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Old 7th January 2007, 12:01 AM   #1
mikee55 is offline mikee55  United Kingdom
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Angry Can't Regulate, Help!

Hi all.

I've built a dual rail supply, with a pair if 22.6volt rails. One plus one minus both need to be regulated to 15volts. I can't get the negative reg to work.

Un-regulated I have 22.6 volts either side of earth, the 7815 pos regulator gives +15 volts. The TS7915 won't work. Both regs are TO220 style cases and logic states it should work. Both centre pin 2(and tag) is 0 volts, both pin 1 in and pin 3 out. Both regs are from Maplin Electronics(UK) and I'm on my second negative reg. Take the regs out and I get + - 22.6 volts, dual rail to where pin 1 should be, 0volts where pin 2 should be?????

Help!!! Please
cheers mikee55
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Old 7th January 2007, 12:09 AM   #2
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Add a 4.7k resistor from negative reg's output to ground.
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Old 7th January 2007, 12:32 AM   #3
jnmar is offline jnmar  Portugal
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Hi Mike.


You are not making the right connections on the 7915 they don't have the same pinout that the 7815.
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Old 7th January 2007, 12:33 AM   #4
mikee55 is offline mikee55  United Kingdom
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Default Hello there

The regulator cooks as soon as I apply power! Can you please explain why you'd add this resistor?,is this a load?

cheers Mike
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Old 7th January 2007, 12:41 AM   #5
mikee55 is offline mikee55  United Kingdom
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Default jnmar

I connect meter leads one to tab, the other to centre pin in cotinuity check. Meter says tab connects to centre pin. Looking above left pin in centre ov right pin out????



cheers mike
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Old 7th January 2007, 01:13 AM   #6
mikee55 is offline mikee55  United Kingdom
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Default Thanks for your help

Cheers guys, been and re-wired it to see if it was too late and the thing was dead.I got a reading of minus 4 volts then nothing.
The case was too hot to handle. I guess Maplin Electronics need a telling off. It should state that although its a TO 220 style case, its pins are not the same. Don't know if you're aware of Maplin ,but they've gone down hill over the past few years.

I will be complaining.

Many thanks for your help.

Cheers Mike
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Old 7th January 2007, 03:22 AM   #7
radtech is offline radtech  United States
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Default Re: Thanks for your help

Quote:
Originally posted by mikee55
I guess Maplin Electronics need a telling off. It should state that although its a TO 220 style case, its pins are not the same. Don't know if you're aware of Maplin ,but they've gone down hill over the past few years.

I will be complaining.
I wouldn't exactly blame Maplin, it's pretty much common knowledge in the electronics field that 79xx series have a different pinout than 78xx. Generally if the manufacturer doesn't package documentation with the parts, the supplier isn't going to put it them in there either. They do however usually supply them on their websites, and leave it up to you to look them up. Here's a link to them:

TS7900 series docs (PDF) from Maplin site
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Old 7th January 2007, 11:24 AM   #8
mikee55 is offline mikee55  United Kingdom
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Default Didn't have PC available at the time

but had a catalogue to hand. I was not aware that the pos and neg regulators had different pinouts. It seems logical to me to give them identical pin outs or to state in print if they have different pin outs.

Frustrated Mike
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