Hello all,
I've been working on this problem for a few hours now, and what seems
to be simple is not working correctly in Multisim. I'd like your guys (and girls ) opinion on my problem, here are the steps I've taken so far. Attached is an image of my Multisim circuit and its results.
To be brief, I am attempting to design a relay driver circuit. What I'd like to happen is to set an output pin high (5v) from a microcontroller (ATTiny24). This, in turn, will power a 12v relay that requires 180mA to energize the coil. The relay has a coil resistance of 160ohms. The microcontroller can only sink up to 20mA of current, so I'm attempting to use a 2n2222 transistor in saturation mode to switch the relay on.
The 2n2222 transistor has a hFE of 100 and Vbe of .6v. Some research on this site advised me that, if not necessary to design for power efficiency, I should assume the worst case hFE. The datasheet lists that as 40 at Ic = 500mA and Vce = 10v.
So in order to create an Ic of 180mA to energize the coil, with an hFE (worst case) of 40 I need an Ib of 4.5mA. My Rb = (Vcc - Vbe) / Ib = 1kOhm.
Using all that I modeled the circuit in Multisim as shown below. I expected an Ic of, at minimum, 180mA. The results are far from that number. Where am I going wrong?
Thanks
Mike
I've been working on this problem for a few hours now, and what seems
to be simple is not working correctly in Multisim. I'd like your guys (and girls ) opinion on my problem, here are the steps I've taken so far. Attached is an image of my Multisim circuit and its results.
To be brief, I am attempting to design a relay driver circuit. What I'd like to happen is to set an output pin high (5v) from a microcontroller (ATTiny24). This, in turn, will power a 12v relay that requires 180mA to energize the coil. The relay has a coil resistance of 160ohms. The microcontroller can only sink up to 20mA of current, so I'm attempting to use a 2n2222 transistor in saturation mode to switch the relay on.
The 2n2222 transistor has a hFE of 100 and Vbe of .6v. Some research on this site advised me that, if not necessary to design for power efficiency, I should assume the worst case hFE. The datasheet lists that as 40 at Ic = 500mA and Vce = 10v.
So in order to create an Ic of 180mA to energize the coil, with an hFE (worst case) of 40 I need an Ib of 4.5mA. My Rb = (Vcc - Vbe) / Ib = 1kOhm.
Using all that I modeled the circuit in Multisim as shown below. I expected an Ic of, at minimum, 180mA. The results are far from that number. Where am I going wrong?
Thanks
Mike