If the terminal numbers correspond to the datasheet, 1=base, 2=collector, 3=emitter; the base emitter junction looks like it's shorted. Don't see how the collector voltage could be lower than the emitter.

Are you certain of the terminals and connections?
View attachment 224145

I thought I had posted a reply last Friday with thanks but it didn't post. I had gotten the pinout wrong on the 2N3904. With it wired right, I get 14.4V after the TIP31C. Hooray!

But, when I add the remainder of the circuit the voltage drops at the TIP31C to .66V.
It's also .66V at leg 1 (input) of the L7809CV.
I'm stumped again.

 

But, when I add the remainder of the circuit the voltage drops at the TIP31C to .66V.

It would be helpful if you posted the relevant part of your circuit.

What are the voltages on the TIP31C terminals? What is the voltage and current capability of your power source?

 

It would be helpful if you posted the relevant part of your circuit.

What are the voltages on the TIP31C terminals? What is the voltage and current capability of your power source?

I tried a couple of experiments:
- no L7809CV
- only .1uF cap after the L7809CV
- a .22uF cap before the L7809CV and the .1 uF cap after

Results:

no L7809CV .1uF cap .1uF + .22uF caps

TIP31C base 15.01V 15.33V .65V
TIP31C collector 41.3V 41.1V 38.7V
TIP31C emitter 15.05V 15.36V .65V

L7809CV Input N/A 15.36V .65V
L7809CV Output N/A 0V 0V

I thought about the dropout voltage (2V). That's why I went 9V instead of 12V. So the input voltage should be sufficient for the L7809CV.

What am I missing?
Carlo

 

You must have something wired wrong - and your data is incredibly difficult to read.

Take the measurements with everything in the circuit. You only have a half dozen components and it won't be difficult to see what's not working.

EDIT: and put a 20mA load on the regulator. The regulator isn't guaranteed to work with little or no load.

 

You must have something wired wrong - and your data is incredibly difficult to read.

Take the measurements with everything in the circuit. You only have a half dozen components and it won't be difficult to see what's not working.

EDIT: and put a 20mA load on the regulator. The regulator isn't guaranteed to work with little or no load.

Sorry for the hard-to-read data. I had everything lined up but I guess AAC compacts things. I ran out of time today before the workshop closed. I'll take these suggestions and get back next Friday. As always, thanks for your time and expertise!

Carlo

 

Hello again and Happy Friday! I took the whole circuit apart and carefully redid it.

I put a 680ohm resistor on the end as I calculated 20mA load to be R = 14V/.02 = 700ohm.

I get the following:

without a load:
into circuit: 38V
at TIP31C Emitter: 17.5V - so far so good

with the load:
into circuit: 39V
at TIP31C Emitter: .6V
L7809cv Input: .6V
L7809CV Output: 0V

Stumped again.

Carlo

 

with the load:
into circuit: 39V
at TIP31C Emitter: .6V
L7809cv Input: .6V
L7809CV Output: 0V

That doesn't make sense. The transistors and zener can't drop more than about 11.5V.

What are the voltages on the bases of the transistors?

EDIT:
BTW, the 151 ohm resistor can be an eighth or quarter watt.
\(P = \frac{V^2}{R} = \frac{1.4V*1.4V}{151\Omega} = 13mW\)

 

That doesn't make sense. The transistors and zener can't drop more than about 11.5V.

What are the voltages on the bases of the transistors?

2N3904 Base = .6V (stable)
TIP31C Base = not stable but fluctuating around about .6V to 1V

I am attaching a drawing of how my wires are actually running in case there's an obvious error there.

EDIT:
BTW, the 151 ohm resistor can be an eighth or quarter watt.
\(P = \frac{V^2}{R} = \frac{1.4V*1.4V}{151\Omega} = 13mW\)

Thanks! I'll work on calculating the amps (I also have more 1W than 1/4W supplies).

 

I'll work on calculating the amps

You don't need to calculate anything. I asked for the voltages on the bases of the transistors.

 

What are the voltages on the bases of the transistors?

2N3904 Base = .6V (stable)
TIP31C Base = not stable but fluctuating around about .6V to 1V

Thanks!

 

Which is the schematic have you actually built ? The one in post #63 or the one in post #66 ? #63 should work. In #66 the two transistors and the resistor serve no purpose as the resistor is shorted out.

Les.

 

2N3904 Base = .6V (stable)
TIP31C Base = not stable but fluctuating around about .6V to 1V

The voltages don't make sense. Do you have a cap on the output of the regulator? That helps with transient response (another way of saying oscillations).

Black text are your measured voltages. Red are the expected voltages.

 

Which is the schematic have you actually built ? The one in post #63 or the one in post #66 ? #63 should work. In #66 the two transistors and the resistor serve no purpose as the resistor is shorted out.

I built #66. To the best of my (very humble) understanding, it is the circuit suggested in #50 plus the resistor load (20mA) suggested in 50.

Les.

Do you have a cap on the output of the regulator? That helps with transient response (another way of saying oscillations).

I did in an earlier iteration. I removed it for the most recent versions hoping that simplifying the circuit would help me find the problem. (I know this is probably very ignorant logic). I can replace it.

Red are the expected voltages.

Did my drawing in #68 suggest why I'm so far off?

Thanks to you both.

 

Did my drawing in #68 suggest why I'm so far off?

I gave it one glance and then ignored it. I don't like reading wiring diagrams and you didn't label the terminals so it's useless.

 

I made an error in post #71. I wrote post #66 where I should have wrote #68. The schematic in post #66 should work. From the voltage reading you give on the bases of the transistors I would say that the zener diode is open circuit. I agree with the voltages that Dennis has calculated.

Les.

 

Nothing you've posted gives any clue why you're measuring 0.6V on the emitter of the TIP31C.

If the zener was open, you'd should see about 38V due to the leakage current in the TIP31C which should be less than 0.3mA.

 

I would say that the zener diode is open circuit

If the zener was open, you'd should see about 38V due to the leakage current in the TIP31C which should be less than 0.3mA.

Hooray!! It turns out that I must have destroyed the zener with one of my screw-ups experiments. The interior was black and burnt (like my soul). I now have stable 9V coming out of the L7809CV. Another hurdle over!

So I attached the fan and it runs for one second and stops. I'm guessing I have something wrong or missing with capacitors. It will do it over and over so I didn't burn up the fan.

The output of the L7809CV is as follows:
- without the fan attached: 9.0V
- attach fan: drops immediately to 3.3V

I am attaching my new complete project schematic.

Thanks!

Carlo

 

The output of the L7809CV is as follows:
- without the fan attached: 9.0V
- attach fan: drops immediately to 3.3V

Does the 130A in the fan box mean it wants to draw 130 amps?

 

Does the 130A in the fan box mean it wants to draw 130 amps?

On top of all my other flaws is bad handwriting. That should read .30A.

 

On top of all my other flaws is bad handwriting. That should read .30A.

Putting the customary zero in front of the decimal point might have caused it to be read it as 0.3A.

The voltage regulator seems to be current limiting, but it's rated for 1.5A with sufficient heatsinking.