TWI596991B - A bridgeless circuit and induction cooker for induction cooktops - Google Patents

Description

Bridgeless circuit and induction cooker for induction cooker

Field of the Invention This invention relates generally to the field of electrical circuits, and more particularly to a bridgeless circuit and an induction cooker for an induction cooktop.

The induction cooker, also known as the induction cooker, is the product of the modern kitchen revolution. It does not require open flame or conductive heating to allow heat to be generated directly at the bottom of the pot, so the thermal efficiency is greatly improved. The induction cooker mainly comprises the following two parts: a circuit system for generating a high-frequency alternating magnetic field; and a structural outer casing for fixing the circuit system and carrying the cookware.

Figure 1 shows a schematic diagram of the working principle of the induction cooker. As shown in Fig. 1, the induction cooker adopts the principle of magnetic field induced eddy current, and uses the infinite closed magnetic field generated by the high-frequency alternating current through the toroidal coil to make the body itself heat rapidly to achieve heating of the food in the pot. Specifically, when a high-frequency alternating current is passed through the toroidal coil, a high-frequency alternating magnetic field is generated around the toroidal coil; when the magnetic flux generated by the high-frequency alternating magnetic field passes through the bottom of the magnetically permeable material (for example, the bottom of the pot of the iron pot) Under the action of the high-frequency alternating magnetic field, the bottom of the pot will produce numerous small eddy currents, so that the bottom of the pot quickly releases a large amount of heat to achieve the purpose of heating the food in the pot.

Figure 2 shows a schematic diagram of the circuitry of the induction cooker. As shown in FIG. 2, the circuit system of the induction cooker includes a main circuit and a control circuit. The main circuit includes a rectifier bridge 202, an LC filter component 204, an electromagnetic coil (ie, the above-mentioned toroidal coil) 206, and a resonant capacitor 208. And a power switch 210 (for example, an insulated gate bipolar transistor (IGBT)); the control circuit includes a transconductance amplifier 212, a comparator 214, a comparator 216, a valley sensing unit 218, and a logic operation unit 220.

In the main circuit of the induction cooker, the rectifier bridge 202 and the LC filter component 204 perform full-wave rectification and LC filtering on the AC input voltage V _AC to generate a rectified input voltage Vin, that is, a sinusoidal half-wave voltage Vin; the power switch 210 is continuously turned on. And turning off, wherein the sinusoidal half-wave voltage Vin is applied across the electromagnetic coil 206 when the power switch 210 is turned on, the forward current flowing through the electromagnetic coil 206 is increased, and the electromagnetic coil 206 and the resonant capacitor 208 are turned off when the power switch 210 is turned off. Forming a high frequency resonance, the voltage on the electromagnetic coil 206 is reversed, and the current flowing through the electromagnetic coil 206 is reduced; the varying current flowing through the electromagnetic coil 206 forms a high frequency alternating magnetic field, and the magnetic lines of force generated by the high alternating frequency variable magnetic field pass through the bottom of the pot. Make the bottom of the pot hot. Since the input power of the induction cooker is equal to the product of the AC input voltage and the input current, and the AC input voltage is a substantially fixed grid voltage, the input power of the induction cooker can be controlled by controlling the input current. Here, the input current refers to a current flowing from the grid end into the induction cooker, which flows into the induction cooker when the power switch 210 is turned on and stops flowing into the induction cooker when the power switch 210 is turned off, so that the induction cooker can be controlled by controlling the turning on and off of the power switch 210. Input power.

In the control circuit of the induction cooker, the transconductance amplifier 212 integrates the current sensing voltage Vcs with a preset reference voltage Vref to generate a compensation voltage Vcomp, wherein the current sensing voltage Vcs is a current sensing resistor connected in series with the power switch 210. The upper voltage can reflect the magnitude of the input current; the comparator 214 compares the compensation voltage Vcomp with a preset ramp voltage Vramp to generate a control signal off that controls the power switch 210 to be turned off, wherein the power switch 210 is at the control signal off The high level is turned off on time; the comparator 216 compares the compensation voltage Vcomp with the highest on voltage Vth_H or the lowest on voltage Vth_L of the power switch 210 to generate a control signal burst that controls whether the power switch 210 is in an intermittent operation state, wherein the power switch 210 is The control signal burst of the intermittent operation state is in the off state when the high level is on; the valley sensing unit 218 senses the switching voltage V _IGBT on the power switch 210, and forms a control signal on which the power switch 210 is turned on based on the switching voltage V _IGBT , wherein The power switch 210 is turned on when the control signal on is at a high level; The calculation unit 220 generates a control signal gate that controls the on and off of the power switch 210 based on the control signal off, the control signal on, and the control signal burst.

Here, the comparison result of the ramp voltage Vramp and the compensation voltage Vcomp determines the timing at which the power switch 210 is turned off, that is, the on-time Ton of the power switch 210; after the power switch 210 is turned off, the electromagnetic coil 206 resonates with the resonant capacitor 208; When the switching voltage V _IGBT on the switch 210 resonates to the bottom, the power switch 210 is turned on. Since the inductance of the electromagnetic coil 206 and the magnitude of the resonant capacitor 210 are constant, the resonant period is substantially constant, and the switching voltage V _{IGBT of the} power switch 210 resonates to the valley bottom, that is, the off time Toff of the switch 210 is substantially constant, only It is necessary to adjust the on-time Ton of the power switch 210 to adjust the input power of the induction cooker. When the on-time Ton is long, the input power is large, and when the on-time Ton is short, the input power is small.

Fig. 3 is a view showing the flow of current in the main circuit of the induction cooker when the power switch 210 is turned on. Figure 4 shows a schematic diagram of the current flow to the resonant capacitor 208 in the main loop of the induction cooker when the power switch 210 is turned off. Figure 5 shows a schematic diagram of the current flow in the main loop of the induction cooker for reverse charging of the resonant capacitor 208 when the power switch 210 is turned off. Next, the specific operation of the circuit system shown in Fig. 2 will be described in detail with reference to Figs. 3 to 5.

As shown in FIG. 3, when the power switch 210 is turned on, the sinusoidal half-wave voltage Vin forms a current loop through the electromagnetic coil 206 and the power switch 210, and the electromagnetic coil 206 is equivalent to an inductor having a magnitude L, flowing through the electromagnetic coil 206. The current increases. During the on-time Ton of the power switch 210, the current flowing through the current coil 206 rises to the peak current I _pk . Where: L. I _pk = V _in . T _on (1)

As shown in FIG. 4, when the power switch 210 is turned from on to off, the current stored in the electromagnetic coil 206 flows into the resonant capacitor 208 connected in parallel to form an LC resonant circuit. The resonant frequency of the LC resonant tank is: Where L is the inductance of the electromagnetic coil 206 and C is the capacitance of the resonant capacitor 208.

When all of the energy in the electromagnetic coil 206 is transferred to the resonant capacitor 208, the voltage across the resonant capacitor 208 is highest, at which point the switching voltage V _IGBT on the power switch 210 reaches the resonant peak V _PEAK .

Substituting formula (2) into formula (3), you can get:

As shown in FIG. 5, when all the energy in the resonant capacitor 208 is transferred to the electromagnetic coil 206, a negative current is formed between the electromagnetic coil 206 and the resonant capacitor 208, and the energy in the electromagnetic coil 206 is all transferred to the resonant capacitor 208. A reverse voltage is formed, and the switching voltage V _IGBT on the power switch 210 reaches the resonance valley V _VALLEY : V _VALLEY = 2. V _in - V _PEAK (5)

Substituting the formula (4) into the formula (5), you can get:

As can be seen from equation (6), the resonant valley V _{VALLEY of the} switching voltage V _IGBT varies with the on-time Ton of the power switch 210. When the input power of the induction cooker decreases, the on-time Ton of the power switch 210 also decreases, and the resonant valley V _{VALLEY of the} switching voltage V _IGBT , that is, the turn-on voltage of the power switch 210 increases.

Generally, when the input power of the induction cooker is reduced to a certain power (for example, 1000 W), the resonant valley V _{VALLEY of the} switching voltage V _IGBT rises to 100V. If the on-time Ton of the power switch 210 continues to decrease, the resonant valley V _{VALLEY of} the switching voltage V _IGBT will exceed 100V, the safe turn-on voltage of the power switch 210. If the power switch 210 is turned on at this time, the power switch 210 may be damaged due to excessive switching loss. Therefore, when the input power of the induction cooker is less than a certain power (for example, 1000 W), the on-time Ton of the power switch 210 is no longer reduced, but is fixed at a certain value (for example, 7 us), and the circuit system of the induction cooker enters the intermittent operation. The burst mode, that is, the power switch 210 is in a normal high frequency operating state for a period of time, and the power switch 210 is in an off state for another period of time.

Fig. 6 is a view showing waveforms of the compensation voltage Vcomp, the sine half-wave voltage Vin, and the control signal gate in the circuit system shown in Fig. 2.

As shown in FIG. 6, in conjunction with the circuitry of the appliance of FIG. 2 through FIG. 5 described, to adjust the time period of the power switch 210 is in the normal operating state T ₁ of the high frequency and in an off state by the compensation voltage Vcomp T ₂ thus regulates the input power of the induction cooker. Specifically, when the compensation voltage Vcomp is higher than the highest on-voltage _{Vth_H} of the power switch 210, the power switch 210 operates normally; when the compensation voltage Vcomp is lower than the lowest on-voltage _{Vth_L} of the power switch 210, the power switch 210 is in an off state. Due to the presence of the filter capacitor Cin in the LC filter element 204, when the circuit system of the induction cooker enters the burst mode, the sinusoidal half-wave voltage Vin is charged to the AC input during the time T ₂ when the power switch 210 is in the off state. The maximum value of the voltage V _AC and the output current is not output when the power switch 210 is in the off state, so the sinusoidal half-wave voltage Vin on the filter capacitor Cin and the switching voltage V _IGBT on the power switch 210 are always maintained at the AC input voltage V. The maximum value of _AC is until the end of time T ₂ when power switch 210 is in the off state, and the next operating time T ₁ begins. When the next operating time T _{1 of the} power switch 210 starts, the switching voltage V _IGBT on the power switch 210 instantaneously drops from the maximum value of the AC input voltage V _AC to zero volts, which causes a large impact on the power switch 210. The current causes the instantaneous loss of the power switch 210 to be extremely large. In addition, when the circuit system of the induction cooker exits the intermittent mode and the power switch 210 is turned on for the first time, the sinusoidal half-wave voltage Vin is at the maximum value of the AC input voltage V _AC , and the input current of the induction cooker is sinusoidal half-wave voltage Vin. Charging to a larger current, so the current flowing through the solenoid in the induction cooker will mutate from zero to a larger value, which usually produces a harsh sound.

The present invention provides a bridgeless circuit and an induction cooker for an induction cooker.

According to an aspect of an embodiment of the present invention, a bridgeless circuit for an induction cooker is provided, comprising: a first switch connected in parallel with a first diode of a full-wave rectifier bridge; a second switch, and a full-wave rectifier bridge The second diode is connected in parallel; the third switch is connected in parallel with the third diode of the full-wave rectifier bridge; the fourth switch is connected in parallel with the fourth diode of the full-wave rectifier bridge; the first control unit is configured to control a switch and a fourth switch are turned on and off; and a second control unit configured to control turn-on and turn-off of the second switch and the third switch. Among them, the power in the induction cooker When the switch is in an off state in the intermittent operation mode, the first control unit controls the first switch and the fourth switch to be turned on when the AC input voltage is positive, and controls the first switch and the fourth switch to be turned off when the AC input voltage is negative; The second control unit controls the second switch and the third switch to be turned off when the AC input voltage is positive, and controls the second switch and the third switch to be turned on when the AC input voltage is negative.

According to another aspect of an embodiment of the present invention, there is provided a circuit system for an induction cooker comprising: a first switch in parallel with a first diode of a full wave rectifier bridge; a second switch, and a full wave rectifier bridge The four diodes are connected in parallel; the control unit is configured to control the on and off of the first switch and the second switch. Wherein, when the power switch in the induction cooker is in an off state in the intermittent operation mode, the control circuit controls the first switch and the second switch to be turned on when the AC input voltage is positive, and controls the first switch and the first when the AC input voltage is negative The second switch is turned off.

According to still another aspect of an embodiment of the present invention, there is provided an induction cooker comprising the bridgeless circuit described above.

202‧‧‧Rectifier Bridge

204, 704, 1104‧‧‧LC filter components

V _IGBT ‧‧‧Switching voltage

Ton‧‧‧ On time

206, 706, 1106‧‧‧ electromagnetic coil

208, 708, 1108‧‧‧ resonant capacitor

210, 710, 1110‧‧‧ power switch

212‧‧‧Transconductance amplifier

214, 216‧‧‧ comparator

218‧‧‧ Valley bottom sensing unit

220‧‧‧Logical unit

V _AC ‧‧‧AC input voltage

Vin‧‧‧Sinusoidal half-wave voltage

Vcs‧‧‧ current sensing voltage

Vref‧‧‧reference voltage

Vcomp‧‧‧compensation voltage

Vramp‧‧‧ ramp voltage

Vth_H‧‧‧highest turn-on voltage

Vth_L‧‧‧ minimum turn-on voltage

G2_b‧‧‧delay control signal

Off, burst, on, gate, g1, g2, g3, g4‧‧‧ control signals

L‧‧‧ inductance value of electromagnetic coil 206

C‧‧‧ Capacitance of Resonant Capacitor 208

T ₁ ‧‧‧Time of normal high frequency operation

T ₂ ‧‧‧Time at the cut-off

V _L ‧‧‧voltage at the first input terminal

V _N ‧‧‧voltage at the second input terminal

Toff‧‧‧Shutdown time

I _pk ‧‧‧peak current

V _PEAK ‧‧‧ resonance peak

V _VALLEY ‧‧‧Resonance Valley

V _L1 ‧‧‧first characterization voltage

V _N1 ‧‧‧second characterization voltage

V1‧‧‧ threshold voltage

Cin‧‧‧Filter Capacitor

702, 1102‧‧‧ bridgeless circuit

702-1‧‧‧First Control Unit

702-2‧‧‧Second Control Unit

S1, S2, S3, S4‧‧ switch

D1, D2, D3, D4‧‧‧ diodes

R1, R2, R3, R4‧‧‧ resistance

1102-1‧‧‧Control unit

1102-2‧‧‧Delay unit

Other features, objects, and advantages of the invention will be apparent from the description of the accompanying drawings.

1 is a schematic view showing the operation principle of the induction cooker; FIG. 2 is a schematic view showing the circuit system of the induction cooker; and FIG. 3 is a schematic view showing the flow of current in the main circuit of the induction cooker when the power switch 210 is turned on; 4 is a diagram showing a current flow direction for positively charging a resonant capacitor in a main circuit of the induction cooker when the power switch 210 is turned off; FIG. 5 is a view showing a flow in the main circuit of the induction cooker when the power switch 210 is turned off. Schematic diagram of the current flow direction of the reverse charging of the resonant capacitor; FIG. 6 is a waveform diagram showing the compensation voltage Vcomp, the sinusoidal half-wave voltage Vin, and the control signal gate in the circuit system shown in FIG. 2; A schematic diagram of a circuit system including an electromagnetic induction furnace having a bridgeless circuit according to a first embodiment of the present invention; and FIG. 8 is a diagram showing a compensation voltage Vcomp, sinusoidal half when the circuit system shown in FIG. 7 is in a burst mode Waveform voltage Vin, control signal gate, control signals of switches S1 and S4, and waveform diagrams of control signals of switches S2 and S3; FIG. 9 shows an induction cooker including a bridgeless circuit according to a second embodiment of the present invention A schematic diagram of circuitry; AC input circuitry of FIG. 10 illustrates a voltage of 9 V _AC, half sine-wave voltage Vin, the signal control gate, the switching control signals S1 and S4, g1 and g4, switch S2 And waveform diagrams of the control signals g2 and g3 of S3, the compensation voltage Vcomp, and the control signal burst of the intermittent operation mode; FIG. 11 is a schematic diagram showing the circuitry of the induction cooker including the bridgeless circuit according to the third embodiment of the present invention; Figure 12 shows the AC input voltage V _AC , the sine half-wave voltage Vin, the control signal gate, the control signals of the switches S2 and S1, the delay control signal, the compensation voltage Vcomp, and the intermittent operation in the circuit system shown in Fig. 11. Waveform of the mode control signal burst.

Features and exemplary embodiments of various aspects of the invention are described in detail below. In the following detailed description, numerous specific details are set forth However, it will be apparent to those skilled in the art that the present invention may be practiced without some of the details. The following description of the embodiments is merely provided to provide a better understanding of the invention. The present invention is in no way limited to any specific configurations and algorithms presented below, but without departing from the spirit and scope of the invention. In the drawings and the following description, well-known structures and techniques are not shown in order to avoid unnecessary obscuring the invention.

In view of the above circumstances, the present invention proposes a bridgeless circuit for an induction cooker, which can eliminate a large current on the power switch when the induction cooker exits the intermittent mode Impact, so that the induction cooker does not produce abnormal sound when working at any power.

Fig. 7 is a view showing a circuit system of an induction cooker including a bridgeless circuit according to a first embodiment of the present invention. As shown in FIG. 7, the main circuit of the circuit system includes a bridgeless circuit 702, an LC filter component 704, a solenoid 706, a resonant capacitor 708, and a power switch 710 (eg, an insulated gate bipolar junction transistor (IGBT); The bridgeless circuit 702 includes a switch S1, a switch S2, a switch S3, and a switch S4 respectively connected in parallel with the diode D1, the diode D2, the diode D3, and the diode D4 of the full-wave rectifier bridge for controlling a first control unit 702-1 for turning on and off the switches S1 and S4, and a second control unit 702-2 for controlling the on and off of the switches S2 and S3; in the intermittent operation mode of the power switch 710 In the off state, the first control unit 702-1 controls the switch S1 and the switch S4 to be turned on when the AC input voltage is positive, and controls the switch S1 and the switch S4 to turn off when the AC input voltage is negative; the second control unit 702-1 is When the AC input voltage is positive, the control switch S2 and the switch S3 are turned off, and when the AC input voltage is negative, the control switch S2 and the switch S3 are turned on. Here, it should be noted that the control circuit for the circuit system shown in FIG. Similar to the control circuit shown in Figure 2, because Here not shown and omitted.

Specifically, the switches S1-S4 respectively connected in parallel with the diodes D1-D4 may be small power MOSFETs. When the power switch 710 is in operation, the diodes D1-D4 are normally turned on. When the power switch 710 is in the off state: during the positive half cycle of the AC input voltage V _AC (ie, when the AC input voltage is positive), the switch S1 and the switch S4 are turned on, the switch S2 and the switch S3 are turned off; at the AC input voltage V _AC Negative half cycle (ie, when the AC input voltage is negative), switch S1 and switch S4 are turned off, switch S2 and switch S3 are turned on; in the left half cycle of sinusoidal half-wave voltage Vin, that is, when AC input voltage V _AC rises The AC input voltage V _AC charges the filter capacitor Cin in the LC filter component 704; during the right half cycle of the sinusoidal half-wave voltage Vin, that is, when the AC input voltage V _AC falls, the filter capacitor Cin in the LC filter component 704 The stored energy is fed back to the grid side via the switches S1 and S4 or the switches S2 and S3, so that the sinusoidal half-wave voltage Vin can always follow the AC input voltage V _AC . Therefore, at the zero crossing of the AC input voltage V _AC , the control signal gate for controlling the on and off of the power switch 710 is at a high level, the sinusoidal half-wave voltage Vin on the filter capacitor Cin and the switching voltage V on the power switch 710 _{The IGBTs} are all close to zero, the power switch 710 can achieve zero voltage conduction, reducing the switching loss of the power switch 710; and at this time, since the sinusoidal half-wave voltage Vin on the filter capacitor Cin is close to zero, the power switch 710 is turned on and flows through. The current of the induction cooker is also close to zero. Then, as the AC input voltage V _AC gradually increases, the operating current of the induction cooker gradually becomes larger, and no sudden change occurs, thereby eliminating the original abnormal sound. Figure 8 is a diagram showing the waveforms of the compensation voltage Vcomp, the sine half-wave voltage Vin, the control signal gate, the control signals of the switches S1 and S4, and the control signals of the switches S2 and S3 when the circuit system shown in Fig. 7 is in the burst mode. Figure.

Fig. 9 is a view showing a circuit system of an induction cooker including a bridgeless circuit according to a second embodiment of the present invention. Here, it should be noted that the portions of the circuit system shown in FIG. 9 other than those described below are similar to those of the circuit system shown in FIG. 7, and will not be described again.

As shown in FIG. 9, the switch S1, the switch S2, the switch S3, and the switch S4 are respectively connected in series with resistors R1, R2, R3 and R4, and the resistance values of the four resistors are small, for example, the resistance value is 10 ohms. Thus, the AC input voltage V _AC positive half cycle, when the AC input voltage V _AC to the filter capacitor Cin charge, while switches S1 and S4 are turned on, but since the diodes D1 and impedance D4 is much smaller than the respective switches S1 and S4 The resistance of the series resistors R1 and R4, so the input current will still flow through the diodes D1 and D4; when the AC input voltage V _AC drops below the sinusoidal half-wave voltage Vin on the filter capacitor Cin, the diode D1 and D4 cannot be turned on, and the sinusoidal half-wave voltage Vin on the filter capacitor Cin is fed back to the grid side through the switches S1 and S4. In the negative half cycle of the ac input voltage V _AC when the AC input voltage V _AC to the filter capacitor Cin charge, while switches S2 and S3 is turned on, but since the diodes D2 and D3 impedance is much smaller than the resistance, respectively S2 and S3 connected in series The impedance of R1 and R4, so the input current will still flow through diodes D2 and D3; when the AC input voltage V _AC drops below the sinusoidal half-wave voltage Vin on the filter capacitor Cin, the diodes D2 and D4 cannot Turning on, the sinusoidal half-wave voltage Vin on the filter capacitor Cin is fed back to the grid side through switches S2 and S3.

As shown in FIG. 9, the first control unit 702-1 includes a first comparator and a first isolation unit, and the second control unit 702-2 includes a second comparator and a second isolation unit, wherein: the first comparator receives _Dividing a first characterization voltage V _{L1 of the} input voltage V _AC and comparing the first characterization voltage V _L1 with the threshold voltage V1 to generate a control signal g4 for controlling the on and off of the switch S4; the first isolation unit enables The voltage difference between the control signal g1 and the first characterization voltage V _L1 is equal to the control signal g4, that is, the voltage difference between the drain voltage and the source voltage of the switch S1 is equal to the control signal g4; when the first characterization voltage V _{L1 is} higher than At the threshold voltage V1, the control signal g4 is at a high level, the switches S4 and S1 are turned on; the second comparator receives the second characterization voltage V _{N1 of the} AC input voltage V _AC and compares the second characterization voltage V _N1 with the threshold voltage V1 To generate a control signal g3 for controlling the on and off of the switch S3; the second isolation unit makes the voltage difference between the control signal g2 and the second characterization voltage V _N1 equal to the control signal g3, that is, the drain voltage of the switch S2 Between the source voltage and G4 pressure equal to the control signal; characterized by when the second voltage V _N1 is higher than the threshold voltage V1 (e.g., 0.2V), the control signal g3 at a high level, the switches S3 and S2 are turned on. No bridge circuit 702 through the first input terminal and a second input terminal for receiving an input AC voltage V _AC, a first voltage V _Ll was characterized by a first voltage V _L at the input terminal for dividing the second voltage V Characterization _N1 is obtained by dividing the voltage V _N at the second input terminal. Here, the first and second isolation units may be any electrical isolation unit, such as a transformer isolation unit or an optocoupler isolation unit as shown.

Figure 10 shows the AC input voltage V _AC , the sinusoidal half-wave voltage Vin, the control signal gate, the control signals g1 and g4 of the switches S1 and S4, and the control signals of the switches S2 and S3 in the circuit system shown in Fig. 9. Waveforms of g2 and g3, compensation voltage Vcomp, and control signal burst of the intermittent operation mode. As can be seen from Fig. 10, in the circuit system shown in Fig. 9, the sinusoidal half-wave voltage Vin on the filter capacitor Cin can follow the AC input voltage V _AC regardless of whether the output has a load or not.

Fig. 11 is a view showing the circuit system of the induction cooker including the bridgeless circuit of the third embodiment of the present invention. As shown in FIG. 11, the main circuit of the circuit system includes a bridgeless circuit 1102, an LC filter component 1104, an electromagnetic coil 1106, a resonant capacitor 1108, and a power switch 1110 (for example, an insulated gate bipolar junction transistor (IGBT)). . Bridgeless circuit 1102 A switch S1 and a switch S2, a control unit 1102-1, and a delay unit 1102-2, respectively, in parallel with the diode D1 and the diode D4 of the full-wave rectifier bridge are included.

As shown in Fig. 11, the switch S1 and the switch S2 are connected in series with the resistor R1 and the resistor R2, respectively. Thus, the AC input voltage V _AC positive half cycle, when the AC input voltage V _AC to the filter capacitor Cin charge, while the switches S1 and S2 is turned on, but since the diodes D1 and impedance D4 is much smaller than the respective switches S1 and S2 The resistance of the series resistors R1 and R4, so the input current will still flow through the diodes D1 and D4; when the AC input voltage V _AC drops below the sinusoidal half-wave voltage Vin on the filter capacitor Cin, the diode D1 and D4 cannot be turned on, and the sinusoidal half-wave voltage Vin on the filter capacitor Cin is fed back to the grid side through the switches S1 and S2.

As shown in FIG. 11, the control unit 1102-1 includes a comparator and an isolation unit, wherein: the comparator receives the characterization voltage V _{L1 of the} AC input voltage V _AC and compares the characterization voltage V _L1 with the threshold voltage V1 to generate a control voltage g2 for controlling the on and off of the switch S2; the voltage difference between the control signal g1 for controlling the on and off of the switch S1 and the characterization voltage V _L1 is equal to the control signal g2, that is, the switch S1 is the voltage difference between the drain voltage and the source voltage equal to the control signal g2; when the divided voltage V _L1 characterization higher than the threshold voltage V1 (e.g., 0.2V), the control signal g2 at the high level, the switches S1 and S2 are turned on. No bridge circuit 1102 receives the ac input voltage V _AC input via a first terminal and a second input terminal, a first voltage V _L1 is characterized by a first voltage V _L at the input terminal is obtained by dividing. Here, the isolation unit may be any electrical isolation unit, such as a transformer isolation unit or an optocoupler isolation unit as shown.

The delay unit 1102-2 receives the control signal g2 generated by the control unit 1102-1 and delays the control signal g2 to generate the delay control signal g2_b. The delay control signal g2_b is a level signal, and when the delay control signal g2_b is at a high level, the induction cooker can be controlled to exit the burst mode.

Here, when the characterization voltage V _{L1 is} higher than the threshold voltage V1, the control signal g2 is at a high level, the switches S2 and S3 are turned on; when the compensation voltage Vcomp is lower than the lowest on-voltage Vth_L of the power switch 1110, the circuit shown in FIG. The system enters the intermittent mode (burst) mode, and the power switch 1110 is turned off; when the compensation voltage Vcomp voltage is higher than the highest on-voltage Vth_H of the power switch 1110, the circuit system shown in FIG. 11 must wait until the switches S1 and S2 are turned off, and the filter capacitor The voltage on Cin has all been fed back to the AC grid. When Vin is close to zero, it exits the burst mode and the power switch 1110 starts to work. At this time, the sinusoidal half-wave voltage Vin on the filter capacitor Cin and the switching voltage V _IGBT on the power switch 1110 are both close to zero, and the power switch 1110 can achieve zero voltage conduction, reducing the switching loss of the power switch 1110; The sinusoidal half-wave voltage Vin on the capacitor Cin is close to zero, and the current flowing through the induction cooker is also close to zero. Then, as the AC input voltage gradually increases, the operating current of the induction cooker gradually becomes larger, and no sudden change occurs. It eliminates the original abnormal sound.

Figure 12 shows the AC input voltage V _AC , the sine half-wave voltage Vin, the control signal gate, the control signals of the switches S2 and S1, the delay control signal, the compensation voltage Vcomp, and the intermittent operation in the circuit system shown in Fig. 11. Waveform of the mode control signal burst.

The circuit system described above in combination with FIG. 7 to FIG. 12 can eliminate the abnormal sound of the conventional induction cooker under low power operation, and remove the large current impact on the power switch when the induction cooker exits the intermittent mode, and reduce the power switch. The switching loss makes the power switch work safer.

The invention may be embodied in other specific forms without departing from the spirit and essential characteristics. For example, the algorithms described in the specific embodiments can be modified, and the system architecture does not depart from the basic spirit of the invention. The present embodiments are to be considered in all respects as illustrative and not limiting, and the scope of the invention All changes in the scope of the invention are thus included in the scope of the invention.

704‧‧‧LC filter components

V _IGBT ‧‧‧Switching voltage

706‧‧‧Electromagnetic coil

702‧‧‧Bridgeless circuit

708‧‧‧Resonant capacitor

702-1‧‧‧First Control Unit

710‧‧‧Power switch

702-2‧‧‧Second Control Unit

Cin‧‧‧Filter Capacitor

S1, S2, S3, S4‧‧ switch

Vin‧‧‧Sinusoidal half-wave voltage

D1, D2, D3, D4‧‧‧ diodes

Vcs‧‧‧ current sensing voltage

Gate, g1, g2, g3, g4‧‧‧ control signals

Claims (8)

A bridgeless circuit for an induction cooker, comprising: a first switch connected in parallel with a first diode of a full-wave rectifier bridge; a second switch connected in parallel with a second diode of the full-wave rectifier bridge; a third switch a fourth diode connected in parallel with the third diode of the full-wave rectifier bridge; a fourth switch connected in parallel with the fourth diode of the full-wave rectifier bridge; a first control unit configured to control the first switch and Turning on and off the fourth switch; and a second control unit configured to control turn-on and turn-off of the second switch and the third switch, wherein the power switch in the induction cooker is in an intermittent mode of operation In the off state, the first control unit controls the first switch and the fourth switch to be turned on when the AC input voltage is positive, and controls the first switch and the when the AC input voltage is negative The fourth switch is turned off, the second control unit controls the second switch and the third switch to be turned off when the AC input voltage is positive, and controls the second when the AC input voltage is negative The switch and the third switch are turned on; The first control unit includes: a first comparator configured to generate a first control for controlling turn-on and turn-off of the fourth switch by comparing the first characterization voltage of the AC input voltage with a first threshold voltage And a first isolation unit configured to cause a voltage difference between a gate voltage and a source voltage of the first switch to be equal to the first control signal; the second control unit comprising: a second comparator Configuring to generate a second control signal that controls turn-on and turn-off of the third switch by comparing a second characterized voltage of the AC input voltage with a first threshold voltage; The second isolation unit is configured to make a voltage difference between a gate voltage and a source voltage of the second switch equal to the second control signal. The bridgeless circuit of claim 1, wherein the first switch, the second switch, the third switch, and the fourth switch are respectively coupled to the first resistor, the second resistor, and the first The three resistors and the fourth resistor are connected in series such that the input current still flows through the first diode and the fourth diode when the first switch and the fourth switch are turned on, in the second The second diode and the third diode are still flowing when the switch and the third switch are turned on. The bridgeless circuit of claim 1, wherein the bridgeless circuit receives the AC input voltage through a first input terminal and a second input terminal, the first characterization voltage being The voltage at an input terminal is divided by voltage. The bridgeless circuit of claim 1, wherein the bridgeless circuit receives the AC input voltage through a first input terminal and a second input terminal, and the second characterization voltage is passed to the The voltage at the two input terminals is divided by voltage. A bridgeless circuit for an induction cooker, comprising: a first switch connected in parallel with a first diode of a full-wave rectifier bridge; a second switch connected in parallel with a fourth diode of the full-wave rectifier bridge; a control unit, Configuring to control turn-on and turn-off of the first switch and the second switch, the control unit comprising: a comparator configured to generate by comparing a characterized voltage of the alternating input voltage with a threshold voltage a control signal for controlling conduction and deactivation of the second switch; and an isolation unit configured to cause a voltage difference between a gate voltage and a source voltage of the first switch to be equal to the control signal; When the power switch is in an off state in the intermittent operation mode, the control circuit controls the first switch and the second switch to be turned on when the AC input voltage is positive, when the AC input voltage is negative The first switch and the second switch are controlled to be turned off. The bridgeless circuit of claim 5, wherein the first switch and the second switch are respectively connected in series with the first resistor and the second resistor to cause an input current in the first switch and the When the second switch is turned on, the first diode and the fourth diode are still flowing. The bridgeless circuit of claim 5, wherein the bridgeless circuit receives the AC input voltage through a first input terminal and a second input terminal, the characterization voltage being passed to the first input The voltage at the terminal is divided by voltage. The bridgeless circuit of claim 5, further comprising: a delay unit configured to generate a delay signal based on the control signal, and provide the delay signal to a control circuit of the induction cooker to The power switch begins to operate after the first switch and the second switch change from conducting to turning off.