Hello , I am trying to use an ultra fast comparator to transform 0 to 3V pulse into -5V to 0 pulse.
However as you can see in the simulation file and photos Its 0 to +5.
Why this comparator cannot output the -5V rail to the output?
Thanks.

 

hi yef,
Pleases post your LTS asc file.
E

 

Hello Eric, The simulation files and photos are attached in the zip file,
Thanks.

 

LT1713 outputs do not go below GND.
Use LM311 instead since the collector and emitter of the output transistor are not committed to any load.

 

hi yef,
As post #4 states.
E

 

Hello ,I have tried exactly as you said using LM311 , but still its from 0 to 5 not 0 to -5.
Photos and LTspice simation is attached.
Where di I go wrong?
Thanks.

 

I was advices to do the following:
given that this advice is correct, could you reccomnd such open collector comparator I could use at first?
Thanks.
" A comparator with an open collector/drain output, followed by a buffer. Connect the output to 0V, via a suitable pull-up resistor. The buffer can be a logic IC such as the 74LVC2G04, with 0V for the VCC and -5V for GND. "

 

but still its from 0 to 5 not 0 to -5.

That's because R4/R5 are connected to GND instead of -5V.
Vpp = 0V, Vmm = -5V. Reference voltage divider also supplied from 0V/-5V. Additionally a suitable voltage divider from INPUT to - 5V.

 

Here's a way to use the LT1713 to give a 0 to -5V output.

But don't ground the unused outputs as that can cause a large output current and zap the device. You can typically ground unused inputs but not unused outputs.
It may work in the sim but not with a real circuit.

 

Here's a way to use the LT1713 to give a 0 to -5V output.

Woudn't a single LT1713 already be sufficient due to the complementary outputs?

 

Woudn't a single LT1713 already be sufficient due to the complementary outputs?

That would seem so.

 

Hello crutschow , yes it worked with one component.
my negative rail is not -5V but -15V.
This circuit needs to controll the following switch according to the truth table.
few questions:
1. What kind of regulator component you reccomend to perform this -15V to -5V to use for this purpose?
2. regarding the load as you can see I got very sharp good pulses,do you think I need to plug these 1K resistors on the load?
Thanks.
https://cdn.macom.com/datasheets/MASW-008322.pdf

 

UPDATE:
Hello crutschow,I see that your Idea in the simulation is working however if we look in the datasheet.
The LT1713 will not work when one of its inputs is more than 0.1V above its positive supply pin as shown below in the photo.
If I am correct , is there a similar method like you shown?
https://www.analog.com/media/en/technical-documentation/data-sheets/171314f.pdf

 

1. What kind of regulator component you reccomend to perform this -15V to -5V to use for this purpose?

You can use the common 7905/79L05 (or similar) negative linear regulator to get -5V from -15V.
Be sure and include the recommended decoupling capacitors at the input and output of the regulator.
Also use a 100nF ceramic capacitor directly from the comparator minus voltage pin to ground.

2. regarding the load as you can see I got very sharp good pulses,do you think I need to plug these 1K resistors on the load?

No, it needs no load.

The LT1713 will not work when one of its inputs is more than 0.1V above its positive supply pin as shown below in the photo.

True, but your circuit is not like mine.
If you look at my sim, you will see that, due to the Vmm negative bias voltage, the comparator In voltage is always negative and never goes higher than -850mV, while the other input is biased at -1.66V by Vref (below):

 

It’s likely related to the comparator’s output stage and how it’s powered. Many ultra-fast or TTL-compatible comparators use an open-collector output and can only pull low relative to ground, not actively drive to a negative rail. If the device is powered from 0 V and +5 V only, it typically can’t swing below ground, so you’ll see 0 to +5 V in simulation. To get a −5 V to 0 V output, the comparator usually needs dual supplies and an output stage that supports negative swing. Check the datasheet for the output type, supply configuration, and voltage swing limits, and make sure your sim matches those requirements.