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Re: New opto coupler/fiber receiver

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  • sleeper75se
    ... attachment) Thanks! I ve made and uploaded a SwitcherCAD schematic and screen dump. The specs differ a bit from my previous simulation. Apparently the laws
    Message 1 of 4 , Mar 30, 2002
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      --- In buildcheapeeg@y..., "Joerg Hansmann" <info@j...> wrote:
      > Hi,
      >
      > ----- Original Message -----
      > From: sleeper75se <sleeper75se@y...>
      > To: <buildcheapeeg@y...>
      > Sent: Friday, March 29, 2002 6:00 PM
      > Subject: [buildcheapeeg] New opto coupler/fiber receiver
      > ...
      >
      > > Joerg: I failed to import the MAX987 into SwitcherCAD, but if you
      > > want to take a closer look at this circuit, I guess you know how!
      >
      > It was a bit of patching required. But here it is (in the
      attachment)

      Thanks!

      I've made and uploaded a SwitcherCAD schematic and screen dump. The
      specs differ a bit from my previous simulation. Apparently the laws
      of "physics" differ a bit between SPICE simulators.

      http://groups.yahoo.com/group/buildcheapeeg/files/hardware%
      20design/RS232TX/

      Current: +3.5mA/-2.5mA at 3kOhm/1000pF load.
      Propagation delay: (rise/fall) 1.25us/1.75us at this load.

      I think this one looks promising. Comments?

      Regards,

      Andreas
    • sleeper75se
      ... A simple change increases the speed *and* lowers the current consumption (how often does this happen? :-). Replace the 10k resistors with 47k and add two
      Message 2 of 4 , Apr 4, 2002
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        --- In buildcheapeeg@y..., "sleeper75se" <sleeper75se@y...> wrote:

        > Current: +3.5mA/-2.5mA at 3kOhm/1000pF load.
        > Propagation delay: (rise/fall) 1.25us/1.75us at this load.

        A simple change increases the speed *and* lowers the current
        consumption (how often does this happen? :-).

        Replace the 10k resistors with 47k and add two 470pF (exact value not
        critical) capacitors, one between the base of Q1 and the comparator
        output, and the other between the base of Q3 and the comparator
        output. (Schematic is updated...)

        The capacitors work as shortcuts for the base currents during
        switching, causing Q1 and Q3 to change faster and sooner,
        significantly reducing the time when both transistors are conducting
        simultaneously (which wastes current).

        New data:

        Current +0.5mA/-1.6mA at 3kOhm/1000pF load.
        Propagation delay: (rise/fall) 300ns/200ns at this load.

        http://groups.yahoo.com/group/buildcheapeeg/files/hardware%
        20design/RS232TX/

        Andreas
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