mosfet switching transients

[chaitanya2k6er]

HI, I have designed a current source circuit of 5ma to 5A, with switching loads. Please find the attachment. I have used IRS21853 mosfet high side driver to drive AUIRF3205 mosfets Q1, Q2. When one of the mosfet is in on condition the other will be in off state. Q1 will be always in on state, were as Q2 will be in on condition only for a span of 5ms. I have used two isolated supplies for Vb1, Vb2 in mosfet driver. Actual the problem is, when switching from Q1 to Q2(that too above 1A), i could find a transient at the load(50v, 700ns time). What can be done to remove this. May be because of this the driver ic is getting failed frequently. Any help from your side will be really appreciable.

 

[crutschow]

Post a diagram of the transistor circuit.

 

[godfreyl]

?!
All I see in the attachment is this:

 

[chaitanya2k6er]

Post a diagram of the transistor circuit.

Hai, Please find the attached circuit diagram.

 

[crutschow]

Using isolated supplies for this circuit makes it not very practical. A better design would avoid isolated supplies.

 

[FvM]

Q1 will be always in on state, were as Q2 will be in on condition only for a span of 5ms.

The description doesn't comply to the schematic diagram, which provides double-tjrow switching only.

To get 50 V spikes with 25V supply, there must be some amount of circuit inductance which can't be guessed from the schematic.

The switching time sequence (break-to-make) will matter.

By the way, I doubt that the current source transient behaviour is very good.

 

[chaitanya2k6er]

Using isolated supplies for this circuit makes it not very practical. A better design would avoid isolated supplies.

Actually using isolated supply was recommended by international rectifier. I have seen one of the application note with isolated supplies in international rectifier website. May i know what is the problem with using isolated power supplies.

- - - Updated - - -

The description doesn't comply to the schematic diagram, which provides double-tjrow switching only.

To get 50 V spikes with 25V supply, there must be some amount of circuit inductance which can't be guessed from the schematic.

The switching time sequence (break-to-make) will matter.

By the way, I doubt that the current source transient behaviour is very good.

Actaually i am using one of the section for setting the current and the other for switching the load. Q1 MOSFET will be always in on condition, were as Q2 will be in on for only 5ms(So to on mosfet continuously, i have used isolated supply rather than bootstrapping technique ). And yes the circuit inductance is bit more, as the load resistor(1E) and setting resistor(3E) are bit away from the circuit. So there is a chance of transient. What can be done to reduce the transients in this condition?

Thank you

 

[FvM]

Q1 MOSFET will be always in on condition

Not with the circuit shown in post #4.

 

[chaitanya2k6er]

Not with the circuit shown in post #4.

I mean to that circuit, in the post 4. In order to on the mosfet continuously i have used the isolated supply.

 

[FvM]

I was referring to the input signal in post #4. There's no option to set Q1 always on. Operation is alternating only.

 

[chaitanya2k6er]

I was referring to the input signal in post #4. There's no option to set Q1 always on. Operation is alternating only.

I didn't get u? The input of the circuit i.e. logical input is always in a fixed state such that Q1 will be always on and Q2 will be in off state.

 

[FvM]

You described the circuit this way:

Q1 MOSFET will be always in on condition, were as Q2 will be in on for only 5ms.

In the present circuit, Q1 can't be on while Q2 is on.

 

[chaitanya2k6er]

You described the circuit this way:

In the present circuit, Q1 can't be on while Q2 is on.

Yes you are correct. Only one mosfet will be in on state at a time, that i have told in the post #1 itself.

 

[chaitanya2k6er]

what can be done to reduce the transients??