SMBJ5342B-TP – SMBJ Diode

Resilient attenuator on the cheap

When adjusting voltage levels for process computers, accuracy is not always important: in many cases, good isolation from the incoming high voltage spikes is of more significance.

A primitive design for an attenuator usually follows the lines shown in figure 1 – a small diode and a “stock” resistor is used, which works while the incoming spikes are not particularly large.

This simple design works, but is not particularly resilient

As EMV demands increase, cascaded zener diode designs get attention – the first references to them can be found inside Seifart’s Classic from the GDR. In principle, these designs follow the ideas outlined in figure 2.

The second diode limits the voltage across the first one

While this design works, it is not particularly efficient from size and cost points of view. Furthermore, the voltage of Z1 is usually selected to be significantly larger than that on Z2, thereby leading to the well known antipattern of “wagging the reference”.

The brutality dividend

A very interesting alternative comes from Micro Commercial Components, and has seen quite a bit of use in process computer designs by yours truly. The SMBJ5xx8 family contains a set of Zener diodes which can dissipate toasty five watts of power – let us look at the SMBJ5342B-TP, which is priced as following:

With that settled, a circuit similar to the one shown in figure three can be designed. Here, the main loss takes place in the filter resistor, with the series resistor limiting the current flowing into any clamping diodes inside of the process computer.

A high-power zener makes life a lot easier

In practice, such designs can survive insanely high voltages if the resistor is beefy enough – a system designed by yours truly handles literally dozens of volts while transferring down to 3V3. Of course, this problem can be solved in a variety of ways-for example, multiple smaller resistors can be connected into a series circuit. But this, sadly, is a topic for a rainy day

Attention

The datasheet of this part family contains an explicit warning about fakes. This practice, which happens relatively rarely, indicates that this part is especially “hot” – make sure to purchase the diode from approved distributors.

Recent Articles
Go with OPTO! Watch this free Webinar about Broadcom’s Isolation Products in Electrical Chargers
Broadcom Webinar: Isolation Products for High Speed Inverters/Converters in Electrical Chargers DC fast chargers shorten charging time from hours to mere minutes. Such high-powered equipment requires... Read Article
Efficient DC Power Distribution in Data Centres
The consistent use of direct current in a data centre makes sense. Losses can be massively reduced. On the power side, the IEC has defined the... Read Article
AC/DC Power Supplies 15 – 450 W from Traco Power
Engineered to stay cool High performance, ultra-compact AC/DC power supplies with minimal heat dissipation. Available in four different mechanical packages, these high-efficiency power supplies utilize industrial grade... Read Article
Bluetooth Mesh Solutions for IoT Based Designs
Cypress Best-in-class Bluetooth Mesh Cypress’ Bluetooth Mesh Eval Kit is a multi-node platform featuring a certified Bluetooth 5 module, sensors, and multiple mesh example projects with... Read Article
Check out the newly expanded TE Connectivity Online Store!
Buy Now with PayPal The TE Store now accepts PayPal! This feature gives you a wider range of payment options and the ability to pay for... Read Article
Compact, low power microphone with IC Interface.
This high performance MEMS audio sensor from STMicroelectronics is desigined with an IC Interface and capacitive sensing element. Ideal for a number of applications such as... Read Article