Photovoltaic IGBT drivers

[Mark R]

Anyone used these?

These look so much simpler than traditional high-side drivers. Is there a catch?

 

[William Gaatjes]

Anyone used these?

These look so much simpler than traditional high-side drivers. Is there a catch?

Do you have a part number ?

That reminds of these :
Solid state photovoltaic relays from Fairchild.
http://uk.farnell.com/international...elay-photovoltaic-300v/dp/9104070?Ntt=9104070

http://www.farnell.com/datasheets/65313.pdf

The only thing i can think of is that the turn on time is primarily determined by the amount of light used. The turn off time is determined by leaking away of the charge in these solid state photovoltaic relays.

Although these issues can be solved by a smart design. Two photovoltaic devices where 1 is used to turn on and 1 is used to turn off. One would charge and the other would rapidly discharge the load( the IGBT gate). This could work as long as the delay of the individual 2 photovoltaic drivers is a lot smaller when compared to the duty cycle of the square wave that is used to drive the setup.

But i do not know much about the newest advancements...

 

[William Gaatjes]

This manufacturer claims switching times in the order of 100 microseconds.
Not bad at all.

http://www.dionics-usa.com/product_index_1.htm


Photovoltaic part with active discharge circuitry :

http://www.dionics-usa.com/PDFs/DIG-1115-SM.pdf

 

[William Gaatjes]

I should add that these devices explain this at best :

http://www.dionics-usa.com/PDFs/dig1106030.pdf


In essence this is how it works :

A led outputs light on a photovoltaic element(The real name for a solar cell).
This generates voltage with a certain amount of power(in watts or coulomb whatever you like). This is then used to drive the gate of a mosfet. The catch is that the gate of a mosfet is actually a capacitor. And a capacitor is usually an element that causes delay because of limited means to charge and discharge it.
But it does not end there. Common push pull mosfet drivers are capable of peak currents of 1 to 4 Amperes or more. For example the TCN442/27/28 from microchip do 1.5 Amperes but there are 3 Amperes versions as well. For a small gate to source equivalent capacitor one would think this is enough. But the drain to gate equivalent capacitor must be added as well. And this one can be quite large depending on the drain to source voltage. This is also known as the Miller effect IIRC.
For fast discharging and charging of capacitors, high currents are needed.
It is easy to blow up a power mosfet if the driver cannot meet the demands.

These formulas are most important :

Q= I * T and Q = U * C.

 

[William Gaatjes]

One thing to add :

Although i mention mosfets a lot, IGBT are similar as mosfet because IGBT also have a gate. And IIRC a photovoltaic cell can be seen as a voltage source with a high output impedance. IIRC Large solar cells behave in a sense similar as voltage sources and after the maximum current is drawn, start to behave similar as a current source. Assuming maximum light intensity.

 

[Mark R]

Hmm. It looks like these are quite slow. They look adequate for gate drive for line-frequency devices (e.g. VFDs)

But, they don't look adequate for high-frequency devices, e.g. pure sine inverters. However, they would serve a useful role as an isolated gate driver PSU. You could then use a conventional opto-transistor-isolator to drive the gate.

 

[William Gaatjes]

The "easiest" setup is using a transformer. Use the transformer to drive the IGBT or if you want to do it really nice, use an smps transformer where the output is used to generate power. Because you have some power it may become easier to make a nice solid signal to drive the IGBT with a signal from an optocoupler. This way it is easier.

There are a lot of options depending on the design.
A real easy way is using an optocoupler together with a small form factor dc dc converter to power the circuitry: It depends on how much current you need to supply. These xp power dcdc converters are rated up to 1 kV.

This is a small version.
http://uk.farnell.com/xp-power/ir1212sa/dc-dc-converter-semi-reg-3w-12v/dp/1860997

EDIT:
You definitely will need an IGBT driver after the optocoupler unless you have an IGBT driver combined with an optocoupler Such as for example :

ACPL-3130-300E from Avago.

http://uk.farnell.com/avago-technologies/acpl-3130-300e/optocoupler-smd-igbt-driver/dp/1640539

datasheet :
http://www.farnell.com/datasheets/76297.pdf

This part has an active push pull output. But it will need a steady power supply.