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Monday, April 10, 2017

K40 Laser Power Driver Circuits

K40 Laser HV Power Driver 

As the investigation of the laser drive methods continues we now aspire to understand how HV power is applied to the K40 laser tube.
This post is a continuation of laser-power-supply-control-take-2.html, Whereas the focus in that post was the understanding and implemenation of digital controls, this post continues with a focus on understanding the internal driver circuitry of the LPS.

Other related posts are:


+Don Kleinschnitz


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Your donations help fund additional research, tools and parts that I will return to the community as information.
For other information on the K40-S build use the  K40-S BUILD INDEX with schematic




YOU ARE ENTERING A ZONE WHERE 20,000 Volts will be present!





Most people are not skilled enough to be even near and certainly not inside a high voltage power supply such as this without special training and equipment. As an example this is the specially designed and built lab environment that I use to work on Laser Power Supplies. Nothing less is acceptable. 
Hopefully there is enough information on my blog to satiate your curiosity about your LPS or help you troubleshoot outside of the LPS's guts. 
The output of these supplies are a lethal 20,000 Volts but there are equally lethal voltages that can be found in the driver circuits (400 volts). This means that even if you disconnect the fly-back (where the highest voltage is created) lethal and high voltages are present in the voltage multiplier circuits.
These high voltages can also damage test equipment such as meters and oscilloscopes if grounding and input attenuation are not carefully planned.

LPS Scematics

The  updated schematic is used as the base for the theoretical theory of operation given below.
Note: this schematic is created from a G-G-G-G style LPS.

Embedded schematic below .....

PWM control

Much of the PWM's operation was covered in the related post so it is not repeated here.


The output of the PWM drives, with a complimentary signal, an Hswitch which in turn drives a transformer in a push-pull fashion. The secondary of this transformer drives the HV driver MOSFETs.

Charge/Voltage Doubler

The charge (voltage) that is dumped through the HV flyback is created using a doubler technique. Each of the doubler capacitors it charged respectively on each 1/2 cycle of the input AC through the full wave bridge. This results in 2x the input voltage on the series combination of the two capacitors.
This reference is what helped me decode this circuit: PowerSourcesForCW-Lasers

AC Line Voltage selection

There is a selection switch on these supplies for 115 and 240 volt operation. When the switch is in the 115 volt position only one of the capacitors is charged at time so the voltage across each is equal to the line voltage (115) and when in series they add to 2x line voltage (230).
When the switch is in the 230 volt position the capacitors are charged in series so each capacitor has 1/2 AC Volts or 115 volts each. The net result with 230 VAC in is the same as 115 VAC in. 

The operation is simplified in the image below.

Voltage Doubler Operation

HV Driver

The HV driver uses the complimentary signal from the Hswitch to dump the charge from the doubler capacitors through the flyback's primary. This results in a secondary high voltage that is roughly proportional to the flyback's winding ratio * primary voltage.

The image below is a simplified view of its operation. It shows that the current is dumped through the flyback in two directions, creating an AC like signal that has a period equal to the PWM.  I need to verify this theory with a scope.
Simplified Flyback Driver

Sense Transformer

In series with the flyback and in turn its current is a transformer that converts the flyback current to a proportional DC voltage. This voltage provides current (I) feedback to the PWM controller.

Open question: This method senses current in the flybacks primary but how does that know and regulate the current in the tube. The tube exhibits a negative resistance when it fires so how is the current in the tube measured and regulated, seems it isn't. 

Flyback Transformer

I am unsure at this time if the flyback module contains a ballast resistor and HV diode. I suspect that it does.

HV diode 

Enjoy and comment
Maker Don

Sunday, April 9, 2017

Adding an Analog Milliamp Meter to a K40

Instructions for Adding an Analog Meter to a K40

Some vintages of K40's now have digital meters and pots. Some users find then sufficient and convenient others have found that having more information about the position of the pot and an analog representation of the laser tubes current to be advantageous.  

While you are adding this meter to your K40 you may also consider adding a high resolution pot and/or a pot position indicator: 
Thanks, to +Bob Buechler for testing out these instructions, doing the drawings and reporting on the results in this post.


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Your donations help fund additional research, tools and parts that I will return to the community as information.
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Installing the Analog Meter

Summary of the installation.

The analog meter is going to be installed in series with the wire that routes from the lasers cathode to the -L connection on the Laser Power Supply (LPS). 
[the -L connection is the leftmost pin on the leftmost connector on most LPS's]

Here is a simplified wiring drawing of the installation, courtesy of +Bob Buechler:


You will need the following materials

  • New Meter Note: this meter is larger than used in the stock K40
  • Wire, as needed for your installation
  • Heat shrink tubing, as needed for your installation
  • Ring tongues, as needed for the meter you choose
  • Terminal Pin  and crimper

You will need the following tools:

  • Wire cutters
  • Soldering iron & or crimp-er to match the terminals you are using
  • Pliers or small wrench for tightening the meter nuts

Meter Mechanical Installation

  • Pick an appropriate place to install your meter, cut hole(s) as needed and install

Meter Wiring

  1. 1. Pre-check:
    1.  Verify that with the "Laser Switch" enabled, when you push the test function the laser fires.
    2. Power down and unplug the mains from your machine
  2. Find the wire that connects to the cathode (the end the laser light comes out of) end of the laser tube. Often its a black or green wire. 
  3. Trace that wire to its other end which should be connected to ground (L-) at the LPS. Note: never not ground the cathode or the (-) side of the meter directly to the frame. The lasers current must return to the LPS itself on pin -L. 
  4. Find the lasers ground port on the LPS. Its usually called L-, its the leftmost connection on the leftmost connector. Do not confuse this with the L that is on the rightmost connector with the DC voltages.
    L- on LPS with all green connectors

    L- on LPS with green and white connectors
  5. Remove the existing wire from L- and verify with an ohmmeter that that the LPS pin (L-) is connected to the FG pin on the LPS and that both of those pins (L- & FG) are connected to the frame of the machine. There should be close to 0 resistance to ground (frame) on these pins. Note: this is a good time to test that there is 0 ohms to GND at the frame pin on the mains connector.
  6. We want to reroute the existing wiring (that went from the tubes cathode to the LPS) to the (+) side of the meter. Do such by pulling the L- end of the wire that connects to LPS out of the harness enough to reroute it to the + side of the newly installed meters terminals. Note: Unless absolutely necessary do NOT disconnect the wire from the cathode as that is difficult to replace. When this step is finished the wire that previously was routed from the lasers cathode to the L- is now rerouted to the + side of the meter.
  7. Connect the wire of step #6 to the meters + terminal with an appropriate terminating terminal. Usually the meter has threaded studs with nuts and washers. I recommend using a ring tongue terminal soldered to the wire. See parts list above.
  8. It is common for the meters terminals not to be marked. If not marked start by connecting this wire to the left terminal of the meter (looking from the back), its a guess!
  9. Get a new piece of wire that is long enough to route back to the LPS (L-) pin from the (-) of the meter. 
    1. Use the same size or larger wire (yes it matters) and the same color if possible (colors do not matter but will be easier to trace later). 
    2. Connect this wire from the meters (-) terminal to the L- of the LPS.  
    3. Terminate the meter end with a ring tongue like step #7. For the LPS end use a crimped pin of the correct wire size. If you do not have the ability to crimp a pin at least strip back and tin the wire with solder. Insert the wire into the L- terminal and tighten securely.
  10. After insuring that you have not shorted anything with shards of wire etc prepare to return power to the machine. As a rule I vacuum my machine in the area I have been working with a crevice tool. Be careful not to create a static charge.
  11. Return power to the machine with your hand on the switch in case of smoke. No smoke? Then proceed.
  12. Turn the power adjustment pot (or digital control) to about 1/3 or less of its range. In case the meter is in backward we do not want to stress it. 
  13. To test the meter enable the laser [Laser Switch] and then push the [Laser Switch] while watching for movement in the meters needle. The meter should read the lasers current and you are done.
  14. If no movement is noticeable on the meter these things could be wrong:
    1. An error in the wiring, recheck using the steps above.
    2. The meter is in backward. Swap the wires on the back of the meter and return to step 10.
    3. The laser is not firing, check to see if the tube ionizes?
    4. If you cannot get it to work post a picture of all of the above connections and wiring with my G+ address +Don Kleinschnitz in the Laser Engraving 

Links on G+

"Ideally you want to cut the wire in a way that the meter can physically be placed in series with it leaving the cathode and the LPS end terminations alone. Just putting ring tongues where you cut it to connect the the meter. i.e The meter is placed in series with the current wire.

If the wire is not long enough cut the cathode wire long enough to reach the meter and put a ring tongue on it and connect it to + of the meter. Get another wire that is long enough to reach the LPS and put a ring tongue on it connected to the - side of the meter. Put a pin terminal on the LPS end.

Don't have a pin terminal and crimp-er? Alternatively tin the wire with a liberal amount of solder and insert and screw that into the LPS terminal.

If you want to keep the pin terminal you can splice it and a section of wire to a longer piece just insure you solder properly and cover it with shrink wrap."

Soldering Ring Tongues

I solder these type terminals because I have had problems with crimps corroding and/or vibrating loose. Theory is that if you crimp correctly this will not happen however soldering insures it does not.

Prepare the wire:

Strip the wire back far enough so that the bare end inserts fully into the barrel to its end


Cut and slide over the wire a piece of heat-shrink that will cover the barrel of the terminal after soldering. The plastic cover may or may not come off or loose from heating. Most of the time I remove the plastic before starting.


Put the ring tongue on a heat restive surface or in a clamp. I lay mine flat on a piece of 600 grit sandpaper (the surface is heat resistant). Insert the wire through the barrel. Press with the iron on the ring tongue side of the terminal and heat while applying solder until the barrel of the terminal fills up. Depending on the size it may take a fair amount of heat. Don't put so much solder on it that it flows around the ring as that will impede attaching it to screws.


Clean flux from the terminal and slide the heat shrink up over the barrel and shrink it over the plastic if its still there. Sometimes the plastic falls off or needs to be cut off.

Some say this is overkill because its a pain to do but I have never had one fail over years of use.

Enjoy and comment!

Monday, March 27, 2017

Measuring Laser Marking Quality


There comes a time when you need to measure the output (markings) of your K40 with a known pattern in an accurate and repeatable way. This post focuses on tools to do just that. 


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Your donations help fund additional research, tools and parts that I will return to the community as information.
For other information on the K40-S build use the  K40-S BUILD INDEX with schematics

Laser Marking Measurement Magnifier

This loop (not sure this one comes with the reticle) was acquired while I was developing laser printers. These magnifiers have optics and a removable reticle. The reticle in this loop allows you to measure lines spaces, line weights and spots.
Although this magnifier is nice because it has a reticle designed for measuring graphics art any magnifier with a graticule could be used and the phone table design adapted.

Some Other Magnifier Sources


Phone Holder Table

I wondered if I could get good quality photos from my phone (S7active) laying on top of the magnifier which is below a fixed FL table.
Answer: Yes!.

I designed a simple table from acrylic that can be of course cut on your K40.

Table with LED light source (HF). Phone sits on top.

Measurements Photos

1 line on 2 lines off pattern. Measured output of laser printer

Marking Test Patterns

The most critical part of this tool is of course the pattern. The pattern was created in Inkscape as vectors. Vectors were drawn at the pixel level to create various resolution patterns in horizontal, vertical and diagonal directions. Line patterns with alternating line weights and spaces are used to test the systems response and the edges of these patterns when vector drawn and raster-ized can easily show errors. Some measurement values in mm are included on the pattern for reference.

Pattern labels:  the patterns are labeled with line and space values that indicate line and space values respectively [line&space]. Example: 1&2  = "one line width* ON and 2 line widths OFF. 
* Line Widths are relative to the images resolution in this case SVG resolution or 90.07dpi. Also note that the resolution of Inkscape can change as its version changes.

The .svg file is Resolution Test Pattern. I will keep it updated as I improve the patterns.

This file can be used in at least two ways and in any position(s) on the work-space:
  1. Download convert to Gcodes in your favorite CAM tool, I use LaserWeb. Then print this file on the test material subsequently measuring the image artifacts to insure that line width, position, spacing and edge acuity is correct. This tests vector marking.
  2. Save the .svg file as a .jpg and convert the image to a raster scan Gcodes in your favorite CAM tool, I use LaserWeb. Then print this file on the test material subsequently measuring the image artifacts to insure that line width, position, spacing and edge acuity is correct. This tests raster scan marking.

Picture courtesy of and marked by +Chris Menchion

Picture courtesy of and marked by +Chris Menchion

A micrometer will work accurately if you measure across multiple strokes.
Picture courtesy of and marked by +Chris Menchion


This tool should be able to show errors caused by optics, electronics and mechanisms:

  • Errors in vector moves: "Positions, distance and start stop accuracy".
  • Raster scan synchronization from scan to scan: "Edge wiggling".
  • Resolution errors: "Lines not spaced properly"
  • Dot size adjustment errors: "Vector lines should create close to an even black fill if the spot size is correct"
The source of different errors can be isolated by comparing vector vs image marking of the same pattern. 
Example: vertical "wiggling" is noticed when marking. If there is no vertical "wiggling" on vector vertical strokes but there is on image vertical strokes this may indicate that there is a problem when the gantry reverses its horizontal motion. In the vector case the stroke is drawn vertically in one move. In the raster case the stroke is drawn by placing one dot under the other on each scan. When the gantry is scanning it marks a dot going right moves down a scan and then marks a dot going the other direction. Maybe a loose X stepper belt or its pulley?


This tool should help in optimizing for materials!

Marking quality with a laser has inherently two challenges:
  • The power in a laser beam is Gaussian distributed with less power at its perimeter than in the middle. Therefore when two perfectly placed lines are marked parallel to each other the lower energy at the edge results in lower surface exposure and a banding effect** can be seen. This uneven power characteristic of lasers complicates the selection of beam size. Increasing the spot or power can reduce the uneven exposure due to overlay, but at the cost of resolution. 
    A Simplified Explanation of Exposure
  • From material to material exposure (how it burns) characteristics can vary widely. What darkly marks one material at a certain speed, spot size and power may not even mark another material at all. In the case of wood moisture content can even cause differences in the same wood type. 
** Banding can be caused from multiple types of errors in the system, including exposure, optical, electronic positioning and mechanical instabilities. 

This tool will help with optimization by making it easier to measure position, line weights, spot sizes while viewing their effect on the visual appearance of the pattern.

Enjoy and comment,

Monday, March 6, 2017

Laser Response Charcteristics

Laser Response Characteristics

I moved the research that I have been doing into "laser response" to this post to capture it in a more focused way. 
Understanding the lasers response is an important part of getting to the best engraving control possible. The engraving control basics are described in Engraving-and-pwm-control.html. 
Understanding the relationship between the HV power (voltage and current), the tubes gas discharge characteristics and the lasing process of the C02 is integral to an understanding of how to optimize digital control of its power.


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Your donations help fund additional research, tools and parts that I will return to the community as information. For other information on the K40-S build use the  K40-S BUILD INDEX with schematics as a source of information 

Links to Related Posts

Electrical Modulation of a CO2 Laser

"Low frequency modulation can be achieved by pulsing or chopping the electrical power to the discharge. As the frequency is increased, the effect of the varying input decreases and above a few kHz, disappears entirely. The output of a DC or RF excited CO2 laser are both CW beams.
(From: David Toebaert (
This remark really holds for any kind of CO2 laser (the effect gets worse at higher pressure). It's just nature: it takes time for the molecules to 'meet' one another causing the delay. For a laser at 100 mbar (around 76 Torr) and a typical gas mix, the cut-off frequency is about 3 kHz. Above that the modulation of the input power is strongly damped and hardly visible anymore in the output power.

Simply think of the discharge as a *low pass filter for the input power, no matter how you excite the discharge. Of course, it's possible to modulate the input power at much higher frequencies (e.g. an RF supply can easily be modulated up to 100 kHz, that is, the Mhz signal is modulated at 100 kHz), but from the point of view of wanting to modulate output power, it makes no sense. Maybe it's beneficial for other reasons (e.g., discharge stability)."

*Whats a low pass filter?

The Effect of Modulation Cutoff Frequency 

The article above says that the laser cannot transfer input power changes that occur at a rate > than 3kHz. That means that the max time between changes that will be useful is: 3kHz  = 1/3000 = .00033 = 330 us. 
This means that in the model above the suggested pwm period (200us = 5kHz) is longer than the response time of the lasers gas ionization. 

If that is true then:
  1. The PWM period needs to be much longer or the gantry slowed down considerably
  2. The much faster times I measured (2us) by monitoring current suggests that it is not a  indication of the speed of light output. Is the current flow during ionization much faster than the light output?
More testing needed :(.

Laser Gas Discharge Characteristics

Negative Resistance
Negative resistance of a gas discharge: the voltage and current increase as described by ohms law until the discharge point. Then rapidly the voltage decreases and the current increases.

The hypothesis used in testing (above) and modelling; that the current flowing through the laser tube can be used as a faximile of the response of its light output does not track with the above modulation information :).

Laser Power Sources

Electric Discharge

Pumping the Laser

This video shows measurements of response speeds in the 4ms region.

Laser Operation

Lots of info here: 

CO2 Info Summarized From Links

Gas mixture & its function:
13.5% N2 :    excited by gas discharge (pink glow) collides with and moves CO2 to level 3
9.5%   CO2: molecule that lases at energy level 3-2.
77%    He:    collides with CO2 at level 2 and then collides with tube walls for cooling
2%      H2:    gas discharge disassociates CO2 into CO and 02. H2 mixes with CO & O2 to regenerate CO2  

Ionization Voltage: 25 KV
Voltage at lasing:    13-15 KV
Negative resistance: 200-300K

Breakdown voltages

CO2: Air *.95
Air:  3,000,000 V meter

Laser Tubes

Synrad 40 W Lasers: Specifies a 100us rise time.

References To Aricles and Previous Work
Understanding CO2 lasers
Principles of plasma discharge
Dynamic PSpice Model of C02 Laser Tube
Gas Laser Electronics
Basic Laser Principles

Enjoy and leave comments and discussion;

Maker Don

Tuesday, February 28, 2017

K40 Clamping Table


I have seen many versions of power and static tables, in fact I have both.
This table design, which was invented by +Scorch Works, is the simplest I have ever seen. I decided to see if I could document the design and add a few features. Then I will likely build one.
After using both the static table and the powered one I found the following:
  • The static table is hard to adjust and therefore changing out materials is a pain.
  • The powered table is a lot more expensive and seems like overkill for most of my work which is 1/8-1/4 materials. It requires power and switches, then again it does have a nice matrix of pin holes.


Please consider donating (button to the right of this post).
Your donations help fund additional research, tools and parts that I will return to the community as information.
For other information on the K40-S build use the  K40-S BUILD INDEX with schematics

The Origin

The original design was first posted on G+ bu +Scorch Works and deservedly garnered a lot of praise for its simplicity and innovative approach.Whereas most designs lift the target item up to the right height this design simply keeps the surface of the target at a predetermined height using a clamping bar. The top of the clamping bar is pre-adjusted such that its under-surface is at the right focal point for the laser. 
The clamp can be used without a bed. Alternately, a bed made of any kind of surface can be inserted into the clamp below the material.The thickness of the bed does not effect the focal point since it is below the target. In fact for engraving the thickness of the material does not matter either. 
Struts can be placed flat or on edge in the clamps or under the target material providing additional options for leaving a gap between the bed and the material as it is being processed.

For cutting most materials the laser should be focused 1/2  (1/2T) way through the material. Getting this setting with this design is unsolved and still an open brainstorming item.


Its seemed only fair that since +Scorch Works shared this approach someone should create a set of drawings to share the build, although the design is simple enough to build without them.

Design Considerations

I set these design goals for any new design I would attempt:
  • Top adjustable reference plate with lock
    • Uses top accessible and floating 1/2-20 screws that capture and adjust the upper plate up/down
    • Loosen locking nut, adjust height then lock the nut. A one time adjustment.
  • Spring loaded clamp
    • Uses the original design
  • Easy to insert/extract from the machine [no screws]
    • The unit sits on the floor and the throat can be collapsed by releasing the locking knob and sliding the front clamp forward.
  • Easy initial install [no drilling or taping into the K40]
    • Fits between the Y gantry and rests on the floor
  • Maximize the clamping thickness 
    • The adjusting screws have substantial travel
  • Adjustable throat
    • The center shaft allows the front clamp brackets to slide forward and back with a locking knob.
  • Cutting and engraving capable
    • Haven't found a good way to lift the target above the reference plane by T/2. Thinking of an adapter that goes under the clamp and allows material to "stick up" T/2. You would need a set for each size though :(.
  • Fabrication in home shops with standard materials.
    • All the materials can be purchased at Home Depot except the threaded Nutserts (rivet nuts). Nutserts are available in many nut-bolt stores and on Amazon. 
    • Fail: the 1/4-20 shoulder bolts will need a shoulder cut in them to accommodate side mount retaining clip.
    • Aluminum from HD fabricated with pop rivets.

Faults With this Model

1. The reference angle brackets may not hold well in the middle without an additional post. I wanted to keep as much clamping surface as I could so I omitted a middle post in the inaugural design. If needed posts can be added reaching down to the floor frame. Alternately the lower clamping plate could be replaced by angle material.
2. Positioning the target T/2 upward for cutting
3. Fixed sized floors will be necessary (if floors are used).
4. Potential binding of the front bracket as it is moved rearward. If needed plastic guide wheels can be added under the adjustment screws.
5. The entire assy, might move due to vibration in K40 bed. Add rivet nuts under the back bar and attach with wing nut screws.

The Design Model

Models below using actual K40 dimensions.The gantry is not shown but the key side frame surfaces are accounted for. This is not built yet but suitable for reviewers to beat up!
Leave your comments.

Enjoy and comment
Maker Don

Sunday, January 29, 2017

When the Current Regulation Pot Fails!


When your "Current Regulation" pot fails there is a better part to replace it with.
This new pot is $6.99 and features 10 turn linear resolution with a smooth rotary action.


Please consider donating (button to the right of this post).
Your donations help fund additional research, tools and parts that I will return to the community as information.
For other information on the K40-S build use the  K40-S BUILD INDEX with schematics


The wipers fold back.
I guess I turn the pot to fast!
There are supposed to be multiple wipers. 


Getting the knob off was a B*%^+. I had to grab the shaft with a vice grips. Then wedging a flat blade between the vice grips and the knob I pried it off. I think the knob was glued on ..... seriously!

After the gripping experience with the knob the rest was easy. Simply wire in a new pot.
This one is a linear multi-turn wire wound pot which gives much better current resolution and feels nice!

Purchase here

Wiring & Diagram

The replacement is pretty simple if you pay attention to the pots connections when you take the old one out. The only confusion might be that the new pots connections are not in order. The wiper is the first pin (2) from the end opposite the shaft.
If the pot operated backward reverse the leads 1&3.

Here is some help ....

Careful the wiper is on the left.

Pot with DVM current readout
I wired in a plug to make disconnect easy and modular

Installed in the panel 


I added a DVM across the pot so that I could get a digital representation of the pots postion and the relative current. 
When setting up a job type I record the digital value and then next time I do that same job I just reset the pot to that value to accurately repeat the setting.

Note: you need a 3 wire DVM so that you can read from 0.

See the wiring diagram above for installation.

The green film in this pack works for a filter when making a plastic bezel .


This knob might look nice and installs with a set screw.

Purchase here

Enjoy and comment
Maker Don

Saturday, January 28, 2017

K40 LPS Configuration and Wiring


This post captures the many K40 PS configurations that I am/have worked on.

READ THIS POST if you want to know about how to digitally control a K40 LPS: 

I need Laser Power Supply's (LPS) (dead or alive) to test:

If anyone has a LPS schematic or a blown LPS that we can use to better understand its interface please contact me at: or comment below.


Please consider donating (button to the right of this post).
Your donations help fund additional research, tools and parts that I will return to the community as information.
For other information on the K40-S build use the  K40-S BUILD INDEX with schematics

Reverse engineering Information:

From Scott Marshall on G+:

This is the manufacturers page there's specs and such there, minimal, but some info.

Inputs P+ and K+ directly drive these optos:

Driving this PWM Controller by good old Texas Instruments

Inputs are speced at 5v, but look to work on 3,3v (show 3v logic High)

It's pretty conventional switching supply stuff from there. The Hv circuit seems to be a flyback running at about 440hz (awful low) with a tripler output.
300W 11kv nominal 4-20ma (26kv insulation breakdown)


Shown in "[approx value]" are the measurements taken from my machine as a help in troubleshooting.

These measurements are approx and your actual readings may vary.
However if they are way off that may be an indication your have a problem.

BTW: wire colors also match my machine but yours may be different.

AC Power Connector

Not always in this order
  • -L (cathode of laser) [0 ohms to frame and to cathode of laser]
  • FG (frame ground, directly connected to frame)[0 ohms to frame]
  • AC (one side of main power)*
  • AC (other side of main AC power)*
* measured AC across the mains = [whatever your mains volts is]

 DC Power Connectors:

The DC Power connector on the LPS typically contains these signals:

[* ] = measurements with DC connector disconnected
  • 5VDC (Yellow) [*5VDC to frame & gnd]
  • GND (Black) [*0 ohms to frame]
  • 24VDC (Green) [*24VDC to gnd and frame]
  • L (Pink) (the M2 Nano LO pin connects to this pin in stock K40's) [*4VDC]

DC output capacity specs:
  • 24v@ 1 amp
  • 5V @1 amp

General LPS specs for GWWG LPS from ebay:

Taken from ebay site

Understanding K40 Laser Power Supply Configurations

To effectively test, repair, replace and convert K40 LPS it is necessary to know that kind of supply you have.
This section attempts to identify and categorize the LPS I have encountered. There are two parts to identifying the LPS:
  • Physical Configuration
  • Control Schema
An example configuration might be: GGGR-A. The notation is explained below.

Power Supply Physical Configurations:

Key to my physical configuration labelling

First Letter: color of AC power connector
Second Letter: color of control connectors
Third Letter: color of DC power connector
Fourth Letter: color of Power LED

Physical Configuration GWWG

Label on back of my LPS supply, I got to it with a video borescope :)
Ebay: MYJG40 (first time I have seen one like mine for sale)

MYJG40W [S/N: 2015090481]

Mine looks like this (I think this type is out of production): 

Physical Configuration GGGR


Laser Power Supply (LPS) Control Interface Schema's

K40 LPS typically have either 1 green 6 pin connector or 3 white connectors for control (located between the AC and DC connectors. In all cases some combination of their signals perform the same basic functions of:

  • laser enable 
  • laser
  • analog power control. 
To make things more complex in some configurations the 6 Pin green connector contains different control signals than other green connectors with the same pin #'s. For that reason along with the physical configuration it is necessary to know what control schema is used.
The basic way these signals are used is shown in the sketch below.

Showing the interface equivalent circuit.

Control Schema Labels A-C

I arbitrarily labeled the two types of control interfaces "A" - "C" to simplify the documentation.

Type "A"  LPS Control Schema

This is a common K40 supply and is usually physical configuration GWWR or GWWG.
This schema uses 3 separate white connectors in the order below from left to right.

Laser Switch (enable)

  • P+ Laser Switch [**4.28VDC]
  • P- gnd return for Laser Switch [0 ohms to frame]

Test Switch ("FIRE")

  • K+: Test switch [**4.28 VDC]
  • K-: gnd return for laser [0 ohms to frame]

    Current regulation

    • Ground: signal ground [0V to frame]
    • IN: laser current control 0-5VDC [**not sure, likely floating]***
    • 5VDC: 5V power [** 5.02 VDC]
    Note: the "Current Regulation" pot is connected across these three signals with the center tap connected to IN.
    *** you can partially test "IN" by measuring the resistance across IN to gnd while turning the Current Regulation POT on the panel. The resistance should vary with pot position.

    ** voltage measured with connectors removed

    Type "B" LPS control interface

    These supplies often have black cases and sometimes have only the control and AC connectors. They usually do not provide DC power.

    Terminal Definition as follows:

    THInput SignalOn-Off laser control,TH≥3V, emitting laser; TL≤0.3V, no laser.
    TLInput SignalOn-Off laser control,TH≥3V, no laser; TL≤0.3V, emitting laser
    WPInput SignalOn-Off laser control,TH≥3V, no laser; TL≤0.3V, emitting laser
    GGNDThis foot must be connected well with the laser machine shell and the ground of control board.
    INInput SignalThe control of laser power: Both 0-5V analog signal and 5V PWM signal can control the laser power.
    5VOutput PowerOutput 5V, the maximum output current is 20mA.

    Note: WP = water protection, this is an interlock loop for the water pump.

    Type "C" LPS Control Interface

    I think this is the configuration that ships with newer K40's.

    Type D Control Schema

     Same schema as a Type A but a "D" signal replaces the "P" and works the same.

    Special LPS Wiring

    Special wiring for this supply, note part # at top of drawing

    Converting From One Supply Type to Another

    Conversion of GGGG-C to GWWR-D

    LPS Related Album

    Enjoy and comment
    Maker Don