CN217693775U - Current-limiting constant current circuit composed of discrete devices - Google Patents
Current-limiting constant current circuit composed of discrete devices Download PDFInfo
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- CN217693775U CN217693775U CN202221607522.4U CN202221607522U CN217693775U CN 217693775 U CN217693775 U CN 217693775U CN 202221607522 U CN202221607522 U CN 202221607522U CN 217693775 U CN217693775 U CN 217693775U
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Abstract
The utility model discloses a current-limiting constant current circuit who comprises discrete device relates to the power technology. The voltage divider comprises a voltage dividing unit, a slow start protection unit, a triode Q1 and a field effect transistor Q2; the input end of the voltage division unit is used as a power supply input end; the output end of the voltage dividing unit is electrically connected with the collector of the triode Q1, the base of the triode Q1 is electrically connected with the input end of the voltage dividing unit, and the base of the triode Q1 is electrically connected with the emitter of the triode Q1 through a third resistor R3; two ends of the slow start protection unit are respectively electrically connected with a base electrode and a collector electrode of the triode Q1; the collector of the triode Q1 is electrically connected with the grid of the field effect transistor Q2 through the fifth resistor R5, the emitter of the triode Q1 is electrically connected with the source of the field effect transistor Q2, and the drain of the field effect transistor Q2 is used as the output end of the current-limiting constant current circuit. The utility model discloses low cost, and the flexibility of its output current modulation is higher, and the circuit that discrete device constitutes is favorable to the holistic heat dissipation of circuit.
Description
Technical Field
The present invention relates to power supply technology, and more particularly, to a current-limiting constant current circuit composed of discrete devices.
Background
In a conventional electronic circuit design, for example, a 10-100mA LED lamp driving circuit generally utilizes a current-limiting constant current circuit to regulate and control current, and the regulation and control quality directly affects the control performance of the whole system. The current-limiting constant-current circuit used at present is mostly a solution of an IC integrated circuit, such as a chip with a model number of OC5031B, a chip with a model number of TX6410B, and the like. However, in the environment of shortage and price increase of semiconductor devices, the cost of IC integrated circuit solution is more than doubled. In addition, the IC integrated circuit is in a limited package, and the heat dissipation performance and the heat accumulation are serious. If work for a long time, its phenomenon of generating heat is especially serious, can lead to the problem that the product life-span reduces.
SUMMERY OF THE UTILITY MODEL
The to-be-solved technical problem of the utility model is not enough to prior art, provide a current-limiting constant current circuit of constituteing by discrete device, solved because of leading to the drive circuit price to double under the general big environment that rises at present IC integrated circuit price to and because of IC integrated circuit integrates and causes its heat dispersion poor problem in limited encapsulation.
The utility model relates to a current-limiting constant current circuit composed of discrete devices, which comprises a voltage dividing unit, a slow start protection unit, a triode Q1 and a field effect tube Q2; the input end of the voltage division unit is used as a power supply input end and is electrically connected with an external voltage source; the output end of the voltage division unit is electrically connected with the collector electrode of the triode Q1, the base electrode of the triode Q1 is electrically connected with the input end of the voltage division unit, and the base electrode of the triode Q1 is electrically connected with the emitting electrode of the triode Q1 through a third resistor R3; two ends of the slow start protection unit are respectively and electrically connected with a base electrode and a collector electrode of the triode Q1; the collector of the triode Q1 is electrically connected with the grid of the field-effect tube Q2 through a fifth resistor R5, the emitter of the triode Q1 is electrically connected with the source of the field-effect tube Q2, and the drain of the field-effect tube Q2 is used as the output end of the current-limiting constant-current circuit.
The voltage division unit comprises a first resistor R1 and a second resistor R2; one end of the first resistor R1 is used as an input end of the voltage division unit, the other end of the first resistor R1 is electrically connected with one end of the second resistor R2, and the other end of the second resistor R2 is grounded; and the connection end of the first resistor R1 and the second resistor R2 is used as the output end of the voltage division unit.
The slow start protection unit is a first capacitor C1.
An absorption unit consisting of a second capacitor C2 and a fourth resistor R4 is arranged between the source electrode and the drain electrode of the field effect transistor Q2; one end of the second capacitor C2 is electrically connected to the source of the field effect transistor Q2, and the other end of the second capacitor C2 is electrically connected to the drain of the field effect transistor Q2 through the fourth resistor R4.
A voltage stabilizing diode ZD1 is electrically connected between the emitter and the collector of the triode Q1, the anode of the voltage stabilizing diode ZD1 is electrically connected with the collector of the triode Q1, and the cathode of the voltage stabilizing diode ZD1 is electrically connected with the emitter of the triode Q1.
The triode Q1 is an NPN triode.
Advantageous effects
The utility model has the advantages of: the current-limiting constant current circuit composed of discrete devices such as a resistor, a capacitor and a transistor solves the problem that the price of a driving circuit is doubled due to the rising price of the current IC integrated circuit scheme. Compared with an IC integrated circuit scheme, the driving circuit scheme composed of discrete devices is lower in cost, higher in flexibility of output current modulation and more beneficial to heat dissipation of the circuit.
Drawings
Fig. 1 is a circuit schematic diagram of the current-limiting constant current circuit of the present invention.
Detailed Description
The present invention will be further described with reference to the following examples, which are not intended to limit the scope of the present invention, but are intended to be covered by the appended claims in any way.
Referring to fig. 1, the utility model discloses a current-limiting constant current circuit by discrete device is constituteed, including partial pressure unit, the protection unit that slowly starts, triode Q1 and field effect transistor Q2. The triode Q1 is an NPN triode. The input end of the voltage division unit is used as a power supply input end, is electrically connected with an external voltage source and supplies power for the current-limiting constant-current circuit.
In order to realize voltage division of the external voltage source, and from the economic point of view, the voltage division unit of the embodiment is composed of a first resistor R1 and a second resistor R2. One end of the first resistor R1 is used as an input end of the voltage dividing unit, the other end of the first resistor R1 is electrically connected with one end of the second resistor R2, and the other end of the second resistor R2 is grounded. The connection end of the first resistor R1 and the second resistor R2 is used as the output end of the voltage division unit. Thereby realizing the voltage division function of the output voltage of the external voltage source.
The output end of the voltage dividing unit is electrically connected with the collector of the triode Q1, the base of the triode Q1 is electrically connected with the input end of the voltage dividing unit, and the base of the triode Q1 is electrically connected with the emitter of the triode Q1 through the third resistor R3. In this embodiment, the transistor Q1 is an overcurrent transistor. When the output current of the current-limiting constant current circuit exceeds the threshold current, the triode Q1 is conducted, so that the V of the field effect transistor Q2 GS When the current is reduced, the internal resistance of the field effect tube Q2 is increased, so that the impedance on an output loop of the current-limiting constant-current circuit is increased, and the effect of reducing the current to the threshold current is achieved.
The third resistor R3 is used to adjust the threshold current. The threshold current of the present embodiment can be determined by the following calculation formula:
I 0 ＝V BE /R 3 。
wherein, V BE Is the forward bias voltage of the base electrode and the emitting electrode of the triode Q1, and the voltage is generally 0.4-0.7V; i is O Is a threshold current; r 3 Is the resistance value of the third resistor R3.
Two ends of the slow start protection unit are respectively electrically connected with the base electrode and the collector electrode of the triode Q1. The slow start protection unit has the function of enabling the switching action of the field effect transistor Q2 to be started slowly, and can avoid the problem that a current-limiting constant current circuit is damaged due to unstable input voltage and current when being electrified.
Specifically, the slow start protection unit is a first capacitor C1. The first capacitor C1 may be an electrolytic capacitor or a tantalum capacitor. When the current-limiting constant current circuit is just powered on, the input current firstly charges the first capacitor C1. After charging is completed, current flows through the voltage dividing unit, so that the terminal voltage of the first resistor R1 is ensured to be slowly increased after power-on, namely V of the field effect tube Q2 GS Is slowly increased, thereby realizing the slow start of the switching action of the field effect transistor Q2.
The collector of the triode Q1 is electrically connected with the gate of the field effect transistor Q2 through a fifth resistor R5. The fifth resistor R5 is V of the field effect transistor Q2 GS The voltage of the parasitic capacitor is discharged to the current limiting resistor. The emitting electrode of the triode Q1 is electrically connected with the source electrode of the field effect transistor Q2, and the drain electrode of the field effect transistor Q2 is used as the output end of the current-limiting constant current circuit and is connected with a load.
Preferably, an absorption unit composed of a second capacitor C2 and a fourth resistor R4 is disposed between the source and the drain of the field effect transistor Q2. One end of the second capacitor C2 is electrically connected to the source of the field effect transistor Q2, and the other end of the second capacitor C2 is electrically connected to the drain of the field effect transistor Q2 through the fourth resistor R4. The RC absorption circuit formed by the fourth resistor R4 and the second capacitor C2 is used for absorbing the high voltage between the drain and the source of the fet Q2, thereby preventing the fet from being easily damaged.
Preferably, a zener diode ZD1 is electrically connected between the emitter and the collector of the triode Q1, an anode of the zener diode ZD1 is electrically connected to the collector of the triode Q1, and a cathode of the zener diode ZD1 is electrically connected to the emitter of the triode Q1. The voltage stabilizing diode ZD1 is used for preventing V of the field effect transistor Q2 when the input voltage fluctuates GS Voltage exceeding V of field effect transistor Q2 GS And the maximum value plays a role in protecting the field effect transistor.
V about field effect transistor Q2 GS Is equal to the voltage across the first resistor R1 in the voltage dividing unit. I.e. V GS ＝VCC/(R 1 +R 2 )*R1。
Wherein, V GS The voltage value between the grid electrode and the source electrode of the field effect transistor Q2; VCC is the input voltage；R 1 Is the resistance value of the first resistor R1; r 2 Is the resistance value of the second resistor R2.
In practical applications, the third resistor R3 and the fifth resistor R5 have small resistance values, and both voltage drops thereof are below 1V, which is much smaller than the voltage across the first resistor R1. For the convenience of analysis, the voltage drop generated by the third resistor R3 and the fifth resistor R5 is neglected in this embodiment, so as to obtain the above-mentioned V GS Equal to the voltage across the first resistor R1 in the voltage dividing unit.
The utility model discloses a theory of operation is: and after the current-limiting constant current circuit is connected with the load, the current-limiting constant current circuit is electrified.
When the load current output to the load by the current-limiting constant-current circuit is less than the threshold current, the voltage difference between the two ends of the third resistor R3 is less than V BE Therefore, the transistor Q1 is turned off and not operated, and the fet Q2 is turned on. The third electron R3 and the field effect transistor Q2 form a discharge circuit, and the magnitude of the output load current completely depends on the magnitude of the load. That is, the larger the load current required by the load at this time, the larger the current outputted from the current-limiting constant current circuit.
When the load current output to the load by the current-limiting constant-current circuit exceeds the threshold current, the voltage drop of the third resistor R3 also exceeds V BE The transistor Q1 will be on. At this time, the electric energy stored in the capacitor formed between the gate and the source of the fet Q2 is discharged through the transistor Q1. I.e. V GS The voltage will drop, so that the field effect transistor Q2 works in the variable resistance area; and as the VGS voltage value decreases, the equivalent resistance between the drain and the source of the field effect transistor Q2 increases. And when V GS When the resistance between the drain and the source decreases to a certain value, that is, when the resistance between the drain and the source increases to a certain value, the total impedance of the entire circuit remains unchanged. Therefore, although the load impedance of the load is reduced to increase the required load current, the load impedance and the impedance of the fet Q2 form negative feedback due to the increased resistance between the drain and the source of the fet Q2, thereby limiting the tendency of the load current to exceed the threshold current due to load weighting.
The utility modelIn the novel current-limiting constant current circuit, because of the arrangement of the triode Q1 and the field effect transistor Q2, the current of the whole discharge loop is clamped at the threshold current; and V of field effect transistor Q2 GS Stabilized at VCC/(R) 1 +R 2 )*R 1 Therefore, dynamic balance of negative feedback is formed, and the output current of the current-limiting constant current circuit achieves the effect of current-limiting constant current.
The above is only the preferred embodiment of the present invention, and it should be noted that for those skilled in the art, without departing from the structure of the present invention, several modifications and improvements can be made, which will not affect the utility model and the utility of the patent.
Claims (6)
1. A current-limiting constant current circuit composed of discrete devices is characterized by comprising a voltage division unit, a slow start protection unit, a triode Q1 and a field effect transistor Q2; the input end of the voltage division unit is used as a power supply input end and is electrically connected with an external voltage source; the output end of the voltage division unit is electrically connected with the collector electrode of the triode Q1, the base electrode of the triode Q1 is electrically connected with the input end of the voltage division unit, and the base electrode of the triode Q1 is electrically connected with the emitting electrode of the triode Q1 through a third resistor R3; two ends of the slow start protection unit are respectively and electrically connected with a base electrode and a collector electrode of the triode Q1; the collector of the triode Q1 is electrically connected with the grid of the field effect transistor Q2 through a fifth resistor R5, the emitter of the triode Q1 is electrically connected with the source of the field effect transistor Q2, and the drain of the field effect transistor Q2 is used as the output end of the current-limiting constant current circuit.
2. The current-limiting constant current circuit composed of discrete devices according to claim 1, wherein the voltage dividing unit comprises a first resistor R1 and a second resistor R2; one end of the first resistor R1 is used as an input end of the voltage division unit, the other end of the first resistor R1 is electrically connected with one end of the second resistor R2, and the other end of the second resistor R2 is grounded; and the connection end of the first resistor R1 and the second resistor R2 is used as the output end of the voltage division unit.
3. The current-limiting constant current circuit composed of discrete devices according to claim 1, wherein the soft start protection unit is a first capacitor C1.
4. The current-limiting constant current circuit composed of discrete devices according to claim 1, wherein an absorption unit composed of a second capacitor C2 and a fourth resistor R4 is arranged between a source electrode and a drain electrode of the field effect transistor Q2; one end of the second capacitor C2 is electrically connected to the source of the field effect transistor Q2, and the other end of the second capacitor C2 is electrically connected to the drain of the field effect transistor Q2 through the fourth resistor R4.
5. The circuit according to claim 1, wherein a zener diode ZD1 is electrically connected between the emitter and the collector of the transistor Q1, the anode of the zener diode ZD1 is electrically connected to the collector of the transistor Q1, and the cathode of the zener diode ZD1 is electrically connected to the emitter of the transistor Q1.
6. The circuit according to claim 5, wherein the transistor Q1 is an NPN transistor.
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| Application Number | Priority Date | Filing Date | Title |
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| CN202221607522.4U CN217693775U (en) | 2022-06-23 | 2022-06-23 | Current-limiting constant current circuit composed of discrete devices |
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| CN202221607522.4U CN217693775U (en) | 2022-06-23 | 2022-06-23 | Current-limiting constant current circuit composed of discrete devices |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116722630A (en) * | 2023-08-07 | 2023-09-08 | 国网信息通信产业集团有限公司 | Self-adaptive charging circuit based on field effect transistor |
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2022
- 2022-06-23 CN CN202221607522.4U patent/CN217693775U/en active Active
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116722630A (en) * | 2023-08-07 | 2023-09-08 | 国网信息通信产业集团有限公司 | Self-adaptive charging circuit based on field effect transistor |
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