beginner: troubleshooting a non-working circuit

[nyoo]

Apologies for this stream of questions. I do hope the answers are of general interest to novices.

I was hoping someone could give me a few tips about trouble-shooting. My first attempt to solder a circuit does not work.

It's supposed to be a DC-to-DC step-down voltage converter, reducing 14V to 12V. As expected, my voltmeter measures Vin to GND(in) at about 17V. Not as expected, it measures Vout to GND(out) at about 0.03V. Whether or not the input voltage is applied, I still get 0.03V.

Attached are two pictures, what Rohm suggests and what I (think I) built. But they do not represent very well my inability to control the soldering iron, or the number of perf board holes whose copper-clad rims were unnecessarily filled with solder. I even bent the leads of the BA00BC0WT, two holes between the leads, to get a bit of distance between solder points. As built, the nodes between R2 and C1 are not as distinct as the drawing would lead you to think.

When I saw the 0.03V output, I took ericgibbs's advice to another trouble-shooting question, and looked up the references.

I don't smell or see any burnt components. I'm afraid to apply anything more than a short burst of input voltage, so the tests I made are mostly with an ohmmeter. I connected a 100-watt light bulb across each capacitor before taking my measurements.

GND(in) to GND(out) = 0 ohms. I take this as a good sign.
BA00 pin 1 to GND(out) = 0 ohms
BA00 pin 3 to GND(out) = 0 ohms
Pin 4 to GND(out) = 0 ohms
Vin to pin 2 = 0 ohms
GND(in) to pin 4 = no reading
Pin5 to GND(out) = 35K ohms

And then, some very unexpected readings.

Across the leads of R2 = ohms continually increasing!
Across the leads of R1 = ohms continually increasing!
Pin3 to Vout = increased in the range of 300K while I was measuring
Pin5 to Vout = cycles 72K to 110K ohms and back to 72K!

Any obvious advice or next steps? Any hunches?
Thanks once again.

 

[Mikebits]

GND(in) to GND(out) = 0 ohms. I take this as a good sign.
BA00 pin 1 to GND(out) = 0 ohms
BA00 pin 3 to GND(out) = 0 ohms
Pin 4 to GND(out) = 0 ohms
Vin to pin 2 = 0 ohms
GND(in) to pin 4 = no reading
Pin5 to GND(out) = 35K ohms

Ok, something in what you say does not make sense here. Your gnd (in) and gnd (out) read 0 ohms, so they are tied together as same gnd. So far okay, but then you : Pin 4 to GND(out) = 0 ohms then you say, GND(in) to pin 4 = no reading. Now how can that be? If GND(in) = GND(Out) then your measurements from GND(in) to pin4, and GND(out) to pin 4 should be the same. In either case your readings did not look right, as you should have read something >330k.
Recheck your pin 4 measurement.

 

[AllVol]

I would think there should be some voltage on pin 1 to turn on the device.

 

[nyoo]

Trying again, with the ohmmeter....

Vin to pin2 = 0 ohms
GND(in) to pin2 = no reading
pin2 to Vout = no reading
pin2 to GND(out) = no reading

Vin to pin4 = no reading
GND(in) to pin4 = 109K ohms
pin4 to Vout = 0
pin4 to GND(out) = 109K

If I reverse the ohmmeter probes, then where I was getting 109K, I get readings constantly rising for 2-3 seconds until I get "no reading". Any idea why?

hilt to hilt on R1 gives 36K ohms.
hilt to hilt on R2 gives 327K.

Does that pin4-to-Vout reading mean the circuit is complete?
Thanks.

 

[jpanhalt]

What happens if you put a capacitor between pin 1 and ground as shown in the mfgr recommendations? John

 

[Mikebits]

The data sheet that I found for that part states a max input of 16V.

 

[nyoo]

Thanks.

The regulator's datasheet says Max Supply Voltage of 18V, and recommended Input power supply voltage (Vcc) of 16V. Could the no-load 17V from a 14V wall adapter damage the component?

I did see the symbol on CTL (pin 1) in the manufacturer's schematic. This turns on the regulator at 2V or higher. I thought it was the symbol for a battery, not a capacitor! Maybe naively, I was also reading it as optional: the circuit could switch directly to ground, or it could switch through a battery/capacitor to ground.

The size of this pin 1 capacitor is not specified. What would you recommend?

As a aside, there's also a 2nd capacitor mentioned on pin 2 (Vcc). I'm struggling with what capacitors do, but aren't they additive when in parallel? If you wanted more capacitance, wouldn't you just choose something bigger than the .33uF specified?

Could someone please help me understand why the ohmmeter sometimes shows increasing resistance? That spooks me.

Could someone help me understand if the measurements made so far prove the circuit is complete?

My own hunches, based on zero electronics experience of course, are
1. as the voltages on the capacitors were unspecified, I chose to high or too low a voltage; or
2. I destroyed the BA00 through static discharge while I was wrestling it into the perf board.

Any obvious tests to prove these?

I do appreciate the help.

 

[Mikebits]

18V is absolute max rating. If you look at the operating range spec it is 16V.
https://www.electro-tech-online.com/custompdfs/2008/06/ba00bc0wt-e.pdf
The increase meter reading is due to the cap in the circuit, the dc from the meter is charging the cap.

 

[jpanhalt]

Thanks.

I did see the symbol on CTL (pin 1) in the manufacturer's schematic. This turns on the regulator at 2V or higher. I thought it was the symbol for a battery, not a capacitor!

The size of this pin 1 capacitor is not specified. What would you recommend?

It does look like a battery, and that was my first impression too. However, there were other aspects of your two circuits that were a bit confusing, including some of the voltage/current readings you got.

As you note, the device is off, when that pin is grounded. You have that pin grounded.

I have seen some regulators that use a small capacitor on the control pin to pull it high, as from a small bias current. Grounding it, turns them off. The capacitor size used in those regulators, as I recall, was 0.1 to 0.01 uF. You could also just use a pull-up resistor to pull the pin high. In any case, the pin can't be grounded, if you expect it to work.

John

 

[AllVol]

Attached are two pictures, what Rohm suggests and what I (think I) built.

Just out of curiosity, where did you obtain the manufacturer's diagram? What you are showing gives more detail than that on the Rohm data sheet, and could be leading to some confusion.

Edit:
I'm still concerned about the status of your pin 1. It is labeled as CTL, which leads me to believe it is to control something, but simply putting it to ground and leaving it there gives either an always on or always off situation.

 

[blueroomelectronics]

Why not just use an LM2940-12

 

[gerty]

The "built" drawing shows the positive output getting its source through the IC.
The other drawing appears to have a Vcc connection in the upper right corner . Are they internally connected? I'm not at all familliar with your device ,but that looks like it could be a problem..

 

[logicnibble]

nyoo,

Do you have the BA00BC0WT or the BA00BC0WT-V5.
The difference is that R1 and R2 are already inside the V5 chip.

Pin1 will turn the device on and off: if Vctl > 2V the devide is ON; if < 0.8V the device is off.
You can connect pin1 to Vcc (yours 17V) and you don't need extra parts.

Check your ohmmeter: it may have low battery because if you reverse probes place, you should get the same result!

 

[nyoo]

Just out of curiosity, where did you obtain the manufacturer's diagram? What you are showing gives more detail than that on the Rohm data sheet, and could be leading to some confusion.

The Rohm web site has two documents for this series. The schematics came from https://www.electro-tech-online.com/custompdfs/2008/06/1a_ldo-e.pdf .

 

[nyoo]

nyoo,

Do you have the BA00BC0WT or the BA00BC0WT-V5.
The difference is that R1 and R2 are already inside the V5 chip.

Pin1 will turn the device on and off: if Vctl > 2V the devide is ON; if < 0.8V the device is off.
You can connect pin1 to Vcc (yours 17V) and you don't need extra parts.

Check your ohmmeter: it may have low battery because if you reverse probes place, you should get the same result!

I have the adjustable regulator BA00BC0WT. I worked out that with
Vout = Vref * (R1 + R2) / R1, and Vref defined as 1.25V, I should get Vout = 11.82V.

Thanks. I changed the ohmmeter's battery. The readings that were variable, based on which way round I held the probes, have gone away. The readings that were variable, whichever way I held the probes, are still variable; I'll write that off to "capacitor stuff" and figure it our later (with the help of you all, of course).

Now, about that CTL pin1. If it's supposed to accept a voltage higher than 2V, why does the schematic show it connected to ground? Taking Vin and GND at the same time? I'm confused.

 

[Mikebits]

ROHM data sheets are the worst and confusing as heck, one reason I refuse to use their parts. Be that as it may, if you look at their test conditions CTL is @ 2v or 3v. Also take note on your data sheet the max recommended operating input voltage.

 

[jpanhalt]

Now, about that CTL pin1. If it's supposed to accept a voltage higher than 2V, why does the schematic show it connected to ground? Taking Vin and GND at the same time? I'm confused.

The manufacturer's does not show that. The as built schematic that you posted does. Did you draw that one or download it from somewhere? It seems to be an error, which is what I based my comment on. John

 

[nyoo]

Why not just use an LM2940-12

Because this is the first circuit I ever built.

I wanted it useful; I have collected a few 14VDC wall adapters over the past year, and most of the next-level circuits I'm looking at are for 12VDC.

But I also wanted the first circuit to have about half a dozen components, just enough to make me work (and make you work, too, as it turns out). I would not have realised there was so much wire and solder -- under and over the board -- for 5 components, until I tried it.

I still haven't discovered the best cheap connector for securing external wires, with a pins that go into perf board holes. This time, I just epoxied the wires directly to the board!

 

[Mikebits]

If you just want a simple power supply why not build something like this one.
Regulators and Power Supplies
Not to say that you should abandon your current project, I am sure you can solve your minor troubles, or opportunities as this old engineer use to say.

 

[nyoo]

ROHM data sheets are the worst and confusing as heck, one reason I refuse to use their parts. Be that as it may, if you look at their test conditions CTL is @ 2v or 3v. Also take note on your data sheet the max recommended operating input voltage.

This all has been a great help. In the end, it looks like I just forgot to turn the component on!

Yes, thanks, I have taken serious note of the difference between max absolute and recommended operating voltage.

What would you recommend to limit the 14V wall adapter, whose no-load condition could be 17V? Would it solve the problem, by running Vcc directly into a resistor before it goes to pin1 and pin2 of the BA00?