Wrong mosfet choice for h-bridge

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BC547

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Hi Folks,
This is my first post here, so don't be to hard on me. :thumbsup:

I need an very precise ac 64Khz square wave current source of 200µA.
To accomplish this i'm using a **broken link removed** in combination with a h-bridge.
This works not that bad, except that during the switching there's a small delay before the mosfet switches on and the other switching off. This causes that the current source sees the R-load not for that short moment and overshoots for a short moment.
I think this has to do with the mosfet's i have chosen (irlml6302,2803). What mosfet do you advice or at what parameters i have to look to get it working correct.

 

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I would use CMOS analog switches like CD4053 for this rather small current.
 
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    BC547

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Both the input capacitance, and the 470 ohm gate resistor, will delay turn on/off somewhat. You didn't indicate how much a delay you are having, but I'd first experiment with reducing the gate resistance value to 100-200 ohms, if your driving device can handle the current. What sort of method are you using to avoid shoot-through?
 
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    BC547

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Thanks for the reply.

@FvM, i had already had an look at the CD4053, but the on resistance (>80 ohm x2) is to high. R-load will change and by adding to much R-load the measuring range will decrease to much.
@Chuckey & ftsolutions, I tried already different gate resistors values, even 0 ohm but the delay of 1,7µS is still there. I looks indeed that the driving device can't handle the current.
I didn't do anything about shoot trough, never heard of it before. I'm gone read what it is and how to something about it.
 

CD4053 was just an example. CMOS analog switches are available with Rdson downto a few ohms.

Generally CMOS switches have (almost) balanced gate charge, so the switch signal to output feedthrough is considerably smaller. And the required level converters are integrated in the IC.
 
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    BC547

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