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  1. CommanderLake

    Create controlled 50v pulse

    Actually I think saturation switching might be fast enough, here are the results from further testing with my test circuit with... 500 ohm load 500 ohm Picaxe to base 130 ohm base to emitter 1.74us pulse from Picaxe Pulse width from/to half supply voltage 12v to load: 1.78us 15v to load: 1.74us...
  2. CommanderLake

    Create controlled 50v pulse

    Its showing the full 12v at the gate with 14.33v across the load. I just realised that because the driver is inverting, the way I cut off the PWM wont work.
  3. CommanderLake

    Create controlled 50v pulse

    Pulsout 1 is 1.75us at 32MHz, I will experiment further with turning pwm on and off in code. I only use an ideal simulator because its super quick and makes it immediately obvious in realtime if theres a problem with simulated scopes and current flow. With an n-MOSFET the voltage from the driver...
  4. CommanderLake

    Create controlled 50v pulse

    When I asked what type of MOSFET I need I meant the one on the right thats connected to the LED, it wont switch on fully with your driver circuit with either n or p. I use an appropriate current limit on the bench supply, if the current is slightly out of spec with a pulse it doesn't matter as...
  5. CommanderLake

    Create controlled 50v pulse

    I figured out how to get accurate sub microsecond pulses from my picaxe by using its PWM output with a controllable pulse length and a low frequency such as 1ms then turn it on and off with another of its pins via a MOSFET to isolate a single pulse from its PWM generator. Do I use an n or p...
  6. CommanderLake

    Create controlled 50v pulse

    I made a light with a CMA3090-0000-000Q0U0A40G (~172w LED) and a 50cm (25cm focal length) Fresnel lens that can light up the clouds but I figured that because LED's turn on and off super fast I could use it as a camera flash in a dark room to capture super fast moving objects with amazing...
  7. CommanderLake

    Create controlled 50v pulse

    The Vce of the 2N3904 is too low. I'm testing the circuit in post #15 with a spare BC547C, a 910 ohm load and a USB oscilloscope and I can see how the turn off time increases with a higher resistance to base which explains the slow turn off time with saturation switching as Bob said. But...
  8. CommanderLake

    Create controlled 50v pulse

    This Darlington has a suspiciously fast transition frequency: https://uk.farnell.com/allegro-sanken/2sd2390/darlington-transistor-to-3p/dp/1208637 What do you think?
  9. CommanderLake

    Create controlled 50v pulse

    What MOSFET? I mean Picaxe>BJT>Load, obviously the hFE would need to be sufficiently high.
  10. CommanderLake

    Create controlled 50v pulse

    So what BJT do you suggest? With the BJT switching on the low side it only needs a very small amount of voltage and a current draw determined by the hFE so if the hFE were sufficient the picaxe could probably drive it directly, 1000hFE and a 1k resistor would reduce the current to well within...
  11. CommanderLake

    Create controlled 50v pulse

    But I thought BJTs were slow? ... I just assumed MOSFETs were faster because they are used in switching electronics but it turns out thats just because of the low switching power required. So thats a win win then with speed AND low on resistance!
  12. CommanderLake

    Create controlled 50v pulse

    I finally figured out your circuit, how fast can I expect it to be, how close will it get to the supply voltage when driven with 12v and can the BJTs be replaced with MOSFETs to speed it up? How about this MOSFET, it has a nice low on resistance: https://uk.rs-online.com/web/p/mosfets/7840290/...
  13. CommanderLake

    Create controlled 50v pulse

    I cant figure out how to use that circuit, do I replace the BJT's with MOSFET's, what does the loose end on the right connect to?
  14. CommanderLake

    Create controlled 50v pulse

    I might have to give up on this project I just cant find a simple enough solution.
  15. CommanderLake

    Create controlled 50v pulse

    All of the drivers I can find with the required voltage are SMT, I'd prefer through hole for prototyping.
  16. CommanderLake

    Create controlled 50v pulse

    I would like to create a controlled 50v pulse of a configurable duration for a high power LED with less than 4 amps possibly using a Picaxe as I've used one before, so I have 2 questions... 1. Can the picaxe create fairly accurate a pulse down to 1 microsecond, I've not tried. 2. What circuit...
  17. CommanderLake

    Designing a 4th order 3 way crossover

    I'm designing a 4th order 3 way crossover for some 3 way speakers consisting of the following Dayton Audio speakers: ND25TA-4 RS52AN-8 RS225-8 I know very well a speaker is not just a resistor and inductor but thats as close as I can get with my favourite circuit simulator, enable European...
  18. CommanderLake

    Audio Amplifier problem

    Decoupling is effectively a low pass RC filter on the power supply (R being the resistance of the supply and C being the decoupling capacitor) to absorb the high frequency changes in voltage as the load changes.
  19. CommanderLake

    Decoupling capacitors

    I've just tested the volt drop of various electrolytics, film and ceramic capacitors with my USB oscilloscope, a 3.8v battery source and a 10 ohm load and the results are as follows: With no capacitor there are wild peaks and dips when the load is applied. Aluminium electrolytics remove noise...
  20. CommanderLake

    Decoupling capacitors

    http://uk.farnell.com/tdk/c3216x5r1h106k160ab/cap-mlcc-x5r-10uf-50v-1206/dp/2346951 Surely the low ESR of a 10µF ceramic will take care of the high frequency ripples?
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