Are TS555's really supposed to suck this much?
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From: Jim Thompson on 21 Jan 2010 09:22 On Wed, 20 Jan 2010 21:18:43 -0800, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Wed, 20 Jan 2010 20:22:49 -0800 (PST), Tim Williams ><tmoranwms(a)gmail.com> wrote: > >>I was trying to blink LEDs from a TS555IN today, and discovered the >>awful truth that its output stage stinks. Somehow it's rated for 10mA >>source, 50mA sink (at 12V, 2V max. Vds(sat)). You're NOT looking at the data sheet for a _TS555_. You have the data sheet for a high-powered version. >>The datasheet happens >>to overlook the fact that internal voltages change when the output is >>loaded. No, the inadequacy of current drive stands out to all who can read ;-) >>Specifically, in astable mode, frequency drops and duty cycle >>drops. When heavily loaded, oscillation stops altogether. ONLY if you are using feedback from output. >> >>It seems like there's an insane amount of resistance in series with >>the power supply pin, and any current draw causes the rest of the >>circuit to poop out (i.e. dragging down the control voltage divider, >>comparator, etc.). >> >>So what's the deal with this? Are they really supposed to be so >>shitty? I know lots of CMOS is supposed to drive CMOS, but even >>CD4001 will drive a damn LED. >> >>Tim > >Well, duh, it's a 555. > >John Well, duh! TS555 is a MICRO power version. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Cranky Old Git With Engineering Mind Faster Than a Speeding Prissy
From: Tim Williams on 21 Jan 2010 10:47 "Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com/Snicker> wrote in message news:8iogl5197829hba31j9f0dbj32pkrtuofb(a)4ax.com... > You're NOT looking at the data sheet for a _TS555_. You have the data > sheet for a high-powered version. Nope! The bipolar goes to +/-200mA. 'TS specifically says 10 up, 50 down: http://www.datasheetarchive.com/pdf/Datasheet-072/DSA00360793.pdf bottom page 2. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: John Fields on 21 Jan 2010 13:09 On Wed, 20 Jan 2010 21:18:43 -0800, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Wed, 20 Jan 2010 20:22:49 -0800 (PST), Tim Williams ><tmoranwms(a)gmail.com> wrote: > >>I was trying to blink LEDs from a TS555IN today, and discovered the >>awful truth that its output stage stinks. Somehow it's rated for 10mA >>source, 50mA sink (at 12V, 2V max. Vds(sat)). The datasheet happens >>to overlook the fact that internal voltages change when the output is >>loaded. Specifically, in astable mode, frequency drops and duty cycle >>drops. When heavily loaded, oscillation stops altogether. >> >>It seems like there's an insane amount of resistance in series with >>the power supply pin, and any current draw causes the rest of the >>circuit to poop out (i.e. dragging down the control voltage divider, >>comparator, etc.). >> >>So what's the deal with this? Are they really supposed to be so >>shitty? I know lots of CMOS is supposed to drive CMOS, but even >>CD4001 will drive a damn LED. >> >>Tim > >Well, duh, it's a 555. --- It's like Invasion of the Body Snatchers, where a Sloman pod was placed next to Larkin while he was asleep... ;) JF
From: Bill Sloman on 21 Jan 2010 19:15 On Jan 21, 7:09 pm, John Fields <jfie...(a)austininstruments.com> wrote: > On Wed, 20 Jan 2010 21:18:43 -0800, John Larkin > > > > <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > >On Wed, 20 Jan 2010 20:22:49 -0800 (PST), Tim Williams > ><tmoran...(a)gmail.com> wrote: > > >>I was trying to blink LEDs from a TS555IN today, and discovered the > >>awful truth that its output stage stinks. Somehow it's rated for 10mA > >>source, 50mA sink (at 12V, 2V max. Vds(sat)). The datasheet happens > >>to overlook the fact that internal voltages change when the output is > >>loaded. Specifically, in astable mode, frequency drops and duty cycle > >>drops. When heavily loaded, oscillation stops altogether. > > >>It seems like there's an insane amount of resistance in series with > >>the power supply pin, and any current draw causes the rest of the > >>circuit to poop out (i.e. dragging down the control voltage divider, > >>comparator, etc.). > > >>So what's the deal with this? Are they really supposed to be so > >>shitty? I know lots of CMOS is supposed to drive CMOS, but even > >>CD4001 will drive a damn LED. > > >>Tim > > >Well, duh, it's a 555. > > --- > It's like Invasion of the Body Snatchers, where a Sloman pod was placed > next to Larkin while he was asleep... ;) It's more that John Larkin is good at electronic design, and has recognised precisely how useful the 555 is - which is to say, not a useful device in most applications. -- Bill Sloman, Nijmegen
From: Archimedes' Lever on 21 Jan 2010 20:24
On Thu, 21 Jan 2010 12:09:00 -0600, John Fields <jfields(a)austininstruments.com> wrote: >On Wed, 20 Jan 2010 21:18:43 -0800, John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >>On Wed, 20 Jan 2010 20:22:49 -0800 (PST), Tim Williams >><tmoranwms(a)gmail.com> wrote: >> >>>I was trying to blink LEDs from a TS555IN today, and discovered the >>>awful truth that its output stage stinks. Somehow it's rated for 10mA >>>source, 50mA sink (at 12V, 2V max. Vds(sat)). The datasheet happens >>>to overlook the fact that internal voltages change when the output is >>>loaded. Specifically, in astable mode, frequency drops and duty cycle >>>drops. When heavily loaded, oscillation stops altogether. >>> >>>It seems like there's an insane amount of resistance in series with >>>the power supply pin, and any current draw causes the rest of the >>>circuit to poop out (i.e. dragging down the control voltage divider, >>>comparator, etc.). >>> >>>So what's the deal with this? Are they really supposed to be so >>>shitty? I know lots of CMOS is supposed to drive CMOS, but even >>>CD4001 will drive a damn LED. >>> >>>Tim >> >>Well, duh, it's a 555. > >--- >It's like Invasion of the Body Snatchers, where a Sloman pod was placed >next to Larkin while he was asleep... ;) > >JF I noticed that too, but did not want to alarm anyone. |