Brief Analysis of 400W High Power Voltage Stabilizing Inverter Circuit

The 400W high-power voltage-stabilizing inverter circuit is composed of TL494. The excitation conversion part uses TL494, and VT1, VT2, VD3, and VD4 form a current-injection drive circuit to drive two 60V/30A MOS FET switch tubes in each channel. If the output power needs to be increased, 3 to 4 switch tubes can be used in parallel for each channel, and the circuit remains unchanged. The application method of TL494 in this inverter is as follows:

Pins 1 and 2 form a voltage-stabilizing sampling and error amplification system. The positive input pin 1 inputs the 15V DC voltage output by the inverter secondary sampling winding rectification. After R1 and R2 divide the voltage, the pin 1 has a sampling voltage of nearly 4.7 to 5.6V when the inverter is working normally. The negative input pin 2 inputs a 5V reference voltage (output from pin 14). When the output voltage decreases, the voltage of pin 1 decreases, the error amplifier outputs a low level, and the output voltage is increased through the PWM circuit. Normally, the voltage value of pin 1 is 5.4V, the voltage value of pin 2 is 5V, and the voltage value of pin 3 is 0.06V. At this time, the output AC voltage is 235V (square wave voltage). Pin 4 is connected to R6, R4, and C2 to set the dead time. The normal voltage value is 0.01V. Pins 5 and 6 are connected to CT and RT to set the oscillator triangle wave frequency to 100Hz. Normally, the voltage value of pin 5 is 1.75V, and the voltage value of pin 6 is 3.73V. Pin 7 is the common ground. Pins 8 and 11 are the collectors of the internal drive output transistors, and pin 12 is the front-stage power supply terminal of TL494. These three terminals control the start/stop of TL494 through switch S, and serve as the control switch of the inverter. When S1 is turned off, TL494 has no output pulse, so the switch tubes VT4~VT6 have no current. When S1 is turned on, the voltage value of these three pins is the positive voltage of the battery. Pins 9 and 10 are the emitters of the internal drive-stage transistors, which output two positive pulses with different timings. The voltage value is 1.8V under normal conditions. Pins 13, 14, and 15, of which pin 14 outputs a 5V reference voltage, so that pin 13 has a 5V high level, controls the gate circuit, and the trigger outputs two drive pulses for the push-pull switch circuit. Pin 15 is connected to an external 5V voltage to form the inverting input reference voltage of the error amplifier, so that the in-phase input pin 16 forms a high-level protection input terminal. In this connection, when the input of pin 16 is higher than 5V, the output voltage can be reduced by voltage stabilization, or the drive pulse can be turned off to achieve protection. There is almost no possibility of output overvoltage in the self-excited inverter, so pin 16 is not used in this circuit and is grounded by resistor R8.

The inverter uses a 400VA power frequency transformer, and the core uses 45×60mm2 silicon steel sheet. The primary winding uses 1.2mm diameter enameled wire, two wires are wound in parallel for 2×20 turns. The secondary sampling winding uses 0.41mm enameled wire for 36 turns, with a center tap. The secondary winding is calculated at 230V, and 0.8mm enameled wire is used for 400 turns. Switching tubes VT4~VT6 can be replaced by any type of 60V/30A N-channel MOS FET tube. VD7 can use 1N400X series ordinary diodes. The circuit can work normally almost without debugging. When the positive terminal voltage of C9 is 12V, R1 can be selected between 3.6~4.7kΩ, or adjusted with a 10kΩ potentiometer to make the output voltage the rated value. If the output power of this inverter is increased to nearly 600W, in order to avoid excessive primary current and increase resistive loss, it is advisable to change the battery to 24V, and the switch tube can use a high-current MOS FET tube with a VDS of 100V. It should be noted that it is better to use multiple tubes in parallel rather than a single switch tube with an IDS greater than 50A. The reasons are: first, the price is higher, and second, it is too difficult to drive. It is recommended to use 100V/32A 2SK564, or three 2SK906s in parallel. At the same time, the cross-section of the transformer core must reach 50cm2, and the number of turns and wire diameter must be calculated according to the calculation method of ordinary power transformers, or the transformer in the waste UPS-600 can be used as a substitute. If it is used to power refrigerators and electric fans, please do not forget to add LC low-pass filters.