CN200987065Y - Over-current protection circuit of power supply - Google Patents

Abstract

An overcurrent protection circuit of a power supply provides a circuit module structure of an overcurrent and short-circuit protection circuit, and achieves the overcurrent protection function of an automatic recovery mode or a quick locking mode by replacing a specific element. Comprises the following steps: an input signal detecting unit; a signal comparison circuit; a timing circuit; a positive feedback sample and hold unit; and an output action switch. The overcurrent protection in the automatic recovery mode enables the circuit to be in a locking state in a protection period, and simultaneously achieves the automatic recovery to a normal state after the overcurrent or short-circuit state disappears, so that the power supply can supply power again. The overcurrent protection in the fast lockout mode enables the circuit to be in a lockout state in a protection period, and when the overcurrent or short-circuit state disappears, the power supply needs to be turned off and then power is supplied again, so that the normal power supply state can be recovered.

Description

Over-current protection circuit of power supply

technical field

The utility model relates to a power supply, in particular to an overcurrent protection circuit of the power supply.

Background technique

Electronic power supply devices, such as power supplies, are usually equipped with an over current protection (O.C.P) circuit to prevent damage to the system due to improper operation by the user or abnormality of the product itself. At present, the overcurrent protection of the switching power supply at the output terminal for over loading (over loading) uses a current limiting method to limit the output current to a certain range, so as to achieve the purpose of circuit protection. However, when the circuit is in a state of overcurrent for a long time, the product may experience high temperature or waste a certain range of energy, resulting in circuit damage or wasted energy.

There are two main types of overcurrent protection, one is fast latch mode (latch off mode), and the other is auto recover mode (auto recover mode). In fast lockout mode, when the output terminal of the switching power supply is short-circuited or over-current, it will shut itself off. When the short-circuit or over-current disappears, the product must be turned off and then turned on again, so that the product can resume normal power supply. The auto-recovery mode includes cycle-by-cycle mode and hiccup mode. In cycle protection mode, a fixed amount of energy is consumed per cycle. In hiccup mode, when the output of the switching power supply is overloaded or short-circuited, the output of the product itself will be turned off, and it will restart itself after a period of time. If the output of the product is still short-circuited after startup, the output of the product will be turned off , so that the internal power consumption of the product is controlled within a safe range until the short circuit is removed.

However, when the product needs to have the functions of fast latch off mode and auto recover mode at the same time, the relative controller is expensive, which will cause the problem of increased product cost. Moreover, current low-priced controllers generally only have the function of cycle-by-cycle mode, so additional protection circuits of other modes must be added to achieve the same purpose.

Contents of the invention

The utility model is an over-current protection circuit of a power supply, and its purpose is to provide a circuit module structure of an over-current and short-circuit protection circuit, and by replacing specific components, the product can select a fast latching mode (latch off mode) and an automatic Recovery mode (auto recovermode) over-current protection function.

According to the overcurrent protection circuit of the power supply proposed by the utility model, it includes: an input signal detection unit for receiving the current sensing signal to further determine the time for the overcurrent protection circuit to return to normal operation; a signal A comparison circuit, which is connected to the input signal detection unit, is used to compare the reference voltage and the input voltage signal converted by the current sensing signal and the first feedback current to generate a comparison voltage; a timing circuit, which is connected to the signal comparison circuit , used to determine the operating cycle of the over-current protection circuit according to the current level of the second feedback current; a positive feedback sampling and holding unit, which is connected to the input signal detection unit, the signal comparison circuit and the timing circuit, for according to Compare the voltage to judge whether to provide the second feedback current to the timing circuit, and provide the first feedback current to the input signal detection unit; Whether the current protection circuit inhibits the output of the power supply.

Through the above-mentioned circuit features, the utility model provides the advantage of using the charging and discharging circuit to control the operation period of the over-current protection circuit.

Another advantage provided by the present invention is that the positive feedback circuit is used to control the charging and discharging circuit to perform charging or discharging operations.

Another advantage provided by the present invention is that the comparison voltage output by the comparison circuit is used to control whether the positive feedback circuit operates.

Another advantage provided by the utility model is that the overcurrent protection circuit can have the overcurrent protection functions of fast latch off mode and auto recover mode at the same time by using the exchange of specific components.

Description of drawings

Fig. 1 is the overcurrent protection circuit diagram of the utility model power supply;

Fig. 2 is the schematic diagram of the waveform of the input voltage signal of the positive input terminal of the operational amplifier in the overcurrent protection circuit of the present invention;

Fig. 3 is the waveform schematic diagram of the output voltage signal of the drain terminal of the field effect transistor of the utility model overcurrent protection circuit;

FIG. 4 is a graph of the operating cycle of the overcurrent protection circuit of the power supply of the present invention;

FIG. 5 is an overcurrent protection circuit diagram of a power supply according to another embodiment of the present invention.

Explanation of symbols in the figure

Input signal detection unit 10

Diode D1

Resistor R1

Capacitor C1

Signal comparison circuit 210

Proportional resistor R2, R3

Operational Amplifier OP1

Timing circuit 220

Capacitor C2

Charging resistor R5

Discharge resistor R4

Discharge diode D2

Divider resistor R7

Positive feedback sample and hold unit 30

Feedback Transistor Q1

Feedback resistor R6

Output Action Switch 40

Field Effect Transistor Q2

Constant voltage source VDD

Input voltage signal Vi

Output voltage signal Vo

Current sense signal I _CT

Reference voltage _VREE

The first feedback current I _FB1

Second feedback current I _FB2

Detailed ways

The utility model is applied to the current overload and short-circuit protection of the circuit in the power supply. During the period of protection, the output of the circuit is closed, and it will start again after a period of time; The output of the circuit is turned off until the current fault disappears, and the circuit is automatically turned on again immediately.

Please refer to FIG. 1 , which is an overcurrent protection circuit diagram of the power supply of the present invention. The overcurrent protection circuit of the power supply includes an input signal detection unit 10 , a signal comparison circuit 210 , a timing circuit 220 , a positive feedback sampling and holding unit 30 and an output action switch 40 . The input signal detection unit 10 is connected to the output terminal (not shown) of the signal comparison circuit 210 and the power supply. The signal comparison circuit 210 is connected to the timing circuit 220 . The timer circuit 220 is connected to the output operation switch 40 . The positive feedback sample and hold unit 30 is connected between the input signal detection unit 10 , the signal comparison circuit 210 and the timing circuit 220 . The output action switch 40 is connected to the load circuit connected to the output terminal of the power supply.

The input signal detection unit 10 includes a diode D1 and a charging and discharging circuit composed of a resistor R1 and a capacitor C1, and the signal comparison circuit 210 includes an operational amplifier OP1 and a pair of proportional resistors R2 and R3. The reverse end of the diode D1 is connected to one end of the resistor R1 and the capacitor C1, and connected to the positive input end of the operational amplifier OP1. The inverting input terminal of the operational amplifier OP1 is connected to the junction of the proportional resistors R2 and R3, and the proportional resistors R2 and R3 are connected between the constant voltage source VDD and ground, and the output terminal of the operational amplifier OP1 is connected to the timing circuit 220 .

The timing circuit 220 includes a charging resistor R5, a discharging resistor R4, a discharging diode D2 and a capacitor C2, the positive feedback sampling and holding unit 30 includes a feedback transistor Q1 and a feedback resistor R6, and the output action switch 40 includes a field effect transistor Q2. The reverse terminal of the discharge diode D2 is connected to the output terminal of the operational amplifier OP1 and the emitter terminal of the feedback transistor Q1, and the discharge diode D2 and the discharge resistor R4 form a discharge path of the capacitor C2. One end of the capacitor C2 is respectively connected to the charging resistor R5, the discharging resistor R4 and the gate of the field effect transistor Q2, and the other end of the capacitor C2 is grounded. The source terminal of the field effect transistor Q2 is grounded, and the drain terminal is the output terminal of the overcurrent protection circuit.

The base terminal of the feedback transistor Q1 is connected to the charging resistor R5 to form a charging path for the capacitor C2. The collector terminal of the feedback transistor Q1 is connected to one terminal of the feedback resistor R6, and the other terminal of the feedback resistor R6 is connected to the reverse terminal of the diode D1.

First, the diode D1 guides the current sense (CT) signal I _CT at the output end of the power supply to the input signal detection unit 10, charges the capacitor C1, and generates an input voltage signal Vi, which is the positive input end of the operational amplifier OP1. voltage level. The inverting input terminal of the operational amplifier OP1 divides a certain voltage source VDD through proportional resistors R2 and R3 to obtain a reference voltage V _REF .

When the over-current protection circuit is in a normal state, that is, when the input voltage signal Vi is less than or equal to the reference voltage V _REF , the voltage level of the comparison voltage output by the output terminal of the operational amplifier OP1 will be in a low state. The comparison voltage in a low state will turn off the feedback transistor Q1, and the capacitor C2 will discharge to the ground through the discharge path formed by the discharge resistor R4 and the diode D2. Since the capacitor C2 has been discharged, the voltage between the gate terminal and the source terminal of the field effect transistor Q2 is lower than the turn-on voltage, so that the field effect transistor Q2 is turned off, and the current sensing signal I _CT cannot drive the over-current protection circuit.

When the over-current protection circuit is in a protection state, that is, when the input voltage signal Vi is greater than the reference voltage V _REF , the voltage level of the comparison voltage output by the output terminal of the operational amplifier OP1 will be in a high state. The high potential state of the output terminal of the operational amplifier OP1 will make the junction between the emitter terminal and the collector terminal of the feedback transistor Q1 present a forward-bias conduction. The turned-on feedback transistor Q1 provides the first feedback current I _FB1 to charge the capacitor C1 through the feedback resistor R6, and also provides the second feedback current I _FB2 to charge the capacitor C2 through the charging resistor R5. When the first feedback current I _FB1 charges the capacitor C1 , the output terminal of the operational amplifier OP1 generates a positive feedback response through the feedback transistor Q1 , so that the output terminal of the operational amplifier OP1 can be kept at a high potential state. When the second feedback current I _FB2 charges the capacitor C2, so that the capacitor voltage of the capacitor C2 is higher than the critical voltage for making the gate terminal and the source terminal of the field effect transistor Q2 conduct, there will be a gap between the drain terminal and the source terminal of the field effect transistor Q2. conduction. Therefore, the output voltage signal Vo of the power supply will be shut down by the action of the over-current protection circuit.

In addition, while the interface between the emitter terminal and the base terminal of the feedback transistor Q1 is forward-biased, the second feedback current I _FB2 of the feedback transistor Q1 will charge the capacitor C2 through the charging resistor R5, so that the feedback transistor Q1 enters a linear operation from the saturated operation region area, and then the first feedback current I _FB1 passing through the feedback resistor R6 gradually decreases. Finally, the input voltage signal Vi of the positive input terminal of the operational amplifier OP1 will be lower than the reference voltage V _REF of the negative input terminal, so that the output terminal of the operational amplifier OP1 is zero voltage. At this time, the capacitor C2 discharges the ground terminal through the discharge diode D2 and the discharge resistor R4. When the capacitor voltage of the capacitor C2 is discharged to be lower than the critical voltage for turning on the field effect transistor Q2, the field effect transistor Q2 is turned off, and the power supply resumes normal operation. When the output current exceeds the protection point again, the protection circuit is restarted.

Wherein, the feedback transistor Q1 may be a PNP bipolar junction transistor (BJT), the discharge resistor R4 may be an adjustable resistor, and the field-effect transistor Q2 may be an N-type field-effect transistor (FET).

Please refer to FIG. 2 , which is a schematic waveform diagram of the input voltage signal of the positive input terminal of the operational amplifier in the overcurrent protection circuit of the present invention. In the figure, the characteristic curve measured by the positive input terminal of the operational amplifier is represented by a solid line curve, while the other part of the figure represented by a dotted line curve is the characteristic curve of the output voltage signal Vo of the overcurrent protection circuit . The characteristic curve of the input voltage signal Vi at the positive input terminal is mainly divided into five sections, namely the first section I, the second section II, the third section III, the fourth section IV and the fifth section V .

The first section I measures the voltage characteristic curve obtained when the current sensing signal I _CT begins to charge the capacitor C1. In the second section II, in the self-holding state, the characteristic curve of the voltage across the capacitor C1 is measured. The maximum voltage value curve of the non-inverting input terminal of the third section III operational amplifier OP1. The characteristic curve of the voltage across the capacitor C1 when the feedback transistor Q1 of the fourth section IV enters the linear operation region and the first feedback current I _FB1 decreases. In the fifth section V, when the input voltage signal Vi of the positive input terminal of the operational amplifier OP1 is lower than the reference voltage V _REF of the negative input terminal, so that the output terminal of the operational amplifier OP1 is at a low potential, the voltage characteristics at both ends of the rapidly discharged capacitor C1 curve.

Please refer to FIG. 3 , which is a schematic waveform diagram of the output voltage signal at the drain terminal of the field effect transistor of the overcurrent protection circuit of the present invention. In the figure, the characteristic curve measured by the positive input terminal of the operational amplifier is represented by a dotted line curve, while the other part of the figure represented by a solid line curve is the characteristic curve of the output voltage signal Vo of the overcurrent protection circuit . The characteristic curve of the output voltage signal Vo is mainly divided into two sections, respectively a first section I and a second section II. The characteristic curve of the output voltage signal Vo in the normal working state of the first section I. The characteristic curve of the output voltage signal Vo under the overcurrent protection state of the second section II.

It can be seen from the above that the overcurrent protection circuit of the present invention can adjust the discharge time of the capacitor C2 by adjusting the size of the discharge resistor R4, that is, adjust the delay time for entering the protection state. In addition, the output voltage signal Vo can also be directly obtained from the output action switch 40 without being amplified. Please refer to FIG. 4 , which is a graph of the operating cycle of the overcurrent protection circuit of the power supply of the present invention.

Although the above-mentioned over-current protection circuit is applied in a power supply and has the function of hiccup mode protection in auto-recover mode, it is not limited thereto. As far as the over-current protection circuit itself is concerned , which can change the over-current protection circuit with automatic recovery function into an over-current protection circuit with fast blocking function by substituting specific components.

As shown in FIG. 5 , it is a schematic circuit diagram of the overcurrent protection circuit of the power supply of the present invention. In this embodiment, the overcurrent protection circuit of FIG. 1 is replaced by a voltage dividing resistor R7 to replace the capacitor C2. In this way, the voltage dividing resistor R7 and the charging resistor R5 will form a voltage dividing resistor structure, so that the overcurrent protection circuit It can have an over-current protection mechanism with a fast blocking function.

The accompanying drawings are provided for reference and illustration only, and are not intended to limit the present utility model. The above descriptions are only preferred feasible embodiments of the present utility model, and therefore do not limit the patent scope of the present utility model. Therefore, all equivalent structural changes made by using the description of the utility model and the contents of the icons are all included in this utility model in the same way. Within the scope of utility models, it is agreed to Chen Ming.

Claims (19)

1. the circuit overcurrent protection of a power supply unit is characterized in that comprising:

One input signal detecting unit produces an input voltage signal in order to receive a current sensing signal;

One signal comparator circuit, it is linked to this input signal detecting unit, in order to relatively this input voltage signal and a reference voltage, to produce a comparative voltage;

One positive feedback sampling and holding unit, it is linked to this input signal detecting unit, this signal comparator circuit, in order to one second feedback current and one first feedback current to be provided according to this comparative voltage, and this first feedback current feeds back to this input signal detecting unit, replys the time that operates under the normal condition with this circuit overcurrent protection of further decision;

One timing circuit, it is linked to this signal comparator circuit and this positive feedback sampling and holding unit, in order to the electric current position standard according to this second feedback current, decides the operation period of this circuit overcurrent protection; And

One output action switch, it is linked to this timing circuit, in order to according to this second feedback current, decides this circuit overcurrent protection whether to suppress the output of this power supply unit.

2. the circuit overcurrent protection of power supply unit according to claim 1; it is characterized in that this input signal detecting unit comprises a diode, a resistance and an electric capacity; and this resistance and this electric capacity is in order to determining this input voltage signal, and influences this circuit overcurrent protection and reply the time that operates under normal condition.

3. the circuit overcurrent protection of power supply unit according to claim 1; it is characterized in that this timing circuit comprises a charge path and a discharge path; with provide this positive feedback sampling and holding unit via this charge path to the charging of this timing circuit, this timing circuit then discharges to this signal comparator circuit and this positive feedback sampling and holding unit via this discharge path.

4. the circuit overcurrent protection of power supply unit according to claim 3 is characterized in that comprising an electric capacity and a charging resistor on this charge path, and this charging resistor is linked to this positive feedback and holding unit, and this electric capacity is ground connection then.

5. the circuit overcurrent protection of power supply unit according to claim 4; it is characterized in that comprising on this discharge path a discharge diode, a discharge resistance and this electric capacity, this discharge resistance by this discharge diode respectively with this signal comparator circuit and this positive feedback sampling and holding unit binding.

6. the circuit overcurrent protection of power supply unit according to claim 1 is characterized in that this signal comparator circuit comprises an a pair of proportion resistor and an operational amplifier.

7. the circuit overcurrent protection of power supply unit according to claim 1; it is characterized in that this positive feedback sampling and holding unit comprise a feedback transistor and a feedback resistance; and this feedback transistor is linked to this timing circuit and this signal comparator circuit; and be linked to this input signal detecting unit by this feedback resistance, with this timing circuit of further control.

8. the circuit overcurrent protection of power supply unit according to claim 1 is characterized in that this output action switch comprises a transistor.

9. the circuit overcurrent protection of a power supply unit is characterized in that comprising:

One operational amplifier, in order to the voltage level on the positive input of the voltage level on the reverse input end of this operational amplifier relatively and this operational amplifier, decide this operational amplifier | the voltage level of the comparative voltage on the output;

One feedback transistor, it is linked to the output of this operational amplifier, in order to according to the voltage level of this comparative voltage so that one first feedback current and one second feedback current to be provided;

One timing circuit, it is linked to this output of this feedback transistor and this operational amplifier, in order to the electric current position standard according to this second feedback current, decides the operation period of this circuit overcurrent protection; One output action switch, it is linked to this timing circuit, in order to according to this second feedback current, decides this circuit overcurrent protection whether to suppress the output of this power supply unit.

10. the circuit overcurrent protection of power supply unit according to claim 9; it is characterized in that this circuit overcurrent protection further comprises a diode and a charge-discharge circuit; one current sensing signal of this power supply unit can be via this charge-discharge circuit charging of this diode pair; and this first feedback current can be to this charge-discharge circuit charging, with the voltage level on this positive input that this operational amplifier is provided.

11. the circuit overcurrent protection of power supply unit according to claim 9 it is characterized in that voltage level one reference voltage on this reverse input end of this operational amplifier, and this reference voltage is produced to certain voltage source dividing potential drop by a pair of proportion resistor.

12. the circuit overcurrent protection of power supply unit according to claim 9; it is characterized in that this timing circuit comprises a charge path and a discharge path; to provide this feedback transistor to charge to this timing circuit via this charge path, this timing circuit is then via the earth terminal discharge of this discharge path to this operational amplifier.

13. the circuit overcurrent protection of power supply unit according to claim 12 is characterized in that comprising an electric capacity and a charging resistor on this charge path, this charging resistor is linked to this feedback transistor, and this electric capacity is ground connection then.

14. the circuit overcurrent protection of power supply unit according to claim 13; it is characterized in that comprising on this discharge path a discharge diode, a discharge resistance and this electric capacity, this discharge resistance is linked to this output and this feedback transistor of this operational amplifier by this discharge diode.

15. the circuit overcurrent protection of power supply unit according to claim 9 is characterized in that this output action switch comprises a transistor.

16. the circuit overcurrent protection of a power supply unit is characterized in that comprising:

One operational amplifier in order to the voltage level on the positive input of the voltage level on the reverse input end of this operational amplifier relatively and this operational amplifier, decides the voltage level of a comparative voltage;

One feedback transistor, it is linked to an output of this operational amplifier, in order to according to the voltage level of this comparative voltage so that one first feedback current and one second feedback current to be provided;

One divider resistance structure, it is linked to this output of this feedback transistor and this operational amplifier, in order to the electric current position standard according to this second feedback current, produces dividing potential drop;

One output action switch, it is linked to this divider resistance structure, in order to the dividing potential drop that is produced according to this divider resistance structure, decides this circuit overcurrent protection whether to suppress the output of this power supply unit.

17. the circuit overcurrent protection of power supply unit according to claim 16; it is characterized in that this circuit overcurrent protection further comprises a diode and a charge-discharge circuit; one current sensing signal of this power supply unit can be via this charge-discharge circuit charging of this diode pair; and this first feedback current can be to this charge-discharge circuit charging, with the voltage level on this positive input that this operational amplifier is provided.

18. the circuit overcurrent protection of power supply unit according to claim 16; it is characterized in that further comprising a pair of proportion resistor; voltage level one reference voltage on this reverse input end of this operational amplifier, and this reference voltage is produced certain voltage source dividing potential drop by this Comparative Examples resistance.

19. the circuit overcurrent protection of power supply unit according to claim 16 is characterized in that this output action switch comprises a transistor.

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