Featured Engineer

Interview with Peter B. Green

Peter B. Green

Peter B. Green - LED Group Manager, International Rectifier

How did you get into electronics/ engineering and when did you start?

I first started to get interested in electronics at about 13 years old. I started by taking things apart then moved on to buying parts from a local hobbyist shop and trying to build things. I started to collect old test equipment and eventually bought one of the first affordable home computers back in the 80’s.

What are your favorite hardware tools that you use?

I work mostly with off line applications so the tools I use mostly are;
LeCroy digital oscillscope (with x10,x100 and HF current probes), Fluke true RMS digital multimeter, Agilent signal generator, Voltech power meter

What are your favorite software tools that you use?

ORCAD schematic capture, Protel 99SE schematic capture and PCB layout, Pentalogix Viewmate Gerber viewer, Simetrix simulator, Mathcad 11, Microchip MPLAB IDE with HITECH C compiler.

What is the hardest/trickiest bug you have ever fixed?

Some of the trickiest bugs to fix are related to PCB layout in switching power supplies. Although the circuit may be connected correctly, it is also critical to route the traces to avoid ground loops and noise pickup. Such problems can cause severe instability and poor performance. Some parts of the circuit are extremely sensitive to noise so very careful routing. Some very strange circuit behavior can occur where the cause is very hard to track down. Other big headaches can occur when debugging embedded code.

What is on your bookshelf?
  • The Art of Electronics – Horowitz & Hill
  • Circuits, Devices and Systms – Smith & Dorf
  • Elements of Power Electronics – Krein

Non-technical

  • The greatest show on earth – Dawkins
  • The demon haunted world – Sagan
  • The moral landscape – Harris
Do you have any tricks up your sleeve?

For problem solving on the bench I always use a simple process of elimination, isolating different parts of the circuit and testing section by section until the problem area is identified. I always use an oscilloscope to look at waveforms at different points in the circuit to find out the point where the circuit goes from working correctly to not working correctly. I believe many electronics engineers with years of design experience do this, which enables us to find problems much more quickly than most of the younger guys. No matter how much education you have there’s no substitute for experience.

What has been your favorite project?

Designing dimmable electronic ballasts for fluorescent lamps, especially with digital dimming using the DALI standard. I enjoy designing mixed analog power /digital systems and writing embedded C code.

Do you have any note-worthy engineering experiences?

In more than 30 years I have blown up so many components and been shocked more times than I can remember especially early on in my career. Fortunately that happens only very rarely now and I always use an isolated AC power source. With experience I can usually see when a circuit is at risk of blowing up by testing the temperature of components, looking at waveforms and sometimes listening for the sound stress or instability.

What are you currently working on?

I am developing a range of ASICs for LED driver applications aimed at replacing; incandescent, fluorescent, halogen and HID lighting in general lighting applications ranging from lightbulb and CFL replacements to high power street lamps. I am also working on application support material such as technical papers and evaluation boards to support these products.

When designing an LED driver, what aspects of a design effect efficiency the most?

Efficiency in an LED depends on several factors and there are several different circuit topologies used the choice of which depends on the input and output voltage and current requirements. Simple single stage circuits such as Buck or Flyback converters are most efficient at low power levels although for compatibility with triac based dimmers additional bleed circuits are usually added which reduce the efficiency. Two stage approaches are generally used at power levels above about 50W, for example a Flyback plus Buck or a Boost plus half-bridge. These offer better efficiency at higher power levels.

In all converter designs there are switching losses of power transistors that increase with frequency as do the core losses in inductors and transformers. There is a tradeoff between component size and losses which determines the optimum switching frequency. There are also conduction losses in the circuit which are dependent on current and DC resistance in inductors and on resistance or on state voltage in power switches. In designs where the output current driving the LEDs is relatively high there are also significant losses in the output rectifier diodes to be taken into account.

What do you think it will take for mass adoption of LED lighting?

At the moment there are two main barriers to mass adoption of LEDs. The biggest is cost. Although long operating life can be shown to save money of long periods of time, LED based lights are still very expensive at the moment. A typical LED lightbulb replacement product often retails around $30 compared with a CFL at under $5. Although the superior quality and performance of LED lighting is widely understood, the high cost of this new technology will limit it to early adopters for the most part.

The other issue is luminous efficacy expressed in Lumens per Watt (lpw). Many are still arguing that LED based light fixtures do not produce equivalent lpw compared with fluorescent and HID products. Widely varying lpw figures are being quoted for LED lights from 25 to 90 depending on the type of LEDs used, termperature, optics and how the measurement is made. LED technology is constantly improving however and it seems inevitable that in the next few years devices will become widely available that can clearly demonstrate superior performance over the alternatives.

What direction do you see your business heading in the next few years?

I believe my field of SMPS design focusing on LED drivers and lighting ballasts will move towards greater integration into smart ICs, however the basic power supply design process and techniques will not change too much. With the introduction of smart power ICs and new high voltage switch technoligies like GaN, I expect to see increases in efficiency and reduction in size in power converters due to higher frequency operation.

What challenges do you foresee in our industry?

The challenge is to produce quality products, which provide performance, safety and reliability aimed at preserving the environment. Unfortunately we need to compete with cheap, poor quality, mass produced products designed to fail within a short time and end up in land fills. I believe that electronic products should be made to last to cut down on waste and pollution and preserve the planets resources as much as possible. This is a challenge with technology advancing so rapidly so we must also recycle where possible.

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