This article explains the basic concepts of linear regulators and switching mode power supplies (SMPS). It is aimed at system engineers who may not be very familiar with power supply designs and selection. The basic operating principles of linear regulators and SMPS are explained and the advantages and disadvantages of each solution are discussed. The buck step-down converter is used as an example to further explain the design considerations of a switching regulator. by HENRY ZHANG
by Zhongming Ye:
Flyback converters are widely used in isolated DC/DC applications because of their relative simplicity and low cost compared to alternative isolated topologies. Even so, designing a traditional flyback is not easy—the transformer requires careful design, and loop compensation is complicated by the well known right-half plane (RHP) zero and the propagation delay of the opto-coupler.
Linear Technology’s no-opto flyback converters, such as the LT3573, LT3574, LT3575, LT3511, and LT3512, simplify the design of flyback converters by incorporating a primary-side sensing scheme and running the converter in boundary mode.
Micropower Isolated Flyback Converter with Input Voltage Range from 6V to 100V - [Link]
The LT8301 is a monolithic flyback regulator that significantly simplifies the design of isolated DC/DC converters. By sampling the isolated output voltage directly from the primary-side flyback waveform, the part requires no opto-isolator or third winding for regulation. The LT8301 operates over a 2.7V to 42V input voltage range, has a 1.2A/65V power switch and delivers up to 6 watts of output power, making it well suited for a wide variety of industrial, medical, datacom, military and automotive applications. The LT8301 is available in a small TSOT-23 package. Extended and industrial versions operate over a junction temperature range of -40°C to 125°C. A high temperature automotive grade operates from -40°C to 150°C and a military grade operates from -55°C to 150°C.
LT8301 – 42VIN Micropower No-Opto Isolated Flyback Converter with 65V/1.2A Switch - [Link]
The LTC3128 is a high efficiency, input current-limited buck-boost supercapacitor charger with active charge balancing for 1 or 2 series supercapacitors. The LTC3128 features an average input current limit that can be programmed up to 3A with +/-2% accuracy, preventing power source overload while minimizing capacitor recharge time. Highly efficient active charge balancing eliminates dissipative external ballast resistors, ensuring balanced operation and charging with mismatched capacitors, and less frequent recharge cycles. A programmable maximum capacitor voltage clamp actively monitors and enforces the voltage across each capacitor in the series stack, ensuring reliable operation as capacitors age and develop mismatched capacities. The low noise buck-boost topology allows the output supercapacitor to be charged whether above or below the input.
LTC3128 – 3A Monolithic Buck-Boost Supercapacitor Charger and Balancer - [Link]
by Hua (Walker) Bai:
The meaning of the term “high power LED” is rapidly evolving. Although a 350mA LED could easily earn the stamp of “high power” a few years ago, it could not hold a candle to the 20A LEDs or the 40A laser diodes of today. High power LEDs are now used in DLP projectors, surgical equipment, stage lighting, automotive lighting, and other applications traditionally served by high intensity bulbs. To meet the light output requirements of these applications, high power LEDs are often used in series. The problem is that several series-connected LEDs require a high voltage LED driver circuit. LED driver design is further complicated by applications that require fast LED current response to PWM dimming signals.
Design Notes: 60V, Synchronous Step-Down High Current LED Driver - [Link]
The LT6015 is a single Over-the-Top operational amplifier with outstanding precision over a 0V to 76V input common-mode voltage range. It incorporates multiple built in fault tolerant features, resulting in no-compromise performance over wide operating supply and temperature ranges. Over-the-Top inputs provide true operation well beyond the V rail. The LT6015 functions normally with its inputs up to 76V above V-, independent of whether V+ is 3V or 50V. Input offset voltage is 80μV max, input bias current is 5nA and low frequency noise is 0.5μVP-P, making the LT6015 suitable for a wide range of precision industrial, automotive and instrumentation applications. Fault protection modes guard against negative transients, reverse battery and other conditions. The LT6015 is available in a 5-lead SOT-23 package and is fully specified over -40°C to 85°C, -40°C to 125°C, and -55°C to 150°C temperature ranges.
LT6015 – 3.2MHz, 0.8V/μs Low Power, Over-The-Top Precision Op Amps - [Link]
The LT8614 is a 4A, 42V input capable synchronous step-down switching regulator. A unique Silent Switcher architecture reduces EMI/EMC emissions by more than 20dB, well below the CISPR 25 Class 5 limit. Even with switching frequencies in excess of 2MHz, synchronous rectification delivers efficiency as high as 96% while Burst Mode operation keeps quiescent current under 2.5μA in no-load standby conditions. Its 3.4V to 42V input voltage range makes it ideal for automotive and industrial applications.
LT8614 – 42V, 4A Synchronous Step-Down Silent Switcher with 2.5μA Quiescent Current - [Link]
The LTC2057 is a high voltage, low noise, zero-drift operational amplifier that offers precision DC performance over a wide supply range of 4.75V to 36V (or 4.75V to 60V for the LTC2057HV). Offset voltage and 1/f noise are suppressed, allowing this amplifier to achieve a maximum offset voltage of 4μV and a DC to 10Hz input noise voltage of 200nV peak to peak (typ). The LTC2057’s self-calibrating circuitry results in low offset voltage drift with temperature, 0.015μV/°C (max), and zero-drift over time. The amplifier also features an excellent power supply rejection ratio (PSRR) of 160dB and a common mode rejection ratio (CMRR) of 150dB (typ).
LTC2057 – 60V Zero-Drift Operational Amplifier with 220nVP-P Noise - [Link]
Linear Technology have announced the LTM4624 14V, 4A step-down µModule® (micromodule) regulator in a 6.25 x 6.25 x 5.01mm BGA package. Along with two (1206 package) ceramic capacitors and a (0603 or smaller package) resistor this complete regulator solution fits within 1cm² on a single-sided or 0.5cm² on a double-sided PCB. Like other µModule regulators in the range, the LTM4624 contains the DC/DC controller, power switches, inductor and compensation on-board. It is designed to operate from a 4V to 14V input supply, delivering a regulated output adjustable between 0.6V to 5.5V which according to Linear Technology make it ideal for applications in communications, storage, industrial, and medical systems. [via]
4A Step Down µModule in less than 1cm² - [Link]
Steve Taranovich writes:
Linear Technology Corporation announced the LT8705, a very high efficiency (up to 98%) synchronous buck-boost DC/DC controller that operates from input voltages above, below or equal to the regulated output voltage. This device has four feedback loops to regulate the input current/voltage, along with the output current/voltage.
Convert any input voltage from 2.8V to 80V into a fixed output voltage or output current - [Link]