What's this please? (Component Advice)

[Rufus]

anyone know whats this is?

Looks like a Schurter PTC fuse.

[Psi]

i think you might be right.  Digikey said they dont want it back so i took it out and had a look.

It's 1.5ohms in either direction, which fits your idea of a PTC fuse.

[Architect_1077]

Hi!
Please... does anyone know what this little piece is? It's part of a 230v -> 120v stepdown tx circuit. The part is circled in red in the following pics:

[SeanB]

I would guess it is a NTC thermistor, probably there to shut down the unit when the triac gets too hot.

Basically it is a near open circuit until it reaches a preset temperature, where it then drops to around 100R or so in resistance, and then the voltage across the diac is too low for it to trigger the triac into conduction.

At least is is self resetting, unlike a thermal fuse, though operating the device in the region where this protection is operating is not good.

[Architect_1077]

Thanks!

[nitro2k01]

SeanB is right.
(Not so) useless trivia: Another use for NTC resistors is for ring core transformers. You put them in series with the primary side as a cheap way to limit the current spike that these transformers will draw when powered on. This current spike can otherwise make the circuit breaker trip.
NTC means negative temperature coefficient, so the resistance will go down as the resistor gets hotter. When used with a ring core transformer, the resistor value is chosen so that the resistor heats up and goes down to near zero resistance within a second.

[SeanB]

NTC's are used in SMPS input stages as well, to reduce inrush current. I have used them on incandescent lamps as a life extender, as the lamp will generally last thousands of hours, as the most stress occurs during switch on, and the added resistance reduces this until the filament is so weak that it blows during use. I had to do this on an old plate maker that used 40 40W golfball lamps as a light source, that had a switch on surge that would trip the 30A mains breaker 50m away down the corridor. I could not find a NTC that would handle the load ( and this was in the 1970's when I was a teenager) so used a slow start circuit which had a triac controlled by a unijunction transistor (now near impossible to get) and a few other components to provide a slow charge ( 1 second from zero to full brightness) and a non isolated supply for the circuit.

I did a similar thing for my variac, it has a very large core and a correspondingly annoying switch on surge.

[icon]

Hi

This resistor is across the mains input of a device. Looks like a 1M to me, but I'd like to be sure - not familiar with the red band.



I'm going to replace it along with the dodgy looking cap...

Cheers
John

[amspire]

It looks like a 1M 1% resistor. The red band means 50ppm/C stability.

If you replace the capacitor, make sure it is a 250V AC rated Class Y2 capacitor.

[SeanB]

Note that if the resistor is ok do not replace it, as you need to use a 1W metal film resistor to get a voltage rating that will handle mains voltage. Those RIFA capacitors do craze as they get old, but it is mostly cosmetic. Stress from the different expansion rates of the housing and the epoxy encapulant. It just shows that they did bond really well, otherwise there would be a non visible shear along the bond line.

[Jad.z]

Hi,

What are this stuff??? I searched all over the internet and couldn't find a thing about them, not even a picture!
I got them from the local store, the owner gave me a bunch of them for free.
He said he didn't know what they are (nobody was buying them  ) so he was giving them away with every order.

My best guess would be colour sensors. Could they simply be LEDs ?

[amspire]

They are two LED bar graph displays.

The LED connections are Pins 6(anode) to 1, and pins 3(anode) to 4. The middle pin is not used. Pin 1 will have a little chamfer on the corner of the case.

About 2.5mCd brightness at 10mA forward current.

Richard

[Jad.z]

Thank you Richard

[hydroman1976]

Bridge rectifiers. Can I take 2 and put them in parallel or series for better results? What if I make one that has 2 diodes per leg or side? (8 total) Would this be better. I know about using a capacitor in parallel with bc. I have a setup with no cap with input voltage of 120vac but 70vdc out. Does this mean the bc are bad or do you need the caps to make them work?
Thanks in advance for your help.
hydroman1976@gmail.com

[rowant]

If you put two bridge rectifiers in parallel you can double the current, in series you won't do anything but lose voltage drop over two of the diodes (since it's already DC the other two won't do anything anyway).

[vk6zgo]

Bit of a waste of time,though,it your original  AC source can't provide double the current.
In any case,it would be better just to buy a higher rated bridge.

[nitro2k01]

If you put two rectifiers in parallel, won't the load be lopsided between the two because of a slight voltage drop variation?

[whonline]

Nitro is right.  The forward voltage drop of a diode has a negative temperature coefficient.  Slight differences in paralleled diodes will cause more current to flow in one vs the other.  The increase in current in that diode with higher current accelerates it's temperature rise which diverts even more current.  In the end most of the current will be flowing through one diode.  Paralleling diodes won't buy you anything.

Walt 

[orbiter]

Next up fellas..

I found these in the loft today, can't seem to find out what they are from the numbers on them, any ideas please?

Numbers around the top rim of one of them are 771139 and SGS87305



Thank you

orb

[free_electron]

SGS Sociedad Generale Semiconduttori ... Successor to ATES ( Aquila Tubi e Semiconduttori )
now better known as STmicroelectronics

this is a very old part. i couldn't find anything in the archives. probably a custom job.... or could be a prototype .

[orbiter]

SGS Sociedad Generale Semiconduttori ... Successor to ATES ( Aquila Tubi e Semiconduttori )
now better known as STmicroelectronics

this is a very old part. i couldn't find anything in the archives. probably a custom job.... or could be a prototype .

Ok thanks mate. I can confirm that it's really old, its been stuck up in the loft for at least 20 years

These were in a box of parts I'd bought from a place called Greenweld electronics. I think the same company still exists actually (greenweld.co.uk) however their components range has almost disappeared compared to what I seem to remember them having.

Cheers

orb

[bilko]

It could be equivalent to a LM305 regulator. If you have a few it might be worth running some checks and comparing with this data sheet
http://www.ti.com/general/docs/lit/getliterature.tsp?genericPartNumber=lm305&fileType=pdf

First number is probably date code for 1977

[orbiter]

It could be equivalent to a LM305 regulator. If you have a few it might be worth running some checks and comparing with this data sheet
http://www.ti.com/general/docs/lit/getliterature.tsp?genericPartNumber=lm305&fileType=pdf

First number is probably date code for 1977

Ah ok, that gives me something to go on. I'll run a few tests on them and see how they compare.

Thanks mate

orb

[free_electron]

mmm. don't think so. many chips were available in to-100 package in that timeperiod.
SGS never made LMxxx style parts. apart from the LM741. they didn't do 709 and no regulators. they had their own stuff : L4905 L200 etc ... and those came later.

it may even be a matched pair or simply the long-tail of an opamp ...

[amspire]

It is the SGS equivalent of the Fairchild uA711 Dual  40nS comparator. Made in 1973 from the date stamp, but from memory, the design dates back to the 60's.

This is a very dated component, and you probably wouldn't want to use it in a new design. Unlike modern comparators, it requires a positive supply (usually 12V), a negative supply (usually -6V) and a ground rail. The three rail opamps and comparators tended to be very easy to accidentally blow.

Richard