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Switching relays using low current??

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TheWongs

New Member
Hi, I have a circuit for controlling very low currents and want it to be able to switch fairly heavy currents (about 20a max). Is there a simple circuit that would allow me to "amplify" the output of the circuit? The data sheet states that output will be 4.5V. Output current on the IOLines is a max of 20mA so what I need to do is either find a relay that draws a maximum of 20mA capable of switching 20a DC, or boost the output enough to power a larger relay. Any ideas?
 

McGuinn

New Member
There are Wong ways to do this and Write ways... ;-)

One, use a low power relay to the specification you require (if one can be located)
Two, use transistors to interface with a higher current curcuit to drive your current relay.
Three, use MOSFET's.

Maybe sombody can extole the virtues of MOSFETS! I haven't used them.
 

Gene

New Member
Assuming your switched output comes from an IC, you can easily find circuits right here that take that output and turn on a switching transistor (like a 2N2222). When the transistor conducts, it can drive a decent relay that can handle your 20A. You may want to consider adding a diode to your relay contacts. Three parts. Perhaps someone here can draw a little schematic if you nee one.
 

bogdanfirst

New Member
basicly, if you have 12V or whatever voltage your relay has available, then connect a resistor to the output of the IC(or whatever you have) and to the base of you transistor. connect the wmitter of the transistor to GND
and the colector to the relay. conenct the other relay contact to +12V. also connect a diode in paralel with the relay with the cathode to +12V
hope you get me.
 

TheWongs

New Member
:D Thanks alot guys. :D I'll give the circuit a go and let you know how I get on.
 

bogdanfirst

New Member
i think that you need a larger value for the resistor then 1K, but i am not sure....what is the gain of the transistor?
anyway,if the current drawn from the ic is ok in this case there is no problem to use it like this
 

BlurTech

New Member
hi guys, need ur help.
i have a similiar problem here.

my comparator circuit can only produce output of 2.5V & 6mA. My relay require at least 2.2V (obtained already) and 1A in order to swtich over. is there any method which i can boast the output of the small output to almost 1A?

thanks!
 

Jaw174

New Member
for connection so the paralel port that way , on a similar project i did, i used a 4.7 K. the pearalel port puts out (idealy) 5 volts on a HIGH logic, and 0V on LOW logic. it allows about 2.6 ma out of the port, so if you have 2.5V and 6 ma out, thats similar, just tweak the value a little.. go use ur resistor formula. ;)
 

Muskoka

New Member
switch, relais and push button

Hello all,

I am trying to understand a ususal read defoger switch a relay of a car. This switch is a push button, the power is initially at position off, you must turn the ignition on to be able to tunr the defoger on, then at this point it is posible to turn it on or off. What would I need to build a similar circuit ?

A push button (momentarily contact on when pushed)
A relay ...

I would know how to build this circuit with a on / off switch but the push button ?? :?

Thanks a lot !!
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