A friend privately messaged me and asked me to write an article about the MOS tube drive circuit with transformer isolation. Today, the editor of VBsemi will talk about the principle of this MOS tube drive circuit with transformer isolation.

The transformer isolation drive circuit is mainly based on the law of electromagnetic induction and electrical insulation isolation.

Specifically, when an AC voltage is applied to the primary winding of the transformer, an alternating current will be generated in the primary winding, which will form an alternating magnetic field in the iron core.

According to the law of electromagnetic induction, the alternating magnetic field will induce an electromotive force in the secondary winding, thereby realizing the transfer of voltage from the primary to the secondary, and the voltage relationship satisfies V1/V2 = N1/N2. (Where V1 and V2 are the voltage amplitudes of the primary and secondary sides, respectively, and N1 and N2 are the number of turns of the windings of the primary and secondary sides, respectively)

 Next, let's look at the transformer isolation drive circuit (as shown in the figure)

 A PWM duty cycle signal is sent from the IC (control module) to control a primary coil of the transformer, thereby generating self-inductance, and then mutual inductance to the secondary coil.

When the same-name terminal of the primary coil is positive, the same-name terminal of the secondary coil is positive.

At this time, the secondary coil of the transformer (above) drives the MOSFET through the positive pole and R2. Because R2 is at a high potential, the high voltage flows through the MOSFET and the MOSFET is turned on.

When the end of the secondary coil (below) connected to R3 is negative, the voltage at R3 is relatively low, and the MOSFET discharges through R7. At this time, the MOSFET is cut off.

When the duty cycle signal is low, the same-name end of the primary coil is negative. The same-name end of the secondary coil is also negative. At this time, the secondary coil (connected to one end of R3) is positive, and the MOS tube is driven by R7. The MOS tube (lower) is turned on, and the upper MOS tube (when the same-name end of the upper secondary coil is negative) is turned off.

Therefore, when the duty cycle signal sent by the IC is high, the upper MOS tube is turned on and the lower one is turned off. When it is low, the upper MOS tube is turned off and the lower one is turned on.

After the duty cycle signal passes through the transformer, the two MOS tubes are turned on alternately, thus isolating the high and low voltages to prevent interference between the high and low voltages.