Constant current output circuit based on constant voltage Buck DC-DC converter

Abstract

The invention relates to a constant current output circuit based on a constant voltage Buck DC-DC converter, the constant voltage output circuit is composed of a DC-DC converter U1, a diode D1, a group of resistors R1-R3, capacitors C1-C6 and an inductor L1, an operational amplifier U2 is introduced, the input positive end of the operational amplifier is connected with the resistor R3, and the input negative end of the operational amplifier is connected with a reference voltage value Vref. The output end of the operational amplifier is connected with one end of a resistor R4, the other end of the resistor R4 is connected with the positive end of a diode D2, and the negative end of the diode D2 is connected with the output pin 2 of the converter U1. The constant-voltage Buck DC-DC converter has the advantages that the PWM control module, the loop compensation circuit, the overvoltage protection circuit, the overcurrent protection circuit, the temperature protection circuit and other functional circuits are integrated in the constant-voltage Buck DC-DC converter, the conversion efficiency is high, the micro surface-mounted packaging appearance is adopted, the number of components can be reduced, the layout area is reduced, and the constant-voltage Buck DC-DC converter has obvious advantages in the general application of a fuze system with limited space.

Description

Technical Field

[0001] The present invention belongs to the technical field of constant current output circuits, and particularly relates to a constant current output circuit based on a constant voltage Buck DC-DC converter in a fuze system. In situations where a large current output is required, the circuit has overvoltage protection, overcurrent protection, and temperature protection functions, thereby ensuring the safety of system applications. Background Art

[0002] The existing constant current output circuit generally adopts the method of operational amplifier + MOS tube (transistor) + peripheral, such as Figure 1 As shown in the figure, if a large current needs to be loaded on the load RL, since the current also passes through the MOS tube, a high-power MOS tube must be selected, which is not only large in size but also reduces the overall conversion efficiency of the circuit. Summary of the Invention

[0003] The purpose of the present invention is to solve the shortcomings of the existing constant current output circuit, such as large volume and low conversion efficiency, and to provide a constant current output circuit based on a constant voltage Buck DC-DC converter.

[0004] The present invention adopts the following technical solutions: The present invention provides a constant current output circuit based on a constant voltage Buck DC-DC converter, comprising: a DC-DC converter U1, a diode D1, a group of resistors R1-R3, capacitors C1-C6, and an inductor L1 to form a constant voltage output circuit. It is characterized in that an operational amplifier U2 is introduced, the positive input terminal of the operational amplifier is connected to the resistor R3, the negative input terminal is connected to the reference voltage value Vref, the output terminal of the operational amplifier is connected to one end of the resistor R4, the other end of the resistor R4 is connected to the positive end of the diode D2, and the negative end of the diode D2 is connected to the output pin 2 of the converter U1.

[0005] A further technical solution is: the constant voltage output circuit is based on the Buck DC-DC converter U1. Its input terminal 5 pin is connected to the positive terminals of the input power supply VIN, capacitors C1, C2 and C3; The input pin 4 of the DC-DC converter U1 is connected to the negative terminal of capacitor C3; Pin 3 of the DC-DC converter U1 output is connected to the negative terminal of diode D1 and the positive terminal of inductor L. The negative terminal of inductor L is connected in sequence to the positive terminals of capacitors C4 and C5, one end of resistor R1, and the positive terminal of capacitor C6. The output pin 2 of the DC-DC converter U1 is connected to the negative terminal of the diode D2, the other end of the resistor R1 and the negative terminal of the capacitor C6 in sequence; Pin 1 of the output terminal of the DC-DC converter U1 is connected in sequence to the negative terminals of capacitors C1 and C2, the positive terminal of the diode D1, the negative terminals of capacitors C4 and C5, and one end of resistors R2 and R3. The other ends of resistors R2 and R3 are connected to the negative terminal of capacitor C6 and the positive input terminal of the operational amplifier, respectively. The load RL is connected to pin 3 of the output terminal of the DC-DC converter U1 and the positive input terminal of the operational amplifier.

[0006] Compared with the existing technology, the present invention has the following advantages: the constant-voltage Buck DC-DC converter integrates a PWM control module, loop compensation, overvoltage protection, overcurrent protection, temperature protection and other functional circuits, resulting in high conversion efficiency. In addition, the invention adopts a miniature surface-mount package, which can reduce the number of components and the layout area, and has obvious advantages in the space-constrained applications of fuze systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 This is the existing constant current output circuit diagram; Figure 2 It is a structural principle diagram of the present invention; Figure 3 The waveform of the FB point of the present invention is shown in the figure. DETAILED DESCRIPTION

[0008] like Figure 2 As shown, the present invention includes: 1 constant voltage Buck DC-DC converter, 1 operational amplifier, 2 diodes, 4 resistors, and 6 capacitors.

[0009] Figure 2 The meanings of the symbols are as follows: symbol definition Remark VIN System input power GNDI System input power ground VO Output voltage GNDO Output Vref Reference voltage U1 is a PWM mode constant voltage buck DC-DC converter with a wide operating voltage range (8V to 36V), adjustable output voltage (1.25V to 33V), and a maximum output current of 8A. It features low ripple, a built-in low on-resistance power MOSFET, and a built-in loop compensation circuit to reduce the number of external components. It also features an internal constant voltage loop that allows the system's operating state to be set via an external resistor. It also includes overvoltage protection, overcurrent protection, and temperature protection to ensure system safety. The pinout for U1 is as follows:

[0010] The purpose of the present invention is to enable a constant current of 5A to be continuously loaded on the load RL.

[0011] The DC-DC converter U1, diode D1, resistors R1 and R3, capacitors C1 to C6, and inductor L1 form a constant-voltage output circuit. A 1.25V reference voltage is generated at the FB terminal, and resistors R1 and R2 adjust the output voltage to a constant value. In actual use, constant-current output cannot be achieved because the resistance of the load RL fluctuates within the range of 1Ω ± 0.5Ω.

[0012] To solve this problem, an operational amplifier (U2) is introduced, using current sampling to ensure a constant 5A output current. The principle is as follows: the op amp input samples the current value of resistor R3 at the positive terminal, amplifies the difference between the sampled current value and the set reference voltage value Vref, and superimposes the amplified value on the FB terminal through the op amp output, achieving constant current control.

[0013] During design, the margin should be considered and the output voltage constant value should be appropriately increased.

[0014] When the op amp's positive input detects a low output current, the output is low, causing the FB voltage to decrease, and the DC-DC converter to increase the output voltage. When the op amp's positive input detects a high output current, the output is high, causing the FB voltage to increase, and the DC-DC converter to decrease the output voltage. This keeps the output current constant, regardless of load influence.

[0015] The output voltage can be determined by the ratio of resistors R1 and R2, and the calculation formula is:

[0016] For example, when R1 = 10kΩ and R2 = 2.7kΩ, the output voltage is 5.88V.

[0017] The constant output current depends on the reference voltage and the sampling resistor, and the calculation formula is:

[0018] For example, when R3 = 0.05Ω, if an output current of 5A is required, the reference voltage Vref can be set to 0.25V.

[0019] The waveform of FB point is as follows Figure 3 shown.

[0020] Figure 1 The functions of other components are as follows: C1 is the input energy storage filter capacitor, which ensures the working stability of the Buck DC-DC converter and filters out low-frequency glitch interference; C2 is the input filter capacitor, which is used to filter out high-frequency glitch interference in the circuit; C3 is a bypass capacitor used to adjust the internal voltage of the DC-DC converter; C4 is the output filter capacitor, which is used to filter out high-frequency glitch interference in the circuit; C5 is the output energy storage filter capacitor, which ensures output stability and filters out low-frequency glitch interference; C6 is a feedforward capacitor used to improve the stability of the constant voltage loop.

[0021] R4 is a voltage-dividing and current-limiting resistor, used to prevent damage to the DC-DC converter; L1 is the output energy storage inductor, which ensures continuous output when the MOS tube inside the DC-DC converter is turned off; D1 is a freewheeling diode, which ensures continuous output when the MOS tube inside the DC-DC converter is turned off; D2 is an isolation diode, which ensures that the FB point signal is determined by the output of the operational amplifier.

Claims

1. A constant current output circuit based on a constant voltage buck DC-DC converter, comprising a DC-DC converter U1, a diode D1, a set of resistors R1 to R3, a set of capacitors C1 to C6, and an inductor L1, characterized in that: An operational amplifier U2 is introduced, the positive input terminal of the operational amplifier is connected to the resistor R3 and the load terminal, the negative input terminal is connected to the reference voltage value Vref, the output terminal of the operational amplifier is connected to one end of the resistor R4, the other end of the resistor R4 is connected to the positive end of the diode D2, and the negative end of the diode D2 is connected to the output pin 2 of the converter U1.

2. A constant current output circuit based on a constant voltage Buck DC-DC converter according to claim 1, characterized in that: The constant voltage output circuit is based on the Buck DC-DC converter U1. Connect the input pin 5 of Buck DC-DC converter U1 to the positive terminals of input power supply VIN, capacitors C1, C2 and C3. Buck DC-DC converter U1 input pin 4 is connected to the negative terminal of capacitor C3; Pin 3 of the Buck DC-DC converter U1 output is connected to the negative terminal of diode D1 and the positive terminal of inductor L. The negative terminal of inductor L is connected in sequence to the positive terminals of capacitors C4 and C5, one end of resistor R1, and the positive terminal of capacitor C6. Buck DC-DC converter U1 output pin 2 is connected to the negative terminal of diode D2, the other end of resistor R1 and the negative terminal of capacitor C6 in sequence; Pin 1 of the output terminal of the Buck DC-DC converter U1 is connected in sequence to the negative terminals of capacitors C1 and C2, the positive terminal of diode D1, the negative terminals of capacitors C4 and C5, and one end of resistors R2 and R3. The other ends of resistors R2 and R3 are connected to the negative terminal of capacitor C6 and the positive input terminal of the operational amplifier, respectively. One end of the load RL is connected to pin 3 of the output terminal of the DC-DC converter U1 and the other end is connected to the positive input terminal of the operational amplifier.

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