CN218526235U - Constant current protection circuit - Google Patents
Constant current protection circuit Download PDFInfo
- Publication number
- CN218526235U CN218526235U CN202222292486.3U CN202222292486U CN218526235U CN 218526235 U CN218526235 U CN 218526235U CN 202222292486 U CN202222292486 U CN 202222292486U CN 218526235 U CN218526235 U CN 218526235U
- Authority
- CN
- China
- Prior art keywords
- resistor
- control unit
- constant current
- constant
- optocoupler
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Active
Links
Images
Landscapes
- Dc-Dc Converters (AREA)
Abstract
A constant current protection circuit comprises a constant current control unit and a constant voltage control unit, wherein the output end of the constant current control unit is connected with the control end of the constant voltage control unit, when the current of a load end is less than or equal to a set threshold value, the constant current control circuit does not work, and the constant voltage control circuit works normally; when the electric current of load end was greater than the threshold value of settlement, constant current control circuit output control signal to constant current control circuit, constant current control circuit began to intervene work, and switching power supply is in the constant current guard state to realize overpower constant current protection, the utility model discloses on constitute constant voltage control unit's basis by U3TL431, only adopt to put all the way, can realize constant voltage and constant current dicyclo control, the circuit is more retrencied, effectively reduces circuit cost, components and parts occupation of plates area.
Description
Technical Field
The utility model belongs to the switching power supply field, concretely relates to constant current protection circuit.
Background
Switching power supplies have been widely used in various fields because of their high efficiency and high power density. Taking a conventional flyback topology as an illustrative case, in order to implement constant current protection at a load end, two control units are usually arranged in a circuit, including a constant voltage control unit and a constant current control unit. As shown in fig. 1, a constant voltage control unit formed by taking an operational amplifier U1A and a diode D2 as a core, and a constant current control unit formed by taking an operational amplifier U2A and a diode D3 as a core, when no overcurrent condition occurs at a load end, the constant voltage control unit controls voltage to be stably output, and the constant current control unit does not work; when the output current of the load end is larger than the set threshold value, the operational amplifier U2A of the constant current control unit outputs low level, the constant current control unit takes over the constant voltage control unit, the output voltage is reduced, and the output current maintains a constant value, so that the power supply is protected from being damaged.
In the conventional technical scheme, two paths of operational amplifiers are generally adopted to respectively correspond to a constant voltage control unit and a constant current control unit, and the control logic is clear. However, in practical product applications, the requirements for cost and PCB wiring area are as low and compact as possible in the small power flyback topology, and these factors make it necessary to further seek a more concise circuit control scheme.
SUMMERY OF THE UTILITY MODEL
In view of this, the utility model provides a constant current protection circuit only adopts the fortune all the way to put and both can realize constant voltage and constant current dicyclo control, retrencies the components and parts quantity in the circuit, effectively reduces circuit cost.
The utility model provides a technical scheme as follows:
a constant current protection circuit is characterized in that: the constant-current protection circuit adopts one operational amplifier to realize constant-current and constant-voltage double-loop control, and comprises a constant-current control unit and a constant-voltage control unit;
the constant current control unit comprises a resistor RS, a resistor R1, a resistor R2, an operational amplifier U1A and a diode D2; one end of a resistor RS is used as the input end of the constant current control unit and is connected with the negative output end of the switching power supply and one end of a resistor R1, the other end of the resistor RS is grounded, the other end of the resistor R1 is connected with the inverted input end of the operational amplifier U1A and one end of a resistor R2, the other end of the resistor R2 is connected with a reference voltage Vref, the positive input end of the operational amplifier U1A is grounded, the output end of the operational amplifier U1A is connected with the anode of a diode, and the cathode of the diode is used as the output end of the constant current control unit;
the constant voltage control unit comprises optocouplers U2 and TL 431U 3, a resistor R4 and a resistor R5; one end of a resistor R4 is used as an input end of a constant voltage control circuit and connected with a positive output end of a switching power supply, the other end of the resistor R4 is connected with one end of a resistor R5 and a reference end of a TL 431U 3 and is used as a control end of a constant voltage control unit, the anode of the TL 431U 3 and the other end of the resistor R5 are grounded, the cathode of the TL 431U 3 is connected with the second end of an optocoupler U2, the first end of the optocoupler U2 is connected with a power supply end VCC, the third end of the optocoupler U2 is grounded, and the fourth end of the optocoupler U2 is connected with a feedback end of the switching power supply;
and the output end of the constant current control unit is connected with the control end of the constant voltage control unit.
Preferably, the constant current control unit further includes a resistor R3 and a capacitor C2, and the resistor R3 and the capacitor C2 are connected between the output end of the operational amplifier U1A and the inverting input end of the operational amplifier U1A.
Preferably, the constant voltage control unit further includes a resistor R6, a resistor R8 and a capacitor C3, the resistor R6 and the capacitor C3 are connected between the cathode of the TL 431U 3 and the connection point of the resistor R4 and the resistor R5, and the resistor R8 is connected between the first end of the optocoupler U2 and the power supply terminal VCC.
Preferably, the first end of the optocoupler U2 is the anode of the light emitting diode therein, the second end of the optocoupler U2 is the cathode of the light emitting diode therein, the third end of the optocoupler U2 is the emitter of the light sensing triode therein, and the fourth end of the optocoupler U2 is the collector of the light sensing triode therein.
Compared with the prior art, the utility model discloses technical scheme's beneficial effect is:
1. on the basis of a constant voltage control unit formed by U3TL431, the constant voltage and constant current double-loop control can be realized by only adopting one operational amplifier, the circuit is more simplified, the circuit cost is effectively reduced, and the board area occupied by components is effectively reduced;
2. the parameters of the constant current control unit are flexibly set, and the intervention current threshold value of the constant current control unit can be set by setting different values of R1, R2 and RS, so that the current sampling precision and the loss of the balance resistor are facilitated.
Drawings
Fig. 1 is a circuit diagram of a constant voltage control unit and a constant current control unit of the related art;
fig. 2 is a circuit diagram of the constant current protection circuit of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
As shown in fig. 2, the utility model relates to a constant current protection circuit, connect between switching power supply's output and feedback end for realize the constant current protection of output end load, constant current protection circuit includes constant current control unit and constant voltage control unit, wherein, constant current control unit includes resistance RS, resistance R1, resistance R2, resistance R3, fortune is put U1A, diode D2 and electric capacity C2; one end of a resistor RS is used as the input end of the constant current control unit and is connected with the negative output end of the switch power supply and one end of a resistor R1, the other end of the resistor RS is grounded, the other end of the resistor R1 is connected with the inverted input end of the operational amplifier U1A and one end of a resistor R2, the other end of the resistor R2 is connected with a reference voltage Vref, the non-inverted input end of the operational amplifier U1A is grounded, the output end of the operational amplifier U1A is connected with the anode of a diode, a resistor R3 and a capacitor C2 are connected between the output end of the operational amplifier U1A and the inverted input end of the operational amplifier U1A, and the cathode of the diode is used as the output end of the constant current control unit.
The constant voltage control unit comprises an optocoupler U2, a TL 431U 3, a resistor R4, a resistor R5, a resistor R6, a resistor R8 and a capacitor C3; one end of a resistor R4 is used as an input end of a constant voltage control circuit and connected with a positive output end of a switching power supply, the other end of the resistor R4 is connected with one end of a resistor R5 and a reference end of a TL 431U 3 and is also used as a control end of a constant voltage control unit, the anode of the TL 431U 3 and the other end of the resistor R5 are grounded, the cathode of the TL 431U 3 is connected with the second end of an optocoupler U2, a resistor R6 and a capacitor C3 are connected between the cathode of the TL 431U 3 and the connection point of the resistor R4 and the resistor R5, the first end of the optocoupler U2 is connected with a power supply terminal VCC, the resistor R6 and the capacitor C3 are connected between the cathode of the TL 431U 3 and the connection point of the resistor R4 and the resistor R5, the third end of the optocoupler U2 is grounded, and the fourth end of the optocoupler U2 is connected with a feedback end of the switching power supply; the first end of the optocoupler U2 is an anode of an internal light emitting diode, the second end of the optocoupler U2 is a cathode of the internal light emitting diode, the third end of the optocoupler U2 is an emitting electrode of an internal phototransistor, and the fourth end of the optocoupler U2 is a collecting electrode of the internal phototransistor.
The output end of the constant current control unit is connected with the control end of the constant voltage control unit, when the current of the load end is less than or equal to the set threshold value, the constant current control circuit does not work, and the constant voltage control circuit works normally; when the current of the load end is larger than a set threshold value, the constant current control circuit starts to intervene in work, and the switching power supply is in a constant current protection state.
The utility model discloses a theory of operation specifically as follows:
(1) When the current at the load end is less than or equal to the threshold value, the voltage value at the inverting input end of the operational amplifier U1A is approximately as follows:
because the value of resistance RS is less than the value of R1 far away, consequently the voltage of fortune amplifying U1A inverting input is higher than the voltage of normal phase input end, satisfies V + < V-, fortune amplifying U1A output low level, constant current control unit is out of work, and constant voltage control unit normally works, because of diode D2 possesses reverse cut-off characteristics, can prevent that the electric current of constant voltage control unit U3TL431 reference end from backward flowing towards fortune amplifying U1A, from not influencing the normal work of constant voltage unit.
(2) Along with load current constantly increases, the voltage value of both ends on the resistance RS reduces thereupon, when the electric current of load end is greater than the threshold value of settlement, the positive negative input end of operational amplifier U1A satisfies promptly: v + > V-, the operational amplifier U1A outputs high level, the constant current control unit starts to intervene, the level of the output end of the operational amplifier U1A is gradually increased, the voltage flowing through a diode D2 and the reference end of the U3TL431 is gradually increased, the current flowing through a light-emitting diode in the U2 optical coupler is reduced, the voltage error output to the feedback end of the switching power supply by the constant voltage control unit is reduced, the switching power supply controls the output voltage to be reduced, and the current is kept constant, so that the over-power protection is realized.
Through the analysis, when the reference voltage Vref of the operational amplifier U1A is a fixed value, the current threshold value of the intervention work of the constant current control unit can be set through different values of the resistor R1, the resistor R2 and the resistor RS.
The utility model discloses in on the basis of constituting constant voltage control unit by U3TL431, only adopt the fortune of the same kind to put, can realize constant voltage and constant current double-ring control, the circuit is more retrencied, effectively reduces circuit cost. The problem that the requirement of a small-power flyback topology on cost and PCB wiring area is as low as possible and compact in practical product application is effectively solved.
Claims (4)
1. A constant current protection circuit is characterized in that: the constant-current protection circuit adopts one operational amplifier to realize constant-current and constant-voltage double-loop control, and comprises a constant-current control unit and a constant-voltage control unit;
the constant current control unit comprises a resistor RS, a resistor R1, a resistor R2, an operational amplifier U1A and a diode D2; one end of a resistor RS is used as the input end of the constant current control unit and is connected with the negative output end of the switching power supply and one end of a resistor R1, the other end of the resistor RS is grounded, the other end of the resistor R1 is connected with the inverted input end of the operational amplifier U1A and one end of a resistor R2, the other end of the resistor R2 is connected with a reference voltage Vref, the non-inverted input end of the operational amplifier U1A is grounded, the output end of the operational amplifier U1A is connected with the anode of a diode, and the cathode of the diode is used as the output end of the constant current control unit;
the constant voltage control unit comprises optocouplers U2 and TL 431U 3, a resistor R4 and a resistor R5; one end of a resistor R4 is used as an input end of a constant voltage control circuit and connected with a positive output end of a switching power supply, the other end of the resistor R4 is connected with one end of a resistor R5 and a reference end of a TL 431U 3 and is used as a control end of a constant voltage control unit, the anode of the TL 431U 3 and the other end of the resistor R5 are grounded, the cathode of the TL 431U 3 is connected with the second end of an optocoupler U2, the first end of the optocoupler U2 is connected with a power supply end VCC, the third end of the optocoupler U2 is grounded, and the fourth end of the optocoupler U2 is connected with a feedback end of the switching power supply;
and the output end of the constant current control unit is connected with the control end of the constant voltage control unit.
2. The constant current protection circuit according to claim 1, wherein: the constant current control unit further comprises a resistor R3 and a capacitor C2, and the resistor R3 and the capacitor C2 are connected between the output end of the operational amplifier U1A and the inverting input end of the operational amplifier U1A.
3. The constant current protection circuit according to claim 1, wherein: the constant voltage control unit further comprises a resistor R6, a resistor R8 and a capacitor C3, wherein the resistor R6 and the capacitor C3 are connected between the cathode of the TL 431U 3 and the connection point of the resistor R4 and the resistor R5.
4. The constant current protection circuit according to claim 1, wherein: the first end of the optocoupler U2 is an anode of an internal light-emitting diode, the second end of the optocoupler U2 is a cathode of the internal light-emitting diode, the third end of the optocoupler U2 is an emitting electrode of an internal photosensitive triode, and the fourth end of the optocoupler U2 is a collecting electrode of the internal photosensitive triode.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202222292486.3U CN218526235U (en) | 2022-08-30 | 2022-08-30 | Constant current protection circuit |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202222292486.3U CN218526235U (en) | 2022-08-30 | 2022-08-30 | Constant current protection circuit |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN218526235U true CN218526235U (en) | 2023-02-24 |
Family
ID=85243569
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202222292486.3U Active CN218526235U (en) | 2022-08-30 | 2022-08-30 | Constant current protection circuit |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN218526235U (en) |
-
2022
- 2022-08-30 CN CN202222292486.3U patent/CN218526235U/en active Active
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CN201854007U (en) | High-precision overcurrent protection circuit | |
| CN104868884A (en) | General switching value input signal acquisition circuit | |
| CN210053349U (en) | Current modulator for switching power supply | |
| CN218526235U (en) | Constant current protection circuit | |
| CN116418332A (en) | Optical coupler linear driving interface circuit controlled by PWM duty ratio | |
| CN207706033U (en) | Power supply circuit with temperature compensation function | |
| CN212518763U (en) | Power supply current-sharing controller | |
| CN204669330U (en) | The Acquisition Circuit of universal On-off signal signal | |
| CN104754800A (en) | Device for controlling input surge current of LED module | |
| CN211629858U (en) | Input undervoltage protection circuit and switching power supply system | |
| CN210041625U (en) | Load current-sharing circuit based on operational amplifier | |
| CN203691703U (en) | Device for controlling surge current of LED module | |
| CN210112027U (en) | Network communication system | |
| CN204425314U (en) | A kind of opto-coupled feedback isolator | |
| CN210640811U (en) | Switching power supply circuit capable of detecting current | |
| CN210037954U (en) | Power supply voltage overvoltage and undervoltage protection indicating circuit | |
| CN216449021U (en) | Switching value input/output switching circuit of instrument | |
| CN102420525A (en) | Circuit for improving multi-path output cross regulation rate of switching power supply | |
| CN217741686U (en) | High-power operational amplifier | |
| CN217655190U (en) | Support inside and outside power supply's 4-20mA current signal acquisition circuit | |
| CN212627147U (en) | Overcurrent protection circuit applied to frequency converter | |
| CN212518846U (en) | Excitation system of direct-current generator set | |
| CN205450857U (en) | No branch road leakage current's active current limit circuit | |
| CN218071302U (en) | Constant-current control circuit of switching power supply | |
| CN219659419U (en) | Over-temperature protection circuit and switching power supply |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| GR01 | Patent grant | ||
| GR01 | Patent grant |