Voltage Regulators

Beat the Heat Voltage regulators are a key technology for managing the heat dissipation in an electronic system. In this article, Jeff takes you through the evolution, science and functionality of voltage regulators. He looks at the heat and efficiency characteristics of voltage regulators, and compares linear versus switching technologies. Topics Covered How to understand the evolution, science and functionality of voltage regulatorsWhat are the heat and efficiency characteristics of voltage regulators?How do linear and switching technologies compare? Tech Discussed ST Micro’s L7805Wurth Elektronick’s 173010542XP Power’s TR2024S05Murata Power Solutions’ OKI-78SR-5Traco Power’s TSR 1-2450ETexas Instruments’ TPSM84305CUI’s P7805RECOM’s R-78HE5.0Monolithic Power’s mEZD71201A-G Acouple of resistors are often used to divide an input voltage into some lower output voltage. Each resistor drops a portion of the input voltage. This all works fine in a static situation. However, once the input voltage changes, so does the output voltage. That’s not a good voltage regulator. Substituting a Zener diode for the output resistor can help to keep the output voltage relatively stable, but as you know, this only works if the dynamic parameters all remain within a narrow range of conditions. And voltage regulation under varying conditions has always been a challenge. The transistor made precision voltage regulators possible, but the required circuitry contained many discrete parts. During the 1960s, work began with the integration of transistors into an integrated circuit (IC), which was the combining of discrete parts and their interconnections onto a single substrate. This process enabled analog, digital and mixed-signal circuits to become functional blocks—instead of having to be built from scratch. The first voltage regulator IC I used was the UA723 (Figure 1), developed by Fairchild Semiconductor, now Texas Instruments. Initially