Testing a 78L05 regulator ??

[FatBob]

The input must be higher than ground. If you look at the Hammerhead schematic there is a 7660
used as a voltage doubler so the output is 10 - 12V above the battery positive (marked ground in HH).



It also looks like your batteries all face the same way. They should be plus to minus in a string to get
12V from 3 4V batteries...

Try measuring your batteries with nothing connected and make sure you have 12V to start with.

[ODM]

The Hammerhead has a dual polarity power supply. The negative supply is made with the battery and 7905 negative regulator, the positive supply is made from negative with the charge-pump IC and regulated with 7805 positive regulator.

Not correct, 78L05 only regulates positive voltage. That is why we need another type of regulator for negative voltage use (79L05). Wrong polarity may damage a regulator and certainly its output won't be what it is supposed to be.

A linear series regulator doesn't have the means to invert voltage, this is why we need the charge-pump IC to create an inverted voltage. It is noisy because the IC switches a capacitor back and forth to create that reverse supply, that's why it is regulated with the 7805 into a relatively clean supply for those sensitive high gain analog amplifiers.

[petere]

Thanks for the reply guys

Hi Dooley, I have tried as you suggested on several regulators but still not getting a reading of 5 volts, must have a dud lot I think.

Hi ODM, I have connected the positive lead to ground because that is how it is connected on the Hammerhead. I don't fully understand how it ends up as positive reading on the hammerhead PCB. But am I correct in saying that connecting it either way in the testing still should give an output of 5volts whether it be positive or negative.

[ODM]

You have the red wire, assuming that's positive, as common wire? The polarity would be ok if you're trying to test the 79L05 which is a negative voltage regulator but the pin order is different on the 79L series, compared to 78L series positive regulators.

The connection in your photo is wrong. You should have negative as the common lead. Eg. black negative wire from battery pack goes together with multimeter common to the 78L05 center lead. Red positive from battery pack goes to regulator's input pin, multimeter positive goes to regulator's output pin.

The voltage will show a bit high without a load, 1k resistor will show a more realistic value. If following the application note you should have decoupling capacitors on both input and output of regulator.

[DOOLEY]

hello petere,

just power it up with a higher voltage,
12v will be fine,

put a small load on the output pin,
say 1k or so,
I would also add a small capacitor also.

then check output voltage with multi meter.

poss easier to do on a breadboard.

output voltage usually around 4.95v to 5.05v

[petere]

Have been working on building a Rev C Hammerhead and have struck problems with the +5v output on IC2. I have followed instructions up to IC6 and everything seems good (now that I replaced the ICL7660) except for the voltage at pin 7 on IC 6 and the output of IC2. I have gone through around 15 78L05's and none of them seem to be any good. Is this a valid way to check them? (see pic) The batteries are around 12v.
Thanks