Choosing an op amp and getting the best out of it involves some understanding of what is inside the chip, particularly the input stage. Simple bipolar input stage A conventional bipolar opamp will usually have a long-tailed-pair with two NPN or PNP input transistors as shown below. This explains the limited working range of a […]
Industry Experts
Driving High Power LEDs
High power LEDs, particularly “white” ones are becoming increasingly used in commercial products from cars and domestic lighting to street lighting and with efficiencies which can exceed that of compact fluorescent lamps (CFL). That efficiency is likely to improve as the technology develops but you must also pay attention to your drive circuitry, not simply […]
Choosing and Driving Laser Diodes
Laser diodes come in a wide range of types and power. They are in DVD and CD players and writers, used in fibre-optic communications, visible laser pointers, distance measurement, printers, medicine and industry. The main decision points are: wavelength power pulsed or continuous. Wavelength depends on the application. If you want the laser as a […]
Biasing bipolar transistor circuits
Bipolar transistors used in linear applications need “biasing”, as do other transistors (JFET, MOSFET) when used for linear applications rather than as switches. When used as a “switch” you simply want the transistor to be ON or OFF and don’t really care about having in-between states, although when you are switching high power or switching […]
Energy Harvesting
Energy harvesting is a hot topic at the moment. The desire to save energy, create it at no cost or power devices virtually forever without needing a conventional power source has a certain appeal particularly for remote devices away from conventional power sources. A device “powered” by simple human movement have been around since before […]
MOSFET Drivers – what are they and why do we need them?
There are a lot of MOSFET drivers around these days. MOSFET drivers often contain MOSFETs themselves. There are several reasons for needing MOSFET drivers: Drive current – MOSFETs can have very high gate capacitance. For example, the IRF530NS from International Rectifier is a 90mW device which can withstand 17A continuous drain current at 100V and […]
Switching regulator fundamentals – the buck converter
By Chris Francis Switching regulators are everywhere – buck, boost, SEPIC, Cuk, flyback etc. They are for converting power from one voltage to another in a relatively efficient manner. Whereas with a linear regulator you might lose 50% of the power or more in heat, switching regulators can reach efficiencies of close to 100% for […]
SiGe:C transistors compared with HEMT for non 50 ohm systems
by Chris Francis When dealing with high speed, low noise, non 50 ohm systems such as transimpedance amplifiers, a GaAsFET or HEMT can be a viable choice. On the face of it, devices such as the ATF35143 from Avago (previously known as Agilent) have suitable characteristics – low noise, low bias current and high bandwidth. […]
Linear Technology LT8614 “SilentSwitcher”
The Linear Technology LT8614 “SilentSwitcher” claims to reduce EMI/EMC emissions to well below the CISPR 25 Class 5 limit. It also seems a well specified step-down switching regulator with 2.5µA quiescent current, up to 42V input and 4A output current. It also has a high efficiency of 96% at 1MHz (it is a synchronous regulator). […]