Switching Power Supply Principles and trends

Section frequency switching power supply circuit1, pulse width modulation (Pulse Width Modulation,
High frequency switching power supply consists ofabbreviated as PWM)
the following components:Constant switching cycle, by changing the pulse
1, the main circuit From the AC powerinput, DCwidth to change the way the duty cycle.
output of the entire process, including:2, pulse frequency modulation (Pulse Frequency
1, input filter: its role is to network the existingModulation, abbreviated as PFM)
clutter filtering, but also hindered the clutterConduction pulse width of the constant switching
generated by the unit back to the public grid.frequency by changing the way to change the
2, rectification and filtering: The Power AC powerduty cycle.
directly to DC rectifier is smoother, for the next3, mixed modulation Conduction pulse width and
level of transformation.switching frequency are not fixed and can change
3, inverter: will be rectified DC into high frequencyeach other's way, it is the mixture of these two
alternating current, which is the core ofways.
high-frequency switching power supply, the higherIII development and trends in switching power
the frequency, size, weight and the smaller thesupply
ratio of output power.1955 U.S. Royer (GH.Roger) invented the
4, the output rectifier and filter: the load requiredtransistor self-oscillating push-pull
to provide reliable DC power supply.single-transformer DC-DC converter, frequency
2, control circuit The one hand, sampling from theconversion control circuit to achieve the beginning
output, compared with the standard-setting, andof 1957, the United States Charles race (JenSen)
then to control the inverter, to change theirinvented the self-excited push-pull pair of
frequency or pulse width, to output stability, ontransformers, 1964, U.S. scientists have proposed
the other hand, according to data provided by theto abolish the frequency transformer switching
test circuit, The protection circuit identification onpower supply series idea, which is the power to
the machine control circuit to provide variousdecline in volume and weight were a fundamental
protective measures.way. To 1969 because of pressure to improve
3, detection circuit Addition to providing protectionhigh-power silicon transistors, diode reverse
circuit is run in a variety of parameters, but alsorecovery time shortened components to improve,
provide a variety of data display instruments.and finally made a 25 kHz switching power supply.
4, auxiliary power Provide all the differentPresent, switching power supply to small, light
requirements of a single circuit power supply.weight and high efficiency characteristics are
II switch control regulator principle Switch K to awidely used in a variety of computer-driven
certain time interval repeatedly connect anddevices, communications equipment, etc. Almost
disconnect, the switch K connected, the inputall the electronic equipment is the rapid
power source E through the switch K and thedevelopment of today's electronic information
filter circuit provided to the load RL, the switch isindustry essential a Power Source. Currently on
in the period, power E to provide energy to thethe market the use of switching power bipolar
load; when the disconnect switch K, the inputtransistors made of 100kHz, with 500kHz made
power cut off energy E will be provided. Can beof MOS-FET power, Although practical, but its
seen, input power to provide energy to the loadfrequency needs to be improved. To improve the
is intermittent, for the load to get the energy toswitching frequency, it is necessary to reduce
provide continuous, switching power supply mustswitching losses, and to reduce switching losses, it
have a storage device, the switch is part of theneeds high-speed switching components. However,
energy will be stored in the switch disconnectedthe switching speed of the increase will be
to the load release. In the figure, the inductor L,distributed by the circuit inductance and
capacitor C2 and diode D circuit composed of,capacitance, or diode stored charge of the
they have this feature. Inductor L to storegenerated surge or noise. This will not only affect
energy when the switch off, stored in thenearby electronic equipment, will greatly reduce
inductor L in the energy released through thethe reliability of power supply itself. Which, with
diode D to the load, the load by a continuous andthe switch to prevent Kai - closed by the voltage
stable energy, due to diode D so that the loadsurge occurs, can use RC or LC buffer, while the
current continuously, so as freewheeling diode. ABdiode stored charge due to current surge can be
average in the voltage between the EAB can beused such as magnetic core made of amorphous
expressed as:magnetic buffer . However, for more than 1MHz
EAB = TON / T * E Type of TON for the switchfrequency, resonant circuit to be used to make
each time to connect, T to switch off the workthe switch voltage or current through the switch
of the cycle (that is, the time switch to turn onwas a sine wave, this can reduce the switching
and off-time TOFF TON of and).losses, but also to control the occurrence of
By the above equation, change the switch to turnsurge. This switch is called resonant switch.
on the proportion of time and duty cycle, ABCurrent switching power supply of this very
average value between the voltage also willactive, because this approach does not require
change, therefore, with the load and input supplysubstantial increase in switching speed can be
voltage automatically adjusts the TON and thereduced theoretically to zero switching losses and
ratio of T the output voltage V0 can benoise are small, is expected to be of a
maintained. TON, and connect time to change thehigh-frequency switching power supply main ways.
duty cycle that is changing the pulse duty cycleAt present, many of the world countries are
ratio, which is known as "time ratio control"committed to the converter a few trillion Hz
(TimeRatio Control, abbreviated as TRC).practical research.
By TRC control theory, there are three ways: