This is a training module for Vishay IGBT/Mosfet Gate Drive Optocouplers
Welcome to the training module on Vishay IGBT/MOSFET Gate Drive Optocouplers. This training module introduces basic knowledge of IGBT gate drive optocouplers and Vishay’s product offerings.
To best explain what an IGBT driver does, we will refer to this industrial application; the control of a 600 V, 3-phase motor driving a robotic arm. The low voltage sensitive electronics and user interface are shown on the left while the high voltage and potentially noisy motors are on the right. Notice that there is a feedback loop from the robotic arm to the controller providing speed, position and status data. Let’s first take a closer look at the optocoupler in this loop.
Optocouplers provide isolation. They optically transmit a signal while electrically isolating the transmit and receive side. They play a key role in protecting sensitive electronics from high voltage spikes. In a way, they are like a brick wall keeping noise, EMI, voltage spikes and RFI out while allowing clean data signals to pass.
Here is how they work. First, an electric current turns on the infrared emitting diode. The light from this diode travels through IR transparent epoxy to a photo detector, in this case a phototransistor. Current is generated by the phototransistor and this current is then used in various circuits. Light can travel between the emitter and detector but electricity can not because there is no direct metallic connection.
Let’s see what happens when a high voltage spike comes through a power line into a switch mode power supply. In this case the sensitive electronics are on the right. The transformer blocks the spike but it can pass via the feedback loop and damage the sensitive electronics. Insert an optocoupler in this feedback loop and the voltage spike can’t get past the optocoupler to the output or sensitive circuit.
Back to the robotic arm. Working back from the robotic arm, its motor is driven by an IGBT module. In this case there are six IGBTs in the module. What is an IGBT?
IGBT stands for insulated gate bipolar transistor. It combines the high switching speeds and voltage driven capabilities of a MOSFET with the high current handling capabilities of a bipolar junction transistor. A module is simply a combination of 2, 4 or 6 discrete IGBT in a single component.
IGBTs are found in numerous industrial and consumer applications. Motor drives and motor controls like our robotic arm are using AC motors, DC brushless motors, typically 10 to 20 horsepower and up to 800 V and 50 Amps. They are also used in welding equipment, uninterruptible power supplies, inverters, induction stove tops and plasma display panels.
To power and control the 600 V, 3-phase robotic arm, there are 6 IGBTs, 2 per phase. For each IGBT, there is an IGBT driver , in this example, a total of 6 IGBT drivers.
An IGBT driver provides a drive voltage to the gate of an IGBT to switch it “ON” or “OFF”. The IGBT will then “switch” on to provide high current to drive the load. As an optocoupler, it optically isolates the low voltage control circuitry from the high voltage load like a 3 phase motor. IGBT drivers provide a high output voltage, from 15 V to 32 V, to turn on the IGBT and a low or negative voltage to turn off the IGBT. To do this, the IGBT driver has an emitter and photodetector with an integrated control IC shown here in orange, which drives the two output transistors Tr1 and Tr2 according to the truth table shown.
Vishay Optoelectronics has introduced the VO3120 and VO3150A IGBT drivers. The VO3120 has an output current of 2.5 A while the VO3150A has an output current of 0.5 A. They have the widest operating supply voltage from 15 to 32 V; the highest operating temperature up to 110 °C; and very low input supply current of 2.5 mA or less depending on temperature; and, finally, an isolation voltage of 5300 V. They are available in a DIP8 leaded or surface mount package.
Vishay’s optocouplers provide comfortable head room between breakdown voltage and supply voltage; over 55 V which makes it more rugged in industrial applications.
In order to turn off the IGBT, some larger IGBT’s require negative gate voltage. Because Vishay has such a wide supply voltage, these devices can offer a high side voltage. In this example 22 V, while having a healthy 10 V negative gate voltage. This decreases switching time, reduces losses during turn off, and provides additional dV/dt noise immunity.
Having a low input supply current is a clear benefit to customers. It reduces power consumption, generate less heat and requires smaller heat sinks. As the operating temperature increases, the supply current decreases. Note that at 25°C and higher, the input current will be less than 1.5 mA.
Thank you for taking the time to view this presentation on “ IGBT/MOSFET Gate Drive Optocouplers” . If you would like to learn more or go on to purchase some of these devices, you may either click on the part list link, or simply call our sales hotline. For more technical information you may either visit the Vishay site – link shown, or if you would prefer to speak to someone live, please call our hotline number, or even use our ‘live chat’ online facility. This ends the Vishay Optocoupler Training Module.
Optically transmits a signal while electrically isolating the transmitting and receiving circuits
Protects sensitive electronics (and us) from high voltage spikes
Optocouplers Provide Isolation EMI RFI Voltage Spikes Noise Sensitive electronics Human interface Clean data signals
How It Works – Basic Optocoupler Infrared Emitting Diode Optically Transparent Dielectric Photo Detector An electric current turns on the IRED The IRED is coupled thru the dielectric to the photo detector The photo detector generates a current The current is manipulated by various circuits to perform a function A C C E I f Ic V in V out