-2
\$\begingroup\$

i am using optocoupler SFH1690 to shift a pwm of 5V at 20KHz to 12V 20KHz. but it seems that optocoupler wont work on this high frequency. so is there any other faster technique to do so. currently my pwm is no more a pwm at opto's output (because of rise or fall time issues) need help about is going wrong. i have trid it with SFH1690 and 4N24 but same behaviour. resistor with cathode is 470 ohms and i tried with diff values of pull up resistor and cathode resistor but was unable to get a pwm at o/p of optocoupler. instead a slop enter image description here

\$\endgroup\$

closed as unclear what you're asking by Olin Lathrop, CL., uint128_t, Wesley Lee, Dmitry Grigoryev Apr 19 '17 at 14:03

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • 2
    \$\begingroup\$ Same ground on both sides? Why not just one transistor and two resistors? \$\endgroup\$ – winny Apr 17 '17 at 10:47
  • 2
    \$\begingroup\$ If you don't need isolation, do as winny says. If you do, try using a digital isolator. \$\endgroup\$ – Wesley Lee Apr 17 '17 at 10:51
  • 2
    \$\begingroup\$ As @winny asked, are your two sides actually isolated or is this just a bad schematic? \$\endgroup\$ – TonyM Apr 17 '17 at 10:51
  • 1
    \$\begingroup\$ At first glance this looked like something worth answering. Then I read the first word, then the first word of the second sentence. That's where I quit. Screw this. \$\endgroup\$ – Olin Lathrop Apr 17 '17 at 11:33
  • \$\begingroup\$ +1 to winny's answer. But if you get the output from collector, you'll get inverted PWM (i.e. Input 1s will be 0s at the output and vice versa). \$\endgroup\$ – Rohat Kılıç Apr 17 '17 at 11:41
2
\$\begingroup\$

If you can accept inverting your PWM signal, all you need are one resistor and a transistor:

schematic

simulate this circuit – Schematic created using CircuitLab

If you must retain the polarity/can't invert it, you need two transistors:

schematic

simulate this circuit

\$\endgroup\$

Not the answer you're looking for? Browse other questions tagged or ask your own question.