|
Application Note AN-1852 (pdf 117KB)
Designing with pH Electrodes
Jason Seitz, Applications Engineer
A pH electrode measures hydrogen ion (H+) activity and produces an electrical potential or voltage. The operation of the pH electrode is based on the principle that an electric potential develops when two liquids of different pH come into contact at opposite sides of a thin glass membrane. This was originally discovered in 1906 by Max Cremer. His discovery laid the foundation for Fritz Haber and Zygmunt Klemensiewicz, who published their findings in 1909, to create the first glass electrode which measured hydrogen activity. Today, modern pH electrodes use the same principles to measure pH in a variety of applications including water treatment, chemical processing, medical instrumentation, and environmental test systems.
|
|
Application Note AN-1853 (pdf 102KB)
COT Drivers Control LED Ripple Current
Chris Richardson, Applications Engineer
The constant on-time (COT) control method used by the LM3402 and LM3404 constant-current buck regulators provides a balance between control over switching frequency and fast transient response. Normally this “quasi-hysteretic” control senses the input voltage and adjusts the on-time tON of the power MOSFET as needed to keep fSW constant. Investigating a little more deeply reveals that tON is in fact proportional to the current flowing into the RON pin. The addition of a single, generalpurpose PNP transistor forces tON to be proportional to (VIN – VO) and provides two benefits that are particularly useful to LED drivers: improved tolerance of the average LED current, IF, and constant LED ripple current, DiF.
|
|
