Dear all,

Attached is a circuit to drive a single high side mosfet, the circuit works fine. but when a filter capacitor(470uF/450V) is connected to the load the IR2110 high side driver burns.

Can any one advise on switching a high side mosfet where a filter capacitor is included at the load.


Many thanks

 

How fast and how often does the mosfet switch?
What exactely does the filter filter? (nicely put )

 

I wonder if it is the momentary short to ground when the capacitor is initially put in the circuit? Is the problem cured with a small resistor in series with the capacitor?

BTW, I have a little experience with the 2110, but not with it driving a capacitative load, so this answer is mostly guesswork.

John

 

How fast and how often does the mosfet switch?
What exactely does the filter filter? (nicely put )

the mosfet switch at 10Khz.
the purpose of the 470uf /450V capacitor is as a filter to the output

 

First thing I noticed was your gate diode is backwards, so your turn off time will be slower than predicted. 20 Ohms is too high of a gate resistor, try 4.7-10ohms with that kind of current driver.

I'm not really sure of anything else. Clearly by adding the capacitor, you are increasing the Vs voltage. The datasheet specs that Vs cannot be greater than 0.3+Vb, but I am not sure how the Vb is derived anyways.

Steve

 

I just came across this discussion by Linear of high-side mosfet switching for capacitive loads. About halfway down, it mentions the need to actively turn off/drain the load. Maybe you could use your low-side drive for that?

John

 

I just came across this discussion by Linear of high-side mosfet switching for capacitive loads. About halfway down, it mentions the need to actively turn off/drain the load. Maybe you could use your low-side drive for that?

John

hi is it something like this as attached.

many thanks

 

Sometimes I feel invisible... Diode to gate in backwards.. lalalala

 

owhh im very sorry scubasteve_911,

actually the connection of diode to gate should be in that direction, wouldn't it short the IC if it is in the backward direction

 

It's okay

I believe the diode is not necessary here anyways. It's purpose is to make a symmetrical gate drive with an asymmetrical driver. For example, when the driver can sink more than source current, so it would be in the best interest to increase flow in one direction (sometimes diode in series with another resistor).

Steve

 

Why you dont connect this MOS as a low side driver which easier to control? Is there any reason?

 

@Steve:

I believe you are/were right. The diode is usually used to speed up turn off of the mosfet gate. See page 14 here.

@Sharmilla,

If you can't get the link, let me know, and I will copy it here. Here is the schematic from it, which is essentially what you drew (left circuit).

Also, see AN978 from IR, which goes into more detail about Vs and Vb.

John

 

I was wrong in the reasoning for the diode, it has to do with recovery speeds and stuff. Another example when intuition is incorrect in engineering, since it isn't really natural

Steve