Glenn Morita writes:
The difference between insignificant noise and significant noise is the degree to which the noise affects the operation of the circuit in question.
For example, a switching power supply has a significant amount of output voltage ripple at 3 MHz. If the circuit it is powering has a bandwidth of only a few hertz, such as a temperature sensor, this ripple may be of no consequence. On the other hand, if the same switching power supply powers an RF phase-locked loop (PLL), the result could be quite different.
Understanding the sources of noise, their spectral characteristics, noise reduction strategies, and the sensitivity of the circuits in question to this noise is crucial to successfully designing a robust system.
This application note also attempts to clarify the difference between power supply rejection ratio (PSRR) and internally generated noise, and describes how to apply the data sheet specifications for each parameter.
Noise Sources in Low Dropout (LDO) Regulators - [Link]
The LM22670 switching regulator provides all of the functions necessary to implement an efficient high voltage step-down (buck) regulator using a minimum of external components. This easy to use regulator incorporates a 42V N-channel MOSFET switch capable of providing up to 3A of load current. Excellent line and load regulation along with high efficiency (>90%) are featured.
3A SIMPLE SWITCHER, step-down voltage regulator with synchronization or adjustable switching frequency - [Link]
Sudhansu Sekhar Mishra, Tarun Rehani, and Nishant Thakur write:
A regulator is a closed-loop feedback system. For the LDO to be stable, the phase margin must be positive. In other words, at unity gain crossover frequency of the gain curve, the phase of the system should be positive. This can be measured using a vector network analyzer. Many voltage regulators are of the fixed output variety and include the voltage divider internal to the regulator. There are definite advantages to this approach, which allows active voltage trimming and also minimizes the physical space required. A disadvantage to this approach is that the voltage divider is not available for gain-phase or “Bode” measurement. This leads many to believe that it is not possible (or even necessary) to evaluate the stability of such a regulator. This is simply not true.
Understand linear regulator stability - [Link]
If we want to obtain a 5V voltage from only 2 NiMH batteries, we´ll face the fact, that the most of common DC/DC circuits doesn´t operate at such a low voltage. LT1304 controller belongs among circuits, which handle this situation without problems and it also provides several extra things.
To obtain 3.3 or 5V from a lower voltage is a typical requirement at battery-powered or portable devices. Naturally, to obtain 5V it is also possible to use 4-5 NiMH cells or 2 Li-Po cells, but then the device is uselessly bigger, heavier and more expensive. The solution is just the usage of a suitable step-up circuit. LT1304 from Linear Technology belongs to “MicroPower” DC/DC step-up circuits operating already from a very small voltage, 1.5V typically.
Thanks to a very low power consumption (10uA/Shutdown) and a built-in independent low battery detector, it is optimized for usage with batteries. LT1304 needs for its operation only a few external components – 2 capacitors, 1 inductor and 1 diode is all that is necessary to create an operating DC/DC circuit.
LT1304 is available in 3 versions – LT1304VCS8-5, LT1304CS8-3,3 with fixed voltages and LT1304CS8 with adjustable output. Versions with fixed output voltages don´t need a divider in a feedback, what further simplifies a circuit.
Publitek European Editors :
The low-dropout regulator (LDO) has long been the choice for buck voltage conversion not only where cost is an issue but where noise performance is critical.
The brainchild of Linear Technology co-founder Robert Dobkin, conceived when he worked at National Semiconductor, the core architecture of the regulator is very simple but effective. Dobkin took a fixed-ratio voltage regulator and adapted it so that its output could be adjusted using a voltage divider on the output.¹
In the classic linear regulator, a transistor acts as half of a potential divider. Its output voltage is to control a feedback circuit that has control over the transistor’s gate in the case of a MOSFET, which is normally the case for an LDO regulator. The constant control via feedback over gate voltage provides a stable output voltage at a level set by the reference circuitry. Because of the use of a voltage divider structure, the linear regulator can produce only a voltage that is lower than that of the input. Older regulator circuits could experience a drop of 2 V or more. LDOs were devised to provide easier control over the output voltage and to constrain this dropout voltage to less than 2 V.
Linear Regulators Drive Noise Down - [Link]
Tamara Schmitz writes:
Combining the operation of a boost regulator and a negative voltage converter can generate a negative supply from a single low-voltage supply. The circuit in Figure 1 shows a standard application circuit for a +20 V supply along with two op amps, two diodes and two capacitors to generate the – 20 V supply. This article will discuss the basic operation of a boost converter to generate a larger positive supply voltage. Equations are derived to determine the minimum inductor value to maintain a safe peak inductor current, and a maximum inductor value to maintain continuous conduction mode (CCM) operation. The article will then discuss the generation of a negative supply and the restrictions of the design.
Simple Circuit to Generate Plus and Minus Supplies Using a Boost Regulator - [Link]
All embedded systems require electric power to operate. Most of the electronic components inside them, including the processors, can operate at a wide range of supply voltage. For example, the operating voltage range for the PIC16F1847 microcontroller is 2 to 5.5 V. But there are certain applications where you need a regulated constant voltage to avoid malfunctioning of the circuit or getting erroneous results. For instance, any application that involves analog-to-digital conversion (ADC) requires a fixed reference voltage to provide accurate digital count for input analog signal. If the reference voltage is not stable, the ADC output is meaningless. Here is my latest dual power supply regulator board that provides constant 3.3V and 5.0V outputs from an unregulated DC input (6.5-10V). It is small in size and can be easily enclosed inside the project box along with a project circuit board. It can also be used to power test circuits on breadboard. The board uses two AMS1117 series fixed voltage regulators and receives input power through a DC wall wart or an external 9V battery.
Multi-purpose dual power supply (5.0V and 3.3V) regulator board - [Link]
Semiconductor memory, card readers, microprocessors, disc drives, piezoelectric devices and digitally based systems
furnish transient loads that a voltage regulator must service. Ideally, regulator output is invariant during a load
transient. In practice, some variation is encountered and becomes problematic if allowable operating voltage tolerances
are exceeded. This mandates testing the regulator and its associated support components to verify desired performance under transient loading conditions. Various methods are employable to generate transient loads, allowing observation of regulator response.
Load Transient Response Testing for Voltage Regulators - [Link]
A Switch Mode Power Supply circuit collection from Linear Technology. It covers 12 basic SMPS circuit categories: Battery, Boost, Buck, Buck-Boost, Flyback, Forward, High Voltage, Multioutput, Off Line, Preregulator, Switched Capacitor and Telecom. [via]
Switching regulator circuit collection - [Link]
The TPS54160 device is a 60-V, 1.5-A, step down regulator with an integrated high-side MOSFET. Current mode control provides simple external compensation and flexible component selection. A low ripple pulse skip mode reduces the no load, regulated output supply current to 116 µA. Using the enable pin, shutdown supply current is reduced to 1.3 µA.
2.5MHz DC/DC converter protect against 65-V transients - [Link]