Re: High Side Pulse Transmitter



Winfield Hill wrote: 
John Larkin wrote...

Fred Bloggs wrote:

Winfield Hill wrote:

Here are Jeff Stout's specs:

1. True logic; high input produces high output, etc.
2. Operates with Vcc from 24V to 50V.
3. High output is slightly less than Vcc, low is better than
6V less than Vcc (exa, Vh = Vcc - 0.5, Vl = Vcc - 6.0)
4. Rising and falling edges should be as fast as possible.
5. Load is from 10mA to a maximum of 125mA, and capacitance
from 0 to about 1.5uF.
6. spends most of its time in the high state. 7. It transmits a signal between 1200 BAUD, and 9600 BAUD 

Here's something like the five-part circuit I imagine John had
in mind.  It can provide a non-inverting 6V output with better
than 10us risetime, assuming high-gain transistors, like those
sold by Zetex.  The circuit features a level-shifting current
source (sink actually), which also sets the 6V output swing for
the emitter followers.  A power resistor can be added in Q3's
collector for current limiting (the 6th part John mentioned).

      ------+------+---- + rail
            |      |   24 to 50V
           1.0k    |
            |    |/
            +----|
            |    |\e
            |  Q3  |    noninverting 6V swing
            |      +--- output to 1.5 uF load
            |  Q2  |
            |    |/e    Imax = 750mA
            +----|      BJT beta > 150
            |    |\     dv/dt = i/C = 6V in < 12us
        Q1  |      |
          |/       |
   +5 ----|      gnd etc
          |\e  |
    620     |  V  6.3 mA for
  o--/\/\---'     logic LO
 IN: 5V cmos logic
 with 60-ohm gate Ron

Just to show it can be done with five parts.  A few more parts
could be used to improve the circuit, of course.  Jeff can test
it with spice, if he has the right transistor models.

Now you know that circuit is unusable- so you haven't "done" 

anything with those five parts.

What's unusable about it? It's simple, it satisfies all the stated
requirements and, more important, it should work in the application.



 Hi John.  I surely don't know what Fred is talking about.  Perhaps
 he's referring to my circuit using BJTs instead of FETs?  Nah, his
 latest circuit uses BJTs.  Perhaps he just prefers his solution:

Fred Bloggs wrote...

My latest "parts rich" el cheapo looked something like this- it can drive indefinitely long lines if you lower the baud rate and easily
does 1200 baud into 1.5u- you can make it noninverting by putting
5V on T4 base and driving the bottom of the 1K emitter resistor with
the CMOS signal:
24V-48V
VCC
|
+----+---------+----+-------+-----------+-------->
| | | | | |
.-. | | .-. .-. .-.
100K| | | |47p| | | | 4.7R| |
| | z === | | | | metal| |
'-' A6.2V | '-' '-' oxide'-'
| | |2.2K| 220R| |
| | +----+ | |/
| | | | +---| T1
| | | | | |>
| | 56R | | | | _
| +-|>|-|>|-|__|-+ +-----+ +--|_|--->
| | | | | | F1
| | | v | | 1/2A
| | | - | |<
| | | | +---| T2
| | | | |\
| | | |< |
+------------------------+-----| T5 |
| | | |\ |
| | z | |
.-. | A6.2V .-. .-.
| | | | 100R| | 12R| |
| | | - | | metal| |
'-' | v '-' oxide'-'
|1.8K| | | |
| +----|--------------+-------+-----------+
5V | | - | |
CMOS |/ | ___ ^ |< |
o----| T4 +-------|___|--+-----| T3 |
|> | 470R |\ |+
| | | ===
.-. .-. .-. |100U
| |1K | |1.2K | |100 |
| | | | | | |
'-' '-' '-' |
| | | |
+---------+----------------------+-----------+-------->
===
GND 


 Fred, one comment.  Small is beautiful.  :>)  Oh, a second comment,
 wasn't the circuit supposed to be non-inverting?



Yep- I told him how to do that by making T4 a common base, but one thing everyone overlooks with that idea is that he might not have 5V available at the driver, just the signal, so that's just more parts to derive the base voltage from the high voltage.

.

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