P mosfet

R

Rheilly Phoull

Guest
G'Day All,

I'm trying to use a P type mosfet (IRF 9540) as a PWM switch to charge a
battery.
I cant get it to turn on completely, as a test I have connected the +
supply to the source and the drain to the + of the battery and the neg
of the battery to the neg of the supply. If I take the gate to the neg
it does not turn on completely, there is a volt drop of several volts
across it at 2 amps. This happens with the 2 devices I've tried. They
turn off OK when the gate is held high.
What am I missing here ???

Cheers ....... Rheilly
 
"Rheilly Phoull"
I'm trying to use a P type mosfet (IRF 9540) as a PWM switch to charge a
battery.
I cant get it to turn on completely, as a test I have connected the +
supply to the source and the drain to the + of the battery and the neg of
the battery to the neg of the supply. If I take the gate to the neg
it does not turn on completely, there is a volt drop of several volts
across it at 2 amps. This happens with the 2 devices I've tried. They turn
off OK when the gate is held high.
What am I missing here ???
Click to expand...
** What WE are missing is the battery type and voltage and the nature of
the supply.

Devil, details .....



..... Phil
 
On 10/20/2011 7:46 AM, Phil Allison wrote:
"Rheilly Phoull"
I'm trying to use a P type mosfet (IRF 9540) as a PWM switch to charge a
battery.
I cant get it to turn on completely, as a test I have connected the +
supply to the source and the drain to the + of the battery and the neg of
the battery to the neg of the supply. If I take the gate to the neg
it does not turn on completely, there is a volt drop of several volts
across it at 2 amps. This happens with the 2 devices I've tried. They turn
off OK when the gate is held high.
What am I missing here ???


** What WE are missing is the battery type and voltage and the nature of
the supply.

Devil, details .....



.... Phil






Ya right of course, 12v battery and a regulated variable supply that I
Click to expand...
crank up to set the current flow. The real use will be with solar panels.

Cheers ......... Rheilly
 
"Rheilly Phoull
Phil Allison

** What WE are missing is the battery type and voltage and the nature
of
the supply.

Devil, details .....


Ya right of course, 12v battery and a regulated variable supply that I
crank up to set the current flow. The real use will be with solar panels.
Click to expand...

** You have got a " stopper " resistor is series with the gate - right ?

Say 2.2 kohms - to stop HF oscillation.



.... Phil
 
On 10/20/2011 11:45 AM, Phil Allison wrote:
"Rheilly Phoull
Phil Allison

** What WE are missing is the battery type and voltage and the nature
of
the supply.

Devil, details .....


Ya right of course, 12v battery and a regulated variable supply that I
crank up to set the current flow. The real use will be with solar panels.


** You have got a " stopper " resistor is series with the gate - right ?

Say 2.2 kohms - to stop HF oscillation.



... Phil



Thanks Phil,
Click to expand...
I didn't but putting one in has not changed things.
One other thing is that these are a batch from Hong Kong, I'm wondering
if perhaps they are bodgy ??

Cheers .......... Rheilly
 
"Rheilly Phoull"
Phil Allison

** What WE are missing is the battery type and voltage and the nature
of the supply.

Devil, details .....


Ya right of course, 12v battery and a regulated variable supply that I
crank up to set the current flow. The real use will be with solar
panels.


** You have got a " stopper " resistor is series with the gate - right
?

Say 2.2 kohms - to stop HF oscillation.



I didn't but putting one in has not changed things.
One other thing is that these are a batch from Hong Kong, I'm wondering if
perhaps they are bodgy ??
Click to expand...

** Looks a lot like it.

Rds(on) is about 5 times higher than the spec of 0.2 ohms.



.... Phil
 
On 10/20/2011 12:00 PM, Phil Allison wrote:
"Rheilly Phoull"
Phil Allison

** What WE are missing is the battery type and voltage and the nature
of the supply.

Devil, details .....


Ya right of course, 12v battery and a regulated variable supply that I
crank up to set the current flow. The real use will be with solar
panels.


** You have got a " stopper " resistor is series with the gate - right
?

Say 2.2 kohms - to stop HF oscillation.



I didn't but putting one in has not changed things.
One other thing is that these are a batch from Hong Kong, I'm wondering if
perhaps they are bodgy ??


** Looks a lot like it.

Rds(on) is about 5 times higher than the spec of 0.2 ohms.



... Phil
Click to expand...
Yup, beats me. I'll wander down town and get a known brand and see how
that goes.
Thanks for the help.

Cheers ......... Rheilly
 
On 20/10/2011 1:33 PM, Rheilly Phoull wrote:
On 10/20/2011 7:46 AM, Phil Allison wrote:
"Rheilly Phoull"
I'm trying to use a P type mosfet (IRF 9540) as a PWM switch to charge a
battery.
I cant get it to turn on completely, as a test I have connected the +
supply to the source and the drain to the + of the battery and the
neg of
the battery to the neg of the supply. If I take the gate to the neg
it does not turn on completely, there is a volt drop of several volts
across it at 2 amps. This happens with the 2 devices I've tried. They
turn
off OK when the gate is held high.
What am I missing here ???


** What WE are missing is the battery type and voltage and the
nature of
the supply.

Devil, details .....



.... Phil






Ya right of course, 12v battery and a regulated variable supply that I
crank up to set the current flow. The real use will be with solar panels.

Cheers ......... Rheilly
Click to expand...
What's the measured Vgs when it is supposed to be turned on?
 
On 10/20/2011 1:14 PM, swanny wrote:
On 20/10/2011 1:33 PM, Rheilly Phoull wrote:
On 10/20/2011 7:46 AM, Phil Allison wrote:
"Rheilly Phoull"
I'm trying to use a P type mosfet (IRF 9540) as a PWM switch to charge a
battery.
I cant get it to turn on completely, as a test I have connected the +
supply to the source and the drain to the + of the battery and the
neg of
the battery to the neg of the supply. If I take the gate to the neg
it does not turn on completely, there is a volt drop of several volts
across it at 2 amps. This happens with the 2 devices I've tried. They
turn
off OK when the gate is held high.
What am I missing here ???


** What WE are missing is the battery type and voltage and the
nature of
the supply.

Devil, details .....



.... Phil






Ya right of course, 12v battery and a regulated variable supply that I
crank up to set the current flow. The real use will be with solar panels.

Cheers ......... Rheilly

What's the measured Vgs when it is supposed to be turned on?

Well I just grounded the gate so it was around 14v or 0 depending on how
Click to expand...
you view it.
As it turns out I was ripped off once again by the fiendish oriental
trader :)
I've just come back with a brand type one and all is well.
(As Phil A and I were discussing)

Cheers ........ Rheilly
 
On 20/10/2011 3:58 PM, Rheilly Phoull wrote:
On 10/20/2011 1:14 PM, swanny wrote:
On 20/10/2011 1:33 PM, Rheilly Phoull wrote:
On 10/20/2011 7:46 AM, Phil Allison wrote:
"Rheilly Phoull"
I'm trying to use a P type mosfet (IRF 9540) as a PWM switch to
charge a
battery.
I cant get it to turn on completely, as a test I have connected the +
supply to the source and the drain to the + of the battery and the
neg of
the battery to the neg of the supply. If I take the gate to the neg
it does not turn on completely, there is a volt drop of several volts
across it at 2 amps. This happens with the 2 devices I've tried. They
turn
off OK when the gate is held high.
What am I missing here ???


** What WE are missing is the battery type and voltage and the
nature of
the supply.

Devil, details .....



.... Phil






Ya right of course, 12v battery and a regulated variable supply that I
crank up to set the current flow. The real use will be with solar
panels.

Cheers ......... Rheilly

What's the measured Vgs when it is supposed to be turned on?

Well I just grounded the gate so it was around 14v or 0 depending on how
you view it.
As it turns out I was ripped off once again by the fiendish oriental
trader :)
I've just come back with a brand type one and all is well.
(As Phil A and I were discussing)

Cheers ........ Rheilly
There are a couple of Thai dealer who are very good BUT some of the
Click to expand...
honkers and Singa boys sell rubbish
If you find a good one stick with him

--
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