Running at the full Vcc of 16V and the full frequency of 500kHz the 555 got
so hot I had to add a clip-on heatsink.

Tried slowing it down to about 140kHz and the heatsink still gets pretty
warm.

Is this normal?

Thanks.

"Ian Field" wrote in message
...
Running at the full Vcc of 16V and the full frequency of 500kHz the 555
got so hot I had to add a clip-on heatsink.

Tried slowing it down to about 140kHz and the heatsink still gets pretty
warm.

Is this normal?

Thanks.

I've run the NE555 at 12V and it barely got warm.

What load are you driving and what RC? Your dissipation could be coming from
the pin 7 sink discharging a large cap or sinking a high pull-up current.
Output drive doesn't fully saturate (iirc) so it is lossy when driving any
appreciable current.

"Oppie" wrote in message
...
"Ian Field" wrote in message
...
Running at the full Vcc of 16V and the full frequency of 500kHz the 555
got so hot I had to add a clip-on heatsink.

Tried slowing it down to about 140kHz and the heatsink still gets pretty
warm.

Is this normal?

Thanks.

I've run the NE555 at 12V and it barely got warm.

What load are you driving and what RC? Your dissipation could be coming
from the pin 7 sink discharging a large cap or sinking a high pull-up
current. Output drive doesn't fully saturate (iirc) so it is lossy when
driving any appreciable current.

Not using pin 7 at all - the RC is driven by pin 3.

I lowered the frequency still further - 8k2 & 3n3.

On Thu, 12 May 2011 17:55:33 +0100, "Ian Field"
wrote:

Running at the full Vcc of 16V and the full frequency of 500kHz the 555 got
so hot I had to add a clip-on heatsink.

Tried slowing it down to about 140kHz and the heatsink still gets pretty
warm.

Is this normal?

---
No.

Do you have pin 7 shorted to pin 8 or somehow connected to 16V?


--
JF

On Thu, 12 May 2011 17:55:33 +0100, "Ian Field"
wrote:

Running at the full Vcc of 16V and the full frequency of 500kHz the 555 got
so hot I had to add a clip-on heatsink.

Tried slowing it down to about 140kHz and the heatsink still gets pretty
warm.

Is this normal?

Thanks.


Post your schematic or a link to it.

...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 | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

Obama is not the solution, Obama is the problem!

"Jim Thompson" wrote in
message ...
On Thu, 12 May 2011 17:55:33 +0100, "Ian Field"
wrote:

Running at the full Vcc of 16V and the full frequency of 500kHz the 555
got
so hot I had to add a clip-on heatsink.

Tried slowing it down to about 140kHz and the heatsink still gets pretty
warm.

Is this normal?

Thanks.


Post your schematic or a link to it.

I thought you killfiled me.

Ian Field wrote:
Running at the full Vcc of 16V and the full frequency of 500kHz the 555 got
so hot I had to add a clip-on heatsink.

Tried slowing it down to about 140kHz and the heatsink still gets pretty
warm.

Is this normal?

Thanks.


Try again at a somewhat lower voltage, you may have exceeded
vcc for this particular unit and/or caused latching somewhere,
in which case almost the black magic smoke comes out.

"John Fields" wrote in message
...
On Thu, 12 May 2011 17:55:33 +0100, "Ian Field"
wrote:

Running at the full Vcc of 16V and the full frequency of 500kHz the 555
got
so hot I had to add a clip-on heatsink.

Tried slowing it down to about 140kHz and the heatsink still gets pretty
warm.

Is this normal?

---
No.

Do you have pin 7 shorted to pin 8 or somehow connected to 16V?

Pin 7 was working just fine when I had it hooked up to a fast pullup
SB/emitter follower for driving MOSFETs, its not connected to anything now.

"Sjouke Burry" wrote in message
...
Ian Field wrote:
Running at the full Vcc of 16V and the full frequency of 500kHz the 555
got so hot I had to add a clip-on heatsink.

Tried slowing it down to about 140kHz and the heatsink still gets pretty
warm.

Is this normal?

Thanks.
Try again at a somewhat lower voltage, you may have exceeded
vcc for this particular unit and/or caused latching somewhere,
in which case almost the black magic smoke comes out.


Almost every datasheet I've seen says 16V - ISTR the Hitachi DS says 18V.

On Thu, 12 May 2011 19:20:42 +0100, "Ian Field"
wrote:


"Jim Thompson" wrote in
message ...
On Thu, 12 May 2011 17:55:33 +0100, "Ian Field"
wrote:

Running at the full Vcc of 16V and the full frequency of 500kHz the 555
got
so hot I had to add a clip-on heatsink.

Tried slowing it down to about 140kHz and the heatsink still gets pretty
warm.

Is this normal?

Thanks.


Post your schematic or a link to it.

I thought you killfiled me.


That gets automagically withdrawn when a technical question is asked
;-)

...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 | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

Obama is not the solution, Obama is the problem!

On Thu, 12 May 2011 19:48:06 +0100, "Ian Field"
wrote:


"Sjouke Burry" wrote in message
...
Ian Field wrote:
Running at the full Vcc of 16V and the full frequency of 500kHz the 555
got so hot I had to add a clip-on heatsink.

Tried slowing it down to about 140kHz and the heatsink still gets pretty
warm.

Is this normal?

Thanks.
Try again at a somewhat lower voltage, you may have exceeded
vcc for this particular unit and/or caused latching somewhere,
in which case almost the black magic smoke comes out.


Almost every datasheet I've seen says 16V - ISTR the Hitachi DS says 18V.


Perhaps a large capacitive load?

...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 | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

Obama is not the solution, Obama is the problem!

"Jim Thompson" wrote in
message ...
On Thu, 12 May 2011 19:48:06 +0100, "Ian Field"
wrote:


"Sjouke Burry" wrote in message
...
Ian Field wrote:
Running at the full Vcc of 16V and the full frequency of 500kHz the 555
got so hot I had to add a clip-on heatsink.

Tried slowing it down to about 140kHz and the heatsink still gets
pretty
warm.

Is this normal?

Thanks.
Try again at a somewhat lower voltage, you may have exceeded
vcc for this particular unit and/or caused latching somewhere,
in which case almost the black magic smoke comes out.


Almost every datasheet I've seen says 16V - ISTR the Hitachi DS says 18V.


Perhaps a large capacitive load?


Been bench testing with no load (apart from driving the CR) and then with a
BC327/337 complementary emitter follower pair.

On Thu, 12 May 2011 20:38:39 +0100, "Ian Field"
wrote:


"Jim Thompson" wrote in
message ...
On Thu, 12 May 2011 19:48:06 +0100, "Ian Field"
wrote:


"Sjouke Burry" wrote in message
...
Ian Field wrote:
Running at the full Vcc of 16V and the full frequency of 500kHz the 555
got so hot I had to add a clip-on heatsink.

Tried slowing it down to about 140kHz and the heatsink still gets
pretty
warm.

Is this normal?

Thanks.
Try again at a somewhat lower voltage, you may have exceeded
vcc for this particular unit and/or caused latching somewhere,
in which case almost the black magic smoke comes out.


Almost every datasheet I've seen says 16V - ISTR the Hitachi DS says 18V.


Perhaps a large capacitive load?


Been bench testing with no load (apart from driving the CR) and then with a
BC327/337 complementary emitter follower pair.


Post your schematic or a link.

...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 | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

Obama is not the solution, Obama is the problem!

"Jim Thompson" wrote in
message ...
On Thu, 12 May 2011 20:38:39 +0100, "Ian Field"
wrote:


"Jim Thompson" wrote
in
message ...
On Thu, 12 May 2011 19:48:06 +0100, "Ian Field"
wrote:


"Sjouke Burry" wrote in message
...
Ian Field wrote:
Running at the full Vcc of 16V and the full frequency of 500kHz the
555
got so hot I had to add a clip-on heatsink.

Tried slowing it down to about 140kHz and the heatsink still gets
pretty
warm.

Is this normal?

Thanks.
Try again at a somewhat lower voltage, you may have exceeded
vcc for this particular unit and/or caused latching somewhere,
in which case almost the black magic smoke comes out.


Almost every datasheet I've seen says 16V - ISTR the Hitachi DS says
18V.


Perhaps a large capacitive load?


Been bench testing with no load (apart from driving the CR) and then with
a
BC327/337 complementary emitter follower pair.


Post your schematic or a link.


Its at the same location as my other PC with no internet.

Vcc is clamped by a 16V zener and has 680u + 334 mylar all fed by 68 Ohm
from VDD.

With CR= 3n3 & 8k2 its a standard astable except the CR is driven by pin 3
instead of pin 7 + pullup resistor.

There is the customary 10n from pin 5 to GND.

On Thu, 12 May 2011 21:16:15 +0100, "Ian Field"
wrote:


"Jim Thompson" wrote in
message ...
On Thu, 12 May 2011 20:38:39 +0100, "Ian Field"
wrote:


"Jim Thompson" wrote
in
message ...
On Thu, 12 May 2011 19:48:06 +0100, "Ian Field"
wrote:


"Sjouke Burry" wrote in message
.. .
Ian Field wrote:
Running at the full Vcc of 16V and the full frequency of 500kHz the
555
got so hot I had to add a clip-on heatsink.

Tried slowing it down to about 140kHz and the heatsink still gets
pretty
warm.

Is this normal?

Thanks.
Try again at a somewhat lower voltage, you may have exceeded
vcc for this particular unit and/or caused latching somewhere,
in which case almost the black magic smoke comes out.


Almost every datasheet I've seen says 16V - ISTR the Hitachi DS says
18V.


Perhaps a large capacitive load?


Been bench testing with no load (apart from driving the CR) and then with
a
BC327/337 complementary emitter follower pair.


Post your schematic or a link.


Its at the same location as my other PC with no internet.

Vcc is clamped by a 16V zener and has 680u + 334 mylar all fed by 68 Ohm
from VDD.

With CR= 3n3 & 8k2 its a standard astable except the CR is driven by pin 3
instead of pin 7 + pullup resistor.

There is the customary 10n from pin 5 to GND.


How do you post to SED ?:-)

...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 | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

Obama is not the solution, Obama is the problem!

"Jim Thompson" wrote in
message ...
On Thu, 12 May 2011 21:16:15 +0100, "Ian Field"
wrote:


"Jim Thompson" wrote
in
message ...
On Thu, 12 May 2011 20:38:39 +0100, "Ian Field"
wrote:


"Jim Thompson" wrote
in
message ...
On Thu, 12 May 2011 19:48:06 +0100, "Ian Field"
wrote:


"Sjouke Burry" wrote in message
. ..
Ian Field wrote:
Running at the full Vcc of 16V and the full frequency of 500kHz the
555
got so hot I had to add a clip-on heatsink.

Tried slowing it down to about 140kHz and the heatsink still gets
pretty
warm.

Is this normal?

Thanks.
Try again at a somewhat lower voltage, you may have exceeded
vcc for this particular unit and/or caused latching somewhere,
in which case almost the black magic smoke comes out.


Almost every datasheet I've seen says 16V - ISTR the Hitachi DS says
18V.


Perhaps a large capacitive load?


Been bench testing with no load (apart from driving the CR) and then
with
a
BC327/337 complementary emitter follower pair.


Post your schematic or a link.


Its at the same location as my other PC with no internet.

Vcc is clamped by a 16V zener and has 680u + 334 mylar all fed by 68 Ohm
from VDD.

With CR= 3n3 & 8k2 its a standard astable except the CR is driven by pin 3
instead of pin 7 + pullup resistor.

There is the customary 10n from pin 5 to GND.


How do you post to SED ?:-)

Infrequently.

On Thu, 12 May 2011 13:45:28 -0700, Jim Thompson
wrote:

On Thu, 12 May 2011 21:16:15 +0100, "Ian Field"
wrote:


"Jim Thompson" wrote in
message ...

Post your schematic or a link.


Its at the same location as my other PC with no internet.

Vcc is clamped by a 16V zener and has 680u + 334 mylar all fed by 68 Ohm
from VDD.

With CR= 3n3 & 8k2 its a standard astable except the CR is driven by pin 3
instead of pin 7 + pullup resistor.

There is the customary 10n from pin 5 to GND.


How do you post to SED ?:-)

...Jim Thompson
---
Indeed.

He could easily post an LTspice *.asc netlist to any of the text
groups or, using abse, post the same netlist as an attachment, which
will execute if the association is made between .asc and the LTspice
executable.

Failing that he could attach even a scanned, hand-drawn sketch to
abse.

--
JF

On Thu, 12 May 2011 21:59:28 +0100, "Ian Field"
wrote:


"Jim Thompson" wrote in
message ...

How do you post to SED ?:-)

Infrequently.

---
Practice makes perfect.

--
JF

On Thu, 12 May 2011 16:23:57 -0500, John Fields
wrote:

On Thu, 12 May 2011 13:45:28 -0700, Jim Thompson
wrote:

On Thu, 12 May 2011 21:16:15 +0100, "Ian Field"
wrote:


"Jim Thompson" wrote in
message ...

Post your schematic or a link.


Its at the same location as my other PC with no internet.

Vcc is clamped by a 16V zener and has 680u + 334 mylar all fed by 68 Ohm
from VDD.

With CR= 3n3 & 8k2 its a standard astable except the CR is driven by pin 3
instead of pin 7 + pullup resistor.

There is the customary 10n from pin 5 to GND.


How do you post to SED ?:-)

...Jim Thompson
---
Indeed.

He could easily post an LTspice *.asc netlist to any of the text
groups or, using abse, post the same netlist as an attachment, which
will execute if the association is made between .asc and the LTspice
executable.

Failing that he could attach even a scanned, hand-drawn sketch to
abse.

---
Or, God forbid, an ASCIImatic.

--
JF

"John Fields" schreef in bericht
...
On Thu, 12 May 2011 16:23:57 -0500, John Fields
wrote:

On Thu, 12 May 2011 13:45:28 -0700, Jim Thompson
wrote:

On Thu, 12 May 2011 21:16:15 +0100, "Ian Field"
wrote:


"Jim Thompson" wrote
in
message ...

Post your schematic or a link.


Its at the same location as my other PC with no internet.

Vcc is clamped by a 16V zener and has 680u + 334 mylar all fed by 68 Ohm
from VDD.

With CR= 3n3 & 8k2 its a standard astable except the CR is driven by pin
3
instead of pin 7 + pullup resistor.

There is the customary 10n from pin 5 to GND.


How do you post to SED ?:-)

...Jim Thompson
---
Indeed.

He could easily post an LTspice *.asc netlist to any of the text
groups or, using abse, post the same netlist as an attachment, which
will execute if the association is made between .asc and the LTspice
executable.

Failing that he could attach even a scanned, hand-drawn sketch to
abse.

---
Or, God forbid, an ASCIImatic.

--
JF

Well, it's not that bad. Much better anyway then the hand drawn flimsies
some other persons tend to provide
___
+-----+------------+----|___|-----
| | | 68
+-----------------)-----)-------+ |
| |8 |4 | |
| .-----------------. | |
| | V r | | |
| 7| c e | | |
| -|dis c s | | |
| | | | |
.-. | | | |
| | | | | |
| |8k2 | | | |
'-' | | | |
| 6| | | |
+-----------|thr | | |
| | | | |
| | |3| |
| | 555 out|-+-- |
| | | |
| | | |
| 5| | |
| +----|cnt | |
| | | | |
| | | | +----+-------+
| | | | | | |
| | 2| | | | |
+------)----|trg G | - | | +
| | | N | / --- ###
| | | D | Z16V - --- ---
--- --- '-----------------' ^ |330n |680u
---3n3 ---10n |1 | | |
| | | | | |
+------+-------------+---------------+----+-------+---
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de


petrus bitbyter

"John Fields" wrote in message
...
On Thu, 12 May 2011 21:59:28 +0100, "Ian Field"
wrote:


"Jim Thompson" wrote
in
message ...

How do you post to SED ?:-)

Infrequently.

---
Practice makes perfect.


Panic over - I replaced the 555 with a Signetics part, it still runs pretty
warm but is within safe limits without the clip on heatsink.

The one I took out was branded ST.

On Fri, 13 May 2011 11:50:14 +0200, "petrus bitbyter"
wrote:


"John Fields" schreef in bericht
.. .
On Thu, 12 May 2011 16:23:57 -0500, John Fields
wrote:

On Thu, 12 May 2011 13:45:28 -0700, Jim Thompson
wrote:

On Thu, 12 May 2011 21:16:15 +0100, "Ian Field"
wrote:


"Jim Thompson" wrote
in
message ...

Post your schematic or a link.


Its at the same location as my other PC with no internet.

Vcc is clamped by a 16V zener and has 680u + 334 mylar all fed by 68 Ohm
from VDD.

With CR= 3n3 & 8k2 its a standard astable except the CR is driven by pin
3
instead of pin 7 + pullup resistor.

There is the customary 10n from pin 5 to GND.


How do you post to SED ?:-)

...Jim Thompson
---
Indeed.

He could easily post an LTspice *.asc netlist to any of the text
groups or, using abse, post the same netlist as an attachment, which
will execute if the association is made between .asc and the LTspice
executable.

Failing that he could attach even a scanned, hand-drawn sketch to
abse.

---
Or, God forbid, an ASCIImatic.

--
JF

Well, it's not that bad. Much better anyway then the hand drawn flimsies
some other persons tend to provide
___
+-----+------------+----|___|-----
| | | 68
+-----------------)-----)-------+ |
| |8 |4 | |
| .-----------------. | |
| | V r | | |
| 7| c e | | |
| -|dis c s | | |
| | | | |
.-. | | | |
| | | | | |
| |8k2 | | | |
'-' | | | |
| 6| | | |
+-----------|thr | | |
| | | | |
| | |3| |
| | 555 out|-+-- |
| | | |
| | | |
| 5| | |
| +----|cnt | |
| | | | |
| | | | +----+-------+
| | | | | | |
| | 2| | | | |
+------)----|trg G | - | | +
| | | N | / --- ###
| | | D | Z16V - --- ---
--- --- '-----------------' ^ |330n |680u
---3n3 ---10n |1 | | |
| | | | | |
+------+-------------+---------------+----+-------+---
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de


petrus bitbyter

---
Good God, man, have you no decency?!!


..Vcc---------------------------+
.. |
.. +---------------------+ |
.. | | [68r]
.. [8k2] +---------+ | |
.. | | 555 | | |
.. +-----6-|TH OUT|-3-+---|---OUT
.. | |__ | |
.. +----2-O|TR Vcc|-8-----+
.. | | _| |
.. [3n3] +-5-|VC R|O-4-+--+-+-----+
.. | | | GND | |K | |+
.. | [10n] +----+----+ [Z16V][330n][680µ]
.. | | |1 | | |
..GND-+---+--------+---------+----+-----+



--
JF

On Fri, 13 May 2011 14:43:34 +0100, the renowned "Ian Field"
wrote:


"John Fields" wrote in message
.. .
On Thu, 12 May 2011 21:59:28 +0100, "Ian Field"
wrote:


"Jim Thompson" wrote
in
message ...

How do you post to SED ?:-)

Infrequently.

---
Practice makes perfect.


Panic over - I replaced the 555 with a Signetics part, it still runs pretty
warm but is within safe limits without the clip on heatsink.

The one I took out was branded ST.


What was the entire part number? NE555? SA555? SE555? or TS555?



Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

On Sat, 14 May 2011 15:13:16 -0400, Spehro Pefhany
wrote:

On Fri, 13 May 2011 14:43:34 +0100, the renowned "Ian Field"
wrote:


"John Fields" wrote in message
. ..
On Thu, 12 May 2011 21:59:28 +0100, "Ian Field"
wrote:


"Jim Thompson" wrote
in
message ...

How do you post to SED ?:-)

Infrequently.

---
Practice makes perfect.


Panic over - I replaced the 555 with a Signetics part, it still runs pretty
warm but is within safe limits without the clip on heatsink.

The one I took out was branded ST.


What was the entire part number? NE555? SA555? SE555? or TS555?



Best regards,
Spehro Pefhany

There's only a few ways to make a 555 run hot...

VDD higher than spec.

Huge capacitive (or resistive) load on the output

Mis-connecting "Discharge"

Clearly Ian, like lots of posters here, won't post their schematic for
fear of criticism... yet no-schematic is the guaranteed way to get
criticized ;-)

...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 | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

Romneycare is nothing like Obamacare
Except for those parts which are the same ;-)

"Jim Thompson" wrote in
message ...
On Sat, 14 May 2011 15:13:16 -0400, Spehro Pefhany
wrote:

On Fri, 13 May 2011 14:43:34 +0100, the renowned "Ian Field"
wrote:


"John Fields" wrote in message
...
On Thu, 12 May 2011 21:59:28 +0100, "Ian Field"
wrote:


"Jim Thompson"
wrote
in
message ...

How do you post to SED ?:-)

Infrequently.

---
Practice makes perfect.


Panic over - I replaced the 555 with a Signetics part, it still runs
pretty
warm but is within safe limits without the clip on heatsink.

The one I took out was branded ST.


What was the entire part number? NE555? SA555? SE555? or TS555?



Best regards,
Spehro Pefhany

There's only a few ways to make a 555 run hot...

VDD higher than spec.

Huge capacitive (or resistive) load on the output

Mis-connecting "Discharge"

Clearly Ian, like lots of posters here, won't post their schematic for
fear of criticism... yet no-schematic is the guaranteed way to get
criticized ;-)


The circuit is so simple the criticism is best deserved by those who can't
understand the description I gave.

On Sat, 14 May 2011 21:56:56 +0100, "Ian Field"
wrote:


"Jim Thompson" wrote in
message ...
On Sat, 14 May 2011 15:13:16 -0400, Spehro Pefhany
wrote:

On Fri, 13 May 2011 14:43:34 +0100, the renowned "Ian Field"
wrote:


"John Fields" wrote in message
m...
On Thu, 12 May 2011 21:59:28 +0100, "Ian Field"
wrote:


"Jim Thompson"
wrote
in
message ...

How do you post to SED ?:-)

Infrequently.

---
Practice makes perfect.


Panic over - I replaced the 555 with a Signetics part, it still runs
pretty
warm but is within safe limits without the clip on heatsink.

The one I took out was branded ST.


What was the entire part number? NE555? SA555? SE555? or TS555?



Best regards,
Spehro Pefhany

There's only a few ways to make a 555 run hot...

VDD higher than spec.

Huge capacitive (or resistive) load on the output

Mis-connecting "Discharge"

Clearly Ian, like lots of posters here, won't post their schematic for
fear of criticism... yet no-schematic is the guaranteed way to get
criticized ;-)


The circuit is so simple the criticism is best deserved by those who can't
understand the description I gave.


Are you really such a ****-head?

You're so ignorant you don't know the definition of "ignorant"... or
how to read and understand what I actually said.

I knew there was a reason I had you plonked before.

What it is... you don't know **** about electronics... Heat? You
clearly ****ed-up a simple circuit.

So go away and study panhandling... you'll need that knowledge to
survive :-)

...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 | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

Romneycare is nothing like Obamacare
Except for those parts which are the same ;-)

"Jim Thompson" wrote in
message ...
On Sat, 14 May 2011 21:56:56 +0100, "Ian Field"
wrote:


"Jim Thompson" wrote
in
message ...
On Sat, 14 May 2011 15:13:16 -0400, Spehro Pefhany
wrote:

On Fri, 13 May 2011 14:43:34 +0100, the renowned "Ian Field"
wrote:


"John Fields" wrote in message
om...
On Thu, 12 May 2011 21:59:28 +0100, "Ian Field"
wrote:


"Jim Thompson"
wrote
in
message ...

How do you post to SED ?:-)

Infrequently.

---
Practice makes perfect.


Panic over - I replaced the 555 with a Signetics part, it still runs
pretty
warm but is within safe limits without the clip on heatsink.

The one I took out was branded ST.


What was the entire part number? NE555? SA555? SE555? or TS555?



Best regards,
Spehro Pefhany

There's only a few ways to make a 555 run hot...

VDD higher than spec.

Huge capacitive (or resistive) load on the output

Mis-connecting "Discharge"

Clearly Ian, like lots of posters here, won't post their schematic for
fear of criticism... yet no-schematic is the guaranteed way to get
criticized ;-)


The circuit is so simple the criticism is best deserved by those who can't
understand the description I gave.


Are you really such a ****-head?

You're so ignorant you don't know the definition of "ignorant"... or
how to read and understand what I actually said.

I knew there was a reason I had you plonked before.


The absence of your contibutions would be a blessing.

"John Fields" wrote in message
news
On Fri, 13 May 2011 11:50:14 +0200, "petrus bitbyter"
wrote:


"John Fields" schreef in bericht
. ..
On Thu, 12 May 2011 16:23:57 -0500, John Fields
wrote:

On Thu, 12 May 2011 13:45:28 -0700, Jim Thompson
wrote:

On Thu, 12 May 2011 21:16:15 +0100, "Ian Field"
wrote:


"Jim Thompson"
wrote
in
message ...

Post your schematic or a link.


Its at the same location as my other PC with no internet.

Vcc is clamped by a 16V zener and has 680u + 334 mylar all fed by 68
Ohm
from VDD.

With CR= 3n3 & 8k2 its a standard astable except the CR is driven by
pin
3
instead of pin 7 + pullup resistor.

There is the customary 10n from pin 5 to GND.


How do you post to SED ?:-)

...Jim Thompson
---
Indeed.

He could easily post an LTspice *.asc netlist to any of the text
groups or, using abse, post the same netlist as an attachment, which
will execute if the association is made between .asc and the LTspice
executable.

Failing that he could attach even a scanned, hand-drawn sketch to
abse.

---
Or, God forbid, an ASCIImatic.

--
JF

Well, it's not that bad. Much better anyway then the hand drawn flimsies
some other persons tend to provide
___
+-----+------------+----|___|-----
| | | 68
+-----------------)-----)-------+ |
| |8 |4 | |
| .-----------------. | |
| | V r | | |
| 7| c e | | |
| -|dis c s | | |
| | | | |
.-. | | | |
| | | | | |
| |8k2 | | | |
'-' | | | |
| 6| | | |
+-----------|thr | | |
| | | | |
| | |3| |
| | 555 out|-+-- |
| | | |
| | | |
| 5| | |
| +----|cnt | |
| | | | |
| | | | +----+-------+
| | | | | | |
| | 2| | | | |
+------)----|trg G | - | | +
| | | N | / --- ###
| | | D | Z16V - --- ---
--- --- '-----------------' ^ |330n |680u
---3n3 ---10n |1 | | |
| | | | | |
+------+-------------+---------------+----+-------+---
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de


petrus bitbyter

---
Good God, man, have you no decency?!!


.Vcc---------------------------+
. |
. +---------------------+ |
. | | [68r]
. [8k2] +---------+ | |
. | | 555 | | |
. +-----6-|TH OUT|-3-+---|---OUT
. | |__ | |
. +----2-O|TR Vcc|-8-----+
. | | _| |
. [3n3] +-5-|VC R|O-4-+--+-+-----+
. | | | GND | |K | |+
. | [10n] +----+----+ [Z16V][330n][680µ]
. | | |1 | | |
.GND-+---+--------+---------+----+-----+


Close enough.

It still overheats (a new Sign' NE555 failed) even after replacing the 16V
zener with a 12V part and adding a second 68 Ohm resistor inseries as the
dropper.

It occurred to me that it didn't like driving the gate capacitance of an
IRF740, but it still does it with the MOSFET removed.

I've run the point of a scalpel between all the tracks on the stripboard to
eliminate any solder bridges I might have missed.

The only thing left I can think of is maybe I overdid the Vcc decoupling,
the 680u is a very low ESR from a VCR PSU and the 330n might only be making
matters worse.

Its well known that the 555 draws large current spikes during output
transitions, totally OTT decoupling could be whats cooking it!

On Mon, 16 May 2011 15:51:15 +0100, "Ian Field" wrote:
....
.Vcc---------------------------+
. |
. +---------------------+ |
. | | [68r]
. [8k2] +---------+ | |
. | | 555 | | |
. +-----6-|TH OUT|-3-+---|---OUT
. | |__ | |
. +----2-O|TR Vcc|-8-----+
. | | _| |
. [3n3] +-5-|VC R|O-4-+--+-+-----+
. | | | GND | |K | |+
. | [10n] +----+----+ [Z16V][330n][680?
. | | |1 | | |
.GND-+---+--------+---------+----+-----+


Close enough.

It still overheats (a new Sign' NE555 failed) even after replacing the 16V
zener with a 12V part and adding a second 68 Ohm resistor inseries as the
dropper.

From??

It occurred to me that it didn't like driving the gate capacitance of an
IRF740, but it still does it with the MOSFET removed.

It's a little MOSFET, what series gate resistor did you use?

I've run the point of a scalpel between all the tracks on the stripboard to
eliminate any solder bridges I might have missed.

The only thing left I can think of is maybe I overdid the Vcc decoupling,
the 680u is a very low ESR from a VCR PSU and the 330n might only be making
matters worse.

Its well known that the 555 draws large current spikes during output
transitions, totally OTT decoupling could be whats cooking it!

More likely the capacitive load?

Tried a pnp + npn follower for the gate drive? Pointless taking a
gate too far past 10V as you only have to suck the charge out of the
gate again to turn the MOSFET off.

555 has what 200mA output rating? 12V and 200mA gives what series
gate resistor value to stay in spec? Allow for the output drop
driving that 200mA when working out resistor.

Grant.

"Grant" wrote in message
...
On Mon, 16 May 2011 15:51:15 +0100, "Ian Field"
wrote:
...
.Vcc---------------------------+
. |
. +---------------------+ |
. | | [68r]
. [8k2] +---------+ | |
. | | 555 | | |
. +-----6-|TH OUT|-3-+---|---OUT
. | |__ | |
. +----2-O|TR Vcc|-8-----+
. | | _| |
. [3n3] +-5-|VC R|O-4-+--+-+-----+
. | | | GND | |K | |+
. | [10n] +----+----+ [Z16V][330n][680?
. | | |1 | | |
.GND-+---+--------+---------+----+-----+


Close enough.

It still overheats (a new Sign' NE555 failed) even after replacing the 16V
zener with a 12V part and adding a second 68 Ohm resistor inseries as the
dropper.

From??

The second 68 Ohm resistor being in addition to the existing 68 Ohm resistor
which was given in my original description and shown in both examples of
ASCII art produced by other contributors.


It occurred to me that it didn't like driving the gate capacitance of an
IRF740, but it still does it with the MOSFET removed.

It's a little MOSFET, what series gate resistor did you use?

I've run the point of a scalpel between all the tracks on the stripboard
to
eliminate any solder bridges I might have missed.

The only thing left I can think of is maybe I overdid the Vcc decoupling,
the 680u is a very low ESR from a VCR PSU and the 330n might only be
making
matters worse.

Its well known that the 555 draws large current spikes during output
transitions, totally OTT decoupling could be whats cooking it!

More likely the capacitive load?

Like the parasitic capacitance of pin 3 and about half-inch of stripboard
track overwhelmed the output when I removed the MOSFET?


Tried a pnp + npn follower for the gate drive? Pointless taking a
gate too far past 10V as you only have to suck the charge out of the
gate again to turn the MOSFET off.

555 has what 200mA output rating? 12V and 200mA gives what series
gate resistor value to stay in spec? Allow for the output drop
driving that 200mA when working out resistor.

Grant.

In article ,
"Ian Field" wrote:

....
It still overheats (a new Sign' NE555 failed) even after replacing the 16V
zener with a 12V part and adding a second 68 Ohm resistor inseries as the
dropper.

It occurred to me that it didn't like driving the gate capacitance of an
IRF740, but it still does it with the MOSFET removed.

I've run the point of a scalpel between all the tracks on the stripboard to
eliminate any solder bridges I might have missed.

The only thing left I can think of is maybe I overdid the Vcc decoupling,
the 680u is a very low ESR from a VCR PSU and the 330n might only be making
matters worse.

Its well known that the 555 draws large current spikes during output
transitions, totally OTT decoupling could be whats cooking it!

The original 555 does run hot. That's why the CMOS version is popular.

No, it doesn't like directly driving big MOSFETs. When the MOSFET gate
is driven low, inductive ringing on the drain appears on the gate via
capacitive coupling. That ringing wears out the 555 chip by pushing the
output pin below zero volts.

A Schmitt trigger inverting MOSFET driver very roughly resembles a 555
chip having pins 2 and 6 tied together. It could be good enough for
blinking lights and regulated power inverters.
--
I will not see posts from Google or e-mails from Yahoo because I must
filter them as spam

"Kevin McMurtrie" wrote in message
...
In article ,
"Ian Field" wrote:

...
It still overheats (a new Sign' NE555 failed) even after replacing the
16V
zener with a 12V part and adding a second 68 Ohm resistor inseries as the
dropper.

It occurred to me that it didn't like driving the gate capacitance of an
IRF740, but it still does it with the MOSFET removed.

I've run the point of a scalpel between all the tracks on the stripboard
to
eliminate any solder bridges I might have missed.

The only thing left I can think of is maybe I overdid the Vcc decoupling,
the 680u is a very low ESR from a VCR PSU and the 330n might only be
making
matters worse.

Its well known that the 555 draws large current spikes during output
transitions, totally OTT decoupling could be whats cooking it!

The original 555 does run hot. That's why the CMOS version is popular.

No, it doesn't like directly driving big MOSFETs. When the MOSFET gate
is driven low, inductive ringing on the drain appears on the gate via
capacitive coupling. That ringing wears out the 555 chip by pushing the
output pin below zero volts.

Before I changed the 16V zener to 12V it was getting hot enough to self
destruct, at 12V it still needs a clip on heatsink to keep the temp' in save
limits.

By yesterday I was starting to suspect the very low ESR 680u + 330n
decoupling was way OTT and incompatible with the 555 drawing large current
spikes during output transitions - replacing the 680u with a regular quality
330u and deleting the 330n made it run a little cooler, but it still needs
the heatsink.

My original idea required using pin 7 way out of published spec, the
datasheet doesn't say specifically whether it applies to pin 7, but most
pins on the 7555 have an inherent substrate SCR structure so there would be
a risk of latchup and self destruct if I'd attempted what I wanted to do on
a CMOS part.

On Mon, 16 May 2011 15:51:15 +0100, "Ian Field"
wrote:


"John Fields" wrote in message
news
On Fri, 13 May 2011 11:50:14 +0200, "petrus bitbyter"
wrote:


"John Fields" schreef in bericht
...
On Thu, 12 May 2011 16:23:57 -0500, John Fields
wrote:

On Thu, 12 May 2011 13:45:28 -0700, Jim Thompson
wrote:

On Thu, 12 May 2011 21:16:15 +0100, "Ian Field"
wrote:


"Jim Thompson"
wrote
in
message ...

Post your schematic or a link.


Its at the same location as my other PC with no internet.

Vcc is clamped by a 16V zener and has 680u + 334 mylar all fed by 68
Ohm
from VDD.

With CR= 3n3 & 8k2 its a standard astable except the CR is driven by
pin
3
instead of pin 7 + pullup resistor.

There is the customary 10n from pin 5 to GND.


How do you post to SED ?:-)

...Jim Thompson
---
Indeed.

He could easily post an LTspice *.asc netlist to any of the text
groups or, using abse, post the same netlist as an attachment, which
will execute if the association is made between .asc and the LTspice
executable.

Failing that he could attach even a scanned, hand-drawn sketch to
abse.

---
Or, God forbid, an ASCIImatic.

--
JF

Well, it's not that bad. Much better anyway then the hand drawn flimsies
some other persons tend to provide
___
+-----+------------+----|___|-----
| | | 68
+-----------------)-----)-------+ |
| |8 |4 | |
| .-----------------. | |
| | V r | | |
| 7| c e | | |
| -|dis c s | | |
| | | | |
.-. | | | |
| | | | | |
| |8k2 | | | |
'-' | | | |
| 6| | | |
+-----------|thr | | |
| | | | |
| | |3| |
| | 555 out|-+-- |
| | | |
| | | |
| 5| | |
| +----|cnt | |
| | | | |
| | | | +----+-------+
| | | | | | |
| | 2| | | | |
+------)----|trg G | - | | +
| | | N | / --- ###
| | | D | Z16V - --- ---
--- --- '-----------------' ^ |330n |680u
---3n3 ---10n |1 | | |
| | | | | |
+------+-------------+---------------+----+-------+---
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de


petrus bitbyter

---
Good God, man, have you no decency?!!


.Vcc---------------------------+
. |
. +---------------------+ |
. | | [68r]
. [8k2] +---------+ | |
. | | 555 | | |
. +-----6-|TH OUT|-3-+---|---OUT
. | |__ | |
. +----2-O|TR Vcc|-8-----+
. | | _| |
. [3n3] +-5-|VC R|O-4-+--+-+-----+
. | | | GND | |K | |+
. | [10n] +----+----+ [Z16V][330n][680µ]
. | | |1 | | |
.GND-+---+--------+---------+----+-----+


Close enough.

It still overheats (a new Sign' NE555 failed) even after replacing the 16V
zener with a 12V part and adding a second 68 Ohm resistor inseries as the
dropper.

It occurred to me that it didn't like driving the gate capacitance of an
IRF740, but it still does it with the MOSFET removed.

I've run the point of a scalpel between all the tracks on the stripboard to
eliminate any solder bridges I might have missed.

The only thing left I can think of is maybe I overdid the Vcc decoupling,
the 680u is a very low ESR from a VCR PSU and the 330n might only be making
matters worse.

Its well known that the 555 draws large current spikes during output
transitions, totally OTT decoupling could be whats cooking it!

---
According to Maxim:

http://datasheets.maxim-ic.com/en/ds...55-ICM7556.pdf


the current in the spike peaks at about 400mA and zeroes out about
200ns layer, so that's about 200mA average over the 200ns period.

Then, since:

W = qV = (It)V = 2e-1A * 2e-7s * 1.2e1V = 4.8e-7 joules,

that's about 4.8e-7J per spike.

If you're switching at 100kHz, then, you'll have 200,000 spikes per
second, which amounts to a total of

P = Wn = 4.8e-7J * 2e5 = 9.6e-2W = 96 milliwatts.

According to Signetics, the Absolute Maximum power dissipation is
600mW, so it doesn't seem like one-sixth of that should cause a
problem.

Why don't you measure the current spikes and see what's happening?

--
JF

On Tue, 17 May 2011 14:07:28 +0100, "Ian Field"
wrote:


"Kevin McMurtrie" wrote in message
.. .
In article ,
"Ian Field" wrote:

...
It still overheats (a new Sign' NE555 failed) even after replacing the
16V
zener with a 12V part and adding a second 68 Ohm resistor inseries as the
dropper.

It occurred to me that it didn't like driving the gate capacitance of an
IRF740, but it still does it with the MOSFET removed.

I've run the point of a scalpel between all the tracks on the stripboard
to
eliminate any solder bridges I might have missed.

The only thing left I can think of is maybe I overdid the Vcc decoupling,
the 680u is a very low ESR from a VCR PSU and the 330n might only be
making
matters worse.

Its well known that the 555 draws large current spikes during output
transitions, totally OTT decoupling could be whats cooking it!

The original 555 does run hot. That's why the CMOS version is popular.

No, it doesn't like directly driving big MOSFETs. When the MOSFET gate
is driven low, inductive ringing on the drain appears on the gate via
capacitive coupling. That ringing wears out the 555 chip by pushing the
output pin below zero volts.

Before I changed the 16V zener to 12V it was getting hot enough to self
destruct, at 12V it still needs a clip on heatsink to keep the temp' in save
limits.

By yesterday I was starting to suspect the very low ESR 680u + 330n
decoupling was way OTT and incompatible with the 555 drawing large current
spikes during output transitions - replacing the 680u with a regular quality
330u and deleting the 330n made it run a little cooler, but it still needs
the heatsink.

---
The only reason you'd need the electrolytic is if you had really long
leads from the supply, and 100nF right across pins 1 and 8 ought to be
more than enough to take care of the spike.
---

My original idea required using pin 7 way out of published spec, the
datasheet doesn't say specifically whether it applies to pin 7, but most
pins on the 7555 have an inherent substrate SCR structure so there would be
a risk of latchup and self destruct if I'd attempted what I wanted to do on
a CMOS part.

---
So refresh my memory; what are you trying to do?

--
JF

On Tue, 17 May 2011 12:33:41 -0500, John Fields
wrote:

On Tue, 17 May 2011 14:07:28 +0100, "Ian Field"
wrote:


"Kevin McMurtrie" wrote in message
. ..
In article ,
"Ian Field" wrote:

...
It still overheats (a new Sign' NE555 failed) even after replacing the
16V
zener with a 12V part and adding a second 68 Ohm resistor inseries as the
dropper.

It occurred to me that it didn't like driving the gate capacitance of an
IRF740, but it still does it with the MOSFET removed.

I've run the point of a scalpel between all the tracks on the stripboard
to
eliminate any solder bridges I might have missed.

The only thing left I can think of is maybe I overdid the Vcc decoupling,
the 680u is a very low ESR from a VCR PSU and the 330n might only be
making
matters worse.

Its well known that the 555 draws large current spikes during output
transitions, totally OTT decoupling could be whats cooking it!

The original 555 does run hot. That's why the CMOS version is popular.

No, it doesn't like directly driving big MOSFETs. When the MOSFET gate
is driven low, inductive ringing on the drain appears on the gate via
capacitive coupling. That ringing wears out the 555 chip by pushing the
output pin below zero volts.

Before I changed the 16V zener to 12V it was getting hot enough to self
destruct, at 12V it still needs a clip on heatsink to keep the temp' in save
limits.

By yesterday I was starting to suspect the very low ESR 680u + 330n
decoupling was way OTT and incompatible with the 555 drawing large current
spikes during output transitions - replacing the 680u with a regular quality
330u and deleting the 330n made it run a little cooler, but it still needs
the heatsink.

---
The only reason you'd need the electrolytic is if you had really long
leads from the supply, and 100nF right across pins 1 and 8 ought to be
more than enough to take care of the spike.
---

My original idea required using pin 7 way out of published spec, the
datasheet doesn't say specifically whether it applies to pin 7, but most
pins on the 7555 have an inherent substrate SCR structure so there would be
a risk of latchup and self destruct if I'd attempted what I wanted to do on
a CMOS part.

---
So refresh my memory; what are you trying to do?

Find his asshole with a mirror, a flashlight and a helper... but Ian
is failing ;-)

...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 | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

Romneycare is nothing like Obamacare
Except for those parts which are the same ;-)

"Jim Thompson" wrote in
message ...
On Tue, 17 May 2011 12:33:41 -0500, John Fields
wrote:

On Tue, 17 May 2011 14:07:28 +0100, "Ian Field"
wrote:


"Kevin McMurtrie" wrote in message
.. .
In article ,
"Ian Field" wrote:

...
It still overheats (a new Sign' NE555 failed) even after replacing the
16V
zener with a 12V part and adding a second 68 Ohm resistor inseries as
the
dropper.

It occurred to me that it didn't like driving the gate capacitance of
an
IRF740, but it still does it with the MOSFET removed.

I've run the point of a scalpel between all the tracks on the
stripboard
to
eliminate any solder bridges I might have missed.

The only thing left I can think of is maybe I overdid the Vcc
decoupling,
the 680u is a very low ESR from a VCR PSU and the 330n might only be
making
matters worse.

Its well known that the 555 draws large current spikes during output
transitions, totally OTT decoupling could be whats cooking it!

The original 555 does run hot. That's why the CMOS version is popular.

No, it doesn't like directly driving big MOSFETs. When the MOSFET gate
is driven low, inductive ringing on the drain appears on the gate via
capacitive coupling. That ringing wears out the 555 chip by pushing
the
output pin below zero volts.

Before I changed the 16V zener to 12V it was getting hot enough to self
destruct, at 12V it still needs a clip on heatsink to keep the temp' in
save
limits.

By yesterday I was starting to suspect the very low ESR 680u + 330n
decoupling was way OTT and incompatible with the 555 drawing large
current
spikes during output transitions - replacing the 680u with a regular
quality
330u and deleting the 330n made it run a little cooler, but it still
needs
the heatsink.

---
The only reason you'd need the electrolytic is if you had really long
leads from the supply, and 100nF right across pins 1 and 8 ought to be
more than enough to take care of the spike.
---

My original idea required using pin 7 way out of published spec, the
datasheet doesn't say specifically whether it applies to pin 7, but most
pins on the 7555 have an inherent substrate SCR structure so there would
be
a risk of latchup and self destruct if I'd attempted what I wanted to do
on
a CMOS part.

---
So refresh my memory; what are you trying to do?

Find his asshole with a mirror, a flashlight and a helper... but Ian
is failing ;-)


At least I'm not a cantankerous old fart.