- How to turn On/Off a +5vcc power?
- Posted by Johan Harold on August 29th, 2005
I have a set of sensors and actuators all operating at +5v and draw 10mA to
680mA current.
My microcontroller will stwitch these units ON or OFF in various
configuration. My microcontroller has enough output port to drive switching
circuits.
How can I switch these unit ON/OFF without using mechanical relay?
What is the electronic equivalent of relay ? (May be FET/MOSFET ? How to
drive them?)
- Posted by Wing Wong on August 29th, 2005
In aus.electronics Johan Harold <jh14323@gmail.com> wrote:
low on resistance only about 0.2 ohms and a threshold voltage of about 3
volts. Its the cheapest MOSFET I can think of. This is device is a
PChannel device so let me see... tie the source to the 5V, the drain to the
Vcc of the things you want to drive and as for the gate, attaching it to the
output pin of you MC you give you what you want. Driving the line high should
turn it off and driving it low should turn the mosfet on. Depending on the
configuration of your MC, you may need pullup a pullup resistor at the
output pin of the MC.
I think my advice is correct, but don't take my word on it. Feel free to
get a second or third opinion.
--
Wing Wong.
- Posted by Joseph Casey on August 29th, 2005
There's nothing wrong with using discrete mosfets for this but if you
want some of the work done for you I have found BTS 612 N1 from Siemens
handy for similar applications. they need no extra components. A couple
of things to watch with this device: they shut down (brownout detection)
if the supply goes below 5V. Also if your processor is 3.3V that is
right on the edge of the turn on threshold, but I find they work with my
3.3V processors.
Johan Harold wrote:
- Posted by Joseph Casey on August 29th, 2005
If you use a power MOSFET, put a 100R resistor in series with the gate.
This prevents ringing at switchon due to the high gatd capacitance of
power MOSFETs
Johan Harold wrote:
- Posted by dmm on August 29th, 2005
On Mon, 29 Aug 2005 19:27:37 +1000, "Johan Harold" <jh14323@gmail.com> wrote:
Check out Fairchild's FDG312P. Rds(on) = 0.18ohms @ Vgs = -4.5V, Vdss max = -20V, Id = -1.2A
and it's in a SC70-6 package. Sneeze and its gone.. 8-)
- Posted by Paul Carpenter on August 29th, 2005
On Monday, in article
<6rr5h19m8vu644184shmdoe6th82oda9r4@4ax.com>
dmmilne_REMOVE_@ozemail.com.au "dmm" wrote:
Or even Fairchild FDV range logic switching FETs in SOT-23 packages
Rds Id Id (pulsed)
FDV304P 1.1R 460mA 1.5A (4.5V Vds)
FDV302P 10R 120mA 500mA (4.5V Vds)
FDV301N 4R 220mA 500mA (4.5V Vds)
FDV303N 0.45R 680mA 2A (4.5V Vds)
Gate switching < 1.5V so ideal for low load switching in ONE device.
I tend to use FDV304P and FDV303N for lower Rds and higher Id
Available in small quantities Digikey, Farnell......
--
Paul Carpenter | paul@pcserviceselectronics.co.uk
<http://www.pcserviceselectronics.co.uk/> PC Services
<http://www.gnuh8.org.uk/> GNU H8 & mailing list info
<http://www.badweb.org.uk/> For those web sites you hate
- Posted by Gordon McComb on August 29th, 2005
The others have responded regarding solid state switches (MOSFETs would
be my preference, too, though a ULN2003 array would take up less space
if you need more than one or two), but to add to the confusion: is there
a reason to shy away from relays? If only 680mA you could probably get
away with smaller reed relays. You can't hear them, they last for a lot
of switchings, and they don't need heat sinks. One thing, though, is
that you can't always drive a bunch of them at the same time from your
MCU ports. One at a time is usually okay, but of course, check the specs
to be sure.
-- Gordon
Johan Harold wrote:
- Posted by Spehro Pefhany on August 29th, 2005
On Mon, 29 Aug 2005 19:27:37 +1000, the renowned "Johan Harold"
<jh14323@gmail.com> wrote:
Yes you can use a logic-level MOSFET (p-channel for switching +5V or
n-channel for switching the ground). There are some nice dual
low-Rds(on) ones in small 8-pin SMT packages.
Take care with bypass capacitors on the switched side. These parts are
so low resistance that if you switch them quickly the bypass caps on
the switched side can put a glitch on your unswitched power supply.
Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
- Posted by The Real Andy on August 29th, 2005
On Mon, 29 Aug 2005 19:27:37 +1000, "Johan Harold" <jh14323@gmail.com>
wrote:
What are the sensors and actuators? Can you get away with a cheap
trasistor?
