# Using Hex Inverters to generate 0, -5V output

A

#### [email protected]

Jan 1, 1970
0
Hi there, I was wondering if anyone can help me design a simple circuit
to drive a switch. The switch has two states, and expects two inputs.
To put the switch in state one, it needs inputs 0V, -5V and to put it
in state two, it's inputs need to be -5V, 0V. So what I'd like to
design is a driver that takes a 0 / +5V signal, and converts it to the
appropriate output state.

Truth Table:

Input Output 1 Output 2

0V 0V -5V
+5V -5V 0V

Now, I thought I could use a hex inverter in a kind-of negative state
(i.e. Vcc = GND, GND = -5V) to generate the appropriate negative
voltage, but playing around in the lab hasn't been so helpful. Can
anyone suggest a way that I can do this? Switching times aren't
important.

Thanks!

A

#### Andrew Holme

Jan 1, 1970
0
Hi there, I was wondering if anyone can help me design a simple circuit
to drive a switch. The switch has two states, and expects two inputs.
To put the switch in state one, it needs inputs 0V, -5V and to put it
in state two, it's inputs need to be -5V, 0V. So what I'd like to
design is a driver that takes a 0 / +5V signal, and converts it to the
appropriate output state.

Truth Table:

Input Output 1 Output 2

0V 0V -5V
+5V -5V 0V

Now, I thought I could use a hex inverter in a kind-of negative state
(i.e. Vcc = GND, GND = -5V) to generate the appropriate negative
voltage, but playing around in the lab hasn't been so helpful. Can
anyone suggest a way that I can do this? Switching times aren't
important.

Thanks!

What is the switch? Is it sensitive to voltages relative to ground, or only
potential difference between its inputs? What power supply rails do you
have available? Must you use a hex inverter?

N

#### Noway2

Jan 1, 1970
0
What do you have for an incoming power source? If you have a center
tapped secondary transfomer, assuming sufficient secondary voltage, you
could use a 7805 and 7905 regulator to generate both a positive and
negative 5v.

Another possibility for generating the -5v is using a small dc-dc
converter. If you are not talking much power (current output) you
should be able to find one an inexpensive one that will meet your
needs.

Once you have a + and -5V supply, you could use a push - pull or totem
pole output. Basically you use two transistors, one to conduct in the
postive direction and one to conduct in the negative direction. If
this sounds like it might work, search on those terms (push pull and

C

#### Chris

Jan 1, 1970
0
Hi there, I was wondering if anyone can help me design a simple circuit
to drive a switch. The switch has two states, and expects two inputs.
To put the switch in state one, it needs inputs 0V, -5V and to put it
in state two, it's inputs need to be -5V, 0V. So what I'd like to
design is a driver that takes a 0 / +5V signal, and converts it to the
appropriate output state.

Truth Table:

Input Output 1 Output 2

0V 0V -5V
+5V -5V 0V

Now, I thought I could use a hex inverter in a kind-of negative state
(i.e. Vcc = GND, GND = -5V) to generate the appropriate negative
voltage, but playing around in the lab hasn't been so helpful. Can
anyone suggest a way that I can do this? Switching times aren't
important.

Thanks!

Hi,Alex. Even though you didn't state it specifically, I'm assuming
you don't have a +/-5V supply available. If you do, just use an LM393
dual comparator, and place your output pullups to GND instead of the +
supply (note that this comparator, like most, has open collector
output).

|
| VCC
| |
| .-.
| 22K| |
| | |
| '-' VCC
| | +
| | |
| | |\|
| 2.5V o------|-\ 0V/-5V
| | | >-o-----o
| | .---|+/ |
| | | |/ .-.
| | | | |
| Vin | | | |
| o-------)--o '-'
| | | |
| | | ===
| | | |\ GND
| | '---|-\ -5V/0V
| | | >-o-----o
| o------|+/ |
| | |/| .-.
| | - | |
| .-. Vee| |
| 22K| | '-'
| | | |
| '-' ===
| | GND
| ===
| GND
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

However, if you don't have the negative supply, here's one kind of
cheesy way of generating the negative outputs, using a 74C14, 74HC14,
or 40104 hex inverter with schmitt trigger input (view in fixed font or

| ___
| .-|___|-.
| | |
| | |\ | || V1
| .-->|-o-| >O--o-||-o-|<-o--o---.
| | | |/ || | | |
| | --- - --- .-.
| | --- ^ --- | |
| | | | |+ | |
| Vi |\ |\ | | === === '-'
| o-| >O-o-| >O-' === GND GND |
| |/ | |/ GND ===
| | ___ GND
| | .-|___|-.
| | | |
| | | |\ | || V2
| '--------->|-o-| >O--o-||-o-|<-o--o---.
| | |/ || | | |
| --- - --- .-.
| --- ^ --- | |
| | | |+ | |
| === === === '-'
| GND GND GND |
| ===
| GND
|
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

Note that inverters 1 and 2 act as a buffer and inverter of the input
+5V/0V signal. Inverters 3 and 4 are set to be oscillators, with
diodes and caps performing voltage inverter function at the output. At
any given time, either inverter 1 or inverter 2 will be sourcing
current into one of the oscillator caps, preventing that inverter from
oscillating. When that inverter stops, the output load resistor will
pull the charge off the output cap, bringing the output voltage down to
GND.

It's ultra slow, it's clunky, and the output voltage will be a couple
of diode drops short of -5V (use schottky diodes if it helps), but this
might get you where you want to go.

Another option you might be interested in is using a MAX232 or other IC
to get the negative voltage and use a diode to prevent the output from
going above 0V, or use a 4.7V zener if you can live with -4.7V/+0.6V.

Good luck
Chris

A

#### [email protected]

Jan 1, 1970
0
Thanks for all the responses, I'll have to go over them in detail, but
I just thought I'd supply a little more information for those who were
looking for it - the switch is a GaAs DC-20 GHz SPDT switch for a
transceiver. I don't specifically need to use Hex inverters, I was
just under the impression that that's how this kind of thing was done.
The first version will be a bit of a prototype, and I was planning to
just switch a power supply off an on to generate the 0/ +5V input - I
could use 2 power supplies to generate both control signals, but I
think in the end they'll come from some sort of logic circuit, so I'd
like to make it a bit more realistic from the start. A do have some
room to play on the control signals - here are the reqs:

Low: 0 to -0.5V @10 uA Max.
High: -5V @ 3 uA Typ. to -7V @ 10 uA Typ. (+/- 0.5 Vdc)

C

#### Chris

Jan 1, 1970
0
Thanks for all the responses, I'll have to go over them in detail, but
I just thought I'd supply a little more information for those who were
looking for it - the switch is a GaAs DC-20 GHz SPDT switch for a
transceiver. I don't specifically need to use Hex inverters, I was
just under the impression that that's how this kind of thing was done.
The first version will be a bit of a prototype, and I was planning to
just switch a power supply off an on to generate the 0/ +5V input - I
could use 2 power supplies to generate both control signals, but I
think in the end they'll come from some sort of logic circuit, so I'd
like to make it a bit more realistic from the start. A do have some
room to play on the control signals - here are the reqs:

Low: 0 to -0.5V @10 uA Max.
High: -5V @ 3 uA Typ. to -7V @ 10 uA Typ. (+/- 0.5 Vdc)

Hi, Alex. From the sketchy explanation you've given, a dual +/-5V
power supply with a comparator to provide the switching signals is more
realistic. Scratch the second circuit -- you'll definitely have both
sides of the switch on, which won't do you any good if your signals are
low impedance. Also, a lot of modern comparators have complementary
outputs, which should make your job easier.

Using an logic NOT gate oscillator to make an inverter has a couple of
problems for you. First, once you get past the diode drops, you'll
either be right at the edge of a logic high, or out of spec. Second,
your - supply is unregulated, which means that the noise on the
negative power supply might feed through to your signal, especially if
it's right on the edge.

If you don't have a negative power supply handy, you might just want to
add a Simple Switcher, an inductor and a couple of passives to get a
good -5V or -6V supply. Add a comparator with pullups to GND, and
you're done.

Good luck
Chris

A

#### [email protected]

Jan 1, 1970
0
Hi Chris, thanks a lot for your help,

Alex

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