The Circuit Schematic

I have a question regarding Schmitt Trigger. I am trying to design an inverting output (at UTP=Low, at LTP=High) Schmitt Trigger for an application. However, I need to use PNP transistors since the voltage level is relatively high (60V) for opamp application. Unfortunately, on the internet only non-inverting transistor Schmitt trigger is available. Therefore could anyone tell me how I can implement an inverting Schmitt trigger with PNP transistors?

Kind regards,


  • 3
    \$\begingroup\$ Build the non-inverting one you know about, and invert the output with another transistor? \$\endgroup\$ – Colin Mar 14 '18 at 10:33
  • \$\begingroup\$ Show the schematic of what you have found and then maybe we can suggest a modification. \$\endgroup\$ – Bimpelrekkie Mar 14 '18 at 10:38
  • \$\begingroup\$ @Mert Karadeniz: why can't you use a simple voltage divider (2 resistors) to bring the input voltage into the operating range of common OpAmps? Bringing the ouput back to 60V range (if needed) is also not very difficult. \$\endgroup\$ – Curd Mar 14 '18 at 11:34
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    \$\begingroup\$ It's clear that this is an xy problem. Please describe the problem in much more detail, focussing on what you need to do rather than how to implement what you think is the solution. Input signal range. Output signal range. Input waveform. Schmitt thresholds. Input and output impedances. Available power supplies. I notice your comments to @Andy aka's answer seems to imply very wide voltage swings at high frequency - are you aware of the consequences of even modest input capacitances? Likewise output drive requirements? Again, what you need to do, not how to implement your idea of a solution. \$\endgroup\$ – WhatRoughBeast Mar 14 '18 at 11:52

However I need to use pnp transistors since the voltage level is relatively high (60V) for opamp application.

Not true, there are devices that will be ok up to 100 volts: -

enter image description here

They cost about £5 in single quantities.

| improve this answer | |
  • \$\begingroup\$ Yes but the slew rate is very low. 13V/usec which is very slow for my application. I need sth like at least 1000V/usec, however with that output speed the maximum input and supply voltage values are very low. \$\endgroup\$ – Mert Karadeniz Mar 14 '18 at 10:50
  • \$\begingroup\$ @MertKaradeniz please understand this; I have suggested a part that your research drew a blank on. I'm not saying this part is exactly what you need because to do so I'd have to understand the wider context of your requirements. I am pointing out that your prior research didn't uncover any op-amps and my answer is all about encouraging you to do so. \$\endgroup\$ – Andy aka Mar 14 '18 at 10:57
  • \$\begingroup\$ @MertKaradeniz I will also add this: the circuit you have added in your question is extremely unlikely to meet the 1000 volts per microsecond requirement so what is the "non-inverting transistor schmitt trigger" you found on the internet that does meet your requirement? \$\endgroup\$ – Andy aka Mar 14 '18 at 11:01
  • \$\begingroup\$ thanks for the answer. Do you have any topology suggestion for a faster output? \$\endgroup\$ – Mert Karadeniz Mar 14 '18 at 11:15
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    \$\begingroup\$ @MertKaradeniz your question contains very little about what your "real" requirements are so I answered only the part that could be answered. If you are looking for a design you need to be much more detailed in your requirements and amend your question with those requirements. \$\endgroup\$ – Andy aka Mar 14 '18 at 11:28

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