LM317 2N3055 Variable Circuit Problems

[heavyfletch2nd]

Ok thanks bob I will make a 4 diod rectifier and test that , I will let you know soon

 

[heavyfletch2nd]

I have pulled these from a ancient board 1N540 , I did a diod test all read 670 are they good enough to do the job?

 

[heavyfletch2nd]

 

[ModemHead]

Whoa guys... The 30VAC is a massive red herring. This is another misleading reading from an inexpensive DMM. It will happen for *any* small DMM you see on which the lowest AC voltage range is 200V. There are many, some even with reputable brand names, but most popular is the ones with "830" in the model number.

The very common simple design uses DC-coupling for the AC voltage ranges. It uses a single bog-standard diode for AC to DC rectification. The RMS voltage of a half-wave rectified sine wave is 2.22 times the average value, which the meter's A-to-D converter actually responds to. So the reading is scaled up by 2.22 times, giving an approximation of RMS voltage for a sine wave. The diode drop causes some non-linearity at the bottom end of the range, which is why there are no lower AC ranges.

Quick proof: Measure a 9V battery on the 200VAC range. With the probes the "right" way around, it will read around 20V (about 2.2 times the actual DC voltage, minus a diode drop.) Turn the probes the other way, and it will read zero.

 

[duke37]

Do you have another digit after 1N540? Have you looked up the data?

Have you contacted the Worcester amateur radio group?

 

[duke37]

It is often recommended to place a diode across the 317T to prevent any reverse polarity which will kill the 317. If you have an AC component in your power supply, this could do the same thing.

Post a picture of the bridge rectifier showing the connections.

 

[heavyfletch2nd]

Modemhead Should I connect up to the transformer or should I check anything els first , duke no not yet had time to go up with the daughters new born living with me but I will at some point

 

[heavyfletch2nd]

 

[ModemHead]

Modemhead Should I connect up to the transformer or should I check anything els first

Please note the KBJ608G is only a 6A bridge.

For completeness, check the bridge with your multimeter set to diode test. Put the black lead on the positive terminal (seems backwards, I know.) You should get a diode drop reading on both AC terminals (~) with the red lead. Then put the red lead on the negative terminal. You should get a diode drop reading on both AC terminals with the black lead. Reverse the leads and repeat the steps, you should get an open indication for each one.

 

[heavyfletch2nd]

Yes I am getting 605 on the meter both sides of thr bridge , the meter stays on ( I ) on reverse.

 

[ModemHead]

Yes I am getting 605 on the meter both sides of thr bridge , the meter stays on ( I ) on reverse.

Four separate 0.605 readings one way, and four separate open readings the other way, right? If so, then the bridge must be OK.

You have seen the regulator in operation with the 9V battery. Simply switching to your transformer/rectifier/filter-cap supply *should* work exactly the same, except the max voltage should be higher than 8V. I would suggest the same exercise with the two meters, before hooking up any transistors or loads. In other words, one step at a time and verify the regulator is still working at each step. If something were to pop, you need to know exactly what change was made that caused it.

It's possible *steve* had something else in mind for you to check before proceeding, I'm not sure. I think he wanted to know what the filter cap voltage was with the transformer connected.

 

[(*steve*)]

Yes, I wanted to know the voltage after the rectifier with the filter caps connected.

It's not DC coming out of the bridge rectifier, you need the filter caps for that. It sounds like you have the caps connected before the LM317 rather than after the rectifier. Topologically, is the same thing, but I'd prefer them connected after the bridge rectifier so we can do step by step measurements.

Also I concur about no load, and about the millimeter on the ac range not actually measuring ac.

 

[heavyfletch2nd]

Yes Four separate readings and in reverse the ( I ) , I will go ahead and connect , before I connect any fans or transistors I will post a pic of the volts across the caps for steve ,

 

[ModemHead]

Yeah, I figured it was too late to mention this, but I would put the filter cap array on a board by itself. And then solder the LM317 directly to another small board along with its fixed set resistor and any bypass caps desired.

 

[heavyfletch2nd]

Its connected suprising to me no smoke yet 21.5v across caps , the small spur of solder coming off the live rail is the feed to lm317 .

 

[(*steve*)]

No smoke is good

 

[heavyfletch2nd]

Should I connect a transistor , these are new transistors I have metered them too at 690 to 710 all have different readings , to be honest I was expecting to see a 0.5 or somthing like you two have mentioned before as I have not powered them yet.

 

[ModemHead]

Should I connect a transistor , these are new transistors I have metered them too at 690 to 710 all have different readings , to be honest I was expecting to see a 0.5 or somthing like you two have mentioned before as I have not powered them yet.

Have you verified the regulator is behaving as expected, like we did before with the two meters?

About the transistor readings, I think we determined that both your multimeters read diode junctions a little high, one more so than the other. Don't worry about it.

 

[heavyfletch2nd]

Ok one transistor connected still no smoke , "but" with the pot turned down I still have 12.5 v on the out put of emitter 1.27v on pin 2 of lm217 , turn put up and I have 19.5v on emitter 20.6v on pin 2 ?? Lol
hopfully you can see from this pic how it is all connected.

 

[ModemHead]

Well, as usual you've jumped the gun again...

Do you still have that 2200 ohm (red-red-red) resistor laying around? If so attach it between the transistor emitter and ground, and check the measurements. This will provide a very very small load for the transistor, and help stabilize its output voltage.