A circuit for outputting constant power control

Abstract

The present invention relates to a circuit for outputting constant power control, comprising an output voltage terminal V out , reference voltage terminal V ref , Input current reference voltage terminal V maxf , resistor R1, resistor R2, resistor R3, resistor R4, resistor R5, transistor Q1, transistor Q2 and transistor Q3; the output voltage terminal V out , resistor R1, resistor R2, and resistor R3 are connected in series in sequence, the emitter of the transistor Q1 is connected between the resistor R1 and the resistor R2, and the base is connected to the reference voltage terminal V ref The collector is connected to the collector and base of the transistor Q2 respectively, the base of the transistor Q2 is connected to the base of the transistor Q3, and the collector of the transistor Q3 is connected to the resistor R4 and the input current reference voltage terminal V maxf The invention is connected to the resistor R5. Compared with the prior art, the invention has the advantages of greatly reducing the manufacturing cost.

Description

Technical Field

[0001] The invention relates to a switching power supply, in particular to a circuit for outputting constant power control. Background Art

[0002] With the rapid development of power electronics technology, more and more electronic devices have entered our daily work and life, so the application of reliable switching power supplies has become more and more extensive. And the requirements for switching power supplies are getting higher and higher, with high reliability, high safety and low cost.

[0003] If the switching power supply has a constant power characteristic, that is, a preset constant output power, when the output power does not reach the preset constant power value, the current can continue to increase to the rated value. As the output current / voltage increases, when the output power reaches the preset value, it can enter the constant power mode, the output current decreases accordingly, and the total output power remains unchanged, maintaining the preset output power. This function enables the switching power supply to have: 1) a wider output window; 2) protection against power output overpower.

[0004] Therefore, once the switching power supply has the function of "constant power output", it can meet the customer's requirements for high reliability and high safety, and the cost increase is minimal.

[0005] At present, the mainstream method to achieve the "constant power output" function is to add a single-chip microcomputer control unit. The single-chip microcomputer detects the output voltage value in real time to determine whether output current control is required. And the single-chip microcomputer outputs the corresponding pulse width modulation to achieve current reduction or increase, so as to control the output power within the rated range.

[0006] However, after adding the MCU, the switching power supply needs to be burned with software before it can be used normally, which increases the production cost and the complexity of use. Summary of the invention

[0007] The purpose of the present invention is to provide a circuit for outputting constant power control in order to overcome the defects of the prior art.

[0008] The purpose of the present invention can be achieved by the following technical solutions:

[0009] A circuit for outputting constant power control, comprising an output voltage terminal V out , reference voltage terminal V ref , Input current reference voltage terminal V maxf , resistor R1, resistor R2, resistor R3, resistor R4, resistor R5, transistor Q1, transistor Q2 and transistor Q3;

[0010] The output voltage terminal V out, resistor R1, resistor R2, and resistor R3 are connected in series in sequence, the emitter of the transistor Q1 is connected between the resistor R1 and the resistor R2, and the base is connected to the reference voltage terminal V ref The collector is connected to the collector and base of the transistor Q2 respectively, the base of the transistor Q2 is connected to the base of the transistor Q3, and the collector of the transistor Q3 is connected to the resistor R4 and the input current reference voltage terminal V maxf And connected to resistor R5.

[0011] Preferably, the circuit further comprises a diode D1, the anode of the diode D1 being connected to the reference voltage terminal V ref The cathode is connected to the emitter of transistor Q1.

[0012] Preferably, the circuit further comprises a resistor R11, a resistor R12, a resistor R13 and a transistor Q4, and the output voltage terminal V out , resistor R11, resistor R12, and resistor R13 are connected in series in sequence, the emitter of the transistor Q4 is connected between the resistor R11 and the resistor R12, and the base is connected to the reference voltage terminal V ref The collector is connected to the collector of transistor Q3.

[0013] Preferably, the circuit further comprises a diode D2, the anode of the diode D2 being connected to the reference voltage terminal V ref The cathode is connected to the emitter of transistor Q4.

[0014] Preferably, one end of the resistor R13 is connected to the resistor R12, and the other end is grounded.

[0015] Preferably, one end of the resistor R3 is connected to the resistor R2, and the other end is grounded.

[0016] Preferably, one end of the resistor R4 is connected to one end of the resistor R5, and the other end is connected to the reference voltage terminal V ref connect.

[0017] Preferably, the other end of the resistor R5 is grounded.

[0018] Preferably, the emitter of the transistor Q2 is grounded via a resistor R7.

[0019] Preferably, the emitter of the transistor Q3 is grounded via a resistor R6.

[0020] Compared with the prior art, the present invention uses a hardware circuit to achieve output constant power control without adding a single-chip microcomputer control unit, thereby greatly reducing the production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a specific circuit diagram of Example 1;

[0022] Figure 2 This is a specific circuit diagram of Example 2. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0024] Example 1

[0025] The present invention uses the voltage on the output load as negative feedback to control the magnitude of the output current. When it is detected that the output voltage reaches a certain threshold value, the output current is reduced proportionally to achieve output constant power control.

[0026] like Figure 1 As shown, a circuit for outputting constant power control includes an output voltage terminal V out , reference voltage terminal V ref , Input current reference voltage terminal V maxf , resistor R1, resistor R2, resistor R3, resistor R4, resistor R5, transistor Q1, transistor Q2 and transistor Q3;

[0027] The output voltage terminal V out , resistor R1, resistor R2, and resistor R3 are connected in series in sequence, the emitter of the transistor Q1 is connected between the resistor R1 and the resistor R2, and the base is connected to the reference voltage terminal V ref The collector is connected to the collector and base of the transistor Q2 respectively, the base of the transistor Q2 is connected to the base of the transistor Q3, and the collector of the transistor Q3 is connected to the resistor R4 and the input current reference voltage terminal V maxf And connected to resistor R5.

[0028] The circuit further includes a diode D1, the anode of which is connected to the reference voltage terminal V ref The negative electrode is connected to the emitter of transistor Q1. One end of the resistor R3 is connected to the resistor R2, and the other end is grounded. One end of the resistor R4 is connected to one end of the resistor R5, and the other end is connected to the reference voltage terminal V ref The other end of the resistor R5 is grounded.

[0029] The emitter of the transistor Q2 is grounded via a resistor R7. The emitter of the transistor Q3 is grounded via a resistor R6.

[0030] The output voltage detection unit is composed of R1, R2, and R3. When the output voltage V out If it is greater than the threshold, Q1 is turned on;

[0031] The emitter current I1 flowing through Q1

[0032]

[0033] Output current reference V maxf It can be expressed as:

[0034]

[0035] Then through V maxf Establish the relationship with the output current:

[0036]

[0037] Thus, the output current I is established through Eq.1, Eq.2, and Eq.3. out With V out to realize the output power control.

[0038] Example 2

[0039] like Figure 2 As shown, in addition to the content of Example 1, the circuit of this embodiment further includes a resistor R11, a resistor R12, a resistor R13 and a transistor Q4, and the output voltage terminal V out , resistor R11, resistor R12, and resistor R13 are connected in series in sequence, the emitter of the transistor Q4 is connected between the resistor R11 and the resistor R12, and the base is connected to the reference voltage terminal V ref The collector is connected to the collector of transistor Q3.

[0040] The circuit further includes a diode D2, the anode of which is connected to the reference voltage terminal V ref The cathode is connected to the emitter of transistor Q4.

[0041] One end of the resistor R13 is connected to the resistor R12, and the other end is grounded.

[0042] When the output voltage Vout increases to a certain value, Q4 will turn on.

[0043] The emitter current I2 flowing through Q4

[0044]

[0045] V maxf It can be expressed as

[0046]

[0047] Output current I out It can be expressed as

[0048]

[0049] When the second threshold is triggered, the reduction degree of the output current will slow down to achieve a wider output voltage range.

[0050] According to the actual application requirements, you can choose to increase the number of voltage detection resistors and transistor groups.

[0051] Therefore, from the above, with only a very low increase in cost, the switching power supply can have the function of outputting constant power control.

[0052] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A circuit for outputting constant power control, characterized in that: Including the output voltage terminal V out , reference voltage terminal V ref , Input current reference voltage terminal V maxf , resistor R1, resistor R2, resistor R3, resistor R4, resistor R5, transistor Q1, transistor Q2 and transistor Q3; The output voltage terminal V out , resistor R1, resistor R2, and resistor R3 are connected in series in sequence, the emitter of the transistor Q1 is connected between the resistor R1 and the resistor R2, and the base is connected to the reference voltage terminal V ref The collector is connected to the collector and base of the transistor Q2 respectively, the base of the transistor Q2 is connected to the base of the transistor Q3, and the collector of the transistor Q3 is connected to the resistor R4 and the input current reference voltage terminal V maxf And connected to resistor R5.

2. A circuit for outputting constant power control according to claim 1, characterized in that: The circuit further includes a diode D1, the anode of which is connected to the reference voltage terminal V ref The cathode is connected to the emitter of transistor Q1.

3. The circuit for outputting constant power control according to claim 1, characterized in that: The circuit further includes a resistor R11, a resistor R12, a resistor R13 and a transistor Q4. The output voltage terminal V out , resistor R11, resistor R12, and resistor R13 are connected in series in sequence, the emitter of the transistor Q4 is connected between the resistor R11 and the resistor R12, and the base is connected to the reference voltage terminal V ref The collector is connected to the collector of transistor Q3.

4. The circuit for outputting constant power control according to claim 3, characterized in that: The circuit further includes a diode D2, the anode of which is connected to the reference voltage terminal V ref The cathode is connected to the emitter of transistor Q4.

5. The circuit for outputting constant power control according to claim 3, characterized in that: One end of the resistor R13 is connected to the resistor R12, and the other end is grounded.

6. The circuit for outputting constant power control according to claim 1, characterized in that: One end of the resistor R3 is connected to the resistor R2, and the other end is grounded.

7. The circuit for outputting constant power control according to claim 1, characterized in that: One end of the resistor R4 is connected to one end of the resistor R5, and the other end is connected to the reference voltage terminal V ref connect.

8. The circuit for outputting constant power control according to claim 7, characterized in that: The other end of the resistor R5 is grounded.

9. The circuit for outputting constant power control according to claim 1, characterized in that: The emitter of the transistor Q2 is grounded via a resistor R7.

10. The circuit for outputting constant power control according to claim 1, characterized in that: The emitter of the transistor Q3 is grounded via a resistor R6.

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