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Car sine wave inverter power supply design

In Electronic Infomation Category: C | on April 26,2011

With the development of society, more and CY7C131-25JC datasheet and more cars with peoples daily lives, in a car with a DC voltage typically 12V, can not be directly used for portable electronic devices. To this end, vehicle power (DC 12 V voltage is to convert the AC 220 V/50 Hz power supply) the development has attracted much attention.

Generally use the traditional automotive power inverter frequency transformer processing program, it exists a large volume, low efficiency defects. With the new power electronic devices and CY7C131-25JC price and power electronics technology, the program used to implement high frequency link power frequency transformer-free inverter circuit, can solve the problems of traditional car power, car power also ensures the output voltage more stable and CY7C131-25JC suppliers and smooth.

1 vehicle power supply circuit structure and function analysis

Vehicle power system shown in Figure 1. 12V DC voltage through the high frequency inverter and high frequency rectification, to get a meet the requirements of: 350V DC voltage, the part of the control signals generated by the TL494 chip.

Figure 1 automotive power system architecture

Go through a full-bridge DC / AC inverter circuit, get 220V/50Hz AC voltage output. To ensure reliable operation, the main circuit of the control circuit to prevent interference with the main, control circuit means completely isolated, that isolation optocoupler drive signals, the feedback signal isolation transformers, auxiliary power transformer isolation.

For the entire system, the inverter circuit can work properly for the whole system can function properly. Therefore, the design focused on the inverter control and detection.

1.1 SG3525 block diagram and pin functions SG3525

system uses to achieve the output SPWM control signals, the chip and internal block diagram of the pin shown in Figure 2.

Figure 2 SG3525 pin and internal block diagram of the DC Vs

access from 15 feet after the two routes, all the way added to the NOR gate; another way to reference voltage input of regulator, resulting in a stable +5 V reference voltage. +5 V and then to the internal (or external) circuit of the other components as the power supply.

5 feet shall be external oscillator capacitor CT, 6 feet to be an external resistor RT. Oscillator frequency f by the external resistor RT and capacitor CT decision, f = 1.18/RTCT. Inverter bridge switching frequency set at 10kHz, the fog take CT = 0.22, RT = 5k Tong Su Ne U startled female bare saddle blanket rule hinge

All the way to the clock pulses sent to the bistable flip-flop and two NOR gates; another way to ramp in the form sent to the comparator inverting input of the comparators negative input termination of the error amplifier output. The error amplifier output and the sawtooth voltage comparator compares the output of a level with the error amplifier output voltage to change the width of the square wave pulse, and then this square wave pulse delivered to one input of NOR gate. Or non-doors were the other two bistable flip-flop input and oscillator sawtooth. Output of bistable flip-flop the two complementary, alternating high-low output, the PWM pulse sent to the transistor V1 and V2 of the base, saw the role is to join the dead time, to ensure that V1 and V2 are not on simultaneously. Finally, V1 and V2, respectively, the output phase difference of 180 of the PWM wave.

1.2 SPWM modulation signal generation

To get a sinusoidal voltage output, it is necessary to inverter control signals to control the SPWM switching power transistor, the resulting square wave output pulse can be obtained and then filtered sinusoidal output voltage. Achieved through the SG3525 output sinusoidal voltage, the first to get SPWM modulation signal, but to get SPWM modulation signal, have to have a magnitude in the 1 ~ 3.5V, change the bread by sinusoidal wave, to add it to pin 2 SG3525 and compared with the sawtooth, sinusoidal pulse width modulation wave can be obtained.

Achieve SPWM control circuit block diagram in Figure 3 (a) shows the actual circuit points of the waveform shown in Figure 3 (b) below.

(a) SPWM control circuit diagram

(b) SPWM waveform of the primary node circuit

control circuit diagram in Figure 3 and the point of the waveform

Can see from Figure 3, the benchmark 50Hz square wave is generated by the 555 chip, is used to control the output voltage reference value and comparing RMS error signal generated, making it into a 50Hz square wave, after the low-frequency filter, be sinusoidal control signal. When the power supply output voltage changes, will change the amplitude of sinusoidal signal, making the SG3525 output pulse width corresponding changes have taken place, which constitutes a closed feedback loop, stabilizing effect on the output waveform.

1.3 over-current protection

Using current transformer over-current protection device as a current detection, which has a fast enough response time, to allow the over-current in the IGBT to turn off time, play a protective role.

Shown in Figure 1, over-current signal from the CT2, by the partial pressure, filter Bo Houjia to the voltage comparator input with the phase shown in Figure 4. When the inverting input over-current detection signal than the inverting input reference level is high, the comparator output high, so that D2 from the original status of the reverse bias into the forward and enhance the potential client with a high relative level, the stable output voltage comparator has been high. Meanwhile, the over-current signal is also sent to the SG3525 feet 10. When the SG3525 10 feet high, its feet 11 and 14 feet on the PWM output pulse will disappear immediately from zero.

Figure 4 over-current protection circuit

1.4 Drive Circuit

Drive circuit only needs to consider the power transistor turn, can quickly establish a drive voltage, but also consider the need turn-off, can quickly discharge the power MOSFET gate capacitance charge, pull low drive voltage. Specific driver circuit shown in Figure 5

Figure 5 Driver

Its working principle is:

1) When the coupler has the control circuit the primary drive pulse current to flow out of date, optocoupler turns on, so that the base potential of Q1 increased rapidly, leading to D2 turns on, the power control gate voltage rise, the power tube conduction;

2) When the coupler without the control circuit the primary drive pulse current to flow out of date, the optocoupler does not turn on, so that the base potential of Q1 low, while the power transistor gate voltage is also higher resulting in Q1 conduction, the gate charge power MOSFET Q1 and resistor R3 by the rapid discharge, quickly and reliably control the power off.

Course, as important as the protection of the power tube, so the power source and drain pipe to add a buffer circuit between the power tubes are too high to avoid the positive and reverse voltage of the damage.

2 results

Based on the above analysis, carried out experiments on the prototype, the rated output power of 500W, the filter parameters to take L = 3mH, C = 2.2 fog, the prototype is running with load, the measured obtaining the output voltage waveform shown in Figure 6 instructions.

Figure 6, the inverter output waveform

3 Conclusion

Prototype of good quality output voltage waveform, output voltage stability, amplitude independent of the load change, the effect is better. Experimental results show that the proposed system solution is feasible

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