...TWICE!!!
Before I start, I used separate pots for the positive and negative adjust pins but I did however ,turn them simultaneously. was this a bad thing to do with the lm317/337?
Twice now I have put together a simple dual rail 317 337 supply.
First time I used my own and I got voltage from one side, none from the other, then everything got really hot, and poof! The pot burned up something went pop and it was dead.
Second time I used rod elliott's site and just copied his schematic.
Pinout = lm337 = 1 adj) 2 in) 3 out)
pinout = lm317 = 1 adj) 2 out) 3 in)
diodes included and in the right direction, caps are fine, resistor values are 5k pot and 220R min load resistor.
I checked it all close to ten times, being a simple circuit I was sure it was all fine. I wired up my 14-0-14 (was it that I had been using 28V transformer) transformer and turnd it on and after about a minute the same happened again.
I am positive everything was wired correctly both times. Please advise, thank you, your time/knowledge is much appreciated.
Before I start, I used separate pots for the positive and negative adjust pins but I did however ,turn them simultaneously. was this a bad thing to do with the lm317/337?
Twice now I have put together a simple dual rail 317 337 supply.
First time I used my own and I got voltage from one side, none from the other, then everything got really hot, and poof! The pot burned up something went pop and it was dead.
Second time I used rod elliott's site and just copied his schematic.
Pinout = lm337 = 1 adj) 2 in) 3 out)
pinout = lm317 = 1 adj) 2 out) 3 in)
diodes included and in the right direction, caps are fine, resistor values are 5k pot and 220R min load resistor.
I checked it all close to ten times, being a simple circuit I was sure it was all fine. I wired up my 14-0-14 (was it that I had been using 28V transformer) transformer and turnd it on and after about a minute the same happened again.
I am positive everything was wired correctly both times. Please advise, thank you, your time/knowledge is much appreciated.
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What do you mean exactly: did you use two electrically separate pots and maneuvered them simultaneously .... or else?
Just to be sure, you do know that the pin-outs for the 317 Vs. the 337 are different, right? I've seen that mistake made many times.
Whoops, I just looked again at the original post and see you're aware of that, so maybe if you could post schematic/pictures it might help.
Mike
Whoops, I just looked again at the original post and see you're aware of that, so maybe if you could post schematic/pictures it might help.
Mike
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Best not be "positive" unless the circuit is working correctly.
I suspect a ground issue. The 5mA quiescent shouldn't cause a pot to fry.
I suspect a ground issue. The 5mA quiescent shouldn't cause a pot to fry.
Ru sure it is not pin (2) that is the adjust? (the center pin?)
Seems to me I recall that... the negative regulator might have a completely different pinout, not just flipped in/out...
someone can look it up, I am pressed for time at the moment...
Seems to me I recall that... the negative regulator might have a completely different pinout, not just flipped in/out...
someone can look it up, I am pressed for time at the moment...
Looking at the LM337 package with the heatsink on the back, the left pin is one and should go from the pot to ground. Pin 2 in the center should have a 10 uF or larger capacitor to ground. Note the positive is going to ground. There should be negative 35 volts or less voltage from the center pin (2) to ground. The right hand pin should also have a capacitor to ground. In addition a resistor of 120 ohms should go between the right and left pins.
Before you power it up set the pot to center position. Do not connect anything to the LM317. Do not put a load on until you have checked the voltages. keep the load under 25 mA without a heatsink. The tan is electrically hot so it must be insulated from a heatsink.
Before you power it up set the pot to center position. Do not connect anything to the LM317. Do not put a load on until you have checked the voltages. keep the load under 25 mA without a heatsink. The tan is electrically hot so it must be insulated from a heatsink.
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I have bread boarded the three terminal regulators separately and they work fine so it is definitely not a case of fake reg's or mistaken pinout. Here is the second schematic I used from Rod Elliott's ESP site. Since the simple circuit seems only to differ in cap and resistor values this may also be taken as the first schematic. The only differences being 220R for R1 and R2. Also instead of a dual ganged 2K pot, I used two 5K pots connected to ground in the same way as the dual ganged below, but replacing with (obviously) two single gang pots. I wanted to vary positive and negative independently. I used Motorola lm337 pin 123 ADJ IN OUT and ST lm317 123 ADJ OUT IN. I checked the datasheets to be sure. The cap's are connected with the correct polarity... + to + with - to ground and - to - with + to ground. The caps are used but hold charge and have no signs of damage or leakage, they are taken from a fully working amp. I selected two different caps for the second build. I used another one of everything for the second build apart from the rectifier. My ground is from the center tap of the traf to which the two ADJ pots are connected as below (I have checked that the wire I used from the traf' is indeed the center tap) The diodes are 1N4007 and connected for lm337 pin 1 to pin 3 with the line on pin 3 side, and pin 2 to pin 3 with the line on pin 3 side. For lm317, pin 1 to pin 2 line on pin 2 side, pin 2 to pin 3 with the line on pin three side. I used an RS203L bridge and double triple checked correct polarity. The only common components (apart from me) to both builds are the rectifier and the traf' which should give 36.7 VDC. I will find another of each and try again. Is there any info that says not to use separate pots?. He3re is the schematic.
http://sound.westhost.com/p44-fig1.gif
Graphic removed by moderation for copyright reasons.
http://sound.westhost.com/p44-fig1.gif
Graphic removed by moderation for copyright reasons.
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ESP's sch is OK.
The 100r draw ~12.5mA from the output rail to feed the pot.
This current cannot blow up the pot.
What have you done that is different?
The 100r draw ~12.5mA from the output rail to feed the pot.
This current cannot blow up the pot.
What have you done that is different?
I would be tempted to insert a 500 ohm 5w resistor between the raw dc power supply and the regulator to limit the current till you find the problem.
I'd insert a 1 ohm resistor after the pot to ground so that I could measure the current going through the pot.
Are the LM devices mounted on heatsinks ?
Are the LM devices mounted on heatsinks ?
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The cap values are the same as the esp sch but in my original build I had more capacitors on V out. The resistor values are the only difference now. 5K pot and a 220R for min load res
AH HUH! Yes Big E, it does. I will switch it around, power up and hope to keep the smoke in. A few hours time I will post.
Ok so I have re soldered the diodes to the right polarity and triple quadruple checked and checked again. There is not smoke as of yet as I only turn on in short bursts. The lm 317 is fine but the 337 is getting HOT! fast. I will endeavour to rebuild on vero in such a way that wiring can easily checked on a photo. I will then upload. As a single supply ( the 337 negative) it works fine and does not get so hot so fast. With the dual rail the 317 is nice and cool with no load but the 337 is burning to touch. I am somewhat bewildered by this turn of electrical events. Hope you guys can help once I can show the circuit. Thanks for your input 🙂
did you wire up the transformer and PSU and power it up via a bulb tester?
Did the low wattage bulb go out?
Then add on the regulator.
Does the bulb go out this time when you power up?
Did the low wattage bulb go out?
Then add on the regulator.
Does the bulb go out this time when you power up?
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