ua741
in [Basics]
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From: cc on 16 Oct 2009 21:02 I'm aware of uA741 slew rate issues and limited GBW, but I can't even get above gain of 2x with Vcc of +/- 12v and input sine wave of 5mV peak at only 100Hz (yup, one hundred Hz). What?
From: Tim Wescott on 16 Oct 2009 21:10 On Fri, 16 Oct 2009 18:02:16 -0700, cc wrote: > I'm aware of uA741 slew rate issues and limited GBW, but I can't even > get above gain of 2x with Vcc of +/- 12v and input sine wave of 5mV > peak at only 100Hz (yup, one hundred Hz). What? That doesn't sound right. Post your circuit? Are you sure that your power supply voltages are actually getting to the chip? Is it properly bypassed? Could it be any other common weirdness that just happens to be showing low slew rate as a symptom? -- www.wescottdesign.com
From: Bob Eld on 16 Oct 2009 22:57 "cc" <pccmd(a)comcast.net> wrote in message news:37514530-3118-4123-bc52-ff93af7461f1(a)i12g2000prg.googlegroups.com... > I'm aware of uA741 slew rate issues and limited GBW, but I can't even > get above gain of 2x with Vcc of +/- 12v and input sine wave of 5mV > peak at only 100Hz (yup, one hundred Hz). What? Are you applying any feedback? It sounds like you are trying to operate it open loop. At 100 Hz the open loop gain should be about 100 times and, 5mV should give about 500mV out, open loop. However, the DC input offset voltage and offset current could easily drive the open loop amp output into one of its rails causing virtually no AC out. Connect the amp as a gain of 10 with a 1k input resistor and a 10k feedback resistor to the neg input, ground the pos input and be sure there is a DC path to ground through your source and try again.
From: Phil Allison on 16 Oct 2009 23:02 "Bob is too Eld" > At 100 Hz the open loop gain should be about 100 times and, 5mV should > give > about 500mV out, open loop. ** Err - the open loop gain of a 741 is 10,000 times at 100Hz. > Connect the amp as a gain of 10 with a 1k input resistor and a 10k > feedback > resistor to the neg input, ground the pos input and be sure there is a DC > path to ground through your source and try again. ** No need for a DC path exists when the pos input is grounded cos the feedback loop will make sure the neg input is within 1 mV of the pos one. .... Phil
From: Bob Eld on 17 Oct 2009 08:01
"Phil Allison" <phil_a(a)tpg.com.au> wrote in message news:7jsqdsF37c844U1(a)mid.individual.net... > > "Bob is too Eld" > > > At 100 Hz the open loop gain should be about 100 times and, 5mV should > > give > > about 500mV out, open loop. > > > ** Err - the open loop gain of a 741 is 10,000 times at 100Hz. > > > > Connect the amp as a gain of 10 with a 1k input resistor and a 10k > > feedback > > resistor to the neg input, ground the pos input and be sure there is a DC > > path to ground through your source and try again. > > > ** No need for a DC path exists when the pos input is grounded cos the > feedback loop will make sure the neg input is within 1 mV of the pos one. > > > > ... Phil Your right....I had a brain-fart and figured it wrong. For some reason I can't seem to divide a million by 100. Oh well, the fact remains that the OP must be trying to run the amp open loop. |