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  1. M

    Negative Voltage Rail Sag

    Please could you explain to me how this setup works. I'm not sure I understand how you get it to hold -5v. By that I dont understand how the feedback works in this case. Do the + and - inputs both have 1.2v (in the case of having the indicated reference)? How does changing the 910k resistor...
  2. M

    Negative Voltage Rail Sag

    We are a small country miles from anywhere. They ship in what sells. What is not common is generally expensive. I do my part in refusing to buy things that are too expensive. The only person I know in the states is my brothers ex-fiance. He called the wedding off a month or so before it was...
  3. M

    Negative Voltage Rail Sag

    An LM10CN may cost you a cup of coffee but down here RS only sells the LM10CWM (and I cant solder SMT yet), and Farnell sells the LM10CN for $27.33 plus shipping, which is about equal to 10 cups of coffee. I would love to have a nice small all contained chip, but ya gotta work with what youve...
  4. M

    Negative Voltage Rail Sag

    So it doesnt matter what value the voltage reference has, as long as the op-amp knows what it is? The LM10 is an extended range item at RS down here, and is quite expensive. Can I get away with a cheap voltage reference chip (like a TL431C) and a low power op amp? Are there any special...
  5. M

    Negative Voltage Rail Sag

    The LM10 is a little hard to get over here. Is there something else I can use? What part does the voltage reference play in that circuit?
  6. M

    Negative Voltage Rail Sag

    Hi guys, This is part of a motor controller circuit. It is designed to function as an inhibitor from switching directions if the motor is still moving. It works MOSTLY as intended, ie if the motor is spinning forwards (even with no speed demand) and then is flicked into reverse, the circuit...
  7. M

    Latching comparator help

    Aha, got it. I was running the transmission gate off the +9v supply. The PWM signal is between 0 and 12v. All fixed, the gate is now running off the 12v supply and shuts it all off nicely.
  8. M

    Latching comparator help

    I have tried that now, but even with a direct connection to ground on pin 6, the bilateral switch is still letting through the signal. I am most confused.
  9. M

    Latching comparator help

    Righto, clamp diode stays in. I am now having issues with the use of the transmission gate. The PWM signal for the motor is fed into pin 8 and then from pin 9 to the half bridge driver. Pin 6 is the control pin. When the comparator is on, pin 6 has a bit over 8v and everything is cool. The...
  10. M

    Latching comparator help

    I have put an RC filter in, and it seems to make it work fairly nicely. Two questions. 1. Is there an upper limit on values for the resistor and/or the capacitor in the RC filter? 2. Will NOT having the clamp diode result in the -ve output of the comparator damaging the base of the transistor?
  11. M

    Latching comparator help

    Well, I have changed the circuit as per audioguru's diagram. Now it holds a nice +7.5v or so once turned on. Some more background. Vin is a feed from a sense resistor from one of the legs of a motor H-bridge, which goes through an absolute value amplifier before getting to the negative input...
  12. M

    Latching comparator help

    I put the output clamp diode on to protect the transistor from having the base sitting at -9v. Does it not need this?
  13. M

    Latching comparator help

    Hi guys, I have built the following circuit. The Vref is 0.01v. The Vin ranges from 0 to maybe 5v at most. What I was intending was a comparator that latched on once the Vin was less than Vref (and in which case the LED would illuminate). The trouble I have is that when it turns on, the...
  14. M

    Switching idea

    Thanks again for all your help, i'll have a go at building it all and see how it works. Thats a whole lot of turkeys. I thought they were normally black anyway?
  15. M

    Switching idea

    I keep getting confused by these bloody op-amps and comparators and what constitutes "on" and "off". I wanted this to have the transmission gate turn on when the voltage in was less than the reference voltage, and then latch on. And to have the transmission gate off when the voltage in was...
  16. M

    Switching idea

    Right then. One negative supply coming up. Can you have a +12v and a -5v supply into one op amp? or do they have to be equal? Is the comparator set up correctly so that it will latch on? Thanks for all your help audioguru, got big plans for christmas?
  17. M

    Switching idea

    Hows this look I wasnt sure what values to put on the resistors you mentioned, so I took a punt on 1k for both. Are the op-amps going to be able to produce negative voltage output, even though there is no negative supply?
  18. M

    Switching idea

    Whoops. Made a few mistakes in that last one. This one should be better If i'm correct, the switch should stay off while the absolute value of Vin is above Vref. Once Vin drops below Vref, the comparator should switch on, thus turning on the switch and lighting the LED. The comparator should...
  19. M

    Switching idea

    How does that look. Removing the diode across the 1st op-amp isnt going to mess up it's gain is it? How does that transistor/diode setup look? I put the pull down resistor on the output to pull the CTRL of the Cmos to low when the comparator is off. I also put the feedback on the comparator...
  20. M

    Switching idea

    STOP THE PRESS! How about this setup? Would you care to pass your eyes over this please. According to my theory (which we've established is a bit shakey), this should act as an absolute value comparator, which switches high (and turns on the LED) when the absolute value of Vin is greater...
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