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Computer Groups Forum Index » Architecture - Embedded » Followup:MOSFET Turning ON
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| vijayn |
 Posted: Thu Dec 04, 2008 9:07 am |
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Guest
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Actually the did not blow up as we found it is working correctly when the
gate source is supplied with a DC source of 8V. Let me come out with the
problem more specifically. I am actually need to sense a current of 50 mA
through a CT. My requirement is that if the CT responds to a current of 50
mA, the MOSFET should operate. Since the output voltage from CT is very low
I went for an Voltage Amplifier. I gave the output of the amplifier to
MOSFET. The output of the Amplifier was 16V peak to peak pulsating DC
filtered using an electrolytic capacitor. I saw that the MOSFET did not
turn ON when the amplified signal was fed. But it worked perfectly when I
just checked with a 8V DC source. I think I am bit clear now? |
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| Andrew Smallshaw |
| Posted: Thu Dec 04, 2008 11:57 am |
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Guest
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On 2008-12-04, vijayn <vijayn@lntebg.com> wrote:
Quote: Actually the did not blow up as we found it is working correctly when the
gate source is supplied with a DC source of 8V. Let me come out with the
problem more specifically. I am actually need to sense a current of 50 mA
through a CT. My requirement is that if the CT responds to a current of 50
mA, the MOSFET should operate. Since the output voltage from CT is very low
I went for an Voltage Amplifier. I gave the output of the amplifier to
MOSFET. The output of the Amplifier was 16V peak to peak pulsating DC
filtered using an electrolytic capacitor. I saw that the MOSFET did not
turn ON when the amplified signal was fed. But it worked perfectly when I
just checked with a 8V DC source. I think I am bit clear now?
I assume here that CT means current transformer - that particular
acronym has too many meanings.
Your voltage amplifier isn't an open drain/collector output is it?
If so you'll need a pull up resistor in there. How is the cap
connected? It should probably be wired across the output and a
voltage rail - you don't want it in series with the output. What
MOSFET was it again? I know you said that earlier but you've
started a new thread now which makes it difficult to refer back to
your original post.
--
Andrew Smallshaw
andrews@sdf.lonestar.org |
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| Paul Carpenter |
| Posted: Thu Dec 04, 2008 4:31 pm |
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Guest
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In article <lsGdndddUOrqyqrUnZ2dnUVZ_uidnZ2d@giganews.com>,
vijayn@lntebg.com says...
Quote: Actually the did not blow up as we found it is working correctly when the
gate source is supplied with a DC source of 8V. Let me come out with the
problem more specifically. I am actually need to sense a current of 50 mA
through a CT. My requirement is that if the CT responds to a current of 50
mA, the MOSFET should operate. Since the output voltage from CT is very low
I went for an Voltage Amplifier. I gave the output of the amplifier to
MOSFET. The output of the Amplifier was 16V peak to peak pulsating DC
filtered using an electrolytic capacitor. I saw that the MOSFET did not
turn ON when the amplified signal was fed. But it worked perfectly when I
just checked with a 8V DC source. I think I am bit clear now?
A simple circuit as an image on some web space or an ASCII text circuit
would give people more idea as we have no idea what else is in the
circuit.
We have no idea of the DC offset of "16V peak to peak pulsating DC"
with respect to the pins of the FET, or even if all parts of the
circuit are refeneced to the same ground.
We have no idea how you are applying the 8V DC source in particular
where the DC source ground is relative to pins of the FET
--
Paul Carpenter | paul@pcserviceselectronics.co.uk
<http://www.pcserviceselectronics.co.uk/> PC Services
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<http://www.badweb.org.uk/> For those web sites you hate |
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