3 in 1 ;)

Thread Starter

hazim

Joined Jan 3, 2008
419
Here are 3 small questions that made me "twiddle" in the last few days...

1) What is this thing found in most appliances connections before the plug? (see the attachment).

2) In a simple dc analysis of an NPN transistor connected in common emitter,
(E is connected to the ground), and we have only Rc and Rb. Current Ic = βIb, then Ic = β(Vcc-0.7)/Rb. Here is the question, isn't Ic related to Rc?! it seems to be not logical. I even tried it on Multisim with Rc in a potentiometer, as I changed the value of Rc, Ic changes obviously.

3) I searched a lot for an RF controlled switch circuit but I didn't find any. I need a simple one with a transmitter and a receiver which only task is to switch a relay when it detects the RF transmitted from the transmitter.
 

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SgtWookie

Joined Jul 17, 2007
22,201
Here are 3 small questions that made me "twiddle" in the last few days...

1) What is this thing found in most appliances connections before the plug? (see the attachment).
It's a ferrite for RFI/EMI suppression. The device powered by the plug is most likely a switching regulator. Switchers can generate lots of electrical noise in high frequencies; the ferrite blocks it.

2) In a simple dc analysis of an NPN transistor connected in common emitter,
(E is connected to the ground), and we have only Rc and Rb. Current Ic = βIb, then Ic = β(Vcc-0.7)/Rb. Here is the question, isn't Ic related to Rc?! it seems to be not logical. I even tried it on Multisim with Rc in a potentiometer, as I changed the value of Rc, Ic changes obviously.
Sure, Ic is related to Rc. It will limit the maximum current flow.

If you're operating the transistor in the linear region, you will effectively have a current controlled voltage divider; the Ib controls the Ic up to the point of saturation, where increasing Ib does little to increase Ic.

3) I searched a lot for an RF controlled switch circuit but I didn't find any. I need a simple one with a transmitter and a receiver which only task is to switch a relay when it detects the RF transmitted from the transmitter.
Did you look at Mini Circuits site?
http://www.minicircuits.com/

It would help if you more fully described what you are trying to do, but you really should put this question into a separate thread with a more specific title.
 

Thread Starter

hazim

Joined Jan 3, 2008
419
Thank you, you answered my first two questions... but for the last one, it may needs a separate thread yes but the site you mentioned, minicircuits.com is a commercial site only as I found. If there are schematics in it then please give me the specific link where they are.

Thanks
 

SgtWookie

Joined Jul 17, 2007
22,201
I guess you really don't want an answer, because you haven't started a new thread for that specific question.
 
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