An inverter mainly consists of inverter MOSFETs and a standard power transformer. Its output power depends on the MOSFETs and the power transformer. This avoids the cumbersome transformer windings, making it suitable for hobbyists. What is the working principle and circuit diagram of an inverter?
I. Working Principle
Square wave signal generator. Here, six inverters CD4069 are used to form a square wave signal generator. R1 is a compensation resistor to improve the instability of the oscillation frequency caused by power supply voltage variations. The circuit oscillates through a capacitor. C1 completes the charging and discharging process. The oscillation frequency is F = 1/2.2RC. The maximum frequency of the indicator light circuit is:
fmax = 1/2.2 × 3.3 + time; 10³ + time; 2.2 + time; 10⁻⁶ = 62.6 Hz; minimum frequency fmin = 1/2.2 × 4.3 × 10³ × 2.2 × 10⁻⁶ = 48.0 Hz. The actual values may differ slightly due to element errors. For other redundant inverters, the input terminals should be grounded to avoid affecting other circuits.
Since the maximum amplitude of the oscillation signal voltage output by the square wave signal generator is 0~5V, TR1.TR is used to amplify the oscillation signal voltage to 0~122V in order to fully drive the power switch circuit.
Based on the above analysis, we can deduce the working process of the MOSFET circuit from its principle. The working principle is the same as above. This low-voltage, high-current circuit operates at a frequency of 50Hz. When an AC signal passes through the low-voltage winding of the transformer, the high-voltage side of the transformer will sense a high-voltage AC voltage to complete the conversion from DC to AC. It should be noted that in some cases, such as when the oscillator stops working, a large current may sometimes flow through the low-voltage side of the transformer; therefore, the circuit fuse cannot be omitted or short-circuited.
II. Key Points of Production
Circuit board 6. See section 7 for details on the components used. The inverter uses a 12-pole transformer. The current is 10A, and the primary voltage is a 220V commercial power transformer. A P-channel MOSFET (2SJ maximum drain current 300A) is used. When the FET is turned on, the resistance between the drain and source is 25mΩ. If it exceeds 10mΩ, the power dissipation is 2.5W. The maximum drain current of the N-channel MOSFET (2SK) is 50A. When the MOSFET is on, the resistance between the drain and source is 7mΩ. At this time, the power consumed by a 10A current is 0.7W. Therefore, we can also know that under the same operating current, the heat generated by the 2SJ is approximately four times that of the 2471SK2956. Therefore, this should be taken into account when considering the heat sink. Figure 8 shows the location and connection method of the inverter MOSFETs described in this article on the heat sink (1000mm × 100mm × 17mm). Although the heat generated by the MOSFETs is not very large when they are operating in the on/off state, a slightly larger heat sink was chosen here for safety reasons.
III. Inverter Performance Testing
Test circuit. The input power supply tested here has low internal resistance. A large (typically over 1000 A) 12V car battery can provide sufficient input power to the circuit. The test load is a common light bulb. The test method is to change the load and measure the input current and voltage, and the output voltage accordingly. The output voltage decreases as the load increases, and the bulb's power consumption changes with the voltage. We could also calculate the relationship between the output voltage and power. However, in reality, because the bulb's resistance changes with the voltage across it, and neither the output voltage nor the current is sinusoidal, this calculation should only be considered an estimate.
What is the working principle and circuit diagram of an inverter? Taking a 60W light bulb as an example: Assume the bulb's resistance does not change with voltage. Since R<sub>light</sub> = V<sub>2</sub>/W = 210<sup>2</sup>/60 = 735Ω, when the voltage is 208V, W = V<sub>2</sub>/R = 208<sup>2</sup>/735 = 58.9W. This can be translated into the relationship between voltage and power. Through testing, we found that when the output power is approximately 1000W, the input current is 10A. At this time, the output voltage is 2000V.
