level shifter: 12 to 5 volts-PWM

Discussion in 'General Electronics Chat' started by lmartinez, Mar 9, 2009.

  1. lmartinez

    Thread Starter Active Member

    Mar 8, 2009
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    :p

    I have two 100K Hz square waves which are being produced by a TL598 chip set up for a push pull configuration. The magnitude of the square waves are 12 volts peak to peak since the voltage source for the TL598 has to be 12 volts DC. However, I need to convert those square waves' magnitude to 5 volts peak to peak in order to feed them to a high voltage, high speed power mosfet driver (IR2181). Do any of you guys might have an idea of a level shifter that can convert a 12 to 5 volt peak to peak square wave. Please advise if any of you can help me. Thank you in advance
     
  2. mik3

    Senior Member

    Feb 4, 2008
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    You can use a simple resistor voltage divider.
     
  3. lmartinez

    Thread Starter Active Member

    Mar 8, 2009
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    Thank you for your prompt reply. However, a simple voltage divider by using two resistors did not worked as expected. As I understand, at higher frequencies the parasitic capacitance of the resistors is playing a big factor which affected the shape of the square wave symmetry (not a square wave any more). I am still searching for a remedy by adding capacitors in parallel with the voltage divider resistors. So far I have not identified the solution for the problem. Indeed, I would like to come up with a simple circuit to do level shifting from 12 to 5 volts. Any feedback on this question will be highly appreciated.
     
  4. mik3

    Senior Member

    Feb 4, 2008
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    You can use a transistor driver by the 12V signal via a current limiting resistor and a resistor between its collector and 5V supply. Take the output from the collector.
     
  5. Ron H

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    What is the switching frequency? What are the minimum and maximum duty cycles?
     
  6. lmartinez

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    Mar 8, 2009
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    The switching frequency is 100k Hz and the duty cycles will vary from 0 to approximately 50 percent.
     
  7. mik3

    Senior Member

    Feb 4, 2008
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    Can you provide your circuit until now to see if it is well designed?
     
  8. t_n_k

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    Mar 6, 2009
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    I'm not sure I'm really permitted to recommend particular devices / manufacturers.

    Anyway - You could interpose a device similar or equivalent to Philips HEF 4050B or HEF 4049B (inverting type) - these are Hex buffers which should run out to your 100kHz requirement. These will accept input voltages up 15V DC for translation to standard TTL levels. Obviously you'll need a 5V DC supply to go with them.

    Good luck.
     
  9. Ron H

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    What value resistors did you use?
     
  10. lmartinez

    Thread Starter Active Member

    Mar 8, 2009
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    The resistor values were 10k ohms. I will work on getting the drawing posted. I currently only have the schematic on paper. Thank you all for your assistance
     
  11. Ron H

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    According to the datasheet, there is no lower limit for Vc on the TL598. Have you tried connecting Vc to +5V?
     
  12. lmartinez

    Thread Starter Active Member

    Mar 8, 2009
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    The data sheet for the TL598 recommends that the voltage values for Vc shall be within 7 volts minimum and 40 volts DC max. The reasoning for 7 volts DC being a magical minimum voltage is because the TL598 internal five volts reference establishes a stable supply from which the output control logic, pulse steering flipflop, oscillator dead time control comparator, and pulse width modulation comparator are powered from. In addition, the five volts DC reference is also available on pin 14 of the TL598. This makes it easier for me as the designer to develop other circutry to monitor the voltages which are being provided by Vc(Power source in this case) to the TL598. With that in mind, yes I have applied 5 volts to the Vc of the TL598 and the referenced voltage did not provided the five stable voltage reference until the voltage on Vc reached 5.40 volts DC. In addition, I did not observed any square waves on the outputs until Vc reached 5.40 volts DC as well. As you can see, My reasoning for using 12 volts DC is based on what I have just described and also to reduced the amount of circuitry on my design. However, you bring up a good point with regard to Vc. I can possibly utilize the 12 volts DC source and then lower it to about 8 volts DC with a voltage regulator.

    I still would like to come up with a circuit for level shifting the amplitude of the square wave to 5 volts peak to peak. Thank you for taking the time on helping me with this fun project. By the way, it is a DC to AC power inverter project that I am working on.
     
  13. Ron H

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    Have you noticed that Vc and Vcc can be different voltages? I was suggesting that you try changing only Vc to +5V. This will not screw up the reference voltage. It might not work, but it's simple to try.
     
  14. lmartinez

    Thread Starter Active Member

    Mar 8, 2009
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    Yes, indeed, I should of have noticed that you said Vc and not Vcc. It works!!! However, I have severe ringing issues with the output 5 Volts DC square wave. It probably has something to do with having two voltage sources. Thank you very much for all of your help.:)
     
  15. Ron H

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    You need good decoupling between Vcc and GND, and Vc and GND, right at the chip, and with short leads on the caps. 100nF for each one should work.
     
  16. lmartinez

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    Mar 8, 2009
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    OK, I have to ask this? How did you come up with 100nF. And what do you mean by good decoupling at the voltage(Vc and Vcc) sources being utilized for the chip. Thank you:p
     
  17. thatoneguy

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    Feb 19, 2009
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    Decoupling capacitors effectively move the power supply closer to the IC, which reduces the effective source inductance/resistance from several inches to fractions of an inch.

    100nF / 0.1uF is "the standard size" decoupling cap between power and ground. This value works universally well for low to mid frequencies (under 100Mhz), as long as the the supply is stable, and the PCB is designed correctly.

    A long while back, a company actually sold 14, 16, and 18 pin Wire Wrap IC Sockets for TTL with a 0.1uF cap "built in" between the standard TTL supply pins - Vcc and Gnd (opposite corners, such as pins 8 and 16).
     
  18. beenthere

    Retired Moderator

    Apr 20, 2004
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    Mil-Max still makes 'em. Digi carries them. A 14 pin gold flashed socket is $3.60. Or $5.35 for wire-wrap.
     
  19. Ron H

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    I'll essentially reiterate what thatoneguy said:
    If you have ringing on the rising edge of the output, it is probably caused by inductance in the wire between the chip's power pin and the power supply itself,
     
  20. lmartinez

    Thread Starter Active Member

    Mar 8, 2009
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    Thank you all. I will provide a stiff voltage source to the TL598 by reducing the length of the jumpers on my circuit to minimize the inductance and capacitance effects.
     
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