Summary of the invention
The technical problem to be solved in the present invention is, at the defective that above-mentioned cost is higher, current drain is bigger of prior art, provides a kind of cost is lower, current drain is less low-voltage dc power supply commutation circuit and DC power supply thereof.
The technical solution adopted for the present invention to solve the technical problems is: construct a kind of low-voltage dc power supply commutation circuit, comprise first dc supply input, second dc supply input, load output, controlled switch unit and step-down isolated location; Wherein, described controlled switch unit comprises two switch terminals and a control end; Described first dc supply input is connected with described load output by the step-down isolated location, and described first dc supply input also is connected with the control end of described controlled switch unit, and the control end of described controlled switch unit is also by a grounding through resistance; Two switch terminals of described controlled cell are connected to described second dc supply input and described load output; Being switched on or switched off respectively between two switch terminals in described controlled switch unit determined by the potential difference on described two switch terminals and the described control end.
Further, on the described control end current potential more than or equal on described two switch terminals during current potential, described two switch terminals disconnect respectively; Wherein during any one current potential, connect by described two switch terminals less than described switch terminals for current potential on the described control end.
Further, described controlled switch unit is that two its grids link together as control end, the metal-oxide-semiconductor that connects back-to-back.
Further, one source electrode is connected with described second dc supply input in described two metal-oxide-semiconductors, and its drain electrode is connected with the drain electrode of another metal-oxide-semiconductor, and the source electrode of another MOS is connected with described load output.
Further, described metal-oxide-semiconductor is enhancing property P-channel field-effect transistor (PEFT) pipe.
Further, described step-down isolated location is diode, and the anode of described diode is connected with described first dc supply input, and its negative electrode is connected with described load output.
The invention still further relates to a kind of low-voltage dc power supply, be included as the rechargeable battery of load power supply and be connected low-voltage dc power supply commutation circuit between described rechargeable battery positive pole and the load, described low-voltage dc power supply commutation circuit is above-mentioned any described low-voltage dc power supply commutation circuit; Wherein, described rechargeable battery is second DC power supply, its minus earth; Described first dc supply input is connected with the external dc power that charges for described rechargeable battery; Described power supply also comprises the charging control unit that is connected and is described rechargeable battery charging with the described first dc supply input mouth.
Further, described charging control unit is the battery charging management integrated circuit, and it comprises power end and battery link, and described power end is connected with described first dc supply input, and described battery link is connected with described rechargeable battery is anodal.
Further, also comprise by current-limiting resistance and be serially connected in LED between described first dc supply input and the charging integrated circuit status port, that be used for the described rechargeable battery charged state of expression.
Implement a kind of low-voltage dc power supply commutation circuit of the present invention and DC power supply thereof, has following beneficial effect: owing to comprise the controlled switch unit in its DC power supply commutation circuit, and this controlled switch unit by using import the different differences of the output voltage of first DC power supply and second DC power supply, not needing to have realized extra control assembly just can realize automatically disconnection or connection between second dc power output end and the load output just having realized the switching of second DC power supply; Simultaneously, because the particularity of the structure of controlled switch unit makes this controlled switch unit not have voltage difference on two switch terminals basically when conducting, so do not have current drain substantially between two switch terminals when its conducting.So its cost is lower, current drain is less.
Embodiment
Embodiments of the present invention is further illustrated below in conjunction with accompanying drawing.
As shown in Figure 1, in a kind of low-voltage dc power supply commutation circuit of the present invention and DC power supply embodiment thereof, this commutation circuit comprises first dc supply input, second dc supply input, load output, controlled switch unit and step-down isolated location; Wherein, the controlled switch unit comprises two switch terminals and a control end, and the voltage difference on the voltage on this control end and two switch terminals has determined the connection status between two switch terminals in this controlled switch unit.In the present embodiment, first dc supply input is connected with the load output by the step-down isolated location, and namely first DC power supply is the load power supply by first dc supply input and step-down isolated location; In addition, first dc supply input also is connected with the control end of controlled switch unit, and the control end of controlled switch unit is also by a grounding through resistance; Two switch terminals of controlled switch unit are connected to second dc supply input and load output, namely second DC power supply is the load power supply by second dc supply input and above-mentioned controlled switch unit, when two switch terminals in this controlled switch unit were connected, load was by above-mentioned second DC power supply; When two switch terminals of this controlled switch unit disconnected, second DC power supply and load disconnected; As previously mentioned, being switched on or switched off respectively between two switch terminals in controlled switch unit determined by the potential difference on two switch terminals and the described control end; When current potential on this control end respectively more than or equal to above-mentioned two switch terminals on during current potential, two switch terminals of above-mentioned controlled switch unit disconnect; And when current potential on the control end less than above-mentioned switch terminals wherein during any one current potential, two switch terminals of controlled switch unit are connected.
In the present embodiment, in most cases, second DC power supply is rechargeable battery, when first DC power supply connects, when normally this rechargeable battery need charge, at this moment, battery few of electric weight can be powered, in order to keep necessary supply current, its supply power voltage will inevitably be low than theoretical value when sufficient (or electric weight).Certainly, not only beneficial to charging if when arranging, make the theoretical voltage value of a little higher than second DC power supply of the input voltage value of the direct voltage of winning, also make the more stable work, reliable of this commutation circuit.
Fig. 2 is the circuit diagram of commutation circuit in the present embodiment, and as shown in Figure 2, in the present embodiment, the step-down isolated location is diode, and the anode of this diode (D1) is stated first dc supply input and connected, and its negative electrode is connected with the load output.When first DC power supply was connected, its voltage was through supply load after the step-down of diode; Simultaneously, the existence of this diode voltage that makes load or second DC power supply be provided in the load can not be transferred to above-mentioned first dc supply input by this diode.
As shown in Figure 2, controlled switch unit (dotted portion among Fig. 2) is that two its grids link together as metal-oxide-semiconductor control end, that connect back-to-back.One source S is connected with second dc supply input in these two metal-oxide-semiconductors, and its drain D is connected with the drain D of another metal-oxide-semiconductor, and the source S of another MOS is connected with the load output, and these two metal-oxide-semiconductors are enhancing property P-channel field-effect transistor (PEFT) pipes.
In addition, in the present embodiment, also relate to a kind of low-voltage dc power supply, see also Fig. 3.In the present embodiment, this low-voltage dc power supply is included as the rechargeable battery (second DC power supply 34 among Fig. 3) of load power supply and is connected low-voltage dc power supply commutation circuit 35 between the anodal and load (load output) of this rechargeable battery, wherein, this low-voltage dc power supply commutation circuit 35 is above-mentioned low-voltage dc power supply commutation circuits; Wherein, rechargeable battery is second DC power supply 35, its minus earth; First dc supply input is connected with external dc power (first DC power supply 31); Low-voltage dc power supply in the present embodiment also comprises and is connected with the first dc supply input mouth and is the charging control unit 33 of rechargeable battery charging.In the present embodiment, charging control unit 33 is the battery charging management integrated circuit, and it comprises power end and battery link, and its power end is connected with first dc supply input; Its battery link is connected with above-mentioned rechargeable battery is anodal.In addition, in the present embodiment, this DC power supply also comprises by current-limiting resistance and is serially connected in LED between first dc supply input and the charging integrated circuit status port, that be used for the above-mentioned rechargeable battery charged state of expression.(seeing also Fig. 4)
In the present embodiment, when external power source (first DC power supply 31) does not have connection or input voltage to be 0, the controlled switch unit of low-voltage dc power supply commutation circuit 35 is kept closed, make second dc power output end and load output keep being connected, the electricity that rechargeable battery is provided flows to load through low-voltage dc power supply commutation circuit 35; When external power source (first DC power supply 31) connects and suitable input direct voltage is provided, the controlled switch unit of low-voltage dc power supply commutation circuit 35 transfers off-state to from closure state, and load is from the step-down isolated location direct power taking of external power source (first DC power supply 31) by above-mentioned low-voltage dc power supply commutation circuit 35; Simultaneously, external power source (first DC power supply 31) charges by 33 pairs of rechargeable batteries in Charge Management unit (second DC power supply 34).
Fig. 4 is the circuit diagram of above-mentioned low-voltage dc power supply in the present embodiment, and in Fig. 4, U1 is charging management chip, and U2 is rechargeable battery, and Q1, Q2 and R1 form the controlled switch unit of low-voltage dc power supply commutation circuit 35 jointly; D1 is the step-down isolated location of low-voltage dc power supply commutation circuit 35, is diode; This step-down isolated location stops reverse direction current flow, prevents that current reflux from arriving above-mentioned first dc supply input.D2 and D3 are light-emitting diodes, as the charged state indication.R3 is current-limiting resistance, for D2 and D3 provide suitable electric current.R2 adjusts resistance, is used for the above-mentioned charging management chip of fine setting to the maximum charging current of rechargeable battery.
In the present embodiment, U1 is single-unit lithium cell charging managing chip, maximum charging current can reach 500 milliamperes, need not the outside stream pipe that expands, the negative electrode of the 1 pin sending and receiving optical diode D2 of U1, the negative electrode of the 5 pin sending and receiving optical diode D3 of U1,4 pin of U1 connect external power source, and 3 pin of U1 connect the source electrode of rechargeable battery and PMOS pipe Q2, and the drain electrode of Q2 connects the drain electrode of Q1, the source electrode of Q1 connects negative electrode and the using electricity system of D1, the grid of Q1 and Q2 is connected together, and connects resistance R 1 to ground, and the grid of Q1 and Q2 is received external power source simultaneously, by the having and do not have of external power source (first DC power supply 31) voltage, realize the break-make of the controlled switch of low-voltage dc power supply commutation circuit 35.
Q1 and Q2 are enhancement mode P-channel field-effect transistor (PEFT) pipes, the SOT23 encapsulation, and volume is little, and the resistance of opening between the hourglass source electrode has only tens milliohms, can be by the electric current (representative value) up to 4.3 amperes.Q1 and Q2 link together back-to-back, make the parasitic diode of Q1 and Q2 also be connected (seeing also Fig. 4) back-to-back, can stop external power source by parasitic diode battery to be charged.
In the present embodiment, when external power source was imported suitable direct voltage, the voltage of Q1 and Q2 grid was higher than the voltage of source electrode, and Q1 and Q2 all end, and external power source is powered by the load of D1, charges by the battery of U1 simultaneously.When external power source did not have input, R1 was with the grounded-grid of Q1 and Q2, and grid voltage is lower than source voltage, the equal conducting of Q1 and Q2, battery can be powered to using electricity system, and the existence of D1 has separated rechargeable battery (second DC power supply 34) and external power source (first DC power supply 31).Because the conducting resistance of Q1 and Q2 is very little, so the pressure drop on Q1 and the Q2 is very little, and its quiescent current is only less than 1 microampere.Therefore, in the present embodiment, add this commutation circuit and realized that rechargeable battery when charging disconnects and be connected the quickening charging rate with load; Simultaneously, when using the rechargeable battery power supply because conducting resistance is minimum, so on this switch, there is not current loss substantially; In addition, also do not need extra device, for example MCU controls, and provides cost savings.
The above embodiment has only expressed several execution mode of the present invention, and it describes comparatively concrete and detailed, but can not therefore be interpreted as the restriction to claim of the present invention.Should be pointed out that for the person of ordinary skill of the art without departing from the inventive concept of the premise, can also make some distortion and improvement, these all belong to protection scope of the present invention.Therefore, the protection range of patent of the present invention should be as the criterion with claims.