CN204652214U - A kind of little ripple DC conversion power - Google Patents

Abstract

The utility model discloses a kind of little ripple DC conversion power, comprises reverse-connection preventing circuit, current foldback circuit, overvoltage crowbar, filter circuit and power-switching circuit; Reverse-connection preventing circuit, current foldback circuit, filter circuit and power-switching circuit are connected between the positive pole Vin+ of power input and the positive pole Vo+ of output successively; Overvoltage crowbar is connected between the output and ground GND of current foldback circuit; Little ripple DC conversion power designed by the utility model, be adapted at applying under output current is less than the environment of 500mA, minimumly ripple can be transferred to 1%Vout, can not cause interference to the amplification of small-signal and analysis, ensure that the precision and stability of electronic product, the utility model ripple is little simultaneously, efficiency is high, cost is low, and stability is strong, safe and reliable.

Description

A kind of little ripple DC conversion power

Technical field

The utility model relates to electronic technology field, and being specifically related to a kind of input voltage is 23.8V, and output voltage is 4.7V, the power supply that output current is applied under being less than the environment of 500mA.

Background technology

At present, on market, existing DC-DC power source is of a great variety, and its operation principle is different, and common DC-DC power source is mainly divided into three major types: linear power supply, Switching Power Supply and insulating power supply; Above-mentioned three kinds of DC-DC power source are had nothing in common with each other in price, precision, efficiency, driving force, load effect, source effect and temperature coefficient etc., thus can be applied in different field; But non-handlebar ripple is placed on the DC-DC power source that main positions is used as judgment criteria, such as:

Existing technical scheme 1:

The linear stabilized voltage power supply of LM7805 tri-is a power module more common on market, and its circuit is simple, with low cost, stable and not fragile; But in use this power module precision is low, and efficiency is low, heat is large and ripple is bigger;

Existing technical scheme 2:

LM2576 series switch integrated regulator is the substitute of linear Three-end voltage stabilizer (as 78xx series end integrated regulator), it has reliable service behaviour, higher operating efficiency and stronger output current driving force, thus provides strong guarantee for stable, the reliably working of MCU; But there is ripple equally greatly in this serial voltage-stabilizing device, precision and inefficient shortcoming.

As everyone knows, for the electronic product of low level signal amplification and process, if the larger amplifying circuit of ripple directly can amplify the harmonic wave of ripple generation, then the interference of power supply directly has influence on the precision and stability of product, and DC-DC power source of the prior art is usually difficult to meet the demands comparatively greatly due to ripple; The harm of ripple is often embodied in the following aspects:

1. easily on electrical appliance, produce harmonic wave, and harmonic wave can produce more harm;

2. reduce the efficiency of power supply;

3. stronger ripple can cause the generation of surge voltage or electric current, causes burning electrical appliance;

4. can disturb the logical relation of digital circuit, affect it and normally work;

5. bring noise jamming, make vision facilities, stereo set cisco unity malfunction.

Utility model content

Technical problem to be solved in the utility model is to provide a kind of little ripple DC conversion power, be adapted at applying under output current is less than the environment of 500mA, minimumly ripple can be transferred to 1%Vout, can not cause interference to the amplification of small-signal and analysis, ensure that the precision and stability of electronic product, the utility model ripple is little simultaneously, efficiency is high, cost is low, and stability is strong, safe and reliable.

In order to solve the problems of the technologies described above, the utility model is realized by following technical scheme:

The utility model devises a kind of little ripple DC conversion power, comprises reverse-connection preventing circuit, current foldback circuit, overvoltage crowbar, filter circuit and power-switching circuit;

Reverse-connection preventing circuit, current foldback circuit, filter circuit and power-switching circuit, be connected between the positive pole of power input and the positive pole of output successively, overvoltage crowbar is connected between current foldback circuit output and ground;

Filter circuit adopts LC-π type filter circuit, and wherein inductance adopts wideband straight cutting magnetic bead, and electric capacity adopts the electric capacity of 10uF/25V.

Technique effect:

Filter circuit adopts LC-π type filter circuit: find that the type selecting of magnetic bead directly has influence on the ripple of output by experiment repeatedly, through comparison and the long-term experiment of multiple magnetic bead, the utility model adopts wideband straight cutting magnetic bead to coordinate the electric capacity of 10uF/25V, makes ripple reach minimum.

Designed by the utility model little ripple DC conversion power, be adapted at applying under output current is less than the environment of 500mA, minimumly ripple can be transferred to 1%Vout, interference can not be caused to the amplification of small-signal and analysis, ensure that the precision and stability of electronic product; Little ripple DC conversion power ripple of the present utility model is little, and efficiency is high, and cost is low, and stability is strong, safe and reliable.

As a kind of optimal technical scheme of the present utility model:

Further, aforesaid little ripple DC conversion power, reverse-connection preventing circuit is made up of fast recovery diode.

Aforesaid little ripple DC conversion power, current foldback circuit is made up of resettable fuse.

Aforesaid little ripple DC conversion power, overvoltage crowbar is made up of piezo-resistance.

Aforesaid little ripple DC conversion power, power-switching circuit selects LM25574 to be acp chip, connects the frequency modulation resistance that a resistance is 13K between 7 pin of LM25574 chip and earth terminal;

LM25574 is the automotive grade product (work junction temperature scope-40 DEG C to+125 DEG C) by the certification of AEC-Q1001 level; integrated form 42V; 750m Ω N-channel MOS FET; ultra-wide input voltage range 6V to 42V, adjustable output voltage is low to moderate 1.225V, 1.5% feedback reference precision; single resistance is utilized to realize operating frequency adjustable in 50kHz to 1MHz; main or from Frequency Synchronization, adjustable soft start, built-in protection.

Accompanying drawing explanation

The circuit structure block diagram of the little ripple DC conversion power of Fig. 1 designed by the utility model;

Fig. 2 is the schematic diagram of reverse-connection preventing circuit, current foldback circuit, overvoltage crowbar and filter circuit in the utility model;

Fig. 3 is the schematic diagram of power-switching circuit in the utility model.

Embodiment

Below in conjunction with the drawings and specific embodiments, technical solutions of the utility model are described in detail;

As shown in Figure 1, the little ripple DC conversion power of the one originally provided comprises reverse-connection preventing circuit 1, current foldback circuit 2, overvoltage crowbar 3, filter circuit 4 and power-switching circuit 5; Reverse-connection preventing circuit 1, current foldback circuit 2, filter circuit 4 and power-switching circuit 5 are connected between the positive pole Vin+ of power input and the positive pole Vo+ of output successively; Overvoltage crowbar 3 is connected between the output and ground GND of current foldback circuit 2, wherein:

Reverse-connection preventing circuit: as shown in Figure 2, SS14 type fast recovery diode D1 is adopted to be connected on the positive pole Vin+ of power supply input, the diode SS14 conducting when the voltage of positive pole Vin+ is greater than 0.3V, circuit normally works, the both positive and negative polarity of input connects inverse time voltage and is less than 0V diode SS14 and ends, and late-class circuit is protected;

Current foldback circuit: adopt resettable fuse JK30-060, current limliting 0.6A, be that resettable fuse disconnects when electric current is greater than 0.6A, late-class circuit is protected;

Overvoltage crowbar: the piezo-resistance 7D560K adopting DC45V, when voltage is greater than 45V, protection late-class circuit;

Filter circuit adopts LC-π type filter circuit: find that the type selecting of magnetic bead directly has influence on the ripple of output by experiment repeatedly, through comparison and the long-term experiment of multiple magnetic bead, the utility model adopts wideband straight cutting magnetic bead L202 to coordinate electric capacity C203 and C204 of 10uF/25V, makes ripple reach minimum;

Power-switching circuit: as shown in Figure 3, in the present embodiment, power-switching circuit selects LM25574 to be acp chip, LM25574 oscillator frequency is by being connected to the single non-essential resistance between RT pin and RAMP pin, namely frequency modulation resistance R103 is arranged, frequency modulation resistance should very near device, on the RT pin being connected directly between integrated circuit and RAMP pin, for setting required oscillator frequency (F), the frequency modulation resistance of frequency modulation resistance R103 must be determined, following formula can be utilized to calculate:

, in the present embodiment, frequency modulation resistance is 13K.

LM25574 switching regulator provides all necessary functions realizing efficient high voltage voltage-releasing voltage stabilizer with minimum external component, this wieldy pressurizer is integrated with the 42V N raceway groove step-down switching that an output current ability is 0.5A, and pressurizer control method is based on the Controlled in Current Mode and Based utilizing simulated current slope;

Peak-current mode controls to provide built-in linear electric voltage feed forward, Cycle by Cycle current limliting and simple loop compensation, reduce the noise sensitivity of pulse width modulation circuit after using Simulation Control slope, what ensure that the necessary minimum duty ratio of high input voltage occasion can lean on process; Operating frequency can be regulated between 50kHz to 1MHz by user program, oscillator synchronization pin allow the motor synchronizing of multiple LM25574 pressurizer or with an external clock, output voltage can be low to moderate 1.225V;

Failsafe characteristics comprises current limliting, Thermal shutdown and remote shutdown ability; LM25574 can be applied to a lot of occasion, can efficiently reduce unregulated high input voltage, and this device is applicable to the power bus voltage scope of telecommunications, industry and automobile very much;

LM25574 has a double mode internal high pressure to start pressurizer, can provide VCC bias supply for PWM controller and bootstrapping MOSFET gate drivers; Input pin VIN is directly connected with the input voltage up to 42V, for the input voltage lower than 9V, uses a low pressure drop switch directly to connect VCC and VIN;

In this supply district, VCC and VIN approximately equal, for the input voltage VIN higher than 9V, forbidding low pressure drop switch, VCC pressurizer is enable, makes VCC maintain about 7V; The wide operating range of 6V to 42V realizes by using this double mode pressurizer, and within the output current of VCC pressurizer is limited in 25mA, once power on, pressurizer, just as source, makes electric current enter to be connected to the capacitor on VCC pin;

When the voltage of VCC pin more than the VCC under-voltage locking threshold value of 5.35V and the voltage of SD pin is greater than 1.225V time, output switch is enable, and soft start starts; Output switch keeps enable, until VCC drops to 5 below V or SD pin voltage drops to below 1.125V; Auxiliary power supply voltage can be applied to VCC pin to reduce integrated circuit (IC) power consumption; If boost voltage is greater than 7.3V, internal voltage regulator will turn off, thus reduce integrated circuit energy ezpenditure;

VCC pressurizer series of transmission transistor comprises one should the diode of forward bias between VCC and Vin and when normal work, so auxiliary VCC voltage must not more than VIN voltage; In high voltage applications occasion, the voltage of VIN pin is no more than absolute maximum voltage rated value 45V to need great care to ensure; In linear or load transient, self-vibration on VIN line and the voltage exceeding absolute maximum rating can damage integrated circuit, carefully wiring PC plate, use high-quality shunt capacitance near the position of VIN and GND pin, both is all very important;

LM25574 comprises a two level and turns off (SD pin) circuit, and when the voltage of SD pin is lower than 0.7V, pressurizer is in low current shutdown mode; When the voltage of SD pin is between 0.7V to 1.225V, pressurizer is in standby mode; In standby mode, VCC pressurizer activates, but output switch can not work; When the voltage of SD pin is higher than 1.225V, output switch is enable, starts normally to work;

If SD pin is unsettled, the pull-up current source of an inside 5 μ A can configure pressurizer makes it normally work, can use an outer setpoint voltage divider from VIN pin to GND pin that the work input voltage of pressurizer is set, the design of voltage divider must ensure that, when VIN is in target working range, the voltage of SD pin is greater than 1.225V; When calculating outer setpoint voltage divider, must consider inner 5 μ A pull-up current sources, shutoff and standby threshold all contain the sluggishness of 0.1V, use the resistance of a 1k Ω and the Zener of a 8V to clamp down on the inside realizing SD pin and clamp down on; The voltage be added on SD pin must not more than 14V, if the voltage of SD pin is more than 8V, the speed with 1mA/V increases by bias current;

SD pin can be used in performing multiple remote enable/disable function equally, and threshold value SD pin voltage pulled down to lower than 0.7V can make controller can not work completely, if the voltage of SD pin is higher than 1.225V, pressurizer normally works.

The operation principle of the present embodiment is: the error amplifier of the inner high-gain of LM25574 produces an error signal proportional with the difference adjusting output voltage and inner precise reference voltage (1.225V); The output of error amplifier is connected to COMP pin, allow to use loop compensation device, normally II type network, this network produces a direct current limit, a zero point and a noise suppressed high frequency poles, and PWM comparator compares from the simulated current detection signal of RAMP generator and the error amplifier output voltage at COMP pin;

LM25574 comprises unique current detection mechanism, can carry out controlling and overcurrent protection, when arranging correct, simulated current signal just provide one proportional and scale factor is the signal of 2.0V/A with step-down switching signal, this emulation ramp signal is added on Current-Limiting Comparator; If this emulation ramp signal is more than 1.4V (0.7A), current current cycle will stop (Cycle by Cycle current limliting), in the application scenario of low outputting inductance and high input voltage, due to the propagation delay of current comparator, switching current may overshoot;

If there is current over pulse phenomenon, diode current sample circuit will detect excessive conducting current within the turn-off time of step-down switching;

If the DC level of sample/hold circuit is more than the current limitation threshold value of 1.4V, step-down switching will be turned off, and pulse generation is jumped, until diode current sample circuit detects that inductive current decays to below current limitation threshold value; This method can prevent due to propagation delay or the saturated and current run-away state that causes of inductance, because inductive current all can be forced decay when any electric current is excessive;

LM25574 is integrated with a N raceway groove step-down switching and relevant unsettled high level displacement/gate drivers, gate driver circuit and internal body diodes and external bootstrap capacity collaborative work, be recommended between BST pin and SW pin and connect 0.022 shorter μ F ceramic condenser of a cabling, within the step-down switching turn-off time, the voltage of SW pin is approximately-0.5V, and bootstrap capacitor is discharged from VCC by internal bootstrap diode;

When being operated in high PWM duty ratio, step-down switching can be forced to turn off, to ensure that bootstrap capacitor can charge again within the cycle of each 500ns; When load is very little or output voltage is pre-charged, the voltage of SW pin can not keep low level within the step-down switching turn-off time;

If inductive current drops to zero and SW pin voltage improves, so bootstrap capacitor cannot obtain enough voltage step-down switching gate drivers is normally worked;

In such applications, PRE pin can be connected to bootstrap capacitor pre-charged with SW pin, the diode between inner precharge MOSFET and PRE and PGND, can conducting 250ns within each cycle, just in time before new switch periods starts; If SW pin voltage is normal negative level (continuous conduction mode), electric current would not be had to flow through precharge MOSFET/ diode.

Above embodiment is only and technological thought of the present utility model is described; protection range of the present utility model can not be limited with this; every technological thought according to the utility model proposes, any change that technical scheme basis is done, all falls within the utility model protection range.

Claims (5)

1. a little ripple DC conversion power, is characterized in that, comprises reverse-connection preventing circuit (1), current foldback circuit (2), overvoltage crowbar (3), filter circuit (4) and power-switching circuit (5);

Described reverse-connection preventing circuit (1), current foldback circuit (2), filter circuit (4) and power-switching circuit (5) are connected between the positive pole of power input and the positive pole of output successively, and overvoltage crowbar (3) is connected between current foldback circuit (2) output and ground;

Described filter circuit (4) adopts LC-π type filter circuit, and wherein inductance adopts wideband straight cutting magnetic bead, and electric capacity adopts the electric capacity of 10uF/25V.

2. little ripple DC conversion power according to claim 1, is characterized in that, described reverse-connection preventing circuit (1) is made up of fast recovery diode.

3. little ripple DC conversion power according to claim 1, is characterized in that, described current foldback circuit (2) is made up of resettable fuse.

4. little ripple DC conversion power according to claim 1, is characterized in that, described overvoltage crowbar (3) is made up of piezo-resistance.

5. little ripple DC conversion power according to claim 1, is characterized in that, described power-switching circuit (5) selects LM25574 to be acp chip, connects the frequency modulation resistance that a resistance is 13K between 7 pin of LM25574 chip and earth terminal.