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Old 17th April 2012, 01:45 PM   #21
AndrewT is offline AndrewT  Scotland
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Start with a 741.
It has good protection built in, to reduce the risk of damage.
But, the 741 voltage and PINs are different.
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Old 17th April 2012, 01:48 PM   #22
Simon B is offline Simon B  United Kingdom
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Quote:
Originally Posted by AndrewT View Post
there is only one schematic.

A quick mental arithmetic on the 3 PINs gives me about 500mV on +IN and 500mV on -IN and this results in about 1500mV on OUT.
That confirms all these PINs are tied to -ve rail.

Well I've checked that I'm looking at the schematic posted.

The +In connects to ground through a series combination of 1k and 100k, the junction between the two has the input cap feeding in - how do you see 500mV on +In?

The -In connects into the feedback voltage divider, nothing too weird there?

Shurely shome mishtake!
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Old 17th April 2012, 02:04 PM   #23
AndrewT is offline AndrewT  Scotland
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The input bias current times the input resistance to ground gives the voltage across the input resistors. I would expect that voltage to be somewhere between 100mVdc and 500mVdc.

An opamp does what is required with the output to make the voltage on the -IN PIN equal to the voltage on the +IN PIN. If you accept that, then the -IN PIN voltage must also be very close to the +IN PIN.

Working from that you can then determine the approximate output voltage using the feedback resistors and a guess at the -IN bias current.

All three PINs will have voltages close to the -ve rail.

That all assumes that the opamp does not mind having all those PINs near -ve rail.

So I come back to my question. Does the 5534 survive that operating condition?
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Last edited by AndrewT; 17th April 2012 at 02:06 PM.
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Old 17th April 2012, 02:23 PM   #24
oshifis is offline oshifis  Hungary
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Don't give up, here are some ideas how I would start:

- Use 2x 9V batteries (one for pin7 positive voltage, one for pin 4 negative voltage) for experimenting
- Use IC sockets
- Get some cheap opamps (e.g. uA741 that is pin compatible). If that works, just replace the opamp in the socket
- Don't forget the pin numbering is seen from the top, not from the bottom
- Buy the NE5534 from the nearby parts shop, not from eBay. It is dirt cheap anyway...
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Old 17th April 2012, 02:57 PM   #25
Simon B is offline Simon B  United Kingdom
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Quote:
Originally Posted by AndrewT View Post
The input bias current.......

So I come back to my question. Does the 5534 survive that operating condition?


Yes, my mistake, bipolar ic, those 100ks are bigger than they need to be here. The TI 5534 lists Iib as typically 500nA, but possibly as high as 2000nA, with Iio max 400nA.

Just to check, inputs feed into bases of npn diff pair, so input bias currents flowing inwards, ok. With the circuit as shown, ie power supply plain wrong, the +In transistor base is connected to 0v via that 100k resistor - not much current is going to end up flowing in that terminal at all, leaving the -In side to feed the ccs below the input diff pair - if it can.

NE5534_internals.gif

-In has 22k to ground and 56k to Out, which will be down as low as it can get, but feeding into that 56k.

So far I can't see anything melting on account of the circuit as shown, though obviously it has melted!

The difficulty with someone with this little idea of what's what is making a reasonable guess as to what they're doing wrong of course, and to try to offer sensible advice, encouraging without being ludicrously over-optimistic. I think oshifis hits the right note.

Btw, whilst the 741 has no pin connection for compensation, the pinouts are otherwise the same, so as oshifis says, getting a circuit working with a 741 then swapping in another better opamp, including the 5534 would seem sensible. Though it's up to WhiteRhino how much stamina he has for this, a lot of folk do seem to find this stuff less fascinating than we do. I have heard it suggested that that's because they have lives, but those uttering such heresies should just be punched.....



Last edited by Simon B; 17th April 2012 at 03:09 PM.
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Old 17th April 2012, 02:58 PM   #26
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Originally Posted by WhiteRhino View Post
I just blew up the chips ...

never mind my qeustions I have to get another opamps ..
How do you know its blown up??

jan
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Old 17th April 2012, 03:02 PM   #27
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Originally Posted by oshifis View Post
Don't give up,
if some one will draw me a schematic with the ne5534 opamp
I will try again
the ne5534 is very cheep it coast only 2 $ .
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Old 17th April 2012, 03:06 PM   #28
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Originally Posted by janneman View Post
How do you know its blown up??

jan
came out of them allot of smoke , i threw them to trash any way ,
if some will draw me a schematic how to use the 5543 , i will try again
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Old 17th April 2012, 03:21 PM   #29
Simon B is offline Simon B  United Kingdom
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Originally Posted by WhiteRhino View Post
came out of them allot of smoke , i threw them to trash any way ,
if some will draw me a schematic how to use the 5543 , i will try again


Drawing schematics is a bit like hard work WhiteRhino, especially for those of us like me who don't have a scanner connected.

Read my post earlier, and redraw your schematic with the two resistors added, then you should be getting something viable.

Or, take heed of oshifis's suggestion, use a pair of PP3 batteries to give twin rail supply and connect your pin 4 to the -ve rail.
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Old 17th April 2012, 03:51 PM   #30
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ok I make it easier for you .

what do you think about this ?
every thing ok ?
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