LINEAR CHARGER WITH THERMAL REGULATION CIRCUIT

Abstract

A linear charger includes a constant current charging circuit and a thermal regulation circuit. The constant current charging circuit is arranged to generate a charging current, and includes a first transconductance amplifier, wherein the first transconductance amplifier has a positive terminal, a negative terminal, and an output terminal. The thermal regulation circuit is coupled to the output terminal and the negative terminal of the first transconductance amplifier, and is arranged to generate and modulate a thermal regulation current and an amplifier reference voltage with temperature, and transmit the thermal regulation current and the amplifier reference voltage to the output terminal and the negative terminal of the first transconductance amplifier, respectively.

Claims

1. A linear charger, comprising: a constant current charging circuit, arranged to generate a charging current, wherein the constant current charging circuit comprises: a first transconductance amplifier, having a positive terminal, a negative terminal, and an output terminal; and a thermal regulation circuit, coupled to the output terminal and the negative terminal of the first transconductance amplifier, and arranged to generate and modulate a thermal regulation current and an amplifier reference voltage with temperature, and transmit the thermal regulation current and the amplifier reference voltage to the output terminal and the negative terminal of the first transconductance amplifier, respectively.

2. The linear charger of claim 1, wherein the constant current charging circuit further comprises: a first P-type transistor, having a source terminal coupled to a first reference voltage; and a second P-type transistor, having a source terminal coupled to the first reference voltage, and a gate terminal coupled to a gate terminal of the first P-type transistor; a third P-type transistor, having a source terminal coupled to a drain terminal of the first P-type transistor; an operation amplifier, having a positive terminal coupled to the source terminal of the third P-type transistor, a negative terminal coupled to a drain terminal of the second P-type transistor, and an output terminal coupled to a gate terminal of the third P-type transistor; and a setting resistor, having a first terminal coupled to the positive terminal of the first transconductance amplifier, and a second terminal coupled to a second reference voltage; wherein the positive terminal of the first transconductance amplifier is coupled to a drain terminal of the third P-type transistor, the negative terminal of the first transconductance amplifier is coupled to the second reference voltage, and the output terminal of the first transconductance amplifier is coupled to the gate terminal of the first P-type transistor.

3. The linear charger of claim 2, wherein a shutdown temperature of the linear charger is unchanged for different values of the setting resistor.

4. The linear charger of claim 2, wherein the charging current is output from the drain terminal of the second P-type transistor, and a shutdown temperature of the linear charger is unchanged for the charging current corresponding to different current values.

5. The linear charger of claim 4, wherein modulation of the charging current with temperature is linear.

6. The linear charger of claim 1, wherein the thermal regulation circuit comprises: a second transconductance amplifier, arranged to generate and modulate the thermal regulation current with temperature according to a sensing voltage and a temperature reference voltage, and having a positive terminal coupled to the sensing voltage, a negative terminal coupled to the temperature reference voltage, and an output terminal coupled to the output terminal of the first transconductance amplifier; and an amplifier reference voltage generation circuit, coupled to the negative terminal of the first transconductance amplifier, and arranged to generate and modulate the amplifier reference voltage with temperature according to the sensing voltage and the temperature reference voltage.

7. The linear charger of claim 6, wherein the amplifier reference voltage generation circuit comprises: a voltage source, having a first terminal coupled to a reference voltage; a first resistor, having a first terminal coupled to a second terminal of the voltage source, and a second terminal coupled to the negative terminal of the first transconductance amplifier; a second resistor, having a first terminal coupled to the second terminal of the first resistor, and a second terminal coupled to the reference voltage; and a third transconductance amplifier, arranged to modulate the amplifier reference voltage with temperature according to the sensing voltage and the temperature reference voltage, and having a positive terminal coupled to the temperature reference voltage, a negative terminal coupled to the sensing voltage, and an output terminal coupled to the second terminal of the first resistor.

8. The linear charger of claim 1, wherein an offset voltage is applied to the first transconductance amplifier by the thermal regulation current before modulation of the amplifier reference voltage with temperature becomes nonlinear, to make modulation of a setting voltage at the positive terminal of the first transconductance amplifier with temperature linear.

9. The linear charger of claim 8, wherein a voltage value of the offset voltage is equal to a voltage value generated by subtracting the setting voltage from the amplifier reference voltage.

10. The linear charger of claim 8, wherein a current value of the thermal regulation current is equal to a current value generated by multiplying a gain of the first transconductance amplifier and the offset voltage.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 is a diagram illustrating a linear charger according to an embodiment of the present invention.

[0009] FIG. 2 is a diagram illustrating a thermal regulation circuit according to an embodiment of the present invention.

[0010] FIG. 3 is a diagram illustrating a linear charger with the thermal regulation circuit shown in FIG. 2 according to an embodiment of the present invention.

[0011] FIG. 4 is a diagram illustrating relationship between the offset voltage and modulation of the amplifier reference voltage and the setting voltage of the linear charger shown in FIG. 3 with temperature according to an embodiment of the present invention.

[0012] FIG. 5 is a diagram illustrating modulation of associated currents and voltages of the linear charger shown in FIG. 3 with temperature according to an embodiment of the present invention.

DETAILED DESCRIPTION

[0013] FIG. 1 is a diagram illustrating a linear charger 10 according to an embodiment of the present invention. As shown in FIG. 1, the linear charger 10 may include a constant current charging circuit 100 and a thermal regulation circuit 102. In practice, the linear charger 10 may further include a constant voltage charging circuit (not shown). Since the present invention focuses on the thermal regulation design for the constant current charging circuit, further description of the constant voltage charging circuit is omitted for brevity.

[0014] The constant current charging circuit 100 may include a plurality of P-type transistors P1, P2, and P3, a transconductance amplifier 104, an operation amplifier 106, and a setting resistor R.sub.ISET. The P-type transistor P1 has a source terminal coupled to a first reference voltage (e.g. an input voltage V.sub.IN). The P-type transistor P2 has a source terminal coupled to the first reference voltage (e.g. the input voltage V.sub.IN), and a gate terminal coupled to a gate terminal of the P-type transistor P1, wherein a gate voltage V.sub.G is a voltage at a node between the gate terminal of the P-type transistor P1 and the gate terminal of the P-type transistor P2, and a charging current I.sub.1 is output from a drain terminal of the P-type transistor P2. The P-type transistor P3 has a source terminal coupled to a drain terminal of the P-type transistor P1.

[0015] The transconductance amplifier 104 has a positive terminal (+) coupled to a drain terminal of the P-type transistor P3, a negative terminal (−) coupled to an amplifier reference voltage V.sub.REF, and an output terminal coupled to the gate terminal of the P-type transistor P1. The operation amplifier 106 has a positive terminal (+) coupled to the source terminal of the P-type transistor P3, a negative terminal (−) coupled to the drain terminal of the P-type transistor P2 and a battery 101, and an output terminal coupled to a gate terminal of the P-type transistor P3. The setting resistor R.sub.ISET has a first terminal coupled to the positive terminal of the transconductance amplifier 104, and a second terminal coupled to a second reference voltage (e.g. a ground voltage GND), and may be arranged to set the charging current I.sub.1 of the battery 101.

[0016] The thermal regulation circuit 102 may be coupled to the output terminal and the negative terminal of the transconductance amplifier 104, and may be arranged to generate and modulate a thermal regulation current I.sub.2 and the amplifier reference voltage V.sub.REF with temperature, and transmit the thermal regulation current I.sub.2 and the amplifier reference voltage V.sub.REF to the output terminal and the negative terminal of the transconductance amplifier 104, respectively. In addition, the thermal regulation circuit 102 may receive a temperature sensing voltage V.sub.SEN_T and a temperature reference voltage V.sub.TEMP_REF, and modulate the thermal regulation current I.sub.2 and the amplifier reference voltage V.sub.REF according to the temperature sensing voltage V.sub.SEN_T and the temperature reference voltage V.sub.TEMP_REF, wherein the temperature reference voltage V.sub.TEMP_REF is approached to the zero-temperature coefficient reference voltage, and the temperature sensing voltage V.sub.SEN_T is a temperature-dependent voltage. For example, the temperature sensing voltage V.sub.SEN_T increases as the temperature rises, and decreases as the temperature falls.

[0017] FIG. 2 is a diagram illustrating a thermal regulation circuit 200 according to an embodiment of the present invention. By way of example, but not limitation, the thermal regulation circuit 102 shown in FIG. 1 may be implemented by the thermal regulation circuit 200 shown in FIG. 2. As shown in FIG. 2, the thermal regulation circuit 200 may include a transconductance amplifier 202 and an amplifier reference voltage generation circuit 204. The transconductance amplifier 202 may be arranged to generate and modulate the thermal regulation current I.sub.2 with temperature according to the temperature sensing voltage V.sub.SEN_T and the temperature reference voltage V.sub.TEMP_REF. In addition, the transconductance amplifier 202 has a positive terminal (+) coupled to the temperature sensing voltage V.sub.SEN_T and a negative terminal (−) coupled to the temperature reference voltage V.sub.TEMP_REF. As a result, the thermal regulation current I.sub.2 may be modulated with temperature, as expressed by the following equation:

I.sub.2=Max[0,(V.sub.SEN_T−V.sub.TEMP_REF)G.sub.2]

wherein G.sub.2 is a transconductance value of the transconductance amplifier 202.

[0018] The amplifier reference voltage generation circuit 204 may be arranged to generate and modulate the amplifier reference voltage V.sub.REF with temperature according to the temperature sensing voltage V.sub.SEN_T and the temperature reference voltage V.sub.TEMP_REF. The amplifier reference voltage generation circuit 204 may include a voltage source 206, a transconductance amplifier 208, and a plurality of resistors R.sub.1 and R.sub.2. The voltage source 206 has a first terminal coupled to the second reference voltage (e.g. the ground voltage GND), and is arranged to provide a voltage V.sub.CC. The resistor R.sub.1 has a first terminal coupled to a second terminal of the voltage source 206, wherein the amplifier reference voltage V.sub.REF is output from a second terminal of the resistor R.sub.1. The resistor R.sub.2 has a first terminal coupled to the second terminal of the resistor R.sub.1, and a second terminal coupled to the second reference voltage (e.g. the ground voltage GND). The transconductance amplifier 208 has a positive terminal (+) coupled to the temperature reference voltage V.sub.TEMP_REF, a negative terminal (−) coupled to the temperature sensing voltage V.sub.SEN_T, and an output terminal coupled to the second terminal of the resistor R.sub.1, and may be arranged to generate and modulate the amplifier reference voltage V.sub.REF with temperature according to the temperature sensing voltage V.sub.SEN_T and the temperature reference voltage V.sub.TEMP_REF. The amplifier reference voltage V.sub.REF may be modulated with temperature, as expressed by the following equation:

[00001]$V_{\mathrm{REF}}=\mathrm{Min}\left\{\left[V_{\mathrm{CC}}-\left(V_{{\mathrm{SEN}}_T}-V_{{\mathrm{TEMP}}_{\mathrm{REF}}}\right)G_{3}R1\right]\times \left[\frac{R2}{R1+R2}\right],\frac{V\mathrm{cc}\times R2}{R1+R2}\right\}$

wherein G.sub.3 is a transconductance value of the transconductance amplifier 208, R1 is a resistance value of the resistor R.sub.1, and R.sub.2 is a resistance value of the resistor R.sub.2.

[0019] FIG. 3 is a diagram illustrating a linear charger 30 with the thermal regulation circuit 200 shown in FIG. 2 according to an embodiment of the present invention. As shown in FIG. 3, the linear charger 30 may include a constant current charging circuit 300 and the thermal regulation circuit 302, wherein the constant current charging circuit 300 and the thermal regulation circuit 302 may be implemented by the constant current charging circuit 100 shown in FIG. 1 and the thermal regulation circuit 200 shown in FIG. 2, respectively. The constant current charging circuit 300 may include a plurality of P-type transistors P1, P2, and P3, a transconductance amplifier 304, an operation amplifier 306, and a setting resistor R.sub.ISET. For brevity, similar descriptions for this embodiment are not repeated in detail here. The thermal regulation circuit 302 may include a transconductance amplifier 308 and an amplifier reference voltage generation circuit 310, wherein an output terminal of the transconductance amplifier 308 may be coupled to the gate terminal of the P-type transistor P1 (i.e. coupled to the output terminal of the transconductance amplifier 304). The amplifier reference voltage generation circuit 310 may include a voltage source 312, a transconductance amplifier 314, and a plurality of resistors R.sub.1 and R.sub.2, wherein a node between the resistors R.sub.1 and R.sub.2 may be coupled to an output terminal of the transconductance amplifier 314 and a negative terminal of the transconductance amplifier 304. For brevity, similar descriptions for this embodiment are not repeated in detail here.

[0020] Considering a case where the thermal regulation circuit 302 is modified to only include the amplifier reference voltage generation circuit 310 (i.e. the thermal regulation circuit 302 only generates and modulates the amplifier reference voltage V.sub.REF with temperature, and transmits the amplifier reference voltage V.sub.REF to the negative terminal of the transconductance amplifier 304), the modulation of a setting voltage V.sub.ISEt at the positive terminal of the transconductance amplifier 304 with temperature is nonlinear, wherein the modulation of the setting voltage V.sub.ISET is controlled by the modulation of the amplifier reference voltage V.sub.REF. To address this issue, the thermal regulation circuit 302 is configured to have the transconductance amplifier 308 and the amplifier reference voltage generation circuit 310, and may apply an offset voltage ΔV to the transconductance amplifier 304 by the thermal regulation current I.sub.2 before modulation of the amplifier reference voltage V.sub.REF with temperature becomes nonlinear, to make modulation of the setting voltage V.sub.ISET with temperature linear, wherein a voltage value of the offset voltage ΔV is equal to a voltage value generated by subtracting the setting voltage V.sub.ISET from the amplifier reference voltage V.sub.REF at a same temperature (i.e. ΔV=V.sub.REF−V.sub.ISET).

[0021] FIG. 4 is a diagram illustrating relationship between the offset voltage ΔV and modulation of the amplifier reference voltage V.sub.REF and the setting voltage V.sub.ISET of the linear charger 30 shown in FIG. 3 with temperature according to an embodiment of the present invention. As shown in FIG. 4, a dashed line A is the modulation of the amplifier reference voltage V.sub.REF with temperature, and a solid line B is the modulation of the setting voltage V.sub.ISET with temperature. By modulating the thermal regulation current I.sub.2 with temperature, the offset voltage ΔV may be applied to the transconductance amplifier 304 before modulation of the amplifier reference voltage V.sub.REF with temperature becomes nonlinear (e.g. before the temperature of the linear charger 30 reaches a temperature T0 shown in FIG. 4), and the setting voltage V.sub.ISET is equal to 0V at the temperature TO. The offset voltage ΔV may be calculated by an equation as below:

[00002]$\mathrm{\Delta V}=\left(V_{\mathrm{SEN}\_T}-V_{\mathrm{TEMP}\_\mathrm{REF}}\right)\frac{G_2}{G_1}$

wherein (V.sub.sEN_T−V.sub.TEMP_REF)≥0, G.sub.1 is a transconductance value of the transconductance amplifier 304, and G.sub.2 is a transconductance value of the transconductance amplifier 308.

[0022] FIG. 5 is a diagram illustrating modulation of associated currents and voltages of the linear charger 30 shown in FIG. 3 with temperature according to an embodiment of the present invention. It is assumed that the input voltage V.sub.IN that is coupled to the source terminal of the P-type transistor P1 and the source terminal of the P-type transistor P2 is 5V. As shown in FIG. 5, by modulating the thermal regulation current I.sub.2 with temperature, the modulation of the setting voltage V.sub.ISET with temperature may become linear, which makes it easy to estimate the magnitude of the charging current I.sub.1 at various temperatures, and the modulation of the charging current I.sub.1 with temperature is linear. In addition, a shutdown temperature of the linear charger 30 is unchanged for the charging current I.sub.1 corresponding to different current values (e.g. 500 mA, 200 mA, 100 mA, and 50 mA). That is, the shutdown temperature of the linear charger 30 is unchanged for different values of the setting resistor R.sub.ISET. For different gate voltages V.sub.G corresponding to different current values (e.g. 500 mA, 200 mA, 100 mA, and 50 mA) of the charging current I.sub.1, a power stage of the linear charger 30 is guaranteed to be turned off at high temperature (i.e. the gate voltage V.sub.G is equal to the input voltage V.sub.IN at high temperature).

[0023] Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.