 |
|
| Science Forum Index » Electronics Forum » T/C pile switch... |
|
Page 1 of 1 |
|
| Author |
Message |
| Radim S... |
 Posted: Thu Dec 11, 2008 7:02 pm |
|
|
|
Guest
|
Hi,
I have following problem . The Thermopile probe ( 0.5V output at (no spam) 600 Deg C
with internal resistance 2 Ohms ) drives gas valve solenoid with very low
resistance ( approx. 0.023Ohm ) . Approximate holding current is 250mA .
So there is only about 5mV on solenoid . I need to cut off this circuit
with some kind of FEt , MOSFET or opto MOSFET . External circut to control
this switch can have common ground with above circuit. Cannot use relay -
external circuit does not have enought current to drive relay. I see
problem with relativly low switched voltage ( only 0.5V ) and low
resistance of fet needed .
Any ideas what could be good solution ?
Thanks Radim. |
|
|
| Back to top |
|
|
|
| Dave J.... |
| Posted: Thu Jan 08, 2009 9:30 am |
|
|
|
Guest
|
In MsgID<op.ul0syrtv61lwa3 at (no spam) ws_radim.cc.local> on Thu, 11 Dec 2008 23:02:41
GMT, in sci.electronics, 'Radim S' wrote:
[quote:05f0cd579b]Hi,
I have following problem . The Thermopile probe ( 0.5V output at (no spam) 600 Deg C
with internal resistance 2 Ohms ) drives gas valve solenoid with very low
resistance ( approx. 0.023Ohm ) . Approximate holding current is 250mA .
So there is only about 5mV on solenoid . I need to cut off this circuit
with some kind of FEt , MOSFET or opto MOSFET . External circut to control
this switch can have common ground with above circuit. Cannot use relay -
external circuit does not have enought current to drive relay. I see
problem with relativly low switched voltage ( only 0.5V ) and low
resistance of fet needed .
[/quote:05f0cd579b]
Are you still around this group? I read recently about a new design (I
think of the mosfet certainly some variety of fet) that had an incredibly
low junction resistance. I'm not sure if the pd would matter but I suspect
not. If you're still 'here' and you think it possibly relevant I can go
have a look through my web history (I keep about three months worth) or
you can try prodding a search engine.
Dave J. |
|
|
| Back to top |
|
|
|
| Chris Jones... |
| Posted: Fri Jan 09, 2009 5:40 pm |
|
|
|
Guest
|
Dave J. wrote:
[quote:54fd59042d]In MsgID<op.ul0syrtv61lwa3 at (no spam) ws_radim.cc.local> on Thu, 11 Dec 2008 23:02:41
GMT, in sci.electronics, 'Radim S' wrote:
Hi,
I have following problem . The Thermopile probe ( 0.5V output at (no spam) 600 Deg
C
with internal resistance 2 Ohms ) drives gas valve solenoid with very low
resistance ( approx. 0.023Ohm ) . Approximate holding current is 250mA .
So there is only about 5mV on solenoid . I need to cut off this circuit
with some kind of FEt , MOSFET or opto MOSFET . External circut to control
this switch can have common ground with above circuit. Cannot use relay -
external circuit does not have enought current to drive relay. I see
problem with relativly low switched voltage ( only 0.5V ) and low
resistance of fet needed .
Are you still around this group? I read recently about a new design (I
think of the mosfet certainly some variety of fet) that had an incredibly
low junction resistance. I'm not sure if the pd would matter but I suspect
not. If you're still 'here' and you think it possibly relevant I can go
have a look through my web history (I keep about three months worth) or
you can try prodding a search engine.
Dave J.
[/quote:54fd59042d]
There are plenty of MOSFETs with on-resistance of 5 milliohms or less. They
won't be the cheapest ones, but they are widely available. (e.g.
www.farnell.com) Probably the most difficult thing will be making a good
enough connection so that your wiring does not have more resistance than
the MOSFET - it may be necessary to calculate or measure the resistance of
the wire that you intend to use, and plan accordingly.
Chris |
|
|
| Back to top |
|
|
|
|
|
All times are GMT - 5 Hours
The time now is Fri Dec 04, 2009 3:49 am
|
|