Thursday, July 9, 2015

High Voltage Adaptability

VMI Adaptability

Voltage Multipliers Inc. LogoIt’s not unusual for VMI customers to contact us with new, exciting, applications for existing designs.  The questions are often centered around adapting those designs to new applications, new environments, higher outputs, less noise, or new-but-similar product lines.  

VMI can delivery across a range of volumes and time-to-market – anywhere from a few days to a few years, depending on the complexity, and one or two prototype products to full ramp-up.  

(Okay, a project that takes six months or longer would probably be better defined as ‘custom’).  Regardless of the length of development time, VMI treats each application with thoroughness and accuracy.  

No Short Cuts

Development time is directly proportional to the complexity of the design, and when time runs short, it can be vera, vera tempting to cut testing down, or assume things will be okay.  VMI's reputation rests on quality.  Consequently, VMI DOES.NOT.TAKE.SHORTCUTS.
It may take longer, but it will be right.


Our suppliers go through a vendor-qualification process.  Their performance is tracked and monitored.  VMI has an excellent reputation for fairness, accuracy, professionalism, and cooperation, among our suppliers.  We strive to keep our working relationship open, and mutually beneficial, and we want to keep it that way.

The same applies to our customers.  VMI’s reputation is one of delivering high quality products on time, excellent customer service, and responsive Engineering and Sales teams.

We want to keep our relationships with suppliers and customers healthy and happy as evidenced by open communication and working together as a team.  


High voltage has been VMI’s focus for over three and a half decades, and we’re going strong.

Manufacturing Success

Instrumental to our manufacturing success is our philosophy, and manufacturing techniques.  They include -   
  • A lean, Pull-system Factory
  • IPC Certified In-house Trainers and Manufacturing Operators
  • Precision Controlled Encapsulation and Cure Processes
  • RoHS complaint production lines
  • Automatic Inspection Systems
  • Environmental Stress Test Capability
  • Supplier Quality Programs
  • In-house Quality Programs
  • Instrument Calibration Control Systems

To that end, VMI is - 
  • ISO 9001-2008 certified
  • QPL Lab Suitability Qualified

So the next time you need a high voltage design, custom or adapted from a standard product, give us a call.  

Tuesday, July 7, 2015

Current Ratings in High Voltage Diodes, and the SXF6525 in Particular

The current ratings of a diode (including surge currents) are best though of as guidelines.  The thing that keeps a diode from successfully operating at higher currents in excess of the published rating is the generated heat, and the inability to remove the heat from the junction.  

If the diode heats up too fast, the rapid expansion of the materials inside the diode could lead to mechanical breakage (at times heavy surge testing here can cause diodes to fall apart or even ‘pop’ and have a chunk of glass chip out).  The diode is said to have been thermally shocked.  Think of what happens when you pour rapidly boiling water into a glass pitcher.  You might get away with it once or twice, but eventually the pitched will crack, sometimes quite spectacularly.  

Okay, back to diodes.  As the diode heats up more gradually, the VF rating of the diode drops and the diode slows down (TRR increases) which, depending on the system, will likely cause the diode to generate more heat (either through higher forward current from the VF change or more reverse power losses from the TRR decreasing) which will cause the VF to decrease more and the TRR to increase more, which will cause more heating – eventually leading to a thermal runaway situation.

So, the current ratings of diodes are mostly guidelines to manage the heat generated during the operation of the diode.  And how much the diode is going to heat up is going to depend greatly on the application of the diode, and what the thermal path is for the diode.  Since the SXF6525 is a surface mount part, it is good at getting the heat out of the silicon of the diode, but if there is not sufficient heat sinking on the PCB or substrate where the diode is mounted, it can still go into thermal runaway conditions.

From just a guidelines point of view for the SXF6525, we do not advise power derating in the diode until 100°C (See graphs below). 

So we would then advise a repetitive forward surge current of 2A at 75°C.  It is, however, something that should defiantly be tested in the customers specific application with special attention and observation of the temperature of the diode and whether or not it will stabilize or go into thermal runaway.

Heat management is a complicated issue when it comes to semiconductors and therefore current ratings could vary considerably depending on the diode and application.  If you would like clarification or additional information for your application, please contact us.

Thursday, July 2, 2015

200°C, 2kV, 30ns Diode - SXF20FF3HT

SXF20FF3HT 2kV, 200°C,  Diode

Introducing VMI's latest addition to the 200°C, high temperature, high voltage diode family.
The SXF20FF3HT (HT for "High Temperature) is rated at 200°C.  It will block 2kV in the reverse direction and conduct 420mA in the forward direction.  Reverse Recovery Time (Trr) is 30ns or less.

It is the fastest recovery time, and highest current in the high temperature diode line.  If you don't need 30ns, or need a higher reverse voltage and lower forward current, two excellent choices include the SMF6531HT (3kV), and the SMF6533HT (5kV).  Both are rated for operation at 200°C.

Physical Dimensions

The SXF20FF3HT is the same size as both the SMF6531HT, and SMF6533HT.  All are less than 1/4" (6.10mm) in length.  That means you can pack a lot of voltage in a very small package.  For precise dimensions and recommended pad layout, see below.
Physical Dimenions of the SMF6533HT High Temp, High Voltage Diode

Recommended Pay Layout

The dimensions are given in inches, with mm in parentheses. 
Pad layout recommendations for SMF6531HT High Temp Diode
SMF6533HT Pad Layout

Data Sheet

For more information on the 200°C, 5kV, 50mA, 70ns, SMF6533HT diode, download the data sheet.  or contact VMI.