1 Introduction
The switching power supply is small, light, low power consumption, high efficiency, low height, low noise, high intelligence, easy expansion, etc., is widely used in various electronic devices. High reliability, intelligence, and digitization are the development direction of switching power supplies. Sound amplifier requires power supply to automatically adjust the output voltage as load changes, and modulate power to increase power dynamic performance, reduce the internal loss of audio amplifier, but the current switching power supply cannot be implemented. Select TMS320F2812 DSP as the main controller of power release power supply, design a low power consumption. Suitable for new intelligent power release powers for large amplifier systems.
2, intelligent power release switch power supply design
Figure 1 shows the overall principle block diagram of the intelligent audio power release power supply, and the main circuit has always been a constant structure. After the input power frequency 220 V AC circuit is filtered by the filter circuit, the DC voltage is output by a single-phase bridge; the transform circuit uses a full bridge phase reverse circuit to convert the front end DC power into a high frequency alternating current. Then via the secondary rectifier filter output, the detection circuit is sampled after the output voltage signal is sampled, and the output voltage is adjusted by changing the control circuit output pulse width duty ratio; protection circuit achieves overpressure and overcurrent protection The power detecting circuit sampling the transform circuit current, when the output power exceeds 500 W, generates an over-power detection signal, driving the control circuit, and reducing the output voltage: The auxiliary power supply circuit is controlling the control circuit and various op amp.
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2.1 power release power module
Figure 2 is a main circuit of the power release power supply, where VIN is a 220 V AC input via front end filter and full wave rectification, the voltage is 300 V. The input voltage of the full bridge inverter circuit. VQ1, VQ2, VQ3, VQ4 is an IRFP460 high-power MOSFET for converter switching tubes. Since IRFP460 type MOSFET is a majority carrier device, a typical value of switching speed, opening and shutdown time is typically 20 ns, with a high breakdown voltage and a larger operating current. In addition, the input impedance of the MOSFET is high, and the drive circuit is simpler, as long as the voltage of about 10 V is added between the gate source, it can be saturated. L4, C5, and C6 constitute an auxiliary resonant network, take into account the primary side leakage of the transformer, the value of the resonant inductance LT is generally smaller than the actual value, where the inductance value is 34 μH 1μF, which is considered to high frequency pulse Transformer T1 magnetic saturation problem, the original edge winding string is connected to prevent the polarity capacitance, the VD15 and VD16, VD17 and VD18 are all wave rectifier diodes, L1, C13, EC1, EC2 and L2, C14, EC3, EC4 are +35 V, respectively. The filter circuit of the -35 V output loop.
Main circuit of power release power supply
2.2 Power release power supply module control circuit
The control circuit is in the core of DSPTFMS320F2812, mainly including a function of generating a phase pulse waveform, real-time sampling, power conditioning, overvoltage protection, overcurrent protection, over-power protection, filtering algorithm, and a full bridge phase algorithm. The voltage and current samples are achieved by TMS320F2812 16 12-bit high resolution A / D conversion circuits. The minimum conversion time per channel is 80 ns, and the input signal level of the A / D conversion circuit range is from 0 to 3 V. After sampling, the PWM waveform transpare angle of driving the full bridge inverter switch is adjusted by software programming, and the voltage regulator is realized. At the same time, when the output voltage, current is too high or undervoltage, the DSP calls the corresponding subroutine processing burst abnormality event. It plays a protective role. At the same time, the output power can be accurately measured by the A / D sample output voltage current signal, and the value of the event manager related register is adjusted to adjust the output voltage.
The dynamic characteristics and regulator accuracy of the controller are closely related to the regulator design. In the design of the power release power supply, an incremental PID control algorithm is adopted.
Digital control in the power supply design uses digital sampling control, ie calculates the amount of control based on the deviation value of the sampling time. The discrete form of PID control is:
Formula
In the formula, TS is a sampling cycle.
Formula (1) is a positional PID control calculation. In order to increase the reliability of the control system, the incremental PID control calculation is used, that is, the DSP outputs only the increment of the control amount U (K), the formula (1) is the output amount of the first PID controller, then (k-1) ) The output of the second PID controller is:
Formula
Therefore, the incremental PID control algorithm is:
Formula
Formula
The formula (3) and the formula (4) are the incremental PID control calculation of the control program. The incremental PID control is different from the positional PID control, but it only outputs increments, reducing the impact of the control system when the DSP misoperation is reduced, and does not generate points out of control. 3 is a block diagram of a PID controller based on TMS320F2812.
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2.3 Software design of power release
DSP-based power release power supply software design mainly implements the following functions:
(1) The production of all bridge transparent pulses Directly output the circuit pulses in two comparison units in the TMS320F2812 event manager. From the perspective of the phase shift, the lag has a periodic delay relating to the drive between the super-arms, which is a transparent angle. The PWM1 / PWM2 output from the comparison unit 1 separately drives the advance arm switch pipe VQ1, VQ3, and the PWM3 / PWM4 drive hysteresis arm switch VQ4, VQ2 output from the comparison unit 2. The drive pulse between the two tubes per bridge is complementary and the driving of the fixed super bridge arm is issued at 0 time per cycle, and then the comparative event can be obtained as long as the phase of the phase of the phase is obtained. The drive pulse of the lag of the bridge arm is thereby realizing free phase shifts in the range of 0 ° to 180 °.
(2) Overvoltage, overcurrent, over-power detection and protection of DSP-based power release power supply has overvoltage, overcurrent, over-power, overheating and other protection. When an exception occurs. The system enters an exception interrupt service subroutine for processing and latches the PWM output in time. To prevent malfunction, set up 20 unusual signals continuously to read 20 exceptions as circuit exceptions, otherwise it will not process. The module procedures are shown in Figures 4 to 6.
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3, experimental results
According to the previous analysis, a sample is designed, the switching frequency is 100 kHz, and the output voltage is ± 35 V and ± 42 V. Loading experiments based on the DSP control audio power release power source, under light load and overload conditions, the output voltage ripple coefficient is less than 0.5%, and the output voltage accuracy is less than O. 5%.
Figure 7 is a movement waveform of DSP. Wherein, the passage 1 is output from the PWM1 of the comparison unit 1, which is a superward bridge arm; channel 2 is the PWM3 output of the comparison unit 2. From Figure 7, it is clear to see the passage 2 lag passage 1 of about 135 °. Figure 8 is a critical waveform of the hysteresis bridge arm zero voltage, the input voltage is about 175 V, and the output power is 100W. Fig. 8 is the passage 1 for the power MOS tube gate source voltage Vcs waveform, channel 2 is the power MOS tube drain source voltage VDS waveform. When the VDS is turned off, 175 V is turned from Figure 8, and VDS can be seen first down to 0, then VCS rises. At this time, the switch is open to the zero voltage. The heave the load, the more obvious the zero voltage opening. When the output power is 400 W, the input power is 440 W, and the conversion efficiency of the full bridge transducer converter is 90.9%.
DSP shift waveform
Hysteresis bridge arm zero voltage opens critical waveform
The experimental results show that the power output waveform based on the DSPTMS320F2812 is good, the harmonic content is small, the adjustability is excellent. When the load changes in a full range, the switching power supply can maintain a good output performance, and due to the adoption of a full bridge shift soft switch conversion The switch operates in a zero voltage switch state, so the entire power system has a small power consumption, which has better application prospects in high-end high-power amplifier.
4 Conclusion
The control core of the DSP as an audio power release power supply, realizes the digital control of the switching power supply, overcoming the problem of components, heat drift in the simulation control system, and solves the problem of the single-chip control circuit load and the intensive accuracy. Use the full bridge shifting circuit to effectively reduce the internal loss of the power supply to the power release power supply in the audio power release power source, which is applied to the high power audio amplifier system.
Using the software hardware resources of TMS320F2812, implement PWM control, filtering, sampling, and various system protection functions, simplifying control circuits, improving the flexibility of power supply design and manufacturing; additional controller is controllable, easy to expand, easy to upgrade maintenance.
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Responsible Editor: gt
Reprinted from -Wiku Electronic Market Network
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