• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Digitallyndriving IGBT

Status
Not open for further replies.
Hello people. I am building high power dc dc isolated converter. I want to drive IGBTs through PSoC micro-controller. Is it possible? What will be the challenges. One of which i can think of is output of micro-controller will be around 5 V and driving voltage required will be around 15-20V. How to rectify this? and what will be other problems i will be facing?
 

dknguyen

Well-Known Member
Most Helpful Member
It's actually two basic problems:

1. The digital pin output voltage is too so it can't turn on the IGBT,
2. The digital pin sink/source current is too low so it can't charge and discharge the gate capacitance fast enough to turn on and off the IGBT fast enough to minimize the time that the IGBT spends in between the efficient ON and OFF states when switching. This results in increased switching losses at best. At worst, the MOSFET can't even finish switching before you need to to change states again.

You use a gate driver to boost both the voltage, and current to deal with this.

And usually there is a third problem:
3. If you have IGBTs where the source-pin is not connected to ground (i.e. a high-side IGBT with a floating source pin) then the gate-source voltage required to activate the IGBT isn't even sharing the same reference voltage as the digital output pin is.

In this case you need a floating gate driver. The cheapest and most common is a capacitor boostrap gate driver but it has the limitation that it cannot do 100% duty cycle. For that you need a dedicated floating voltage supply to run the gate driver on.

The simplest, but most expensive way is to take a bootstrap capacitor gate driver circuit/IC and just replace the boostrap capacitor and boostrap diode with with an isolated converter. Sometimes you can build a charge pump circuit with a 555 timer that runs when the high-side IGBT is turned on and it replenishes the bootstrap capacitor. Cheaper in parts, but much more components and wiring for what can appear to be a somewhat convoluted circuit. Google app notes. It'll come up real fast.

Sometimes a fourth problem:
4. Ringing and latch-up are also issues. Switch too fast and you get ringing from transmission line effects such as under/over voltage and latch up. Switch too slow and you get too much switching losses as previously mentioned.

Series resistors placed close to the gate pin and measuring observing the gate switching waveform with different gate resistances (1-10 ohms probably) is the simplest method to solving this. Some people also use clamp diodes on the gate and other such things
 
Last edited:

dknguyen

Well-Known Member
Most Helpful Member
They make logic level IGBT's
They also make IGBT's that have driving circuits built in that can make haft H bridges and are 5 volt.
https://www.mouser.com/datasheet/2/389/stgipq8c60t-hz-1074119.pdf
That one only needs 3.3 volts on the input

It's 600 volt 8 amps there bigger one's
Note that you will still need a gate driver on such IGBTs to drive at higher currents if you are planning on doing high frequency switching or floating gate drivers if you are driving IGBTs not referenced to ground.

Since the logic level IGBTs have to make some performance/cost compromises to achieve their logic-level gate voltages, it can preferable to just go with a standard level IGBT if you need a floating gate driver (most floating gate driver ICs need at least 10V to work) or already have 12-18V in your system elsewhere.
 
Last edited:
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top