Increasing PWM output voltage

  • Thread starter Dave, I can't do that
  • Start date
D

Dave, I can't do that

Guest
Hello,

I need to boost a PWM signal at 5KHz and 450mV to 5V at 5KHz and 100mA
max.

Could someone please give me a list of the components I need and a
schematic to do this.

A suggested idea was this...
http://www.cnczone.com/forums/showpost.php?p=501327&postcount=4

But as you can see the guy was unsure of N-channel or P-channel and he
never got back to me.

Thank you.

Dave
 
On Thu, 18 Sep 2008 07:03:55 -0700 (PDT), "Dave, I can't do that"
<davenpete@gmail.com> wrote:

Hello,

I need to boost a PWM signal at 5KHz and 450mV to 5V at 5KHz and 100mA
max.

Could someone please give me a list of the components I need and a
schematic to do this.

A suggested idea was this...
http://www.cnczone.com/forums/showpost.php?p=501327&postcount=4

But as you can see the guy was unsure of N-channel or P-channel and he
never got back to me.

Thank you.

Dave
Click to expand...
Do you need to pull both up and down? What are you driving with the
PWM signal?

At 450mV, not many mosfets will work directly in any case. The easiest
thing would be to use a comparator, and use the output to control a
driver chip like an SN754410:

http://focus.ti.com/lit/ds/symlink/sn754410.pdf

Regards,
Bob Monsen
 
On Sep 18, 9:43 am, Robert Monsen <rcmon...@gmail.com> wrote:

Hi Robert, thanks for the reply.

Do you need to pull both up and down? What are you driving with the
PWM signal?
Click to expand...
I do not know what that means. I am trying to drive a 25W CO2 Laser
marking machine's Laser intensity.

I was given the dead Laser and installed one I bought surplus. I now
have everything working except the intensity. It is supposed to put
out 5v PWM at 5KHz but it is only putting out 450mV. There are no
schematics available as it is such an old model and there are several
EEPROMs on board and I have no idea what they are coded to do.

The PWM is working just not at sufficient voltage to trigger the
Laser. I want to use the existing 450mV PWM output to drive something
that will output the 5v I need.

I have been told that this Laser requires "Output Current, max 100mA
through a 50 Ohm CMOS driver" and that's all I have to go on.

If I can't do that then I will tear out the electronics and install a
2-axis CNC stepper driver board and run it under EMC2. Obviously
getting it to work would be better since it is configured as a printer
for Corel and a simple matter to "print" the part. If I go the CNC
route I will have to add in two more programming stages for every
project.

Dave
 
On Thu, 18 Sep 2008 11:05:58 -0700 (PDT), "Dave, I can't do that"
<davenpete@gmail.com> wrote:

On Sep 18, 9:43 am, Robert Monsen <rcmon...@gmail.com> wrote:

Hi Robert, thanks for the reply.

Do you need to pull both up and down? What are you driving with the
PWM signal?

I do not know what that means. I am trying to drive a 25W CO2 Laser
marking machine's Laser intensity.

I was given the dead Laser and installed one I bought surplus. I now
have everything working except the intensity. It is supposed to put
out 5v PWM at 5KHz but it is only putting out 450mV. There are no
schematics available as it is such an old model and there are several
EEPROMs on board and I have no idea what they are coded to do.

The PWM is working just not at sufficient voltage to trigger the
Laser. I want to use the existing 450mV PWM output to drive something
that will output the 5v I need.

I have been told that this Laser requires "Output Current, max 100mA
through a 50 Ohm CMOS driver" and that's all I have to go on.
Click to expand...
---
What rise time, minimum pulse width, and fall time do you need?

JF
 
Dave, I can't do that wrote:

On Sep 18, 9:43 am, Robert Monsen <rcmon...@gmail.com> wrote:

Hi Robert, thanks for the reply.


Do you need to pull both up and down? What are you driving with the
PWM signal?


I do not know what that means. I am trying to drive a 25W CO2 Laser
marking machine's Laser intensity.

I was given the dead Laser and installed one I bought surplus. I now
have everything working except the intensity. It is supposed to put
out 5v PWM at 5KHz but it is only putting out 450mV. There are no
schematics available as it is such an old model and there are several
EEPROMs on board and I have no idea what they are coded to do.

The PWM is working just not at sufficient voltage to trigger the
Laser. I want to use the existing 450mV PWM output to drive something
that will output the 5v I need.

I have been told that this Laser requires "Output Current, max 100mA
through a 50 Ohm CMOS driver" and that's all I have to go on.
Click to expand...
Maybe what they were referring to is that it must be current regulated
to not exceed the 100 ma or set point since a Laser current is critical.
Dave
Click to expand...

http://webpages.charter.net/jamie_5"
 
On Thu, 18 Sep 2008 16:57:43 -0700 (PDT), "Dave, I can't do that"
<davenpete@gmail.com> wrote:

Hi again,

I don't know about rise times etc as the PWM is already being
generated, but at 450mV and I need to boost that to 5v. I can see the
pulses on a scope and the frequency is around 4.980KHz and they are
nice clean square waves that I can vary by software.

I just need something that can be driven by the existing PWM output
and it in turn outputs the same signal but at 5v.
Click to expand...
---
I have a solution for you, but since it seems that you want to make some
money off of it, I do too.

Email me with your proposal.

JF
 
Hi again,

I don't know about rise times etc as the PWM is already being
generated, but at 450mV and I need to boost that to 5v. I can see the
pulses on a scope and the frequency is around 4.980KHz and they are
nice clean square waves that I can vary by software.

I just need something that can be driven by the existing PWM output
and it in turn outputs the same signal but at 5v.

Thanks

Dave
 
In article
<90462633-ebc8-4f11-a540-53e2e32d4424@z11g2000prl.googlegroups.com>,
davenpete@gmail.com says...
Hi again,

I don't know about rise times etc as the PWM is already being
generated, but at 450mV and I need to boost that to 5v. I can see the
pulses on a scope and the frequency is around 4.980KHz and they are
nice clean square waves that I can vary by software.

I just need something that can be driven by the existing PWM output
and it in turn outputs the same signal but at 5v.

Thanks

Dave
Click to expand...
Have you tried adding a pullup resistor (to +5V) to the output pin
giving you the 450mV? It may just be an open collector type output.

Regards,

Sarah.
 
On Thu, 18 Sep 2008 11:05:58 -0700 (PDT), "Dave, I can't do that"
<davenpete@gmail.com> wrote:

On Sep 18, 9:43 am, Robert Monsen <rcmon...@gmail.com> wrote:

Hi Robert, thanks for the reply.

Do you need to pull both up and down? What are you driving with the
PWM signal?

I do not know what that means. I am trying to drive a 25W CO2 Laser
marking machine's Laser intensity.

I was given the dead Laser and installed one I bought surplus. I now
have everything working except the intensity. It is supposed to put
out 5v PWM at 5KHz but it is only putting out 450mV. There are no
schematics available as it is such an old model and there are several
EEPROMs on board and I have no idea what they are coded to do.

The PWM is working just not at sufficient voltage to trigger the
Laser. I want to use the existing 450mV PWM output to drive something
that will output the 5v I need.

I have been told that this Laser requires "Output Current, max 100mA
through a 50 Ohm CMOS driver" and that's all I have to go on.

If I can't do that then I will tear out the electronics and install a
2-axis CNC stepper driver board and run it under EMC2. Obviously
getting it to work would be better since it is configured as a printer
for Corel and a simple matter to "print" the part. If I go the CNC
route I will have to add in two more programming stages for every
project.

Dave
Click to expand...
Ok, the output is probably too low resistance for the driver you are
using. If you disconnect the thing you are driving, then it probably
will go up to 5V, right? If so, all you need is a follower, which is
an NPN transistor, connected to the PWM output and the input, like
this:

5V ---------------.
|
| collector
base |/
PWM --------|
|>
| emitter
|
'----------Laser

(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

This will decrease the required current at the PWM to 1/50th of what
was required before.

At 100mA, if your PWM drives it the base up to 5V, then the transistor
will only dissipate about 40mW, so any little NPN transistor will
work. Radio Shack will have them. 2N4401, 2N2222, 2N3904, etc.

This is probably worth a try.

Regards,
Bob Monsen
 
On Sep 20, 4:52 pm, Robert Monsen <rcmon...@gmail.com> wrote:

Hi Bob,

Thanks for the reply. No, this is 450mV with or without the Laser
connected. The output remains the same into load no load.

Ok, the output is probably too low resistance for the driver you are
using. If you disconnect the thing you are driving, then it probably
will go up to 5V, right? If so, all you need is a follower, which is
Click to expand...
Dave
 
On Sep 18, 5:32 pm, John Fields <jfie...@austininstruments.com> wrote:

Hi John,

I have a solution for you, but since it seems that you want to make some
money off of it, I do too.
Click to expand...
Yeah, you are right. Here I am retired and living on SS of $1200 a
month. I am trying to make a few extra bucks to brighten my lifestyle
a touch. I bought the replacement Laser about 7 years back when I was
working and it has been sitting waiting to be used for some project or
other. When I was given the dead marking machine, I thought I was on
the way to a little more fiscal independence.

That seems a little ways off still, but I am hopeful and will keep
plugging away at it.

I am sorry, but there seems little point in emailing you as I have
little enough to spend as it is.

Thank you for the offer.

Dave
 
On Sun, 21 Sep 2008 16:46:41 -0700 (PDT), "Dave, I can't do that"
<davenpete@gmail.com> wrote:

On Sep 20, 4:52 pm, Robert Monsen <rcmon...@gmail.com> wrote:

Hi Bob,

Thanks for the reply. No, this is 450mV with or without the Laser
connected. The output remains the same into load no load.

Ok, the output is probably too low resistance for the driver you are
using. If you disconnect the thing you are driving, then it probably
will go up to 5V, right? If so, all you need is a follower, which is

Dave
Click to expand...
Ok, then you'll need to go the comparator route. Here is a simple
circuit that might work, using a TL431 as a comparator:

5V--------------o----------o---------.
| | |
| | |
| .-. |
10k | 1k | | |
___ | | | |
Input -|___|------' '-' |e
A | b |<
| o-------| PNP
| | |\
| .-. |c
| 1k | | |
| | | |
| '-' o-------Output
| | |
| k |
| - TL431 .-.
'----------------r- ^ | | 10k (probably not needed)
a | |
| '-'
| |
| |
GND------------------------o---------'

http://www.fairchildsemi.com/ds/TL/TL431A.pdf

(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

The TL431 is a shunt regulator. If the voltage on the 'r' pin goes
above 2.5V, it'll suddenly become very low resistance between the k
and a leads. So, if you set the pot so that the r lead goes a bit
above 2.5V when the input is 400mV, and a bit below 2.5V when the
input is 0, it'll cause the PNP transistor to turn on and off.

Look at the datasheet link above for more information. You can get
these at electronics surplus places online, or of course mouser or
digikey.

I'm sure there are simpler solutions, but this one will give you a
nice crisp square wave with a minimum of parts.

Regards,
Bob Monsen
 
On Sep 26, 4:31 pm, Robert Monsen <rcmon...@gmail.com> wrote:

Hi Bob,

Ok, then you'll need to go the comparator route. Here is a simple
circuit that might work, using a TL431 as a comparator:
Click to expand...
Thanks for that. I'll keep you posted

Dave
 
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