Fairchild Semiconductor’s Power Supply Demos at APEC 2012 Showcase mWSaver™ Technology

February 2, 2012

As standby power requirements in devices such as notebooks, printers, LCD TVs and monitors continue to decrease, below 50mW in many applications, designers need a solution to address standby power consumption in their current designs. To meet these stringent regulations today, additional circuitry or control devices are needed to remove the power loss, resulting in a much higher BOM cost and a more complex circuit design.


At APEC 2012, in booth #701, February 5-9, 2012, at Disney’s Coronado Springs Resort, Orlando, Fairchild Semiconductor will demonstrate the FAN6756, which provides designers <30mW low standby power; and a high-efficiency dual-switch Flyback solution that provides designers with a reduced bill of materials and an easy to design topology that meets 2013 ErP requirements.


The single-chip FAN6756 is a highly integrated green-mode PWM controller, capable of significantly reducing standby losses in SMPS designs, eliminating up to 15 external components. When compared to competitive IC solutions available today, the device achieves greater power savings and can save the designer up to $.30 in bill of material (BOM) costs.


Fairchild’s dual switch QR flyback topology and secondary synchronous rectification is the ideal solution for AIO applications – providing good overall efficiency, managing low power loss at light load, while providing ease of design.


The Dual Switch Flyback solution from Fairchild is perfectly suited for applications from 75W~230W and consists of the FAN6920MR integrated critical mode PFC and Quasi-resonant Current Mode PWM controller, the FAN7382 gate driver, in tandem with the FAN6204 secondary synchronous rectifier controller for flyback topology and forward freewheeling rectification. Combined, these devices provide best-in-class power consumption at no/light load, enabling designs to meet 2013 ErP standard without the additional circuitry LLC solutions require.


Fairchild Semiconductor’s mWSaver technology offers best-in-class minimum no-load and light-load power consumption to meet current and proposed worldwide standards and regulations and enables designers to achieve reduced form factors, improved reliability and lower system costs.


Join us at APEC 2012 in booth #701 to see our extensive portfolio of power solutions!


Fairchild Semiconductor: Solutions for Your Success^TM


Can’t make it to the show? Follow us on Twitter (@ http://twitter.com/FairchildSemi) to catch the latest from the show floor.

Tags: 2013 ErP standard, APEC, APEC 2012, dual switch QR flyback, FAN6204, FAN6756, FAN6920MR, FAN7382, green-mode PWM controller, high-efficiency dual-switch Flyback, LCD TVs, monitors, mWSaver technology, notebooks, printers, secondary synchronous rectification, standby power consumption

Standby Power Under 10mW Now Possible for Portable Device Chargers

April 19, 2011

With the demand for AC-DC external power supplies projected to increase from just over 3 billion units in 2010 to 4.97 billion units in 2014, and because this is a key growth area of communications, driven by mobile phones, finding ways to reduce standby power is essential.

 These growth numbers are indicators of the scope of the problems associated with reducing standby power consumption. On one level, the growth in external power supplies is a proxy for the growth in the appliances and electronic equipment segments that populate more homes and offices worldwide. On another level, consider that the single biggest application for power adapters-cell phone chargers-typically sit plugged in and unused for 20 hours a day, wasting energy that entire time.

A typical American home has 40 products constantly drawing power (standby power). Together these amount to almost 10 percent of residential electricity use, or about $220 per year. Figures for most developed countries also show 5 percent to 10 percent of power consumption going to standby power.

When you look at the cumulative data, the scope of the situation is more dramatic. In the US the collective bill for standby power usage now exceeds $4 billion annually. Altogether (offices and homes) standby power use is roughly responsible for 1 percent of the global CO₂ emissions. Further, experts agree that a majority of standby power consumption can be eliminated with regulatory policies, smart engineering and changes in personal habits.

 To help designers meet the ultra-low standby power challenge they face, Fairchild Semiconductor developed mWSaver^TM technology. Offering best-in-class power savings for power supplies, with the fewest possible components, devices in this series integrate five patented technologies: off-time modulation, JFET HV start-up and circuit, feedback impedance switch, HV discharge, and PSR control to drop out voltage; as well as burst mode operation and low operation current techniques. It is only by integrating these unique technologies, leveraged together, that the most stringent standby specifications can be met.

Take the FAN302HL for example. This device is a highly integrated PWM that provides several features to enhance the performance of general flyback converters, including constant-current control and a proprietary topology that enables simplified circuit designs without secondary feedback circuitry, especially important in battery charger applications. Using the FAN302HL, the standby power of a typical charger can be reduced to under 10mW, compared to roughly 400mW.

By developing solutions like mWSaver technology and the FAN302HL, Fairchild enables engineers to drive innovation in their designs for maximum performance, simplify designs and reduce bill of materials costs. To learn more, visit http://www.fairchildsemi.com/products/mwsaver/

Tags: AC-DC power supplies, Energy Efficiency, FAN302HL, standby power

LLC Resonant Transformer Design Tips

May 26, 2010

Featuring zero voltage switching and low voltage stress, LLC resonant transformers are suitable for high power and high efficiency power supplies. As LLC resonant power supplies are now being widely used and more and more people are asking questions about LLC transformer design. For this blog, I’ll discuss some frequently asked questions on this topic.

Transformer Saturation Issues

Q: My LLC transformer is designed to work in low magnetic induction intensity (Bm), but why does the temperature of the magnetic core become very high?

 A: The LLC transformer works in LC resonance state. The LC resonance circuit features high Q, which is greater than 1 in your case. Thus, the voltage actually applied on the transformer is larger than the input voltage, which is a problem to be tackled when designing LLC transformers. Otherwise, the transformer will not work in magnetic induction intensity as you designed.

 It is uncommon to have this saturation problem when the input voltage is high, as the switching frequency would also be high and the LC resonance circuit gain is low here. But, when the input voltage is low, the switching frequency will be low and the LC circuit gain is high, and in this case it is likely to have a saturation problem. So, when calculating the minimum turns of the inductance coil that you need, you must multiply your primary calculation by the gain factor. Furthermore, if leakage inductance is considered, it is better to multiply your result by the reciprocal of the coupling factor.

 Choice of Wire

Q: Why does the temperature of the winding become very high during the aging test?

 A: When an LLC transformer works in high frequency, the winding wire with an alternating magnetic field applied, experiences not only skin effect, but also proximity effect. The skin effect is the inherent behavior of the magnetic field going through the wire, while the proximity effect is induced by the magnetic field of the nearby conductor. Unlike flyback transformers, the primary winding of LLC transformers is on the same side, and the current in each of the winding turns flows in the same direction. The proximity effect becomes more significant as the number of winding layers increases. To solve this problem, you must use stranded wire with more wire cores.

 Turns of Secondary Winding

Q: Why does the actual operating frequency deviate from the designed frequency?

A: This is a problem that involves many issues, and therefore it is difficult to explain in a few words. But, I find that designers like to determine first the turns of the primary winding, and then calculate the turns of the secondary winding according to the transformation ratio. The result obtained this way is often not an integer, so designers tend to simply round it up. This can create a large error in the transformation ratio, since the secondary winding usually has only a few turns. It is recommended that designers choose a proper integer for the secondary winding according to the calculation above, and then re-calculate the turns of the primary winding by the transformation ratio and then round up the result. Since the primary winding usually has more turns, the round-up error becomes relatively less significant.

 No-load Voltage

Q: Why does my transformer have high light-load and no-load voltages?

 A: This is also a complicated problem. One of the factors causing the problem might be the parasitic oscillation induced by the leakage inductance of the secondary winding and the parasitic capacitance among different winding layers or turns of the secondary winding. This is common in secondary windings with a large number of winding layers or turns. With light load, the parasitic oscillation is very strong, leading to an output voltage far beyond the designed value. To solve this problem, you can reduce the parasitic capacitance by isolating each secondary winding layer with rubber tapes, and you can also reduce the parasitic oscillation by using pile winding instead of parallel winding, for different winding directions.

 I’d be happy to answer any more questions on LLC resonant transformers – please enter these as a comment to this blog.

You may find these other design resources for LLC resonant converters useful:

Power Seminar presentation and whitepaper: 

 Design Consideration of LLC Resonant Converter (You will find it in the Power Supplies section of the Online Seminars.) http://www.fairchildsemi.com/onlineseminars/index.html

 Application Notes:

 Analysis of MOSFET Failure Modes in LLC Resonant Converter http://www.fairchildsemi.com/an/AN/AN-9067.pdf#page=1

Half-bridge LLC Resonant Converter Design Using FSFR-series Fairchild Power Switch (FPS^TM) http://www.fairchildsemi.com/an/AN/AN-4151.pdf#page=1

 LLC Resonant Converter video: http://www.fairchildsemi.com/company/vids/2009/pcim/PCIM_FSFR2100_FSFA2100_FPP06R001.html

Tags: high power efficiency, LLC resonant translformers, power supplies

Energy Efficient Lighting Solutions

April 23, 2010

Dear Dr. Efficiency,
I’ve read in the news that governments worldwide are now promoting the use of power-efficient lighting through campaigns and initiatives. It seems that power-saving lamps will have a prosperous market. Are there any solutions from Fairchild specifically for this application? – Question Boy

Hello Question Boy,

One of the most popular power-saving lamps is the Compact Fluorescent Lamp (CFL), and they do have a very good market outlook. They offer significant advantages in energy-saving and consume up to 80% less power than traditional incandescent lamps. Thus, they have become popular in domestic and commercial lighting markets. In addition, governments worldwide are banning incandescent lamps and promoting CFL aggressively. It is expected that by 2012, the annual sales of CFL products will go beyond 5 billion units.

There are several products on the market today that provide proven solutions for LED, CFL, LFL and HID lighting applications. For CFLs, a dedicated control IC which works with external MOSFETs can be used for CFL ballast systems; or an integrated device with one control chip and two MOSFETs can be used. Fairchild offers several highly integrated devices that provides designers with less external component, reducing the overall component count, and smaller size, which is vital for space-tight CFL ballast designs.

Check out the datasheet for the FAN7711and FAN7710V  to see if these are right for your design. These devices feature preheating and start up time adjustment through a preheating time set capacitor (CPH) which prolongs the lamp life; ZVS mode operation after start-up; and ‘open-lamp’ state detection without external components to implement protection and other functions.

Depending on your design requirements, you may be interested in a PFC control IC. These devices are ballast-control integrated circuits (IC) and allow the designer to choose the optimum dead time to reduce the power loss on internal switching devices (MOSFETs).  Here’s more information on energy-efficient ICs for lighting.

If you are interested, we could meet to discuss.

Tags: CFL, control IC, FAN7710V, FAN7711, government regulations for lighting, HID, LED, LFL, PFC control IC, power-efficient lighting, ZVS mode operation

Getting More Efficiency with Synchronous Rectification MOSFETs

January 26, 2010

Dear Dr. Efficiency, I used a synchronous rectifier MOSFET with large current and low RDSON in a forward converter structure for synchronous rectification (SR) and expected there would be a significant improvement in efficiency.  However nothing happened.  Why was that?  I thought that the SR MOSFET should make a significant contribution to efficiency improvement.  – XM Wang
Hello XM,
You are on the right track, but may need to make some corrections. To deal with the power loss, we have to consider two aspects.

The power loss of semiconductor switches mainly comes from two sources: the conduction loss resulting from the loss on the RDSON that is generated when ID goes through the body diode during dead time, and the switching loss which can be roughly classified as three components: the loss caused from current-voltage cross when the MOSFET switches between turn-on and cut-off, the loss on the parasitic capacitance during switching, and that caused by the trr time of the body diode in the MOSFET.

The above equations show the close relation between the switching loss and the switching frequency. In particular, the loss during dead time mainly depends on the switching frequency, since the dead time is usually fixed. In general, for a given output power, the higher the frequency the more switching loss portion dominance; the lower the frequency the more conduction loss portion dominance.

In a SR structure, the body diode is already turned on by freewheel current before the MOSFET turns on. Since the voltage drop on the body diode is usually less than 2V, the conduction loss is not significant in equation (1).

Equation (2) shows the effect on the switching caused by the parasitic capacitance (Coss) of the MOSFET. This Coss is the equivalent capacitance between drain and source, with a voltage equal to Vds applied. Thus, this portion of loss is proportional to the switching frequency and Vds. You can check if the loss in your design is mainly caused by Coss by paralleling a smaller capacitance between the drain and the source to make the two MOSFETs have almost the same Coss value, then analyze the results by using the equations given above. You’ll get an idea about why the efficiency improvement is not significant.

Finally, in a forward half-bridge structure, the switching loss contributed by trr is also significant since the secondary current is usually kept in continuous current mode. You can check if the loss in your design is caused by trr by paralleling a schottky diode on the SR MOSFET side and then observing whether the efficiency is improved notably. If the efficiency is improved significantly, you can select a MOSFET with shorter trr time for the SR MOSFET.

Now, go back to your question. For MOSFETs within the same series, the lower the RDSON, the larger the value of parasitic capacitance. For example, FDP047N10 from Fairchild Semiconductor has a RDSON of 4.7mohm and a Coss of 1500pF, whereas FDP100N10 has a RDSON of 10mohm, but its Coss is only 710pF. In other words, it is possible that the lower RDSON FDP047N10 may have a larger loss under high switching frequency due to its larger Coss. Other parameters, such as Qg, parasitic body diode in MOSFET, also contribute to the overall power loss, which compromises the efficiency improvement effect of lower Rds. So, apart from the RDSON, which should be as low are also possible, the parasitic characteristic is an important factor in MOSFET selection.

Hope you are satisfied with my explanation. Let’s go and have a cup of coffee.

Tags: conduction loss, efficiency, MOSFET, power loss, semiconductor switches, switching loss, synchronous rectifier

Peak current mode PWM and slope compensation

January 8, 2010

Dr. Efficiency,

Why does my power supply’s output suffer duty cycle fluctuation? I’m experiencing one big duty cycle followed by a small duty cycle. The pulses with large duty cycles almost occupy the maximum T(on) time and only those with small duty cycles can be modulated. My power supply uses a UC3842 PWM controller. Both the feed and the input voltage are smooth. Can poor PCB layout introduce interference? What are the disadvantages of this issue? How do I solve the problem?   - Mr. Zhang

Mr. Zhang,

According to your circuit architecture, the UC3842 PWM controller used in your power supply works in Peak-Current Mode (PCM) and I think you may be experiencing sub-harmonic oscillation.

The PCM PWM controller has superior load regulation characteristics and anti-input interference capability, which makes it easy to implement current-limiting and over-current protection. It is stable in feedback and easy to compensate, hence widely used.

However, PCM PWM has a unique feature: when in continuous conduction mode (CCM) and with a duty cycle over 0.5, the angle between the rising curve of the inductor current and control voltage are smaller than that between the falling curve and the control voltage.  And in this case, we assume that there is a small disturbance occurring in the initial inductor current in one cycle. Then at the end of this cycle or at the beginning of the next cycle, the disturbance will be amplified and after several cycles of disturbance accumulation, duty cycle fluctuation will become one big duty cycle followed by a small duty cycle, or so-called sub-harmonic oscillation will occur.

This is an inherent feature of any open loop system which uses PCM PWM. It has nothing to do with the feedback or the PCB layout. Here we also understand that even with D<0.5, sub-harmonic oscillation could also be induced, depending on the angle between the rising curve of the inductor current and control voltage and the angle between the falling curve and the control voltage.

Sub-harmonic oscillation can make open-loop systems unstable, more susceptible to interference and in serious cases, it can even reduce the switch frequency by half and decrease the output power. This problem can be solved by making the duty cycle <0.5, or by compensating the current slopes. Slope compensation can be implemented by adding a signal with a fixed slope on the detected current signal or by adding a reverse slope signal on the control voltage to increase the angle between the current slope and the control voltage. With these measures taken, the possibility of sub-harmonic oscillation will decrease and the useable range of duty cycle will be widened.

 However, it should be noted that if the current slope is over-compensated, the advantage of PCM PWM will be off-set. To be specific, the higher the compensation, the more the PWM behaves like a voltage mode PWM. So it is important to have a proper slope compensation design. To facilitate the design procedure, Fairchild has integrated the slope compensation function within its newly introduced FAN6754 and FAN6753 PCM PWM ICs, providing you with more flexibility and a larger duty cycle range during design. In addition, the device also limits the maximum duty cycle, reducing the impact of sub-harmonic oscillation on the system and freeing you from undesirable compensation tasks.

 I hope you are satisfied with my explanation. Let’s go and have a cup of coffee.

Tags: continuous conduction mode, duty cycle fluctuation, FAN6753, FAN6754, PCM PWM ICs, Peak-Current Mode, power supply, Sub-harmonic oscillation, UC3842 PWM controller

What should we do to achieve high efficiency and power in LED street lamps ?

December 21, 2009

The power requirement of LED street lamps being used in China falls in the range of 100~250W. It is widely agreed that if used properly, these kinds of LED street lamps deliver many advantages. What I want to explain here is the ways to make it possible for these lamps to deliver those advantages. The key factors to be considered are high efficiency, power, reliability and cost-effectiveness.

Some low-power lighting requires PFC, while high-power lamps usually require PFC combined with DC/DC requirements. In China where the AC line voltage is 220V, Boundary-Conduction Mode (BCM) PFC controllers, such as the FAN7530 and the FAN6961, become the ideal choice to maintain a balance between the efficiency and performance-cost ratio. These solutions only need a few components.

Low Rds(on) SupreMOS(TM) MOSFETs, can further decrease switch and conduction loss. When used at the boost output, the HyperFAST 2 high voltage diode family with lower Vf can also lower the conduction loss of the diode itself.

For DC/DC topology, there are many choices such as quasi-resonant (QR), double transistor forward (DTF), active-clamp, LLC and asymmetrical half-bridge (AHB). High-power lighting applications, for example in a 100W lamp, where the output voltage is usually a little high, QR working with a synchronous rectifier can achieve up to 92.5% of total efficiency. Moreover, Fairchild has integrated QR and BCM PFC into one package (the FAN6921), reducing external components and simplifying the control.

Another popular topology is zero voltage switch (ZVS). Both an LLC and an AHB can have their two bridges working in zero voltage by implementing a simple circuit. When using Fairchild’s highly-integrated solution (for example, a LLC controller and two MOSFETs in FSFR; an AHB controller and two MOSFETs in FSFA2100), the circuit can be further simplified, with few external components. And the body diode of the MOSFET has good fast recovery characteristic, which can reduce the possibility of short-through, yet provide high reliability with high efficiency. When the output voltage is high, an LLC is the better option; when the output voltage is low, an AHB is more suitable for implementing a self-driven synchronous rectifier, and both can achieve over 93~94% efficiency.

The above solutions are highly integrated solutions and require just a few components, thus delivering high efficiency, high power density, optimized thermal performance as well as high reliability.

Click here for more information on LED lighting from Fairchild.

Tags: Energy Efficiency, Fairchild Semiconductor, LED Lighting