"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.