In terms of the current domestic R & D status of induction heating power supply, high-frequency induction heating power supply is the mainstream R & D and design direction, and it is also the focus of many engineers. In today’s article, we will share a design scheme of driving circuit of high-frequency induction heating power supply based on ir2llo chip. We hope to help you better complete the R & D and design work through this scheme sharing.
In the shared driving circuit design scheme of high frequency induction heating power supply, we use chip ir2llo for the circuit design of driving half bridge series resonant inverter, as shown in Figure 1 below. As can be seen from Figure 1, in this circuit system, VD is a bootstrap diode, and an ultrafast recovery diode 10ia16 with recovery time of tens of nanoseconds and withstand voltage above 500V is adopted. Ch is the bootstrap capacitor, using 0.1 μ F ceramic wafer capacitor. CL is a bypass capacitor, using a 0.1 μ F ceramic wafer capacitor and 1 μ Tantalum capacitor parallel DD and VCC of F are input stage logic power supply and low-end output stage power supply respectively. They use the same + 12V power supply, while VB is high-end output stage power supply. It uses the same power supply with VCC and is generated by bootstrap technology. Here, considering that the surge voltage generated at the drain of the power MOSFET will be coupled to the gate through the Miller capacitor between the drain gates to breakdown the gate oxide layer, 12V voltage regulators D1 and D2 are connected between the gate sources of T1 and T2 to limit the gate source voltage, so as to protect the power M0SFET.
Negative bias and power expansion circuit
After understanding the design diagram of the half bridge series resonant inverter of this high-frequency induction heating power supply, let’s see how to complete the design of negative bias and power expansion circuit. In the figure below, figure 2 shows the specific negative bias and power expansion circuit. On the right of the dotted line is the power expansion circuit, which adopts two pairs of p-channel and n-channel mosfetq1, Q3, Q2 and Q4 to form a push-pull output structure. This is a power buffer with high input impedance, which can produce 8A peak output current, and the quiescent current can be ignored.
During the operation of this negative bias and power expansion circuit design, when the input signal is high level, the gate of Q2 is also high level, so Q2 is turned on, which makes the gate of Q3 low level, so Q3 is turned on, and the output is also high level; When the input signal is at low level, Q1 turns on, which makes the gate of Q4 turn to high level. In this way, Q4 turns on, and the output is also at low level. Among them, Q1 and Q2 are low current drivers for Q3 and Q4, and Q3 and Q4 are output transistors. Their size can be selected according to the needs of output peak current. When the input signal changes state, R1 is limited to the current passing through Q1 and Q2 when the two transistors are turned on at the same time in a few nanoseconds. When the input changes to a new state, the driver transistor quickly releases the charge of the gate and forces the output transistor to turn off. At the same time, the gate of another output transistor is rapidly charged by R1, and the RC time constant composed of R1 and the input capacitance of the output transistor will delay the conduction.
In Figure 2 above, we can see that the design on the left of the dotted line of the system is a negative bias circuit. In this negative bias circuit system, D1, C1 and R2 are level converters for Q2, and C1, C3, D2 and D3 convert the input signal into negative DC voltage to form negative bias. The specific experimental results of this circuit are shown in Figure 3 below. Among them, channel 1 is the driving signal waveform output by IR2110, and channel 2 is the output waveform of the driving signal after passing through the negative bias and power expansion circuit.
Driving signal duty cycle adjusting circuit
In the driving circuit system of high-frequency induction heating power supply designed in this paper, the half bridge series resonant inverter designed based on IR2110 chip mainly uses M0SFET as the main switching device. The design of power device MOSFET in the circuit is shown in T1 and T2 in Figure 1. In the control circuit of this half bridge series resonant inverter, we mainly use the phase-locked loop circuit to realize frequency tracking. However, in this circuit system, the duty cycle of the output signal of the phase-locked loop MM74HC4046 is 50%. If it is directly added to the input of IR2110, the duty cycle of the output drive signal is also 50%, which is added to the gate of the main switching devices T2 and T2, The driving signal will be affected by the line stray inductance, parasitic capacitance, input impedance and internal parasitic capacitance of the MOSFET, so that the duty cycle exceeds 50%, so it is unable to set the correct dead band and meet the normal driving requirements of half bridge series resonant inverter.
To solve the duty cycle problem in the circuit system, we can use a relatively simple method, that is to add a duty cycle adjustment (dead band formation) circuit to the front stage of the driving circuit. The duty cycle of the drive control signal added to the input of IR2110 becomes less than 50%, so that the duty cycle added to the T1 and T2 gate drive signals can be flexibly adjusted to slightly less than 50%, so as to produce a dead band that meets the needs of practical application. The specific circuit is shown in Figure 4 below.
From the duty cycle adjustment circuit diagram shown in Figure 4, we can see that after adding the adjustment circuit, in the circuit system of this high-frequency induction heating power supply, the square wave signal with a duty cycle of 50% output by the frequency tracking circuit is shaped by two stages 74hc14 and sent to the JK Trigger 74hc109 triggered by the rising edge and the dead band adjustment circuit composed of RC respectively, and their outputs are consistent with each other, Two groups of drive control signals as shown in Fig. 4 can be obtained, and they can be sent to the high and low input terminals of IR2110 respectively to obtain the drive signal meeting the actual use requirements.
In the figure below, figure 5 shows the high and low end drive signals of IR2110 adjusted by this duty cycle circuit. In the specific application process, engineers can get different dead band signals by adjusting the potentiometer according to the needs of the actual duty cycle, so they can get the driving signals with different duty cycle, that is, they can get the driving signals with different dead band. After testing, the circuit can work in the frequency range of 50KHz ~ 5MHz, and the duty cycle can be adjusted between 25% and 50%, which can meet most applications.
The above is the design of a high-frequency induction heating power supply driving circuit based on ir21l0 chip shared in this paper. I hope it can be helpful to the design and R & D work of engineers.