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The definition and characteristics of the ripple

Issuing time:2015-07-15

DC-DC converter design and selection

ON Semiconductor (ON Semiconductor, the US Nasdaq: ONNN) With its global logistics network and strong portfolio of power semiconductor devices, power supply, computer, consumer, portable / wireless, automotive and industrial market applications engineers, purchasing professionals, distributors and contract manufacturers in the preferred power solution provider.

DC-DC Converter Selection Guide

An excellent reliability of the power supply circuit is to protect electronic products, what kind of power supply circuit considered excellent power it? Some experienced engineers using the power regulator, the regulator will consider how to reduce ripple, reduce power consumption and improve power conversion efficiency, product size and other issues, because these issues are key to measure the power of good and bad. With the development of semiconductor technology, power regulator ripple getting smaller and smaller, more and more high conversion efficiency, more and more low input voltage, output voltage range more widely, became more powerful, its scope of application covering instruments , communications, security and consumer electronics and many other areas, with the following technical parameters DC-DC converter chip will be described.

Input, output and efficiency

DC-DC converter's input voltage requirements in a specific range, the input voltage is too low to provide enough energy, the input voltage is too high, the chip can not afford. LDO efficiency decreases as the input voltage increases, and the chip is not efficient DC-DC input voltage relationship, which is one of the DC-DC biggest advantages.

Output current capability is the most important parameter contains the FET DC-DC converter, ON the DC-DC devices NCP3102 can output up to 10A, you can meet the demanding requirements of the power supply.

Efficiency is defined as the output power divided by the input power, and higher efficiency means efficient power management, ON the DC-DC devices NCP1595 efficiency up to 95%.


When they start working hard reset circuit, the output capacitor and no energy savings, the voltage is low, the feedback loop circuitry detects a low voltage value, will be used to make the widest PWM output voltage rises as soon as possible, but this process Since the feedback loop respond rapidly to current overshoot can easily lead to damage to circuit elements.

Application of soft start technology advantages:

Slow down the speed of the output voltage rises, starting current is controlled, thereby protecting the load;

Greatly reducing the pre-instantaneous power output state power requirements;

ON Most devices support soft-start technology.

Electric sequential control up and down

Establishing and running an appropriate power supply is essential to maintain the system environment, particularly FPGA, DSP, ARM and other processors are designed in order to avoid latches, power surges or I / O contention issues that may require more up to 4-5 or more power-way in accordance with the provisions of the order and the slope up and down electrically. In addition, many applications also require the gentle slope of rising to power-up sequence can be adjusted to accommodate a variety of different situations.

NCP3120 / 3221/3122/3123 vertically integrated power control function, but also supports cascaded.

Voltage mode control and current mode control

Switching DC-DC converter control feedback loop and voltage characteristics, there are two methods: a voltage mode control and current mode control.

In voltage mode control, converter duty cycle is proportional to the difference between the actual output voltage error between the output voltage and the ideal; in current mode control, the duty cycle is proportional to the rated output voltage and current of the inverter control function between The error difference (control current can be non-isolated topology switching currents or isolation topology transformer primary current).

Voltage mode control only responds to the output (load) voltage. This means that the converter in response to the input line voltage or load current changes, it must "wait" corresponding change in load voltage. This waiting delay will affect the regulation characteristics of the converter.

If you can respond to changes in load current in a single conversion cycle, the "wait" problem and the corresponding voltage mode control load regulation concerning compensation can be eliminated, and this can be done with current mode control. Current mode control in the by-pulse control output current, in other words, current mode control input and output transient response with superior transient response than the voltage-mode control.

Switch mode and frequency

The higher the DC-DC converter operating frequency means smaller external circuit, can provide higher power density in a certain program, the output ripple is also reduced.

PWM (pulse width modulation) pulse width modulation: control constant frequency pulse width variable. This modulation most widely used application.

PFM (pulse frequency modulation) pulse frequency modulation: reference oscillator on-time is fixed, but variable frequency. When the load is relatively light this modulation with more than.

ON the DC-DC devices NCP1526, NCP1522B, NCP1523B operating frequency up 3000KHz.


According to the status of development at home and abroad, electronic components have been widely used lead-free package, ON the DC-DC devices can provide lead-free Green Package (Pb-Free).

Operating temperature range

ON the DC-DC devices are offered in commercial, industrial, and automotive-grade chips. For your workplace, select the appropriate device.

Thermal Shutdown

DC-DC chip in an integrated MOSFET, high current flows through the chip will heat, although the higher efficiency chips, hot chips can be effectively controlled. However, in order to protect themselves, all converter chips are integrated thermal protection. If the temperature is too high the device itself, the converter will automatically stop working and wait until the temperature is reduced to the rated operating temperature range during use.

ON the DC-DC devices it has integrated thermal shutdown.


With the development of semiconductor technology, surface mount inductors, capacitors, and power supply control chip costs continue to reduce the high level of integration, DC-DC converters smaller and smaller. When the on-resistance of the MOSFET is small, the need for an external power FET can be a great power output, such as ON the NCP3101 (6A), NCP3102 (10A)!

With the increased integration of many new DC-DC converter requires only a few external inductor and filter capacitors can work to simplify circuit design and improve the reliability of the product, such as NCP1595 like.

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