help on circuit... -_-

so im creating a temp. operated alarm/switch could you please help me on how to change some parts
since one of my part have been old i have to replace it...

from 2N3704.... to BC548 (thanks to Lord Loh) However the collector current of the BC548 is limited to 100mA while 2N3704 is capable of 500mA.

so below is the schem. and i dont know how to use a sim... T_T

please help me...

thanks

roberto_manero said:

so im creating a temp. operated alarm/switch could you please help me on how to change some parts
since one of my part have been old i have to replace it...

from 2N3704.... to BC548 (thanks to Lord Loh) However the collector current of the BC548 is limited to 100mA while 2N3704 is capable of 500mA.

so below is the schem. and i dont know how to use a sim... T_T

please help me...

thanks

Click to expand...

your diagram shows that your load (what is that a bulb?) only draws 60mA.
This application is very crude, I bet you can find a replacement transistor that can do 500mA. Is that a PTC as the sensor?

Do you intend to turn on TR2 when TR1 turns on? This looks strange. Can you describe how you wish it to function?

Hi,

I get the impression that the circuit has to light the lamp
if R1 gets too warm.
I assume that R1 increases resistance with temperature until TR1
starts to conduct enough to cause TR2 to conduct, at which point the
voltage will rise on the emitter of TR1, i guess this is intended
to cause a step or snap-action to turn on the lamp.
That would also introduce a 'hysteresis' or staggered effect and
hopefully the same effect would happen on the way down, causing
the lamp to go out as quickly as it lit.

Whether or not it actually works like that i don't know.

Regards, John

That's a Schmitt trigger. When the voltage at the base of Q1 goes below the trigger point, the lamp turns on. If your lamp really only draws 60ma, the BC548 should work. I also suggested previously (before you posted a schematic) the 2N2222.

ahh thanks for your help guys... im thinking of replacing the bulb with a LED or fan but dont know wat watage to find... oh yeah the other resistor which is R5 is 68 ohms... i have to create a design again does anyone know on how to use eagle?? oh yeah if there are still something wrong on the circuit or comments im all ears...


arigatou gozaimasu...

i owe you one... all of u..

roberto_manero said:

ahh thanks for your help guys... im thinking of replacing the bulb with a LED or fan but dont know wat watage to find... oh yeah the other resistor which is R5 is 68 ohms... i have to create a design again does anyone know on how to use eagle?? oh yeah if there are still something wrong on the circuit or comments im all ears...


arigatou gozaimasu...

i owe you one... all of u..

Click to expand...

If your 9V is from a small 9V battery, I would suggest not running a fan off of this since you are ok with an LED to signal temp. An LED with a series resistor of about 510 Ohms will be fine. With an LED, you will extend the life of your battery more than the bulb or fan version.

Optikon said:

If your 9V is from a small 9V battery, I would suggest not running a fan off of this since you are ok with an LED to signal temp. An LED with a series resistor of about 510 Ohms will be fine. With an LED, you will extend the life of your battery more than the bulb or fan version.

Click to expand...

ah thanks very much so ill stick with the other parts if im gonna change the trans and bulb?