and a 14-0,700-V power MOSFET into one monolithic device.The device also integrates a high-voltage currentsource,enabling start up and operation directly fromthe rectified mains voltage.UCC28881 is the samefamily device of UCC28880,with higher currenthandling capability.

The low quiescentcurrent of the device enablesexcellent effciency. With the UCC28881 the mostcommon converter topologies, such as buck, buck-boost and flyback can be built using a minimumnumber of external components.

The UCC28881 incorporates a soft-start feature forcontrolled start up of the powerstage whichminimizesthestressthepower-stageOncomponents.

REF35 Ultra Low-Power, High-Precision Voltage Reference

1. Features

• Ultra-low quiescent current:

– 650 nA (typical)

• Initial accuracy: ±0.05% (maximum)

• Temperature coefficient:

– 12 ppm/°C (maximum for −40°C to 105°C)

• Output 1/f noise (0.1 Hz to 10 Hz): 3.3 ppmP-P

• NR pin to reduce noise

• EN pin to reduce shutdown current consumption

• Long-term stability: 40 ppm at 1k hour

• Thermal hysteresis: 70 ppm

• Specified temperature range: −40°C to +105°C

• Operating temperature range: −55°C to +125°C

• Output current: +10 mA, −5 mA

• Input voltage: VREF + VDO to 6 V

• Output voltage options:

– 1.024 V, 1.2 V, 1.25 V, 1.6 V, 1.8 V, 2.048 V,

   2.5 V, 3.0 V, 3.3 V, 4.096 V, 5.0 V

• Small footprint 6-pin SOT−23 package

• Smallest footprint 4-pin WCSP package

2. Applications

• Flow transmitter

• Blood glucose monitor

• Servo drive control module

• Power quality analyzer

• Fault indicator

• Oscilloscope

• Process analytics

• Optical Module

3. Description

The REF35 is a family of nanopower, low-drift, highprecision series reference devices. The REF35 family features ±0.05% initial accuracy with 650 nA typical power consumption. The temperature coefficient (12ppm/°C) and long-term stability (40 ppm at 1000hours) of the device can help improve system stability and reliability. The low power consumption combined with high precision specifications are suitable for wide variety of portable and low current applications.

The REF35 supplies up to 10 mA current with 3.3 ppmp-p noise and 20 ppm/mA load regulation. With this feature set, REF35 creates a strong low-noise, high accuracy power supply for precision sensors and 12–16b data converters. The family is specified for operation from –40°C to 105°C and is functional over –55°C to 125°C. The wide temperature is suited for industrial applications.

REF35 is available in wide output voltage variants starting from 1.024 V to 5.0 V. The device is offered in a space-saving, 6-pin SOT-23 and 4-pin WCSP package options. Contact your local TI sales representative for available voltage and package options.

REF34xx Low-Drift, Low-Power, Small-Footprint Series Voltage Reference

1. Features

• Initial accuracy: ±0.05% (maximum)

• Temperature coefficient : 6 ppm/°C (maximum)

• Operating temperature range: −40°C to +125°C

• Output current: ±10 mA

• Low quiescent current: 95 μA (maximum)

• Ultra-low zero load dropout voltage: 100 mV

(maximum)

• Wide input voltage: 12 V

• Output 1/f noise (0.1 Hz to 10 Hz): 3.8 µVp-p/V

• Excellent long-term stability 25 ppm/1000 hrs

• Multiple small footprint 6 pin SOT-23 p

2. Applications

• Data acquisition systems

• Analog I/O modules

• Field transmitters

• Lab & field instrumentation

• Servo drive control modules

• DC power supply, AC source, electronic load

3. Description

The REF34xx device is a low temperature drift (6 ppm/°C), low-power, high-precision CMOS voltage reference, featuring ±0.05% initial accuracy, low operating current with power consumption less than 95 μA. This device also offers very low output noise of 3.8 μVp-p /V, which enables its ability to maintain high signal integrity with high-resolution data converters in noise critical systems. With a small SOT-23 package, REF34xx offers enhanced specifications and pin-topin replacement for MAX607x, ADR34xx and LT1790 (REF34xxT, no EN pin). The REF34xx family is compatible to most of the ADC and DAC such as ADS1287, DAC8802 and ADS1112. 

Stability and system reliability are further improved by the low output voltage hysteresis of the device and low long-term output voltage drift. Furthermore, the small size and low operating current of the devices (95 μA) benefit portable and battery-powered applications. 

REF34xx is specified for the wide temperature range of −40°C to +125°C.

REF34-Q1 Low-Drift, Low-Power, Small-Footprint Series Voltage References

1. Features

• AEC-Q100 qualified with the following results:

– Device temperature grade 1: –40°C to +125°C

ambient operating temperature

– Device HBM ESD classification level 2

– Device CDM ESD classification level C6

• Initial accuracy: ±0.05% (maximum)

• Temperature coefficient : 6 ppm/°C (maximum)

• Operating temperature range: −40°C to +125°C

• Output voltage options: 2.5V, 3.0V, 3.3V, 4.096V, 5.0V

• Output current: ±10 mA

• Low quiescent current: 95 μA (maximum)

• Low shutdown mode current: 3 μA (maximum)

• Wide input voltage: 12 V

• Output 1/f noise (0.1 Hz to 10 Hz): 3.8 µVPP/V

• Excellent long-term stability 25 ppm/1000 hrs

• Available in 6-pin and 5-Pin SOT-23 package and 8-pin MSOP package

2. Applications

• Body control modules

• On board chargers

• Traction inverters

• Battery management systems

• Advanced driver assistance systems

3. Description

The REF34-Q1 devices are low-temperature-drift (6 ppm/°C), low-power, high-precision CMOS voltage references. The devices have ±0.05% initial accuracy and low operating current with power consumption less than 95 μA. These devices also offer very low output noise of 3.8 µVPP/V, which enable the devices to maintain high signal integrity with high-resolution data converters and noise critical systems.

Stability and system reliability are further improved by the low output-voltage hysteresis of these devices and low long-term output voltage drift. Furthermore, the small size and low operating current of the devices (95 μA) make them an excellent choise for batterypowered applications. The REF34-Q1 features an enable pin that can set the device into shutdown where it consumes a low stand by current (3 μA) to help with overall system power during standby.

The REF34-Q1 family is specified for the wide temperature range of −40°C to +125°C. Contact the Lansheng Technology sales representative for additional voltage options.

REF4132 Low-Drift, Low-Power, Small-Footprint Series Voltage Reference

1. Features

1• Voltage options: 2.5V, 3V, 3.3V, 4.096V, 5V

• Initial accuracy: ±0.05% (maximum)

• Low temperature coefficient :

– A grade: 12 ppm/°C (maximum)

– B grade: 30 ppm/°C (maximum)

• Operating temperature range: −40°C to +125°C

• Output current: ±10 mA

• Low quiescent current: 100 μA (maximum)

• Output 1/f noise (0.1 Hz to 10 Hz): 15 µVPP/V

• Excellent long-term stability 30 ppm/1000 hrs

• Small footprint 5-pin SOT-23 package

2. Applications

• Data acquisition (DAQ)

• PLC analog I/O modules

• Field transmitters

• Motor drive control module

• Battery test equipment

• LCR meters

3. Description

The REF4132 device is a low temperature drift (12 ppm/°C), low-power, high-precision CMOS voltage reference, featuring ±0.05% initial accuracy,

low operating current with power consumption less than 100μA. This device also offers very low output noise of 15 μVp-p/V, which enables its ability to maintain high signal integrity with high-resolution data converters in noise critical systems. Packaged in the same SOT-23-5 package, REF4132 offers enhanced specifications and pin-to-pin replacement for LM4128 and LM4132.

Stability and system reliability are further improved by the low output-voltage hysteresis of the device and low long-term output voltage drift. Furthermore, the small size and low operating current of the devices (100 μA) can benefit portable and battery-powered applications.

REF4132 is specified for the wide temperature range of −40°C to +125°C.