AN3095 datasheet(34/55 Pages) STMICROELECTRONICS

34 / 55 page

Schematic description

AN3095

34/55

Doc ID 16555 Rev 3

The outputs of the microcontroller are the PWM signals used to control the power devices in

each leg of the conversion system.

Power MOSFETs and IGBTs must be interfaced to the control circuit while maintaining

galvanic isolation. Two slightly different solutions were implemented for the DC-DC and the

DC-AC converter. In the first, a L6386 IC with a bootstrap capacitor for a floating drive

supply was selected because of the low cost and the capability of driving a high-side and a

low-side device with a single IC, therefore simplifying the layout of the board. The opto-

isolator receives the signal generated by the microcontroller and performs the level shifting

of this signal from 0-5 V to 0-15 V. The opto-isolator output pin is connected to the L6386

input pin. A totem pole circuit, consisting of a PNP-NPN BJT pair, connects the output of the

IC to the gate of each MOSFET, amplifying the driving current and allowing fast switching,

both at turn-on and turn-off. The +15 V supply voltage of the IC and opto-isolator is provided

by an isolated DC-DC converter, as shown in Figure 20. A similar solution was used to drive

the IGBTs in the inverter bridge. The main difference is the use of a single driver IC, TD350,

characterized by 0.75 A/1.2 A source/sink current capability and includes some dedicated

control and protection functions such as IGBT desaturation, two level turn-off and fault

detection output. The circuit implemented is shown in Figure 21.

AN3095 Folha de dados(PDF) 34 Page - STMicroelectronics