Smart AC-DC Linear Regulators with 2X Power Density
Texas Instruments (TI) expanded its portfolio of over 500 linear regulators by introducing a first-of-its-kind smart ac-dc linear regulator. (see functional diagram above). With 75 percent higher efficiency and two times the power density of other linear regulators, this device boasts the best balance between high efficiency and ultra-low noise while shrinking the power-supply size.
The fully integrated TPS7A78 linear regulator employs a unique switched-capacitor architecture to eliminate discrete components, including transformers and external inductors, as well as miniature circuit breakers and interrupters. TI designed the linear regulators are for tamper-resistant designs in applications such as electronic metering in grid infrastructure and building automation.
The TPS7A78 is a nonisolated linear regulator that converts up to 0.5W from ac to dc with smaller and fewer components. This design optimizes regulation through an active bridge, switch capacitor and integrated low-dropout regulator (LDO). This design results in higher efficiency and a reduced capacitor size compared to linear regulators in traditional capacitor-drop solutions utilizing a Zener diode.
Key features and benefits of the TPS7A78
The linear regulator features low standby power. A unique dynamic, active bridge clamp pre-regulates the input voltage for optimal performance to reduce standby power to 10 mW, which TI says is up to 75% lower compared to conventional capacitor-drop solutions.
Higher power density results from the switched-capacitor architecture that eliminates up to 26 discrete components, including the bridge rectifier. This design reduces capacitor size by 25% compared to traditional capacitor-drop solutions.
The tamper-proof construction of the TPS7A78 is free of costly magnetic shielding, thus meeting the International Electrotechnical Commission (IEC) 61000-4-8 standard required by applications such as electronic metering.
TPS7A78 linear regulator
According to TI, the TPS7A78 improves the overall efficiency and standby power in power supplies. An external capacitor creates a current source and actively clamps the rectified voltage. The device then regulates the voltage down to the application-specific operating voltage.
The unique architecture of the device allows the standby power to be reduced from several hundreds of milliwatts to just a few tens of milliwatts.
The TPS7A78 takes advantage of an innovative switched capacitor stage to reduces the clamped voltage down by approximately 1/4th of the value, which in turn multiplies the current by 4. Thus, the current source capacitor can be much smaller in size, which minimizes standby power, reduces solution size, and can lead to a lower system cost.
Additionally, the TPS7A78 comes with a user-programmable power-fail detection threshold that can provide an early alert to power failures. So, the system can save data before completely losing power. A power-good indication can also be used for sequencing or to provide a reset to a micro-controller.
The TPS7A78 is available in a 14-pin TSSOP (PWP) package.
Features
- Non-isolated power solution for 70Vac to 270Vac, 45Hz to 65Hz (bench tested):
- Up to about 75% efficiency
- Supports output voltages from 1.25V to 5V
- Standby power consumption: 15mW (cap-drop = 150nF)
- Line voltage drop capacitor can be 1/4th the size of linear solutions
- Power-fail detection
- Power-good indication
- 3% precision voltage regulation over line, load, temperature
- Package: 5mm × 6.5mm TSSOP-14 (PWP)
TI will demonstrate the TPS7A78 linear regulator in booth No. 511 at the Applied Power Electronics Conference (APEC) in Anaheim, California, March 18-20, 2019.
Availability, Packaging, and Pricing
Available through the TI store and authorized distributors, the TPS7A78 is offered in a 14-pin, 5-mm-by-6.5-mm thin-shrink small-outline package (TSSOP) and priced in small reels at US$1.00 in 1,000-unit quantities.
