I have a design where I'm using a CD4013 to switch a 12V water solenoid.

My test schematic is....


As you guys can guess, I use KiCAD.

My problem is, well, it doesn't work and the 2N2222 gradually cooks.

My assumptions:
1. I need about 500mA and the hFE of the TIP41 is between 35 and 70 so I worked on 50. This means 10mA at the base.
2. the 2N2222 needs only about 1mA (from my research) and the CD4013 can deliver up to 8mA so I worked to 5mA.

I need sanity checking from someone!

While I'm an engineer, I'm really digital and analog is not my best friend.

Thanks,

Gerard

 

Remove R5.

 

You probably don't have enough base current to get the TIP43 into saturation - you will probably need 50mA.
You don't need a particularly fast switch-off, so R5 could be much larger (2.2k perhaps)
What is the supply voltage of the 4013?
The BAT46 needs to be rated for the full 500mA solenoid current.

 

You probably don't have enough base current to get the TIP43 into saturation - you will probably need 50mA.
You don't need a particularly fast switch-off, so R5 could be much larger (2.2k perhaps)
What is the supply voltage of the 4013?
The BAT46 needs to be rated for the full 500mA solenoid current.

Thanks. The supply to the 4013 is +5v although I'm pretty sure it can run at +12v.

 

If the 4013 is powered by 5V, the emitter of the 2N2222 is at most 4.3V when on. The base of the TIP41 is at 0..6V, so the voltage across the 1K base resistor is 3.7V and the current through it is 3.7 mA.

If your 2N2222 is burning, the circuit us not as shown, because the max current through it is about 36 mA, which it can handle easily.

Edited to add: For 500 mA, a MOSFET is strongly preferred.

 

I need about 500mA and the hFE of the TIP41 is between 35 and 70 so I worked on 50. This means 10mA at the base.

The value of hFE is used in linear operation of the transistor (as in an amplifier), not for switching.
And, at a minimum, you would use the minimum value of hFE, not nominal.

For switching, the normal required base current for full saturation is 1/10th of the collector current (look at the data sheet where they measure hFE and where they measure the saturation voltage).

 

My problem is, well, it doesn't work and the 2N2222 gradually cooks.

One solution wiring the transistors in a darlington configuration.
The 4013 can remain on the 5 volt supply
Use a 1N4007 for D2.

 

Edited to add: For 500 mA, a MOSFET is strongly preferred.

Agree, I tend to look to Mosfet first now for all new applications.

 

Agree, I tend to look to Mosfet first now for all new applications.

I also agree.

But the TS already has the BJT's, so sghioto's post #7 circuit would likely be the easiest modification to get proper circuit operation.

 

Measure the voltage on the power device, either Vce or Vsd, to be sure that the device is saturating.AND power thr 4013 with 12 or 15 volts.

 

But the TS already has the BJT's, so sghioto's post #7 circuit would likely be the easiest modification to get proper circuit operation.

For a rapid and complete turn-off, I would add a 47K pulldown from the Q1 emitter to GND.

ak