Switching power supply is small in size, light in weight, low in power consumption, high in efficiency, small in ripple, low in noise, high in intelligence, easy to expand and so on. It is gradually replaced by power frequency power supply and is widely used in all kinds of electronic equipment. High reliability, intelligence and digitalization are the developing trend of switching power supply. The audio power amplifier requires the power supply to adjust the output voltage automatically with the change of the load, and then adjust the power to improve the dynamic performance of the power supply and reduce the internal loss of the audio power amplifier, but the current switching power can not be realized. TMS320F2812 DSP is chosen as the main controller of the power switch power supply, and a low power consumption is designed. A new type of intelligent power amplifier switching power supply for large power amplifier system.
2 intelligent power amplifier switching power supply design
Fig. 1 is a block diagram of the general principle diagram of an intelligent audio switching power supply. After the input power frequency 220 V AC circuit is filtered, the DC voltage is output by the single-phase bridge rectifier circuit; the converter circuit uses the full bridge phase shift circuit to convert the front DC to the high-frequency alternating current. Then the stable DC voltage is output by the two rectifying filter; the detection circuit is sent to the output voltage signal and sent into the circuit. The control circuit adjusts the output voltage by changing the pulse width of the control circuit to adjust the output voltage; the protection circuit realizes overvoltage and overcurrent protection; the power detection circuit takes the conversion circuit current sampling, when the output power exceeds 500 W, produces the overpower detection signal, drives the control circuit, and reduces the output voltage: the auxiliary power supply circuit is used. Control circuit and all kinds of op amp power supply.
General principle block diagram of switching power supply for intelligent audio amplifier
2.1 power amplifier switch power module
Fig. 2 is the main circuit of the power amplifier switching power supply, where the Vin is 220 V AC input and is obtained by front-end filtering and full wave rectification, and the voltage is 300 V. The input voltage for the full bridge inverter circuit. VQ1, VQ2, VQ3 and VQ4 are IRFP460 type high-power MOSFET, which are used as converter switches. Because the IRFP460 type MOSFET is the most carrier device, the switch speed is very fast, the typical value of opening and closing time is 20 ns, which has high breakdown voltage and larger working current. In addition, MOSFET has high input impedance and simple driving circuit, so that the saturation conduction can be achieved by adding a voltage of about 10 V between the gate sources. L4, C5 and C6 constitute the auxiliary resonant network. Considering the original side leakage inductance of the transformer, the value of the resonant inductance LT is generally smaller than the actual value. The nonlinear saturated inductance of the inductance is 34 mu H, and the nonlinear saturation inductance is 1 u F. Considering the magnetic saturation problem of the high frequency pulse transformer T1, the original side windings are connected to the partial magnetic capacitance, VD15 and VD16, VD17 and VD18. Do not be full wave rectifier diodes, L1, C13, EC1, EC2 and L2, C14, EC3, EC4 are +35 V and -35 -35 output circuit filter circuit.
Main circuit of power amplifier switching power supply
2.2 power amplifier switching power module control circuit
The control circuit is based on DSPTFMS320F2812, which mainly includes phase shift pulse waveform, real-time sampling, power regulation, overvoltage protection, over current protection, overpower protection, filtering algorithm and full bridge phase shifting algorithm. The real-time sampling of voltage and current is realized by 16 12 bit high resolution A / D conversion circuit built by TMS320F2812. The minimum conversion time of each channel is 80 ns, and the input signal level of A / D conversion circuit is 0~3 V. After sampling, the phase shift angle of the PWM waveform that drives the full bridge inverter switch is adjusted by software programming, and the voltage stabilizer is realized. At the same time, when the output voltage, current is too high or undervoltage, DSP calls the corresponding subroutine to deal with sudden abnormal events and play a protective role. At the same time, the output voltage can be measured accurately by the A / D sampling output voltage and current signal, and the output voltage can be adjusted by adjusting the value of the related register of the event manager.
The performance of the controller and the precision of the regulator are closely related to the design of the regulator. In the design of switching power supply, the incremental PID control algorithm is adopted.
Digital control in power supply design adopts digital sampling control, that is, the amount of control is calculated according to the deviation value of sampling time. The discrete form of PID control is:
In the formula, the Ts is the sampling period.
Type (1) is a position PID control formula. In order to increase the reliability of the control system, an incremental PID control formula is used, that is, the increment of DSP only output control amount U (k), and type (1) is the output of the K PID controller, then the output of the (K-1) PID controller is:
Therefore, the incremental PID control algorithm is as follows:
The formula (3) and sum (4) is the incremental PID control formula of the control program. The incremental PID control is different from that of the position PID control, but it only outputs the increment, reduces the effect on the control system when the DSP is misoperated, and does not produce the integral out of control. Figure 3 is a block diagram of the PID controller based on TMS320F2812.
Implementation block diagram of PID controller based on TMS320F2812
Software design of 2.3 power amplifier switching power supply
The software design of power switch power supply based on DSP mainly realizes the following functions:
(1) the generation of full bridge phase shifting pulse directly outputs the pulse of the circuit using two comparator units in the TMS320F2812 event manager. From the basic principle of phase shifting, the lag bridge arm has a periodic delay relative to that of the super forearm, and its delay angle is the phase shift angle. The PWM1 / PWM2, which is output by the comparison unit 1, drives the ultra forearm switch tube VQ1 and VQ3 respectively, and the PWM3 / PWM4 driving the lag arm switch tube VQ4 and VQ2, which is output by the comparison unit 2. The driving pulse between the upper and lower two tubes of each bridge arm is complementary and with the dead zone. The driving of the fixed forward bridge arm is sent out at 0 times of each cycle, then the driving pulse of the lag bridge arm can be obtained by the delay of the phase shift angle phi corresponding time, and the free phase shift in the range of 0 to 180 degrees can be achieved.
(2) overvoltage, overcurrent and over power detection and protection. DSP based power switch power supply has the functions of overvoltage, overcurrent, over power, overheating and so on. When an exception occurs, the system enters abnormal interrupt service subroutine to process, and timely closedown PWM output. In order to prevent misoperation, it is necessary to set 20 consecutive abnormal signals to be identified as abnormal circuits, otherwise they will not be processed. The procedure flow of each module is shown in Figure 4 to figure 6.
3 experimental results
According to the previous analysis, a prototype is designed. The switching frequency is 100 kHz, and the output voltage is 35 V and 42 V. Under the condition of light load and heavy load, the output voltage ripple coefficient is less than 0.5% and the output voltage precision is less than O.5% under the condition of light load and heavy load, which is based on DSP control sound amplifier switching power supply.
Figure 7 is the phase shift of DSP. Wherein, the channel 1 is the PWM1 output of the comparison unit 1, which is the advance bridge arm; and the channel 2 is the PWM3 output of the comparison unit 2. It can be clearly seen from Fig. 7 that the channel 2 lagging channel 1 is about 135 degrees. Fig. 8 is the zero voltage switching critical waveform of the lagged bridge arm, with an input voltage of about 175 V and an output power of 100W. In Figure 8, channel 1 is the power MOS gate source voltage Vcs waveform, channel 2 is the power MOS tube drain source voltage VDS waveform. Turn off VDS is 175 V, from figure 8, we can see that VDS first reduced to 0, then Vcs increased. At this time the switch tube is opened to zero voltage. The more heavy the load is, the more obvious the zero voltage opening phenomenon is. When the output power is 400 W and the input power is 440 W, the conversion efficiency of the full bridge phase shifter is 90.9%.
Phase shift waveform of DSP
Zero voltage opening critical waveform of lag bridge arm
The experimental results show that the output waveform of the power amplifier switching power supply based on DSPTMS320F2812 is good, the harmonic content is less and the regulation is excellent. When the load is changed in the full range, the switching power can maintain good output performance. And because of the full bridge phase shifting soft switching converter, the switch is working in the zero voltage switch state. The whole power system has low power consumption and has a good application prospect in high-end high power amplifier.
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