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MrHeckles

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Everything posted by MrHeckles

  1. So, is the schmitt trigger better with the diode, or the 10k resistor? The PWM signal should be sourcing from the left, and sinking to the right (if that makes sense). Should I set up a voltage divider to get 5v or so (my one has 6v emitter-base voltage) to the base of the PNP transistor. The idea is to make sure that the transistor is stopping the signal, until the window comparator turns it on (then it stays on), without affecting the signal in anyway.
  2. How about this? When the window comparator turns on, it pulls the + input of the right comparator below the - input, turning it on. The output of that right comparator pulls the + input low aswell, thus keeping it on (at least until power is removed from the whole circuit) even if the window comparator turns off again. Does that sound plausible? Also does shifting that 2k resistor provide some current limitation to protect the PNP transistor now? The signal is a PWM pulse to a half-bridge driver input.
  3. Okay, here is a schematic for my idea. At the moment, the window is set between about 3.4v and 1.7v. My big question is.... will this work?
  4. Hey everyone, I would like to design a setup that switches a PNP transistor on when a signal reaches near 0v (it would normally be either +ve or -ve), and then keeps that transistor on until the system is reset. My current thoughts on the matter are to have a window comparator to detect the near 0v, and have that feed into a schmitt trigger with a -ve reference for the turn off level (to keep it on). I figure the reset can be cutting the power to the schmitt trigger. Would this setup work, or is there a better, more simple way? BTW this is intended to be an inhibitor for a reverse switch on a motor controller. I hope to be able to interrupt the PWM to a half-bridge driver if reverse is selected while the motor is still turning (ie producing regen current), and then let the PWM pulse through once the motor has come to a stop. It should hopefully do the same when switching back to forward.
  5. Super yachts aye? Made the changes you suggested. Works a treat now. Many thanks
  6. Heh heh, okay no more fuzzies from me. Thanks audioguru I'll give it a try. BTW, where in Canada do you reside?
  7. Hi guys. I have constructed this circuit. Everything seems to work as expected, except for one small problem. The high output of both the IR2184 drivers is not high enough. I ran into this problem with an earlier circuit (also posted) and was helped to solve it by decoupling the driver between Vcc and Ground. However this has not fixed the problem in this case. The low output is fine, and is turning on the lowside mosfets well. However the high output is only putting out about 1v to the highside mosfet gates. The PWM generator is running at about 25kHz. Any suggestions? Please.
  8. Okay, how about this then. I figure with this setup, when the PWM signal is switched to the other half-bridge driver, the one not selected will hold the lowside mosfet on (which is needed for the reverse). The selected driver will switch the highside and lowside mosfets on as needed. Comments?
  9. My idea behind this mess was to have a motor driver that would have variable forward speed, and when the throttle pot was pulled all the way back, trip a microswitch to activate a preset reverse speed. I thought that I could use the transistors as switches to enable or disable the pulse train from the half-bridge driver to the gate of the appropriate highside and lowside mosfets. Could you perhaps point me in a simpler direction for doing this? I'm a bit lost now as to how to do it.
  10. Yes it is a PWM motor controller. Its a test to see if I can get a variable forward speed, and a set reverse speed with the switch activated. The transistors are supposed to be switches that will allow the appropriate mosfets to be used in either forward or reverse. I thought that grounding the bases of the transistors in certain circumstances (ie switch on or off) could disable the PWM pulse to various mosfets but allow others. Since I am kind of just making it all up as I go along, its very possible that i've missed some point entirely as to how something works. audioguru - can you explain a little more about being nothing to turn the mosfets off. Are the transistors allowing them to stay on even if the pulse from the half-bridge driver is low? Also what do you mean by the transistors wired stangely?
  11. Hi guys. Could someone please have a quick look at the circuit below and let me know if there are any glaring obvious errors that would result in smoke and/or flames when a battery is connected to it. Many thanks
  12. Hi guys, Is there anyone out there that knows of a switch that can be turned off electronically, but needs to be manually switched back on?
  13. Thank you audioguru. I was getting confused about the reverse breakdown voltage. That clears up my misunderstanding nicely.
  14. Could someone please clarify what emitter-base voltage is on a transistor for me. Could I, for example, have a transistor with a Veb of 6v with the base of the transistor connected to a 12v source (assuming the collector-emitter side was also connected to the same 12v source)? What about the same transistor with 12v on the base and 18v on the collector-emitter side. Thanks in advance for clearing up my confusion.
  15. Pretty straight forward question..... If a motor is set up to regeneratively brake, and it is being forced to turn, would that put a negative voltage across a sense resistor on the low side of the H bridge? If not, is there a way to measure the current being produced by regenerative braking?
  16. The PWM pulse is from an earlier post of mine, the current limiting SG3524 setup. It's running a frequency of about 65 kHz.
  17. I put a 0.1 uF ceramic cap in parallel with the big electrolytic, put one between Vcc and Ground, put one back between Vb (after the diode) and Vs, and connected the drain of the highside mosfet to the +ve rail. It all works very well now. The highside output is up to 18v from the driver. None of the fets get hot. The motor speed can be changed rapidly up or down. Thanks guys. Would I be right in assuming that the lack of the decoupling cap for the driver would be the main culprit for it not working?
  18. I have now put in that diode. It made no difference. I removed the cap across Vb and Vs. It made it run a tiny bit better. It still seems like the motor is being driven, then stopped about 1/second. I cannot get the highside out to go above about 3v max. If I try to up the duty cycle going into the chip, the motor will stop completely. Should the setup of the half bridge drive a motor if the high side and low side are turning on alternately? Is there any chance that the circuit design is good, but the chip is busted?
  19. I have built this circuit but it does not appear to work as i expected. I assumed that it would drive a motor quite happily at what ever speed was selected via the variable duty cycle PWM input. If a low duty cycle was selected and the motor needed to slow down the inverse pulse going to the lowside mosfet would provide a regenerative braking action, thus slowing down very quickly. What this circuit does in real life however is a little different. At a low duty cycle setting the motor runs a little jerky slowly. As the duty cycle is increased, the jerkiness increases and then at a high duty cycle, the motor stops. At the highest setting (about 90% duty cycle) the high side mosfet gate only seems to be getting 5v (which is a bit odd I think). At the low duty cycle settings the high side gets less than that, but the lowside seems to get a nice 11.5v (give or take). Could someone let me know if this thing SHOULD work properly (and maybe the driver chip is damaged) or whether the design could cause this issue? Thanks
  20. I put the filter in and after fiddling with the values of things got it all working. Many thanks audioguru
  21. This is my current circuit as it stands What I am trying to get is the LED to turn on when the voltage across the sense resistor (0.32 ohm) gets above 0.2v I have set up the LM311 comparator as shown. However it doesnt seem to work as I thought it would. The LED turns on as soon as there is ANY voltage across the sense resistor (ie when the mosfet starts switching on). I have also tried it with the inputs round the other way. That didnt work as I wanted either. Please could someone let me know where my schematic is incorrect. Thanks
  22. The output at pin 9 is also the output from the error amplifier. It goes above 2v in normal operation when set for a high duty cycle. If I used pin 9 and a darlington transistor, wouldnt it light up the LED whenever a high duty cycle was requested even in normal operation?(pin 9 will control the duty cycle between 0 and 90% with a voltage range of between about 1v and 3.5v) This may be a stupid question, but how would I set up a filter for the LED comparator? And a point to note is that if max duty cycle is requested (via the error amp) and it is current limiting fully, then the voltage on pin 4 will go up to around 0.5v. Though the current limiting does start around 0.2v on pin 4.
  23. The intention is for the comparator to go high when the + input (same as PIN 4 on the SG3524) goes above about 0.2v. Ignore the value of the resistor infront of the LED. Would it work?
  24. Hi guys. I have made this circuit, and it works well. You can vary the duty cycle between 0 and 90% and the current limiting kicks in as the voltage on the C.L (+) sense (Pin 4) starts going above 0.2v. However I would like some sort of indication as to when the circuit starts current limiting, such as an LED coming on. I tried connecting the base of a transistor to pin 4, the collector to pin 16 with a resistor, and the emitter to ground. However that triggered the LED as soon as any voltage was generated on pin 4. So, any ideas?
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