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Date: Sat, 18 Jan 2003 21:42:52 -0700
From: Jim Drew
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Subject: Transistor leaking? :)
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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??
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