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Switch 3A with a small reed switch

Hi there,
I'm wanting to switch around 3A using a reed switch (eg
http://www.dse.co.nz/cgi-bin/dse.storefront/en/product/P7856) with the
aim of driving a SSC P7 LED.
Source voltage will be be around 3.7v (Li-ion) and the max current
through the LED will be 2.8A.

Could I use this MOSFET (BUZ-71 Sipmos Power FET) to achieve this? My
understanding of electronics is basic, so if you could provide a
circuit/guidance it would be much appreciated.

Thanks in advance
 
R

Ross Herbert

Jan 1, 1970
0
On Tue, 5 Aug 2008 19:20:51 -0700 (PDT), [email protected] wrote:

:Hi there,
:I'm wanting to switch around 3A using a reed switch (eg
:http://www.dse.co.nz/cgi-bin/dse.storefront/en/product/P7856) with the
:aim of driving a SSC P7 LED.
:Source voltage will be be around 3.7v (Li-ion) and the max current
:through the LED will be 2.8A.


:
:Could I use this MOSFET (BUZ-71 Sipmos Power FET) to achieve this? My
:understanding of electronics is basic, so if you could provide a
:circuit/guidance it would be much appreciated.
:
:Thanks in advance

Data for your LED http://www.acriche.com/en/product/prd/zpowerLEDp7.asp

I would suggest you do some searching driving high power leds. For example
http://www.instructables.com/id/Circuits-for-using-High-Power-LED_s/

Since you are not an experienced electronics constructor I would suggest you
stick to the simpler constant current drivers to start with.
 
J

Jason

Jan 1, 1970
0
On Tue, 5 Aug 2008 19:20:51 -0700 (PDT), [email protected] wrote:

:Hi there,
:I'm wanting to switch around 3A using a reed switch (eg
:http://www.dse.co.nz/cgi-bin/dse.storefront/en/product/P7856) with the
:aim of driving a SSC P7 LED.
:Source voltage will be be around 3.7v (Li-ion) and the max current
:through the LED will be 2.8A.

:
:Could I use this MOSFET (BUZ-71 Sipmos Power FET) to achieve this? My
:understanding of electronics is basic, so if you could provide a
:circuit/guidance it would be much appreciated.
:
:Thanks in advance

Data for your LEDhttp://www.acriche.com/en/product/prd/zpowerLEDp7.asp

I would suggest you do some searching driving high power leds. For examplehttp://www.instructables.com/id/Circuits-for-using-High-Power-LED_s/

Since you are not an experienced electronics constructor I would suggest you
stick to the simpler constant current drivers to start with.

Thanks,
I've got the driver sorted, but there is still 2.8A going through the
inputs of the driver, therefore I can't switch it with a small reed
switch (hence either using a relay or a mosfet).
 
P

Phil Allison

Jan 1, 1970
0

neon

Oct 21, 2006
1,325
Joined
Oct 21, 2006
Messages
1,325
reed switches are mechanical devices nees a magnet to activate can they carry 3amps sure once.
 
R

Ross Herbert

Jan 1, 1970
0
:> On Tue, 5 Aug 2008 19:20:51 -0700 (PDT), [email protected] wrote:
:>
:> :Hi there,
:> :I'm wanting to switch around 3A using a reed switch (eg
:> :http://www.dse.co.nz/cgi-bin/dse.storefront/en/product/P7856) with the
:> :aim of driving a SSC P7 LED.
:> :Source voltage will be be around 3.7v (Li-ion) and the max current
:> :through the LED will be 2.8A.
:>
:> :
:> :Could I use this MOSFET (BUZ-71 Sipmos Power FET) to achieve this? My
:> :understanding of electronics is basic, so if you could provide a
:> :circuit/guidance it would be much appreciated.
:> :
:> :Thanks in advance
:>
:> Data for your LEDhttp://www.acriche.com/en/product/prd/zpowerLEDp7.asp
:>
:> I would suggest you do some searching driving high power leds. For
examplehttp://www.instructables.com/id/Circuits-for-using-High-Power-LED_s/
:>
:> Since you are not an experienced electronics constructor I would suggest you
:> stick to the simpler constant current drivers to start with.
:
:Thanks,
:I've got the driver sorted, but there is still 2.8A going through the
:inputs of the driver, therefore I can't switch it with a small reed
:switch (hence either using a relay or a mosfet).


If you are using the reed contact correctly it will only be passing minute
current to switch the fet on. The fet will be handling the heavy current.

I would experiment with the circuit shown in Step 8 in the link I gave above
with the reed switch in series with the resistor and zener diode. Forget the PWM
uC part.

For normal operation you would be driving the led at around 1.4A.
 
J

Jasen Betts

Jan 1, 1970
0
Hi there,
I'm wanting to switch around 3A using a reed switch (eg
http://www.dse.co.nz/cgi-bin/dse.storefront/en/product/P7856) with the
aim of driving a SSC P7 LED.
Source voltage will be be around 3.7v (Li-ion) and the max current
through the LED will be 2.8A.
Could I use this MOSFET (BUZ-71 Sipmos Power FET) to achieve this? My
understanding of electronics is basic, so if you could provide a
circuit/guidance it would be much appreciated.

most mosfets like to have atleast 10V worth of gate drive.
The BUZ-71 may not even begin turning on until it sees 4V
(datasheeet says 3 to 4v) and suggests that 10V is needed to be fully
on.

If you've only got about 4v you may have to use a bipolar transistor
instead. eg: TIP41, (use a 100 ohm resistor on the base). but if you
can get another 6V below the Li-ion's negative terminal the BUZ71
could be made to work (9.7V will be close enough).

Bye.
Jasen
 
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