Kirk Wallace wrote: > On Fri, 2008-04-25 at 11:47 -0400, John Kasunich wrote: > ... snip >> That HAL component makes the charge pump signal. I think Kirk is >> looking for the real circuit that uses the charge pump signal to turn on >> a relay. > > Thats correct. > >> I built one for my Shoptask, unfortunately I think I just drew the >> circuit on a piece of paper and don't have it in electronic form. >> >> It is on the board described in this blog posting (the board also >> contains two relays with drivers and three optically isolated digital >> inputs): >> http://jmkasunich.com/cgi-bin/blosxom/shoptask/breakout-board-12-19-07.html >> >> If I remember when I get home I'll try to draw up a little schematic for >> a charge pump and post it. >> >> Regards, >> >> John Kasunich > > Thanks John. If the the 7414 does the whatchdog sensing, I could > probably reverse engineer your pictures. > I just looked at the photos again, and it was enough to jog my memory.
Two sections of the '14 are used for the watchdog, the other sections are used for the relays. The horizontally oriented single-inline-pin component below the relays is a MOSFET array with four FETs in it. I'm using two of them to drive the relays and the third for the watchdog (the watchdog output is open-drain, the watchdog relay is off-board). It looks like I might have paralleled the third and fourth FETs for a lower on resistance, and there is a zener there to clamp turn-off spikes. The charge pump input goes to the input of one section of the '14. The output of that section (call it output 1) goes to the input of another section. So output 1 is inverted, and output 2 is non-inverted. The pump itself is the three diodes in the lower left. They are in series, and the bottom of the diode stack is grounded. The top feeds a filter capacitor (probably a 0.1uF or so), a resistor (to bleed it down, with a time constant of a few tens of milliseconds), and the gate of the output MOSFET. Output 1 of the '14 is connected to the junction of the bottom and middle diodes, through a small "pump" capacitor - I don't recall the value, but it is 1/10 or less of the value of the output filter cap. Output 2 is connected to the junction of the middle and top diodes, with the same size pump cap. This is actually a bit more complex than the simplest charge pump, but it can deliver more voltage. A single-stage charge pump has only two diodes and one pump cap, and can deliver a voltage that is roughly the logic output swing minus two diode drops - maybe 3.5 volts on a good day. This three-diode version with two pump caps running out of phase can deliver more. I want to say it is 2x the logic swing minus 4 diode drops, but I'm not sure if that is exactly right. I do know it is over 5V, enough to nicely saturate a logic level FET, and would probably do OK with a normal FET. If you need more details don't hesitate to ask. Regards, John Kasunich ------------------------------------------------------------------------- This SF.net email is sponsored by the 2008 JavaOne(SM) Conference Don't miss this year's exciting event. There's still time to save $100. Use priority code J8TL2D2. http://ad.doubleclick.net/clk;198757673;13503038;p?http://java.sun.com/javaone _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
