Constant-current charging circuit, energy storage power source and constant-current charging method

Abstract

The present invention discloses a constant-current charging circuit, energy storage power source and constant-current charging method. The constant-current charging circuit includes a DC-DC converting circuit and a current-feedback circuit. A voltage output of the DC-DC converting circuit is a positive output of the constant-current charging circuit. A negative output of the DC-DC converting circuit is connected to a ground. The DC-DC converting circuit is connected to positive and negative terminals for a direct current voltage power supply. The current-feedback circuit includes first to third resistors and a reference voltage terminal. The reference voltage terminal is connected to the ground via the first to third resistors being connected in series. A connection point between the third resistor and the second resistor is a negative output of the constant-current charging circuit. A connection point between the first and second resistors is connected with a feedback terminal of the DC-DC converting circuit.

Claims

1. A constant-current charging circuit, comprising: a DC-DC converting circuit, a voltage output of said DC-DC converting circuit being a positive output (VOUT+) of said constant-current charging circuit, a negative output of said DC-DC converting circuit being connected to a ground, said DC-DC converting circuit being connected to a positive terminal (VIN+) and a negative terminal (VIN−) for a direct current voltage power supply; and a current-feedback circuit comprising a first resistor (R1), a second resistor (R2), a third resistor (R5) and a reference voltage terminal (VREF+), said reference voltage terminal (VREF+) being connected to said ground via said first resistor (R1), said second resistor (R2) and said third resistor (R5) being connected in series, a connection point between said third resistor (R5) and said second resistor (R2) being a negative output (VOUT−) of said constant-current charging circuit, and a connection point between said first resistor (R1) and said second resistor (R2) being connected with a feedback terminal (FB) of said DC-DC converting circuit.

2. Said constant-current charging circuit according to claim 1, further comprising a voltage-feedback circuit which comprises a fourth resistor (R3), a fifth resistor (R4) and a diode (D1), said fourth resistor (R3) and said fifth resistor (R4) being connected in series between said positive output (VOUT+) of said constant-current charging circuit and said ground, a connection point between said fourth resistor (R3) and said fifth resistor (R4) being connected with an anode of said diode (D1), and a cathode of said diode (D1) being connected with said feedback terminal (FB) of said DC-DC converting circuit.

3. Said constant-current charging circuit according to claim 1, wherein a first capacitor (C2) is connected between said positive output (VOUT+) and said negative output (VOUT−) of said constant-current charging circuit.

4. Said constant-current charging circuit according to claim 1, wherein a second capacitor (C1) is connected between said positive terminal (VIN+) and said negative terminal (VIN−).

5. Said constant-current charging circuit according to claim 1, wherein said DC-DC converting circuit adopts a ZTP7129 device.

6. An energy storage power source, comprising an energy storage module and a constant-current charging circuit according to claim 1 for charging said energy storage module.

7. Said energy storage power source according to claim 6, wherein said energy storage module is a lithium battery or a super capacitor.

8. A constant-current charging method achieved by a DC-DC converting circuit and a current-feedback circuit, wherein said current-feedback circuit comprises a first resistor (R1), a second resistor (R2), a third resistor (R5) and a reference voltage terminal (VREF+), wherein said method comprises: connecting a voltage output of said DC-DC converting circuit to a positive output (VOUT+) of said constant-current charging circuit and connecting a negative output of said DC-DC converting circuit to a ground; powering said DC-DC converting circuit by a direct current voltage power supply via a positive terminal (VIN+) and a negative terminal (VIN−); connecting said reference voltage terminal (VREF+) to said ground via said first resistor (R1), said second resistor (R2) and said third resistor (R5) being connected in series; connecting a connection point between said third resistor (R5) and said second resistor (R2) to a negative output (VOUT−) of said constant-current charging circuit; and connecting a connection point between said first resistor (R1) and said second resistor (R2) to a feedback terminal (FB) of said DC-DC converting circuit.

9. Said constant-current charging method according to claim 8, further comprising a step of overvoltage protection which is achieved by a voltage-feedback circuit and said DC-DC converting circuit; wherein said voltage-feedback circuit comprises a fourth resistor (R3), a fifth resistor (R4) and a diode (D1); and wherein said fourth resistor (R3) and said fifth resistor (R4) connected in series are connected between said positive output (VOUT+) of said constant-current charging circuit and said ground, a connection point between said fourth resistor (R3) and said fifth resistor (R4) is connected with an anode of said diode (D1), and a cathode of said diode (D1) is connected with said feedback terminal (FB) of said DC-DC converting circuit.

10. Said constant-current charging method according to claim 9, wherein a first capacitor (C2) is connected between said positive output (VOUT+) and said negative output (VOUT−) of said constant-current charging circuit, and a second capacitor (C1) is connected between said positive terminal (VIN+) and said negative terminal (VIN−).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a principle diagram of a constant-current charging circuit according to an embodiment of the present invention.

(2) FIG. 2 is a circuit of a specific application of the constant-current charging circuit in FIG. 1.

DESCRIPTION OF THE EMBODIMENTS

(3) The present invention will be further described in detail with reference to the drawings and embodiments.

(4) FIG. 1 is a principle diagram is of a constant-current charging circuit according to an embodiment of the present invention, of elements and labels shown in FIG. 1 are referred to as follows:

(5) VIN+ is a positive terminal of an input power source,

(6) VIN− is a negative terminal of the input power source,

(7) VOUT+ is a positive output of an output power source,

(8) VOUT− is a negative output of the output power source,

(9) VREF+ is a positive terminal of a reference power source,

(10) C1 is an input filter capacitor,

(11) C2 is an output filter capacitor,

(12) C3 is a current sampling feedback filter capacitor,

(13) R1, R2, R5 and R3 form a current sampling feedback circuit,

(14) R3 and R4 form a voltage sampling feedback circuit, and

(15) D1 is an isolating diode.

(16) A working principle of the present invention is described as follows.

(17) A stable reference power source is used as a reference voltage and a divided voltage equal to a feedback terminal FB is obtained via resistors R1, R2 and R5, thereby controlling a value of an output current by adjusting an inner PWM signal of a DC-DC converting circuit via the feedback terminal FB. For example, a voltage across the sampling resistor R5 will rise when the output current increases. Since the voltage at the reference voltage terminal VRFE+ is a fixed value, the voltage at the feedback terminal FB also rises. Duty cycle of the PWM signal will decrease due to the rise of the voltage at the feedback terminal FB, therefore the output current will decrease. In such way, a complete feedback can be accomplished so as to achieve the purpose of stabilizing the output current.

(18) Principle of the constant current charging is described as follows:

(19) Assuming that a voltage across the resistor R5 is VIo, the output current is Io, the reference voltage at reference voltage terminal VRFE+ is 2.5V, the voltage at the feedback terminal FB VFB is 0.6V, R5=0.1Ω, R1=40KΩ, R2=10KΩ.
VIo=Io*R5
VFB=VIo+((VREF+−VIo)*R2/(R1+R2))

(20) From above equations, the output current Io can be obtained by following formula.
Io=(VFB*(R1+R2)−R2*VREF+)/R1*R5
if K=(VFB*(R1+R2)−R2*VREF+)/R1,then
Io=K/R5.

(21) It can be seen from the calculation formulas that the output current Io is independent from the output voltage and input voltage. The output current Io is only in relation to VFB, R1, R2, and VREF which all have fixed values in a specific design (the voltage VFB is fixed in a steady state, and its steady-state value is 0.6 v for a constant-voltage chip fp7192), so K is certainly a fixed value. Therefore, the output current has excellent linearity and good controllability.

(22) The value of the output current can be calculated as follow if above parameters are assigned with the specific values set previously.

(23) $\begin{array}{c}\mathrm{Io}=\left(\mathrm{VFB}*\left(R1+R2\right)-R2*\mathrm{VREF}+\right)/R1*R5\\ =\left(0.6*\left(40+10\right)-10*2.5\right)/40*0.1\\ =1.25A\end{array}$

(24) Preferably, the DC-DC converting circuit is a constant voltage driving IC, such as FP7192.

(25) It can be seen from the above equations that a fixed reference voltage is introduced so that the output current Io becomes linearly in relation with the sampling resistor R5. As a result, the output current Io is constant and the purpose of constant current charging can be achieved.

(26) The reference voltage constant-current method in this solution has the following characteristics: 1. It is convenient to control accuracy and stability by using a stable and fixed reference voltage; 2. It is simpler and more reliable by using a resistor divider feedback to replace current sampling; 3. It has wide application and can be used in any circuit which requires constant current; and 4. The cost reduces significantly, for example, the cost for the solution using a constant current IC and having an output of 12V/1 A is about 3 yuan while the cost for the solution provided by the present invention is within 1 yuan.