A new type of high-voltage, high-power, small-signal amplifier circuit

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A new type of high-voltage, high-power, small-signal amplifier circuit [Copy link]

Abstract: The characteristics and working principles of UC3637 dual PWM controller and IR2110 are briefly analyzed. A high-voltage, high-power, small-signal amplifier circuit is constructed by UC3637 and IR2110, and its feasibility is verified through experiments.

Keywords: small signal amplifier; dual pulse width modulation; suspension drive; high voltage and high power

　

　

0 Introduction

Many existing small signal amplifier circuits are composed of transistor or MOS tube amplifier circuits, which have limited power and cannot make the circuit power very large. With the gradual maturity of modern inverter technology, especially SPWM inverter technology, the signal waveform can be well reproduced at the output end, and high voltage, high current and high power can be achieved. There are two ways to implement SPWM technology. One is to use analog integrated circuits to compare the sine modulation wave with the triangle wave carrier to generate SPWM signals; the other is to use digital methods. With the deepening of application and the development of integrated technology, commercialized application-specific integrated circuits (ASICs) and dedicated single-chip microcomputers (8X196/MC/MD/MH) and DSP can simplify the control circuit structure and increase the integration. Since digital chips are generally more expensive, analog integrated circuits are used here. The main circuit adopts a full-bridge inverter structure, and the generation of SPWM waves adopts the UC3637 dual PWM control chip, and the high-voltage floating drive integrated module IR2110 launched by the American IR company is used, thereby reducing the size of the device, reducing costs, and improving the reliability of the system. After amplification by this circuit, the signal can reach 3kV and maintain a good output waveform.

1 Principle and basic functions of UC3637

The principle block diagram of UC3637 is shown in Figure 1. It contains a triangle wave oscillator, an error amplifier, two PWM comparators, an output control gate, a pulse-by-pulse current limiting comparator, etc.

Figure 1 UC3637 block diagram

UC3637 can work with single or dual power supply, with working voltage range of ± (2.5～20)V, which is particularly conducive to bipolar modulation; dual PWM signal, totem pole output, sourcing or absorbing current capacity of 100mA; pulse-by-pulse current limiting; built-in constant amplitude triangle wave oscillator with good linearity; undervoltage lockout; temperature compensation; 2.5V threshold control.

The most distinctive feature of UC3637 is the triangular wave oscillator. The triangular wave generating circuit is shown in Figure 2. The triangular wave parameters are calculated according to formula (1) and formula (2).

I _s = (1)

f = (2)

Where: VTH is the turning (threshold) voltage of the triangle wave peak _;

Vs is the power supply voltage _;

RT _is the timing resistor;

CT is the timing capacitor _;

I _s is the constant current charging current;

f is the oscillation frequency.

Figure 2 Triangle wave generating circuit

UC3637 has a high-speed, 1MHz bandwidth, low-impedance output error amplifier, which can be used as a general fast op amp or a feedback compensation op amp. The main function of UC3637 is the two PWM comparators, and the implementation circuit is shown in Figure 3. Other functions include undervoltage lockout, 2.5V threshold control, etc., which are also implemented in the application circuit.

Figure 3 PWM generation circuit

2 Structure and Application of IR2110

The internal functional block diagram of IR2110 is shown in Figure 4. It consists of three parts: logic input, level shift and output protection.

Figure 4 IR2110 internal functional block diagram

IR2110 has independent low-end and high-end input channels; the floating power supply adopts a bootstrap circuit, and its high-end operating voltage can reach 600V. The static power consumption is only 116mW at 15V; the output power supply end (pin 3Vcc _, that is, the gate drive voltage of the power device) has a voltage range of 10~20V; the logic power supply voltage range (pin 9VDD ₎ is 3.3~20V, which can be easily matched with TTL or CMOS levels, and an offset of ±5V is allowed between the logic power ground and the power ground; the operating frequency is high, up to 100kHz; the turn-on and turn-off delays are small, 120ns and 94ns respectively; the totem pole output peak current is 2A.

The bootstrap principle of the high-voltage side suspension drive is analyzed below.

The circuit of IR2110 for driving half bridge is shown in Figure 5. In the figure, _C1 and VD1 _are bootstrap capacitor and diode respectively, and C2 is the filter capacitor of Vcc . Assume that C1 _has been charged to a sufficient voltage ( Vc1 ≈ _Vcc ) during the shutdown period of _{S1 . When pin 10 ( HIN ) is high , VM1 is} turned on, _VM2 is turned off, Vc1 _is added between the gate and emitter of S1 _, C1 _is discharged _through VM1 _, Rg1 and S1 _{gate -} emitter capacitor Cge1 , and _{Cge1 is} charged. At this time, Vc1 can be equivalent to a voltage source. When pin 10 (HIN) is low, VM2 _is turned on, VM1 _is turned off, and the gate charge of S1 _is quickly released through Rg1 _and VM2 _{, and S1} is turned off. After a short dead time ( td ) _, pin 12 (LIN) is high, S2 _{is turned} on, Vcc charges C1 through VD1 _and S2 _, quickly replenishing energy for _C1 . This cycle _repeats .

Figure 5 IR2110 circuit for driving half-bridge

　

The disadvantages of IR2110 are that it does not have enough protection function and it does not have negative bias voltage. Therefore, a negative bias circuit is added to it, as shown in Figure 6.

Figure 6 Using IR2110 drive circuit

3 Application of UC3637 and IR2110 to form a control drive circuit

Figure 6 is a driving circuit composed of IR2110. It can be seen from Figure 6 that two IR2110s can drive an inverter full-bridge circuit. They can share the same driving power supply without isolation, which greatly simplifies the driving circuit. IR2110 itself cannot generate negative bias. From the driving circuit, it can be seen that this circuit adds a negative bias circuit to each bridge arm. Taking the left half as an example, its working process is as follows: after V _{DD is powered on,} C ₁ is charged through R ₁ , and a +5.1V voltage V _{c1 is formed under the clamping of V W1} . When the pin 1 (LO) output of IR2110 is high, the lower tube has a driving voltage of (V _DD -5.1) V, and a -5.1V bias is formed between the gate and source of the lower tube when the lower tube is turned off; the lower tube is turned on and the pin 1 (LO) outputs a high level through R _g2 , R ₂ turns on the MOSFET to charge C ₃ ; when the pin 7 (HO) output of IR2110 is high, C ₃ discharges to provide the upper tube turn-on current, and charges C ₂ and is clamped to +5.1V by V _W2 . When the lower tube is turned off, V _c2 forms a negative bias. In order to use only the protection function of IR2110, the pin 11 (SD) end is grounded.

Figure 7 is a circuit that uses UC3637 to generate PWM waves. As shown in Figure 7, this is an open-loop small signal amplifier circuit. Because the voltage amplitude of the small signal is too low relative to the amplitude of the triangle wave, the small signal is first amplified by the Error operational amplifier of the UC3637 itself to make its amplitude approximately equal to the amplitude of the triangle wave. This circuit does not use UC3637 as a dead zone, but instead makes a dead zone delay separately. Then the amplified signal is directly compared with the triangle wave, and the inverted SPWM wave is output at pins 4 and 7 of UC3637 respectively, and sent to the IR2110 driver chip through the dead zone delay circuit, the noise filter circuit, and the isolation circuit.

Figure 7 PWM generation circuit using UC3637

When designing a circuit, pay attention to the following issues:

1) The RT and CT of UC3637 should be properly selected to avoid excessive current on RT and damage to the chip;

_{2) The} C2 value in the driving circuit must be much larger than the inter-electrode capacitance between the gate and source of the upper tube;

3) The selection of the bootstrap component capacitor of IR2110 depends on the switching frequency, VDD and the charging requirements of the gate source of the power MOSFET. The withstand voltage of the _diode must be higher than the peak voltage, and its power consumption should be as small as possible and able to recover quickly.

4) The rising edge of the driving pulse of IR2110 depends on Rg _. The value _{of Rg} cannot be too large to avoid making the rising edge of the driving pulse not steep, but the driving average current cannot be too large to avoid damaging IR2110.

5) When the PWM generating circuit is an analog circuit, the signal can be directly connected to IR2110; when using digital signals, isolation should be considered;

6) Pay attention to the DC bias problem.

4 Experimental Results

The UC3637 generates a 63kHz triangle wave with a signal generator simulating the input, and the DC bus voltage is 220 V. This circuit is tested under dummy load and piezoelectric ceramic load, and the output terminal outputs a good amplified signal.

Figure 8 is the driving waveform of the upper and lower power MOSFETs with a single-frequency sinusoidal input signal in the laboratory, Figure 9 is the output of the inverter bridge, Figure 10 is also the output waveform (time parameter changes), and Figure 11 is the load waveform with a dummy load when M = 0.1.

Figure 8 Upper and lower switch tube driving waveform

Figure 9 Inverter bridge output waveform (limited by range)

Figure 10 Inverter bridge output waveform

Figure 11 Load waveform

The real signal is a random signal, and the load is a piezoelectric transducer. When M ≌1.0 and the transformer ratio is 1:7, this circuit can amplify the small signal to a peak value of 3.2kV, and the output effective value can reach 680V. The distortion of the amplified signal is very small, meeting the technical requirements. Since the high-voltage oscilloscope has no interface, the waveform at both ends of the load cannot be photographed.

5 Conclusion

1) UC3637 uses a few integrated circuits to form a complete inverter control circuit. The control circuit is simple and practical, the hardware investment is not high, and the use proves that the performance is stable and reliable;

2) UC3637 and IR2110 have high anti-interference performance. One IR2110 can safely drive the half-bridge of power MOSFET or IGBT at higher power.

3) Since IR2110 has dual-channel driving characteristics, simple circuit, easy to use, and relatively cheaper than EXB841, it has a higher cost performance.