Re: newby needs help

Hi Reg, I used the MPSH10 in simple RF circuits many years ago, and 
discovered that it made for quite a nice high speed switch, but it isn't 
something I've done for almost 20 years, although I have a tray full of 
them somewhere!

Al

On 2/03/2015 4:04 AM, Reginald Beardsley [email protected] [msp430] wrote:
> Al,
>
> Thanks.  That matches my experience.   The DCO MOD makes the timing quite inconsistent.  With the 8 MHz DCO calibrated setting I can see the pulses vary.  There is a complex relationship between the DCO dither and the PWM timer settings, so not adequate for precise work.  Which is why I've been using ACLK w/ the 32 KHz xtal.  Still very impressive for such a cheap piece of silicon.  It's quite hard to get anything off chip to switch that fast.  The fastest pulse I can get switching a 2N3904 is 200-250 ns. And it takes a lot of drive to get it to switch on or off in 100 ns, so I backed off to keep things from getting too hot.  Ive been  looking for a low cost transistor w/ a higher fT, but haven't ordered any yet.
>
> Interesting tidbit.  The 2N3904 has a nice clean ramp up and down whereas a 2N2222 has rather wiggly rise and fall slopes.  It's quite a remarkable difference.  I'm concerned about the pulse spectrum, so the 2N3904 is much preferable.  It has a sinc(x) transfer function with the first zero at 8-10 MHz.
>
> Have Fun!
> Reg
>
>
>
>
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> Posted by: Reginald Beardsley <[email protected]>
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