[SOLVED] 6V regulator putting out 3.3V

Hi all,

I'm currently creating a Arduino controlled laser spirograph, that has 4 motors attached which I'm controlling through an H-bridge. My problem is that upon attaching my 6V regulator (instead of my Vin which is 10V) to the Vcc of the H-bridge, the voltage output of the regulator drops to about 3V. I didn't have this issue when it was wired directly to Vin, and when the regulator is attached to nothing ouputs 6V.

I know that something is wrong here and that it's my fault, I just can't find it. I've tested almost every contact in the entire circuit looking for shorts and can find none. I've triple checked the data sheet to make sure it's wired correctly, and I still can't find where I've gone wrong. The circuit also contains a 3.3V and 5V regulator, both of which are functioning correctly, however when the 6V is connected to the bridge, they drop about 0.2V each. Measuring the total current draw with the 6V attached, it came out to only 150mA, which is in line with 40mA of pots (they're low resistance) and a 7 segment display.

Basically, I'm completely flummoxed as to the problem. Does anyone have some additional troubleshooting tips that could help?

Regards, Will

P.S. Here are the datasheets for the 6V regulator and the H-bridge.

You have an h-bridge chip for each motor? The 7806 is getting hot to the touch? Your 10V source can put out enough current for all the regulators? If not, how are things wired? Are the motors enabled when this happens? Does it happen when they are disconnected? Post a schematic please.

I'm off to bed ...

CrossRoads:
You have an h-bridge chip for each motor?
The 7806 is getting hot to the touch? Your 10V source can put out enough current for all the regulators?
If not, how are things wired?
Are the motors enabled when this happens? Does it happen when they are disconnected?
Post a schematic please.

I’m off to bed …

I have 2 bridges for each motor, for bidirectional control.
My 10V source can output 1A, so is enough. Remember, it was working fine before the 6V regulator was attached, the 3.3 and 5 provided power wonderfully.
All of the regulators are getting warm, but I think it’s due to stepping down the voltage as opposed to current draw (as measured current draw for entire circuit was 150mA)

As for wiring/circuit diagram, I’ll do my best to explain, but can whip up one it Fritzing if you wish.

10V source (Vin) connects to Vin on Arduino, 5V regulator, 6V regulator, 3V regulator. Grounds are all linked.
According to datasheet for H bridge, 1,2EN 3,4EN Vcc connected to 5V regulator output.
Ground/heatsink connected to shared ground.
1-4Y currently disconnected as no motors present.
1-4A connected to 8 Arduino pins, half PWM, half digital. Default LOW.
Vcc2 connected to 6V regulator output.

3V regulator connected to 4x 300ohm resistors in parallel, then to ground.

I hope that’s enough information, again, I can get something up in Fritzing if you wish.

but can whip up one it Fritzing if you wish.

Fritzing does not do schematics, it does physical layouts which are useless for fault finding.

From you description I see there is no mention of input or output capacitors for the regulator. These are needed.

Grumpy_Mike: Fritzing does not do schematics, it does physical layouts which are useless for fault finding.

From you description I see there is no mention of input or output capacitors for the regulator. These are needed.

Fritzing has a circuit schematic viewmode that, although basic, does the job. Want me to create one?

As for input/output capacitors, here's a quote from the datasheet: "No External Components Required" which I assume to mean that no filter capacitors are needed.

here's a quote from the datasheet: "No External Components Required"

Yes but it also says under standard application on the right of the first page:-

  • Cin is required if regulator is located an appreciable distance from power supply filter. ** CO is not needed for stability; however, it does improve transient response. Values of less than 0.1 mF could cause instability.

You are switching a motor so transient response is important to you. So I would treat the first quote as more marketing speak rather than solid fact.

Thanks for the heads up, I'll incorporate one. But it still doesn't explain the voltage drop :~

If I assume everything is wired perfectly, is this normal? Because all I can think of right now is that something, somewhere, is connected to the wrong thing, but if this is a normal (albeit bizarre) thing to be happening I can just go with it.

all I can think of right now is that something, somewhere, is connected to the wrong thing,

I think you might be right, in these cases a schematic and clear photo would help track things down.

My bet is that some ground won't be continuous, it normally is.

I can't get you a clear photo as my wiring is an eyesore - ribbon wires are great on one end, but on the other they're horrific... (It's a PCB prototyping board, so no neat traces here).

There is one thing, which I think isn't the issue, but I'll put it forwards regardless - the H-bridge has 2 ground/heat sink pins on each side, and the regulator ground is connected to one of these pins. This pin does not go directly to ground, but the one on the other side does. This shouldn't be an issue, correct? A continuity test on a multimeter shows they're connected.

Does the 3.3V when connected indicate a ground continuity issue? It's almost as though the other regulators are affecting it in some way...

This pin does not go directly to ground, but the one on the other side does. This shouldn’t be an issue, correct?

While it is not good practice and could lead to ground problems with switching currents I would not expect it to cause this issue.

If you disconnect the H-bridge circuit from the regulator output does it go back to 6V? You have not left any wiring in that still connects this to the 5V rail? Something like the motor flyback diodes.

Yes, the regulator returns to 6V when disconnected. At least this isolates the issue to something in the H-bridge. The 5V rail is currently only wired up to the driver enabling pins (as a 5V digital HIGH) and the power source for the internal circuitry in the bridge (Vcc1).

Can you measure the current that the H-bridge is taking? Wire the meter between the regulator output and dab the other end on the H-bridge. Does the current shoot up? If not I would put a capacitor across the regulator output and try again.

It's difficult to tell whether the current spikes as my digital multimeter has a slow refresh rate, but it stabilises at about 40mA, which is very high.

Can you try this with the motors disconnected to see if it makes a difference?

The motors have been disconnected the entire time, this is why it's confusing me... =(

Do you still have the logic supply of the H-bridge connected to the 5V line?

Yes.

I am running out of ideas but I don't think you have tries a capacitor yet. It says about the output capacitor:-

CO is not needed for stability; however, it does improve transient response. Values of less than 0.1 uF could cause instability.

Which is odd because if the capacitance of your load is less than this, then it suggests you are going to get instability. They might be assuming that any load is going to have 0.1uF decoupling capacitors on it anyway so are saying you don't need any extra. But, if you have none at all that could lead to instability.

I'll scrounge around and find a capacitor to place across the output. Either way, it's late here, so I'll sleep on it and try again in the morning, hopefully finding a solution. Thanks for sticking with me on this so far. :)

I've retested - Still sticks at 6V when disconnected, drops to 3.3/3.2 and draws 40mA when connected, and bizarrely, when disconnected, seems to jump between 6V and 9.5V.

Any ideas as to why it jumps to 9.5V when disconnected? None of my other regulators do this. Maybe it is the regulator...