The D amplifier is modern consumption TV and key component of the audio frequency products realizing the small volume and the high-power audio frequency outputs, but it is rather complicated to construct a high-efficiency D amplifier scheme. Especially the design of the power switch grade, the audio frequency design engineer that design is a very great challenge to not familiar with the power electron ing.

The ready-made D amplifier chip can solve the power and design the difficult problem, but restrained people from optimizing other performance of the amplifier at the same time, the design engineer can’t realize the difference of the products by strengthening performance.

The most ideal situation is to provide a station type solution of realizing electronic function of the power for design engineer of audio frequency, thus let them gather to give play to the speciality of the field of feedbacking the route and exporting the wave filter etc..

Designed the flexibility with D amplifier

In order to help to understand how the D amplifier solution offer these ready-made functionality and design flexibility, Fig. 1 provides the function module picture of the common D amplifier. Input the audio frequency signal to compare with high-frequency sawtooth wave, produce and modulate the square wave on behalf of the pulse width of the input signal. It has a lot more high frequency than the supreme audio frequency signal that the wave frequency of the sawtooth is set up to be, generally about 400kHz, in order to reduce distortedly and simplifying and exporting the wave filter to design.

Fig. 1: Function module picture of the common D amplifier.

Then, adopting the audio frequency signal modulated through the pulse width drives the amplifier to export grade, it may be the whole bridge MOSFET array that this exports one grade of circuit, it may be half a bridge MOSFET array too. Output the topological choice to depend on the system including that cost, output power, power are designed with the signal characteristic requires. For example, half a bridge is outputting one grade of requirements, is defeated by the voltage rail, and the whole bridge can work under the single power to export one grade of circuit, can produce greater output power under the designated switch speed too.

No matter which kind of situation, all pay optimizing in outputting MOSFET characteristic to the D audio-frequency amplifier, in order to maximize efficiency, and guarantee very low total harmonic wave is distorted to add the noise THD N With EMI. This requires low leading the open resistance, in order to realize the high power density in the final products, still require the grid optimized to charge and resume the characteristic to pass with the body diode backward at the same time, in order to realize the fast, high-efficient switch.

The intersection of audio frequency and signal that amplify include, in the intersection of MOSFET and square the intersection of wave and signal that bridge output, need with low to lead to the wave filter strain the frequency except audio frequency, resume the pure audio frequency signal to drive the loudspeaker.

Challenge that one grade of circuit is designed of the switch

For it is unnecessary to be familiar with the design engineer of the electronic design principle of the power of switching, it is the greatest challenge that they face to produce the grid and drive the D amplifier power switch grade of the signal to be designed in MOSFET bridge. In order to obtain excellent audio frequency performance, it is essential that the accurate grid is controlled, this requires pulse width to be distorted and small, high side and low end are driven and matched well between signals, in order to keep the good linearity.

Die the intersection of district and time it inserts to be one very arduous challenge. Damage and export MOSFET in order to assault the direct electric current, must insert district time very much and but will bring to insert district time very much to amplifier characteristic non-linearly, so the design engineer often can’t reach the satisfactory equilibrium between fidelity of audio frequency and security surplus. Realize other protection functions of grid driver and MOSFET such as passing warm protection and overvoltage protection Will also bring more complicated challenge, this requires design engineer to have abundant electronic design tactics of switch power.

Become more and more perfect and very difficult to design to make on condition that face so many challenges, because any defect will cause difficult analysis and calamitous trouble corrected.

In order to help the design engineer to overcome these difficulties, hand over the successful D amplifier products fast, international rectifier IR It has had the built-in intact MOSFET grid driver IRS2092 which protects the function that the company has introduced. This device integrated error amplifier and PWM comparator, allow the design engineer to be fast and realize the audio frequency solution based on D amplifier.

There are some other important amplifier characteristic and closely linked one grade of circuit design of power switch, including reducing the elimination circuit of the clatter sound of during starting and closing. IRS2092 has integrated these functions in inside too, thus has further reduced and designed expenses and device quantity. This scheme has solved the power electron correlated to D amplifier and designed the challenge, and offered the guarantee for the fact that the design engineer use the technology of the specialized audio frequency to further improve the properties of product.

IRS2092 is still designed to have very good flexibility, so that the design engineer can decide to output the wave filter characteristic, and can choose feedbacking some in a lot of positions, in order to obtain best audio frequency performance and amplifier stability under the condition of meeting cost and device quantity.

The difference of the D amplifier is designed

1. Customize and feedback the cycle

It is an important characteristic of realizing D amplifier difference to feedback the cycle and design. Under some situations, making the ring can offer satisfactory performance to dispose, but the inherent time sequence error will increase the distorted and noise in the amplifier. Can utilize negative feedback to well solve this problem. Most simple method to feedback get the intersection of error and input terminus of amplifier some the intersection of switch and signal, carry on preconditioning with passive the intersection of RC and low put through wave filter. A lot of D amplifier chips adopt this kind of feedback mode on the market. However, the design engineer may hope to further optimize the distorted performance of the amplifier, make the feedback signal to reduce load dependence from the place to near the output end even more. For example, it is a bit fartherrest to feedback some ones that may export in the wave filter of the audio frequency, namely just in front of the loudspeaker. Some design engineer might through include, come on further the intersection of improvement and performance in feedbacking cycle the intersection of loudspeaker and electronic device also, because the influence of these devices can considered to be the thing the amplifier output a part of the wave filter. Two kinds of feedback signals that still some may jointly use and adopt to design from the node of the switch and the wave filter outputted.

IRS2092 grid driver chip allows the design engineer to choose considered to be the best feedback to clicking freely. Realize and the compensation to stability, and the noise THD N that it is distorted that the design engineer can make the harmonic wave of the rank of tone quality of high-fidelity through wise feedback Performance.

2. Output the wave filter performance optimally

Outputting the wave filter has influence greatly on total efficiency, dependability and audio frequency performance. The simple LC wave filter is very common, it closes at frequency just above the frequency band of the audio frequency, and have every carrier suppression performance of 40dB frequently of ten times. In a lot of are employed, so long as the impedance of the control loudspeaker carefully, a simple wave filter can offer the performance good enough. But on the other hand, the experienced design engineer may hope to use the more complicated wave filter have higher steps to respond to the characteristic, better falling into Potter or special carrier suppression method ,In order to further improve distorted and noise performance.

Can be regulated freely because of regulating parameters such as the switch frequency,etc., IRS2092 allows the engineer to export the wave filter to design optimally, and choosing can offer the device of the ideal characteristic, such as the inductance of high linearity and low D.C. resistance. An important advantage that the switch frequency can be programmed is, it allows to manage the equilibrium between bandwidth and switch frequency. For example, if use the bandwidth as the bass audio amplifier amplifier of 200Hz, it will be of great advantage to set up into the ability of lower switch frequency.

3. Maximize the damping coefficient

Will influence the output impedance of the amplifier because of feedbacking the design with the circuit of the wave filter, so the design engineer also needs to control the design of the circuit well in order to obtain the damping coefficient sufficiently high. The damping coefficient is important a figures of merit, it is especially right to support the impedance lower system of sound appliances in the car. The design engineer must guarantee the work of the strict control loudspeaker, in order to reach acceptable performance in the car case environment. Control carefully the amplifier outputs and feedbacks and designs the damping coefficient that can realize greater than 100, it is usually enough for most audio-frequency amplifiers.

4. Expansibility

Use the integrated chip solution that has 4 basic D type amplifiers to construct the module like IRS2092 to have another advantage, namely can meet expansibility of high output power or extra passway requirement. Through defining the outside MOSFET of the suitable grade, optimizing district time and overload protection door limit very much again, it can expand the amplifier fast. Design through keeping the same PCB even the same in general design, this kind can shorten the listing time of products while expanding ability fast, and reduce the design cost with development of the terminal products. In addition, design repeatedly many times through what driver – MOSFET made up, can be fast to realize many passway systems. For example, one sound of apparatuses surround to can dispose the high cost performance and 6.1 or 7.2 compact passways fast, conveniently.

The D amplifier is consulted and designed

The D type audio-frequency amplifier chip can solve and design challenging, accelerate the project and finish the progress, can also reduce the device quantity effectively. In order to help the design engineer to further give play to these advantages, the international rectifier company disposed IRS2092 grid driver chip and two IRF6645 DirectFET MOSFETs into the reference of half a bridge of structure and designed after introducing Fig. 2 .

Fig. 2: Design board left on the basis of the A/B amplifier Consult designing with the D amplifier of IR Company right Contrast.

Consults and designs through this, the design engineer can construct the switch amplifier of each passway 120W on PCB area of 61cm2, this area is smaller than the 120W A/B amplifier and consult 16% which are designed the area. Because the D amplifier does not need the radiator while working normally, the decrease of the total volume is very considerable. This intact D amplifier solution only takes the space of 109cm3, is smaller than 6% of the A/B amplifier volume.

In addition, this consults it while designing the power of output 60W in 4Ω support, can be up to 0.005% of the low THD N performance, remains the noise only 170μ V, the damping coefficient of 1kHz place is 170. Utilizing the basic platform of this functionality, the design engineer customizes and feedbacks and exports and strains the wave to design freely, in order to offer best audio frequency performance and overall cost for particular application.