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EEVblog #392 – 555 LED PWM Hack

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EEVblog:


Dave.

Mr Smiley:
Hi,

The advantage of the single pnp output transistor that Dave chose is that it's base resistor is simply grounded by the open collector output of pin 7. All you really have to be aware of with pin 7 is Ic max and Vce Max. Couldn’t be any simpler.  :-DD

(maybe a pull up resistor for the base of the pnp, but it seems not to need it )

Mr Smiley  :)

IanB:
"There's nothing wrong with a bit of heat shrink"

Well maybe, but I'm not so sure. I believe a few of us would have a desire for a mounting arrangement with a little more polish. It's a fancy expensive instrument, it surely wouldn't hurt to have a nice looking box with a knob for the dimming control?

EEVblog:

--- Quote from: IanB on November 29, 2012, 03:09:41 am ---"There's nothing wrong with a bit of heat shrink"
Well maybe, but I'm not so sure. I believe a few of us would have a desire for a mounting arrangement with a little more polish. It's a fancy expensive instrument, it surely wouldn't hurt to have a nice looking box with a knob for the dimming control?

--- End quote ---

Of course not, you can do whatever you want, and I support you. I'm happy with heatshrink  :-+

Dave.

John Wilson:

--- Quote from: Mr Smiley on November 29, 2012, 12:24:02 am ---Hi,

The advantage of the single pnp output transistor that Dave chose is that it's base resistor is simply grounded by the open collector output of pin 7. All you really have to be aware of with pin 7 is Ic max and Vce Max. Couldn’t be any simpler.  :-DD

(maybe a pull up resistor for the base of the pnp, but it seems not to need it )

Mr Smiley  :)

--- End quote ---

Ok, here's a perhaps stupid question for you. What would be required to use an NPN transistor?

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