Re: Switching +/-12V from 6/0V

On Jul 13, 7:51 am, George <gh424NO824S...@xxxxxxx> wrote:
In article <f77kvn$2k...@xxxxxxxxxxxxxxxxxxx>,
ja...@xxxxxxxxxxx says...

>> I tried using two transistors to do this. The 555
>> Output drives the gate of an NPN, with the emitter
>> grounded. The collector of the NPN sinks the base of a
>> PNP, with the emitter connected to +12V, and the
>> collector connected through the solenoid to the -12V
>> lead of the capacitor. And that kinda works. Of
>> course it only lets the cap discharge to ground
>> (because the emitter of the NPN is at ground). So the
>> button push is really short, and I'm not sure it's
>> going to be long enough to be reliable.

> if too short use a larger capacitor.

> your circuit discharges the capacitor from both ends so
> switching one end only shouldn;'t be a problem.

> or try this.

> ------------------+- +10
> |
> +6 --+------------+- |
> | | |
> | + |
> [1k] / |
> | |/ |
> +--[10k]--|~ PNP
> / |\ load
> |/ \
> -[10k]--| NPN + |
> |\| | |
> ~\ | +
> | [1K] /
> -----+--- 0V | |/
> +---| NPN
> | |\|
> 100K ~\
> | |
> +------+-- -10

> Bye.
> Jasen

Ok, thanks very much, Jasen. Yes, I think this is gonna do
it. Three transistors work.

But I'm confused by the 1k resistor at the upper left. It
looks like it just needlessly dumps current through the NPN.

That's kind of optional, but good practice, to turn the NPN securely
OFF.

Wouldn't this work as well and use less power?

> ------------------+- +10
> |
> +6 ----------+----+- |
> | | |
> 100k + |
> | / |
> | |/ |
> +-[10k]-+-|~ PNP
> / |\ load
> |/ \
> -[10k]--| NPN + |
> |\| | |
> ~\ | +
> | [1K] /
> -----+--- 0V | |/
> +---| NPN
> | |\|
> 100K ~\
> | |
> +------+-- -10

Thanks again.

George

You could also do something like this:
+10v
R1 ---
input >--[1k]---. |
| Q1 +------+
'>| PNP | |
|---. [load] |
/| | | |
| --- +-|>|--+ D1
| GND |
| |/
+------------| Q2
R2 | |>. NPN
[10k] |
| |
+--------------+--- -10v

Cheers,
James Arthur

.

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