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From: Spehro Pefhany
Subject: Re: Transistor leaking? :)
X-Newsreader: Forte Agent 1.93/32.576 English (American)
Date: Sun, 19 Jan 2003 05:00:26 GMT
NNTP-Posting-Date: Sun, 19 Jan 2003 00:00:26 EST
On Sat, 18 Jan 2003 21:42:52 -0700, the renowned Jim Drew
>Ok, I have an interesting problem. I designed a simple circuit to allow
>a microprocessor to be turned on and held on with a single push button
>switch (a soft power switch). The problem I am having is that there is
>1.0xx volts and .47ma leaking out of the transistor all of the time.
>The circuit is simple:
>.. 9v Battery |----+---------+
>.. | |
>.. | \
>.. | / 100K
>.. \ E \ PIC <-----|>|---+
>.. \ / | |
>.. \| B | 10K Diode | -----
>.. FZT705 |------+----------/\/\/\/--+--|>|---+-O O
>.. /| | |
>.. / | |
>.. To 7805<-----+/ C | |
>.. | GND
>.. C |
>.. 10K B |/
>.. To HOLD pin on PIC >------/\/\/\/---+------| 2N2222A
>.. | |\
>.. / \
>.. \ E \
>.. 100K / |
>.. \ |
>.. | |
>.. | |
>.. GND GND
>When the button is pressed, the battery voltage flows through the FZT705
>transistor (which can handle the 1 amp of current needed with the 7805
>voltage regulator). When the PIC powers up, it sets a bit that holds
>the power to be on. The 2nd diode isolates the push button and feeds
>the push button to one of the input lines of the PIC (so it can be used
>for data input after the system is powered up).
>Now, why would I be getting voltage out of the FZT705 when the button is
>not being pressed??
Stupid question, perhaps, but are you sure there are no misteaks in
your circuit? Particularly the FZT705 pinout (B-C-E from the top) and
the polarity of the diode to the PIC pin.
Second stupid question.. you've measured the voltage on the base
of the 2N2222A and it is zero?
Third stupid question.. you've put a scope on the PIC pin if
the voltage isn't quite zero?
"it's the network..." "The Journey is the reward"
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