Venus Heat Sealer (VHIB) controller module update

Summary

Other than using a resealable shielded plastic bag for protecting electronic components, the humble heat sealer must come in a close second for a more permanent solution when sealing plastic bags. There is however, a reasonable difference in build quality of heat sealers.

Venus Pack - Heat sealer

This blog shows how a Venus heat sealer controller could be updated, with a view to improving the robustness of the design.

Heat Sealer
The subject of this blog was a product by Venus Pack which had seen a decade of use with only one trip back to the manufacturer for a repair. The actual model was VHIB200.

Heat sealer model VHIB200

After transporting the sealer to a new location, the unit heat sealing became intermittent. Evidently this behaviour was similar to the last issue before manufacturer repair. Time for review and rebuild.

Warning and Disclaimer
The voltages present in this design are 240V AC, which can easily kill. Care and steps should be taken to prevent electrocution. Wiring of this nature should only be performed by experienced persons. I take no responsibility whatever for misuse of the information detailed on this blog.

Heat Sealer Controller
Shown below is an image of the damaged controller. The culprit turned out to be a leaded resistor. Note the leftmost resistor in image below, with the lead snapped from the body.

Heat sealer controller damaged resistor

The board was repaired with a smaller wattage resistor as a temporary fix, shown below.

Heat sealer controller

Controller Design
The heat sealer control board design is a simple single sided board using an RC timer to operate a relay which powers the transformer which drives the heater element. Using the potentiometer the heater element operating period is set.

Below is the original heat sealer schematic showing the main components involved in the units operation. This schematic was taken from the original documentation, PDF available here.

Venus Pack Heat Sealer Schematic

A digital current clamp was used to measure the currents on the primary and secondary of the transformer. The primary current peaked at 2.5A and the transformer secondary current peaked at over 10A. With these currents in mind it was decided to switch the transformer primary in a similar manner to the existing design which used a relay.

Controller Redesign
The changes to the controller design were firstly to move away from a relay to a TRIAC. The relay was responsible for switching of the primary of the transformer which powers the heater element. Secondly the new design was primarily made with surface mount components and separated into two circuit boards for isolation.

Similar to other designs in my blogs, a Cypress PSoC (CY8C4245) was used. For a design with relatively simple control requirements, ADC in and digital out almost any controller could be used, should a few dollars need to be shaved off the project.

Schematic Design (TRIAC and Power Supply)
Unlike the factory circuit design with derived non-isolated DC from the mains AC supply, the redesign was fully isolated between AC and DC. The TRIAC and power supply, essentially the high voltage items, were restricted to one of the circuit boards for the design. To achieve the isolation a small brick AC to DC power supply was utilised from Vigortronix, model VTX-214-001-106. With a dielectric isolated over 4kV this was more than sufficient for mains voltages. The 6V DC output was supplied to a 5V linear regulator as shown below.

Impulse Sealer Power Supply

An optional voltage divider was included on the output of the AC DC supply as a power supply fail sensing feature for the 6V supply.

For the TRIAC, isolation was achieved using one of the well known OnSemiconductor devices, the MOC3041. The OnSemi part has zero crossing, 400V peak blocking voltage.

Impulse Sealer Isolated TRIAC Drive

The TRIAC itself, ST part T810-600B, is rated at 8A 600V with a 5mA to 50mA gate trigger current range. There are a number of resources available for optically isolated TRIAC designs such as this oldie from Panasonic Industrial - Driving Triacs with Phototriacs. Should that link become extinct, here is a PDF version here on Google Drive, credit to the original author. Another article worth a read, originally from Fairchild, Application Note AN-3004 Applications of Zero Voltage Crossing Optically Isolated Triac Drivers or here on Google Drive.

In order to drive the optical isolator LED, some 15mA of current was required. Certainly 15mA of sourcing current is not possible from a single pin on the PSoC device, although some designers are more than willing to parallel up a handful of spare outputs with current sharing resistors - not a good design principle.

MOC3041 Transfer Characteristics

Literally for less than a dollar a SN74LVC2G17 Dual Schmitt Trigger and Buffer was used as the device driven by the PSoC to control the MOC3041. The maximum IO current for this device is 50mA which provides a strong drive current for the LED of the opto isolator.

Schematic Design (PSoC and IO)
The second circuit board used in the design contained devices that operated at lower voltages which included the PSoC, buffers, LED and potentiometer.

In the design shown below the PSoC controller shows inputs and outputs (IO) for the TRIAC control, ADC, LED drive, UART debug, option resistors and programming header. Not shown is the power supply decoupling section.

Impulse Sealer PSoC Design

To provide input protection to the PSoC ADC inputs 10R resistors with rail to rail steering diodes were included in the design.

PSoC Basic Input Protection

Operator control to set the sealer operating time was achieved using a standard wiper based potentiometer and feedback to the operator using a bicolour LED.

Bicolour LED and Potentiometer

Connection of the PSoC controller and peripheral hardware is achieved on an upper level sheet in the design software.

Impulse Sealer Upper Schematic

PCB Design (Sketch)
After performing a brief disassembly of the original impulse sealer controller, the dimensions of single sided circuit board were recorded. These were used to define the size of the new circuit boards.

Impulse Sealer PCB Dimensions

In addition to the overall circuit board dimensions, the original mounting location of the potentiometer, mounting screw and LED were also taken. A hand drawn sketch usually works out to be time saving information for the PCB designer especially when boards contains several or more specifically places components such as connectors, buttons or LED's.

Impulse Sealer Blank Power Supply PCB

Also included on the blank circuit board where a pair of M2.5 mounting holes to mechanically hold the pair of circuit boards - TRIAC and Power Supply together.

PCB Layout (TRIAC and Power Supply)
All schematic parts were checked then brought into the PCB design software. The image below shows a draft parts placement separating the high voltage on the left hand of the board and low voltage with TRIAC control on the right side of the board.

Impulse Sealer Power Supply Draft Placement

Using Saturn PCB Toolkit to check the voltage creep distance for the left and right sides resulted in a distance of more than 2.5mm. The distance between the low and higher voltage is based on the peak voltage not the usual 240VAC RMS measurement. The circuit board layout was updated, as shown in the image below, to allow for more than 5mm between the high and low voltage sections of the design.

Impulse Sealer Power Supply Final Placement

At the top right hand corner of the image above is a 4-way through hole inter board connector. This connector provides power to the controller board, control for the optoisolator and a feedback voltage from the output of the 6V power supply.

Routing the board was achieved using a double sided route. A top layer 0VDC polygon was used for the low voltage side of the board.

Impulse Sealer Power Supply Routed PCB

The circuit board power supply bottom side is shown below in 3D.

Impulse Sealer Power Supply 3D

PCB Layout (Controller)
The blank circuit board for the microcontroller board keeps the same dimensions as the power supply board. Also included on the board were the pair of M2.5 mounting holes, the location of the potentiometer, LED and central mounting hole.

Impulse Sealer Blank Controller PCB

To ensure the location of the potentiometer, LED and central mounting hole were correct the two related parts were placed on the circuit board.

Impulse Sealer Controller PCB - LED and Potentiometer

The image below shows a draft parts placement which kept in mind the orientation of the M2.5 mounting holes and the power supply circuit board interconnect.

Impulse Sealer Controller Draft Placement

Some minor changes were made to layout to facilitate a simpler route, final parts placement is shown in the image below.

Impulse Sealer Controller Final Placement

Routing the board was achieved using a four layer board. Top and bottom were used for signals, bottom for a 0VDC polygon with the two internal planes used for 5V and 0V power.

Impulse Sealer Controller Routed PCB

The circuit board power supply top side is shown below in 3D.

Impulse Sealer Controller 3D

PCB Population
Both the blank circuit boards were populated then fitted together with M2.5 x 12mm brass bolts and spacers. Nylon spacers would be a better solution for a more permanent solution.

Impulse Sealer Controller PCB Populated

The above image shows the controller circuit board with the PSoC, potentiometer and bi-colour LED visible. Connection between the controller and power supply boards was achieved using a 4-way header as shown above.

Impulse Sealer Power Supply PCB Populated

Shown in the above image is the power supply circuit board with the AC to DC power supply module, TRIAC and associated components.


Software PSoC Top Design
At the top schematic sheet of PSoC Creator there are only a few components, some of which are optional. In the image below the pin allocation of inputs and outputs are shown.

Impulse Sealer Pin Allocation

Shown in the image below are the inputs relating to the operational mode (optional) and outputs driving the bicolour LED and TRIAC.

Impulse Sealer Inputs and Outputs

For control of the TRIAC output a 100msec system 'tick' timer was used as part of the software. As an alternative solution, a Timer component could also have been used in a one shot mode. This has some advantages relating to code and timing accuracy.

Impulse Sealer Internal Tick Timer

To convert the potentiometer voltage the usual ADC component was used in single ended mode and referenced to Vref.

Impulse Sealer ADC

Lastly for debugging during software development, a UART component was added to round off the design.

Impulse Sealer UART

Test Code
To test the controller board, operational code was written with some provisions for additional measurements from the PSoC (die) temperature sensor and the output voltage of the AC to DC power supply brick.

The only provision for activation of the TRIAC was to match the Venus 0.2sec ON time and the OFF time was increased to around 3sec.

/*==============================================================================
 *
 * Heat Sealer Project
 *
 * Implements CPU control of a heat sealer design
 *
 * Built with Creator 4.1.0.3210
 *
 * 1/10/2017 - Intial write
 * 
*/

#include <project.h>
#include <stdio.h>

/* Defines */
#define CHANNEL_1           (0u)
#define CHANNEL_2           (1u)
#define CHANNEL_3           (2u)
#define NO_OF_CHANNELS      (3u)

/* ISR Prototypes */
CY_ISR_PROTO(isr_Timer);
CY_ISR_PROTO(isr_ADC);

/* Function Prototypes */
void Initialize();
void LED_Colour(uint8 led_colour, uint8 state);

/* Global Defines */
#define false                           0
#define true                            1
#define red                             1
#define green                           2
#define orange                          3

/* Global Variables */
volatile uint32 windowFlag              = 0;
volatile uint8  dataReady               = 0;
uint16  ADC_Die_Temp                    = 0;        /* Future use */
uint16  ADC_DC_Supply                   = 0;        /* Future use */
uint16  ADC_Run_Pot                     = 0;
uint8 channel                           = CHANNEL_1;
int16 adcVal[4u];

/* Function Prototypes */
void Initialize(void);
void LED_Colour(uint8 led_colour, uint8 state);

//==============================================================================
// Timer Interrupt
//==============================================================================
CY_ISR(isr_Timer)                       
{
    if (ADC_Run_Pot != 0) {
        ADC_Run_Pot--;                              /* Decrement the run timer - 100msec steps */
    }
    isr_Timer_ClearPending();                       /* Reset interrupt */
    Timer_Ticks_ClearInterrupt(Timer_Ticks_INTR_MASK_CC_MATCH);
}

//==============================================================================
// ADC Int
//==============================================================================
CY_ISR(isr_ADC)                        
{
    uint32 intr_status;

    intr_status = ADC_SAR_INTR_MASKED_REG;          /* Read interrupt status registers */
    if((intr_status & ADC_EOS_MASK) != 0u)          /* Check for End of Scan interrupt */
    {
        windowFlag = ADC_SAR_RANGE_INTR_MASKED_REG; /* Read range interrupt status and raise the flag */  
        ADC_SAR_RANGE_INTR_REG = windowFlag;        /* Clear range detect status */
        dataReady = 1u;
    }
    ADC_SAR_INTR_REG = intr_status;                 /* Clear handled interrupt */
    ADC_IRQ_ClearPending();
}

//==============================================================================
// Set LED Colour
// Passed the LED colour and state for driving bicolour LED
//==============================================================================
void LED_Colour(uint8 led_colour, uint8 state)
{
    switch (led_colour)
    {
    case red:
        if (state == true) {
            LED_R_Write(true);
            LED_G_Write(false);
        }
        if (state == false) {
            LED_R_Write(false);
            LED_G_Write(false);
        }
    break;
    case green: 
        if (state == true) {
            LED_R_Write(false);
            LED_G_Write(true);       
        }
        if (state == false) {
            LED_R_Write(false);
            LED_G_Write(false);
        }
    break;
    case orange: 
        if (state == true) {
            LED_R_Write(true);
            LED_G_Write(true);
        }
        if (state == false) {
            LED_R_Write(false);
            LED_G_Write(false);
        }
    break;
    }    
}


//==============================================================================
// Init PSoC 
//==============================================================================
void Initialize()
{
    ADC_SetChanMask(0x1);                                               /* ADC set channel mask - 3 channels */
    ADC_Start();                                                        /* ADC component start */
    ADC_StartConvert();                                                 /* ADC conversion start */
    #if defined DEBUG
        UART_Start();                                                   /* UART start - 115200 8 N 1 */
        UART_UartPutString("Impluse Sealer\r\n");
    #endif
    Timer_Ticks_Start();                                                /* Start 100ms system timer */
    isr_Timer_StartEx(isr_Timer);                                       /* Attach timer handler */
    isr_ADC_StartEx(isr_ADC);                                           /* Attach ADC handler */
}


//==============================================================================
// Main
//==============================================================================
int main()
{
 CyGlobalIntEnable;                                                  /* Enable global interrupts */
    Initialize();
    LED_Colour(orange, true);                                           /* Flash orange LED to verify start */
    CyDelay(250);
    LED_Colour(orange, false);
    while (dataReady == 0u){};                                          /* Read the potentiometer value */
    adcVal[CHANNEL_1] = ADC_GetResult16(CHANNEL_1);
    channel = CHANNEL_1;
    ADC_Run_Pot = 0x138A - ADC_CountsTo_mVolts(channel, adcVal[CHANNEL_1]); /* Invert potentiometer - hardware direction */
    ADC_Run_Pot = (ADC_Run_Pot / 300u) + 2;                             /* Scale the result, 0.2sec min, 3sec max */
    dataReady = 0u;                                                     /* Rearm in case a conversion is required */
    TRIAC_Write(true);
    LED_Colour(green, true);                                            /* Green LED ON to show run cycle */  
    for(;;)                                                             /* Loop here until sealer unpowered */
    {
        if ((ADC_Run_Pot == 0) && (TRIAC_Read() == true)) {             /* Switch OFF only is TRIAC is ON */
            TRIAC_Write(false);
            LED_Colour(green, false);                                   /* Green LED OFF */
        }      
    }  
}
/* [] END OF FILE */

Load Testing TRIAC
To load test the TRIAC on the power supply board an old 2200W 240V AC kettle, partially filled with water, served as the load. In order to keep the circuit AC test voltages low, a step down toroidal transformer was utilised. The transformer used in the test setup shown below had a pair of 18V secondary windings connected in series. Unloaded voltage was 43V AC which was suitably higher than the minimum operating voltage of the TRIAC.

Impulse Sealer Power Supply Board TRIAC Load Testing

During initial setup it was noted that the Vigortronix AC to DC supply was operating with the low 42V AC input voltage providing 6.2V DC and enough current to power the buffer driving the TRIAC. The Vigortronix datasheet states 90V AC minimum for the supply.

To ensure the TRIAC was not conducting when the 42V AC was supplied the control line, usually driven from the PSoC, was connected to 0V as shown in the image below.

Impulse Sealer Power Supply Board 

A full load test was not conducted on the PSU board, although the 27R resistance of the kettle provided over 1A of current through the load - enough to heat the TRIAC.

Impulse Sealer Power Supply Board During Load Testing

When 5V DC was applied to the TRIAC control line the current measured through the load was 1.4A AC, as shown in the image above. The supply voltage dropped to 38V AC when the load was connected.

The input voltage was increased to around 80V AC using a second transformer in series. The waveform seen by the load is seen below. Captured in the waveform is the activation of the impulse sealer, marked by the position of the trigger 'T', then the subsequent voltage supplied to the load as seen by the AC waveform.

Impulse Sealer Load Turn ON

In addition the minimum (0.216sec) and maximum (1.8sec) run time, based on the extents of the potentiometer position, were captured.

Impulse Sealer Min Run Time

Impulse Sealer Max Run Time

Operational Testing
To perform a full load test and check the operation of the design, the controller and power supply boards were fitted together then wired into the existing unit as a mock-up of the completed design.

Impulse Sealer Removed Transformer

Shown in the above image is the step down transformer removed from the impulse sealer chassis. The blue and green cables are the 240V AC mains supply and the two red cables are the primary to the transformer.

Below the image shows the updated controller and power supply fitted together. The existing four way connector on the impulse sealer was removed and replaced with crimped ferrules.

Impulse Sealer New Controller and Power Supply

After the connections were verified the impulse sealer was reassembled, transformer mounted back into the chassis and controller mounted into its original side mounting position.

Impulse Sealer Assembly

A new brushed black aluminium knob was fitted to the controller, no trimming to the potentiometer shaft was needed. The controller was then mounted with a single bolt and bench testing was then performed.

Impulse Sealer Controller Mounted

Below is a short capture of the impulse sealer being tested using an antistatic bag (PET).

Using a Fluke 325 true RMS clamp meter, a number of AC current and voltage measurements were taken when the impulse sealer was activated.

Primary Voltage: 240.3V
Primary Current: 1.75A

Secondary Voltage: 13.3V
Secondary Current: 13.8A

Prototype Release
For those wanting to use this project - schematics, Gerbers and PSoC project is available below.

Bug reports or schematic feedback is invited, enjoy!

Impulse Sealer Controller Schematics

Impulse Sealer PSU Schematics

Impulse Sealer Controller Gerber

Impulse Sealer PSU Gerber

PSoC Creator 4.1 Impulse Sealer

A Note on Improvements
For those looking to update the code, there was additional functionality added to the PCB to allow measurement of the AC DC converter output voltage. A scaled 6V DC output was made available on a PSoC ADC compatible pin.

On the same line of thought relating to code improvements, the internal PSoC die temperature was also made available to the PSoC ADC.

Rigol DP832 with standard banana plugs

Summary

This is more an 'instructables' rather than a blog post and relates to the undersized banana post holes on older model DP832 power supplies.

Rigol DP832

Undersized Binding Post - Early Models

Although I had been using the Rigol DP832 for some time, there only recently became a requirement to upgrade the leads used with the power supply. There has been an issue with the early model DP832 binding posts which had been mentioned on a number of forums such as the EEVBlog.

It should be noted that the newer DP832 models (second half 2017 builds and possibly earlier) have the larger 4mm sized internal hole in the binding posts.

Binding Post Drilling
Armed with a 4mm drill bit in the drill, the first binding post was carefully brought into a state of banana compatibility.

DP832 drilling binding posts

After the first binding post was drilled and the metal shavings removed, a new banana plug was tested - snug fit! Disclaimer - Modify the binding posts at your own risk. This posts shows how the binding posts were modified on my Rigol DP832.

DP832 new banana plug test

Using the 4mm bit results in a fit for the banana plug which is tight and my preference when handling anything power related. A 4.1mm bit was not tried however this was mentioned in the EEVBlog forum.

DP832 with newly drilled binding posts

The depth to drill the binding post is somewhat dependent on the original hole depth. 

DP832 binding post hole depth

On average the depth of the hole in the DP832 binding posts that were drilled was between 16-18mm. It should be noted the exposed metal section of a standard banana plug is approximately 18mm, however contact with the banana plug is achieved in the first 12mm of the banana plug only.

Altium kb4041681 JET database fix for unexpected error

Summary

This blog illustrates how Altium users may be able to resolve the issue created by Microsoft KB4041681, which causes a problem with JET databases in Altium: “Unexpected error from external database driver (1). (Microsoft JET Database Engine). This results in Altium being unusable - until the Microsoft update is rolled back.

Microsoft Updates
As part of Microsoft's October patch and rollout, changes were made breaking the long deprecated JET database. This has been tracked in numerous blogs such as blogs.msdn.microsoft.com. For Altium Dblib users the recommended change was mentioned in the KB4041681 release. There are two methods suggested below for resolving the issue in Altium.

My Windows 10 work computer is connected to a domain and ergo a group policy. Permanently blocking KB4041681 is not a reasonable solution when a group policy is applied to each computer, however for a Altium system originally built on Protel 99, this is fixable.

Users Dblib file

To start the process, Altium is launched and the appropriate Dblib file located and opened.

Just beneath the source of connection section in the Altium dialog box, the JET database error message is shown.

Altium JET database error

For the methods listed below users should use the appropriate link in place of the text <my Altium excel file>.

Method 1: Changing to Excel 2007
As highlighted by the helpful folks on the EEVBlog forums the file type can be changed to Excel 2007. Older systems such as mine used Excel 2003. Changing is achieved using the drop down list box, as shown below, "Select Database Type" from Microsoft Excel to Microsoft Excel 2007.

Setting for Excel file

Any associated Excel files(s) would need to be saved in the new .xlsx format.

Setting for Excel 2007 file

Method 2: Changing from JET

The second method changed the database. This can my ascertained by reading the Microsoft 'kb' release which states "Download and install the Microsoft Access Database Engine 2010 Redistributable, and then modify the DB connection strings in Microsoft Excel to use ACE as a provider. Example: Change Provider=Microsoft.Jet.OLEDB.4.0 to Provider=Microsoft.ACE.OLEDB.12.0."

The connection type is changed by selecting "Use connection String" instead of "Select Database Type".

Connection string for JET in Altium

This connection string however, uses the older JET database so the Microsoft.ACE.OLEDB.12.0 is used to replace the Microsoft.Jet.OLEDB.4.0. The provision is that the database engine redistributable listed by Microsoft is installed.

Connection string for ACE in Altium

At the same time the Excel file is saved as the newer format ".xlsx".

Testing
After saving the updated Dblib file, Altium was launched again. There were no immediate issues placing components in the schematic.

This is by no means the solution for all Altium users. The methods listed in this blog has been tested briefly on a Win 10 Pro machine running Altium 17.1.6 with all Windows updates applied.

Addendum
During testing of the solution listed above, some users noted an additional OLE related exception shown by Altium. A window similar to the image below was displayed when trying to connect to the database.

Altium database OLE exception

This is a known issue that has been documented by a number blog sites such as PCBParts. If an Altium Database File of type DbLib is being used, opening the file from within Altium may show a similar image to that shown below. 

First step is to backup the DbLib file. 

Altium database connection failed

The second step, install an Office 2007 System Driver as provided from the PCBParts blog. This is one known fix.

After installation of the Office 2007 driver two results were reported. Either no further issues were seen or the Altium Database File was overwritten such that previous information about the database structure was removed - fixed by copying the DBLib file backup from the first step.

CUI INC PDQ15 Remote Control Pin

Summary

This blog illustrates the measurement of the remote control pin available on the CUI INC® PDQ15 series of brick power supplies. Similar tests were conducted in a previous post with two MeanWell supplies.

CUI INC PDQ15 power supply

Control Pin
From the CUI INC PDQ datasheet (page 2), the voltages required to drive the ON/OFF pin are listed as greater than 3.5V for ON and less than 1.2V for OFF.

Remote control pin specification

Control Pin Input Voltage Measurements
To verify the operation of the control pin on the CUI INC PDQ converter, two outputs of a Rigol DP832 linear regulator power supply were used in the same manner as a previous blog which used MeanWell converters.

Rigol DP832

An initial test was conducted to determine the ON / OFF voltage hysteresis for the converter. Turn ON was 8.7V DC and turn OFF 8.0V DC. Tests were conducted with no input on the remote control pin (floating).

For the second test, one channel of the power supply provided the input supply to the DC to DC converter and the second channel on the supply provided the supply for the control pin. Both outputs of the power supply had a common 0V connection.

PDQ bench testing

The supply input voltage was increased, from the threshold ON voltage and the control pin threshold voltages determined and recorded.

Measurements for the CUI INC PDQ15 is listed below.

PDQ Measurements for supply vs control pin voltage

A visual representation of the above data is shown below.

PDQ Graphed measurements

The graph shown above is scaled to show the small variation in voltages required to activate the converter using the remote control pin.

Note On Temperature
The cold body temperature of a PDQ15 converter was measured at 19.2C. With a 24VDC input supply connected, no load, the PDQ15 has a quiescent power of just less than 2W. After 30 min the body of the supply had raised to 57.1C.

Summary

For this test of the characteristic response of the PDQ15 remote control pin, the measurements showed that it was similar to the MeanWell SKM series. The remote control ON/OFF voltages were flat after 14VDC although the voltages were not similar to the MeanWell SKM or SDM converters.

MeanWell SDM SKM Remote Control Pin

Summary

This blog highlights the need for verification and validation testing when changing or updating electronic parts. In particular all facets of the device should be reviewed or tested whenever possible.

Background
In a commercial arena, new parts or those parts earmarked for an upgrade, are usually checked on paper for suitability. The time spent on the comparison between parts usually depends on the parts complexity although specifics can be inadvertently overlooked from time to time. After the new part is sanctioned for use it is commonly bench tested or bolted onto an existing design to validate operation before being included in a new hardware (PCB) design.

For this blog two MeanWell products are referenced, the SDM and SKM series of DC to DC converters.

 MeanWell SDM30-24S5

MeanWell SKM15

Operational Characteristics
Comparing the datasheets of the MeanWell SKM to the SDM series, the SKM is technically the better device. After all, the SKM is newer technology and it performs accordingly during bench tests.

One technical aspect of these converters which can be overlooked is the hardware difference between the inputs used to switch the converter ON and OFF. For the SDM this input is called an ON/OFF pin and for the SKM it is called RC for Remote Control.

SDM converter block diagram

The block diagram shown above illustrates in block diagram format how the control pin for the SDM converter enables or disables the PWM portion of the circuit. A similar block diagram for the SKM was not available at the time of writing this blog.

Control Pin Difference
From the MeanWell SDM datasheet, the voltages required to drive the ON/OFF pin are shown as 5.5V ON and 2.5V maximum for OFF.

SDM ON/OFF control voltages

The MeanWell SKM datasheet lists the voltages required to drive the ON/OFF pin as greater than 2.5V ON and 0.5V maximum for OFF.

SKM ON/OFF control voltages

This information is clear enough, well vague enough! Other factors also need to be considered depending on the method used to drive the control pin. These could include, type of input, input voltage range, current required to drive the input, absolute maximum ratings and response times / delays where applicable.

For this blog only the input voltage range of the control pin will be looked at in detail.

Control Pin Input Voltage Measurements
To verify the operation of the control pin on the MeanWell SKM and SDM converters, two outputs of a Rigol DP832 linear regulator power supply were used. 

Rigol DP832

An initial test was conducted to determine the ON / OFF voltage hysteresis for SDM model, 100mV, and the SKM model which had a hysteresis of 2000mV. Tests were conducted with no input on the remote control pin, floating.

MeanWell SDM, SKM supply voltage hysteresis

For the second test, one channel of the power supply provided the input supply to the DC to DC converter and the second channel on the power supply provided the supply for the control pin. Both outputs of the power supply had a common 0V connection.

This is one method of testing the MeanWell supplies. There are other methods that could be used to drive the control pin although a voltage derived from the actual input supply appeared to be a common method for controlling this input pin.

SDM bench testing

The supply input voltage was increased, from the threshold ON voltage and the control pin threshold voltages determined and recorded.

SKM bench testing

Measurements for the two MeanWell supplies are shown below.

SDM Measurements for supply vs control pin voltage

SKM Measurements for supply vs control pin voltage

A visual representation of the above data is shown below.

SDM Graphed measurements

SKM Graphed measurements

Summary

When migrating between MeanWell SDM and SKM DC DC converters, reviewing the design should be performed as a matter of good design principle. 

For designs using the ON/OFF control pin, the drive circuit should be reviewed for a suitable drive level under a range of operating conditions.

At a supply voltage of 24VDC, the SDM series start operating at 3.4VDC whereas the SKM starts operating significantly lower at 1.2VDC. This of course sounds like a better hardware feature. The SKM supply could be driven from designs using lower circuit voltages, however narrowing the operating gap between 0V common and supply has its own drawbacks. Noise immunity, ESD or inadequate earthing can each introduce issues into the design if not considered carefully at design time.