[paparazzi-commits] [4656]

[antoine drouin]

Revision: 4656
          http://svn.sv.gnu.org/viewvc/?view=rev&root=paparazzi&revision=4656
Author:   poine
Date:     2010-03-10 12:45:33 +0000 (Wed, 10 Mar 2010)
Log Message:
-----------


Added Paths:
-----------
    paparazzi4/trunk/hw/booz/README.power_board

Added: paparazzi4/trunk/hw/booz/README.power_board
===================================================================
--- paparazzi4/trunk/hw/booz/README.power_board                         (rev 0)
+++ paparazzi4/trunk/hw/booz/README.power_board 2010-03-10 12:45:33 UTC (rev 
4656)
@@ -0,0 +1,22 @@
+http://ourworld.compuserve.com/homepages/Bill_Bowden/page9.htm
+
+
+
+
+This circuit was adapted from the "Toggle Switch Debounced Pushbutton" by John 
Lundgren. It is particularly useful in controlling a load from several 
locations where the load may be switched on from one location and switched off 
from another. Any number of momentary (N/O) switches or push buttons may be 
connected in parallel.
+
+The circuit uses a N-channel power MOSFET to control the load and can supply 
fairly large currents depending on the MOSFET used. The IRFZ44 is a 50 amp 
device available at Radio Shack for $2.99 and the IRF10 is a 4 amp device 
available for a dollar less.
+
+The combination (10K, 10uF and diode) on the left side of the schematic 
insures the circuit powers on with the MOSFET turned off and the NPN transistor 
conducting. These components can be omitted if the initial power-on condition 
is not a concern. In this initial state (MOSFET off), the voltage at the gate 
of the MOSFET will be near zero and the voltage on the 1uF capacitor connected 
to the switches will also be near zero.
+
+When a switch is closed, the 1uF capacitor is connected to the junction of the 
220 ohm and 470K resistors causing the voltage to fall to near zero turning off 
the NPN transistor. As the transistor turns off, the collector voltage rises 
and turns on the MOSFET when the voltage climbs above about 3 volts. The drain 
terminal (D) of the MOSFET now moves close to ground preventing the NPN 
transistor from turning back on. When the switch is opened, the 1uF cap will 
charge through the 1M and 10K resistors to the full supply voltage. When a 
switch is again closed, the 1uF capacitor will cause the NPN transistor to turn 
back on due to the positive voltage on the capacitor applied to the junction of 
the two resistors (470K, 220). The MOSFET will now turn off and the drain 
voltage will rise to the supply voltage which in turn keeps the NPN transistor 
conducting with a positive voltage on the base. The circuit has now returned to 
the initial turn-on state.
+
+The small (0.1uF) capacitor connected from the transistor base to ground 
functions to filter out noise that could cause false triggering if the switches 
are located far away from the circuit using long wires. If false triggering 
becomes a problem, either the capacitor value (0.1) or the 220 ohm resistor 
value can be increased to provide better filtering. Increasing these values 
however will increase the switching times of the MOSFET (rise and fall times) 
generating more heat when the MOSFET changes state. This is probably not a 
problem with small loads of a couple amps or less, but may be a problem at 
higher load currents. The circuit was tested at 1.5 amps using the IRF510 and 6 
amps using the IRFZ44.
+
+
+FDB8442 — FAIRCHILD SEMICONDUCTOR — MOSFET 
+Rds on:0.0021Ohm
+Id cont.:80A
+Vds typ.:40V
+D2-PAK
+