Small-power numerical control direct-current stabilized power supply

Abstract

The utility model discloses a low-power numerical control direct-current stabilized power supply, which realizes high-efficiency and low-ripple-rate digital controllable direct-current stabilized power supply output. The power supply comprises a switch control circuit, an input filter circuit, a pre-stage switch power supply for converting high direct current into low direct current, a post-stage LDO (Low Dropout Regulator) for reducing electromagnetic interference output by a pre-stage and outputting ripple waves, and an output filter circuit which are connected in sequence, the sampling circuit is used for collecting the output voltage of the rear-stage LDO; and the single chip microcomputer is connected with the switch control circuit, the pre-stage switching power supply and the post-stage LDO, controls the switch control circuit and the pre-stage switching power supply and outputs reference voltage to the post-stage LDO, and the post-stage LDO adjusts output based on the voltage difference between the sampling voltage of the sampling circuit and the reference voltage.

Description

Technical Field

[0001] The invention relates to a low-power digitally controlled direct current voltage-stabilized power supply. Background Art

[0002] DC regulated power supply is an indispensable device in the field of electronic technology. The quality of its performance is directly related to whether electronic equipment can work reliably and safely. At present, DC regulated power supply mainly includes two categories: switching power supply and linear power supply. Since the adjustment tube of the switching power supply works in the saturation and cut-off state, it has low heat generation, high efficiency (more than 75%), and small size, but the output ripple and switching noise are large. The adjustment tube of the linear power supply works in the amplification state, which has high heat generation, low efficiency (about 35%), and large size, but the output ripple and noise are small. Utility Model Content

[0003] The invention provides a low-power digitally controlled direct current voltage-stabilized power supply, which has the characteristics of digital control and high precision, good performance and can meet the requirements of practical use.

[0004] According to one aspect of the embodiment, a DC regulated power supply is provided, comprising: a switch control circuit, an input filter circuit, a front-stage switch power supply for converting high DC power into low DC power, and a rear-stage LDO and an output filter circuit connected in sequence; a sampling circuit for collecting the output voltage of the rear-stage LDO; and a single-chip microcomputer, which is connected to the switch control circuit, the front-stage switch power supply and the rear-stage LDO, controls the switch control circuit and the front-stage switch power supply, and outputs a reference voltage to the rear-stage LDO, and the rear-stage LDO adjusts the output voltage based on the voltage difference between the sampling voltage of the sampling circuit and the reference voltage.

[0005] In some examples, the post-stage LDO includes: an operational amplifier, whose two input terminals respectively input a sampling voltage and a reference voltage; and a MOS tube, whose input terminal is connected to a previous-stage switching power supply, whose output terminal is connected to an output filter circuit, and whose control terminal is connected to the output terminal of the operational amplifier.

[0006] In some examples, the microcontroller is connected to the operational amplifier through an analog-to-digital converter.

[0007] In some examples, the output voltage is changed by changing the reference voltage through a single chip microcomputer.

[0008] In some examples, the output voltage does not exceed a desired set point.

[0009] In some examples, when the current exceeds a preset value, the single chip microcomputer controls the switch control circuit to disconnect.

[0010] In some examples, a sampling resistor is connected between a front-stage switching power supply and a rear-stage LDO, and voltages V+ and V- across the sampling resistor are input to a current detection chip to detect current.

[0011] In some examples, the switch control circuit includes an optocoupler and a switch tube. The microcontroller controls the on and off of the optocoupler by outputting high and low levels, thereby driving the control end of the switch tube to achieve power switch control. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 The utility model is a structural block diagram of a low-power digitally controlled DC regulated power supply according to an embodiment of the utility model.

[0013] Figure 2 The invention discloses a front-stage switching power supply circuit according to an embodiment of the utility model.

[0014] Figure 3 The invention discloses a post-stage LDO circuit according to an embodiment of the utility model.

[0015] Figure 4 The invention is a sampling circuit according to an embodiment of the utility model.

[0016] Figure 5 The invention discloses a voltage sampling input buffer circuit according to an embodiment of the utility model.

[0017] Figure 6 The invention provides a switch control circuit according to an embodiment of the utility model. DETAILED DESCRIPTION

[0018] When the term “connection” is used to indicate the relationship between two devices / modules, it can be either “direct connection” or “indirect connection”, which is common knowledge to those skilled in the art.

[0019] like Figure 1 As shown, the low-power digitally controlled DC regulated power supply includes a single-chip microcomputer, a sampling circuit, and a switch control circuit, an input filter circuit, a front-stage switch power supply, a rear-stage LDO, and an output filter circuit connected in sequence.

[0020] The input filter circuit and the output filter circuit are used to filter out the ripple and noise of the input and output power supplies.

[0021] The front-stage switching power supply converts high DC power into low DC power, for example, converts 24V DC power into 9V-16V DC power.

[0022] The function of the post-stage LDO is to reduce the electromagnetic interference and output ripple of the previous stage output.

[0023] The sampling circuit collects the output voltage of the subsequent LDO.

[0024] The single-chip microcomputer is connected to the switch control circuit to control it. When the sampling current exceeds the preset value, the control switch is disconnected, which has an overcurrent protection function. The single-chip microcomputer is connected to the front-stage switching power supply to change the output voltage of the front-stage switching power supply. The single-chip microcomputer is connected to the rear-stage LDO and outputs a reference voltage to the rear-stage LDO. The rear-stage LDO adjusts the output based on the voltage difference between the sampling voltage of the sampling circuit and the reference voltage.

[0025] The present invention uses a single chip microcomputer as the core controller, and has the functions of output voltage preset, output voltage and current recovery, switch control (overcurrent cut-off external power supply), etc. It converts the external input high voltage into a low voltage output, for example, if the external input power supply is 24V DC, the output is 9V-16V DC, and the power is 60W.

[0026] like Figure 2 , the front-stage switching power supply can use the TPS40200 control chip. The external 24V DC power supply realizes the switching DC / DC output through the PMOS tube controlled by TPS40200, and the regulated switching power supply output can be realized through LC filtering. Pin 4 of TPS40200 is the inverting input terminal of the error amplifier. When working normally, the voltage of pin 4 is equal to the positive input voltage of the error amplifier, and the value is about 0.7V. TRK1 is the voltage of the analog-to-digital conversion chip DAC8411 controlled by the microcontroller through the DAC output buffer circuit. By changing the voltage value of TRK1, the current flowing through R57 can be changed, thereby changing the size of the output voltage, and finally realizing the front-stage output of the digital control DC regulated power supply.

[0027] (1) Switching frequency selection

[0028] According to the data sheet provided by TI and taking into account the size of the power supply, the switching frequency f of TPS40200 is set. sw is 120kHz. sw The size is determined by the resistor R47 and capacitor C52 on pin 1 of TPS40200.

[0029]

[0030] Take R47=169K, C52=470pF.

[0031] (2) Selection of current limiting resistor

[0032] According to the data sheet, the peak current flowing through the output inductor is calculated as shown in formula (2). ILM The inductor voltage is 100mV, and the peak current of the inductor is set to 10A. The current limiting resistor R46 is calculated to be 10mΩ.

[0033]

[0034] (3) Output inductor selection

[0035] The calculation formula of output inductor L5 is shown in (3). Where, V ON is the voltage across L5 when it is turned on, D is the duty cycle, r is the output current ripple rate, I L is the inductor current, f sw is the switching frequency.

[0036]

[0037] The power supply designed by the present invention belongs to the buck topology, so:

[0038] V ON =V INMAX -V O (4)

[0039]

[0040] I L =I O (6)

[0041] Combining formulas (3)-(6) yields:

[0042]

[0043] Take the output current ripple rate r = 0.14, the input voltage is 24V, the output voltage V O =9V, output current is 5A, and the inductance size L5 = 22uH.

[0044] (4) Output capacitor selection

[0045] The calculation formula of output capacitance is shown in formula (8), where V OS is the maximum output peak voltage. Calculation shows that C60 = 470uF.

[0046]

[0047] (5) Determine the soft start time

[0048] According to the data sheet, the soft start time of TPS40200 should meet the following conditions:

[0049]

[0050] The soft start time of TPS40200 is determined by formula (10), where R C The soft start charging resistor inside the chip has a resistance of 105KΩ. SS For C55, V SST is 8V.

[0051]

[0052] Take the soft start time t ss =950us, it can be calculated that C55=0.047uF.

[0053] like Figure 3 As shown, the post-stage LDO realizes low voltage difference linear adjustment based on MOS tube, operational amplifier, digital-to-analog converter and single-chip microcomputer, thereby reducing electromagnetic interference and output ripple of the previous stage output.

[0054] The output voltage V+ of the front stage is realized through the sampling resistor R61 and the adjustment tube Q1 to realize the output of the rear stage LDO. TRK2 is the sampling voltage of the rear stage output, which is input into the buffer circuit through the operational amplifier OPA2171 and compared with the DAC_out2 output by the DAC8411 controlled by the microcontroller. The voltage difference between the two is amplified by the operational amplifier to control the voltage drop of the adjustment tube Q1, thereby outputting a stable voltage and reducing the ripple rate of the output voltage of the front stage.

[0055] When the output voltage decreases, the difference between the reference voltage and the sampling voltage increases, the drive current output by the comparison amplifier increases, and the voltage drop of the series adjustment tube decreases, thereby increasing the output voltage. On the contrary, if the output voltage exceeds the required set value, the front drive current output by the comparison amplifier decreases, thereby reducing the output voltage.

[0056] By changing the output DAC_out2 of the digital-to-analog converter DAC8411 through the single-chip microcomputer, the output voltage can be changed, that is, the controllability of the digitally controlled DC regulated power supply can be achieved.

[0057] Figure 4 A sampling circuit is shown. Figure 4 As shown, the voltages at V+ and V- are the voltages at both ends of the sampling resistor R61. This embodiment uses the high-precision current shunt detector INA226 launched by Texas Instruments as the current detection chip. The INA226 has a maximum offset voltage of 10 microvolts and a maximum gain error of 0.1%, which is 10 times more accurate than the industry's leading competitive products. The device is a complete 16-bit single-chip solution that can provide fully programmable measurements of current, voltage, and power for digital I2C interfaces.

[0058] Figure 5 It is a voltage sampling input buffer circuit. The voltage output Vout2 of the latter stage is divided by the voltage divider resistors R74 and R75, and then passes through the operational amplifier MCP6002. The output voltage ADC0 is converted to digital by the chip MCP3425 and communicates with the microcontroller through I2C. MCP3425 is a single-channel, low-noise, high-accuracy A / D converter with a small package and simple peripheral circuits, which is favored by most hardware designers.

[0059] Figure 6 It is a switch control circuit. Enable is connected to the microcontroller, and controls the on and off of the optocoupler TLP181 by outputting high and low levels, thereby driving the gate of the PMOS tube to achieve power switch control. When the output sampling current is greater than the preset value, the optocoupler is controlled to disconnect, thereby controlling the PMOS tube to disconnect, cutting off the external power input and protecting the subsequent circuit.

[0060] The present invention measures the output voltage value of the rear stage when it is unloaded and loaded, and compares it with the set value. The load is simulated by a 11Ω sliding rheostat, and when the output current is 3.5A, the overcurrent protection circuit is activated.

[0061] Table 1 is the test data when no load is applied. From the data in the table, it can be seen that the output voltage can change with the set value, and the error is less than or equal to 2mV; the error between the voltage sampling value data and the actual output voltage is less than or equal to 1mV.

[0062] Table 2 shows the test data of 12V output voltage under different loads. From the data in the table, it can be seen that as the load current increases, the output voltage value decreases slightly. The output voltage drop value of 3A load relative to no-load is kept within 1mV. The current recovery value is close to the actual current value, and the error is within 4mA.

[0063] Table 1 No-load output voltage

[0064]

[0065] Table 2 Load capacity test (12V)

[0066]

[0067] This paper takes the microcontroller as the core, uses the non-isolated DC / DC controller to control the PMOS tube output as the front-stage switching power supply output, and uses the low voltage drop linear regulator LDO as the back-stage output to achieve digitally controllable low-power, low-ripple DC regulated power supply output. The experiment shows that the DC regulated power supply has the characteristics of digital control and high precision, and its performance is good and can meet the requirements of practical use.

[0068] It should be noted that, although some device models are listed above, it does not mean that these device models must be used to implement the present invention, because different types of chips with the same function are common.

Claims

1. A DC regulated power supply, characterized in that: include: A switch control circuit, an input filter circuit, a front-stage switching power supply for converting high DC power into low DC power, and a rear-stage LDO and output filter circuit for reducing electromagnetic interference and output ripple of the front-stage output, which are connected in sequence; A sampling circuit for collecting the output voltage of the subsequent LDO; and The single chip microcomputer is connected to the switch control circuit, the front-stage switch power supply and the rear-stage LDO, controls the switch control circuit and the front-stage switch power supply, and outputs a reference voltage to the rear-stage LDO. The rear-stage LDO adjusts the output voltage based on the voltage difference between the sampling voltage of the sampling circuit and the reference voltage.

2. The DC regulated power supply according to claim 1, characterized in that: The post-stage LDO includes: an operational amplifier, whose two input terminals respectively input the sampling voltage and the reference voltage; and a MOS tube, whose input terminal is connected to the previous stage switching power supply, the output terminal is connected to the output filter circuit, and the control terminal is connected to the output terminal of the operational amplifier.

3. The DC regulated power supply according to claim 2, characterized in that: The microcontroller is connected to the operational amplifier through an analog-to-digital converter.

4. The DC regulated power supply according to claim 1, characterized in that: A sampling resistor is connected between the front-stage switching power supply and the back-stage LDO, and the voltages V+ and V- across the sampling resistor are input into the current detection chip to realize current detection.

5. The DC regulated power supply according to claim 1 or 4, characterized in that: The switch control circuit includes an optocoupler and a switch tube. The microcontroller controls the on and off of the optocoupler by outputting high and low levels, thereby driving the control end of the switch tube to achieve power switch control.

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