JPH11341699A - Solar battery optimum operating point follow-up circuit in power supply equipment using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solar battery optimum operating point follow-up circuit which can supply the maximum output power from a solar battery at all times, regardless of the operating temperature of the solar battery or the intensity of light. SOLUTION: This circuit is constituted of a temperature compensating voltage detection circuit, which supplies current to a PN junction diode D1 which is located near a solar battery SB and has nearly the same temperature characteristic as that of the solar battery, and then detects the forward drop voltage VB of the PN junction diode as a temperature compensating voltage; an amplifier #A which amplifies the voltage detected by the temperature compensating voltage detection circuit at a specified amplification rate, and then outputs the temperature compensating voltage V1R for the solar battery; a differential amplifier #D which is inputted with the temperature compensating voltage V1R which is the output of the amplifier #A and the output voltage Vs of the solar battery SB; and a comparator ξf which compares a control signal VR which is the output of the differential amplifier and a control signal Vo for stably controlling the output of a switching power supply 1, and then outputs a signal for driving a switch S for controlling the switching power supply 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device for obtaining required power from a solar cell using a switching power supply. The present invention relates to a solar cell optimal operating point tracking circuit of a power supply device that can always supply the maximum output power from the solar cell even when a change such as a light amount occurs.

[0002]

2. Description of the Related Art A solar cell optimum operating point tracking circuit of a conventional power supply device which takes out as much power as possible according to the intensity of light from a solar cell includes a solar cell connected as an input power supply when the power supply device operates. Is set to an arbitrary fixed voltage predicted in advance so that a maximum output can be obtained, an output current is taken out of the solar cell, and power is supplied via a switching power supply.

[0003]

However, in an optimum operating point tracking circuit in which the output voltage of a solar cell connected to a switching power supply is predicted in advance to be a maximum output and is set to an arbitrary fixed voltage. However, there are the following problems. That is, even during one day, the operating temperature of the solar cell changes due to the change of seasons such as morning, noon, night, sunny day and rainy day, and summer and winter. When the optimum operating point is given, the output voltage of the solar cell increases when the operating temperature decreases, so that there is a problem that the maximum output power corresponding to the change in the operating temperature cannot be obtained. Also, when the light intensity (light amount) changes, as in the case of the change in the operating temperature, if the optimum operating point is given in a state where the light amount is large, the maximum current capacity can be supplied when the light amount is large, but in a state where the light amount is small. In the case of (1), only a current capacity smaller than the maximum current capacity can be obtained, and there is a problem that the maximum output power cannot be obtained following a change in the light amount.

As described above, in the optimal operating point tracking circuit that sets the output voltage of the solar cell connected to the switching power supply to an arbitrary fixed voltage in advance, the operating temperature and the light quantity change due to the environmental change of the solar cell installation location. It is difficult to supply the maximum power of the solar cell. The present invention provides a solar cell optimal operating point tracking circuit of a power supply device, which can always supply the maximum output power from the solar cell even when the operating temperature or the light amount changes due to the external environment change of the solar cell installation location. It is a suggestion.

[0005]

According to a first aspect of the present invention, there is provided a solar cell optimal operating point tracking circuit in a power supply using a solar cell, wherein the power supply comprises a switching power supply which receives power from the solar cell. A temperature compensation voltage detection circuit for supplying current to a PN junction diode having a temperature characteristic substantially the same as the temperature characteristic of the solar cell provided near the solar cell and detecting a forward drop voltage of the PN junction diode; An amplifier that amplifies the voltage detected by the temperature compensation voltage detection circuit at a required amplification rate and outputs a temperature compensation voltage of the solar cell, and inputs the temperature compensation voltage of the output of the amplifier and the output voltage of the solar cell. And a control signal for stabilizing the output of the switching power supply by comparing a control signal of the output of the differential amplifier with a control signal for stably controlling the output of the switching power supply. And a comparator for outputting a driving signal of the control switch, following the temperature change of the solar cell installation site is obtained by so as to form a maximum power output of the solar cell.

A solar cell optimum operating point tracking circuit in a power supply device using a solar cell according to the second invention of the present application is provided in the vicinity of the solar cell in a power supply device comprising a switching power supply to which power of the solar cell is input. A temperature compensation voltage detection circuit for supplying a current to a PN junction diode having substantially the same temperature characteristics as that of the solar cell to detect a forward drop voltage of the PN junction diode, and a temperature compensation voltage detection circuit. A first amplifier that amplifies the detected voltage by a required amplification factor and outputs a temperature compensation voltage of the solar cell, a current detection circuit that detects an output current of the solar cell, and a current detection circuit that detects the current. A second amplifier that converts a current into a voltage, amplifies the voltage with a required amplification factor, and outputs a current compensation voltage of the solar cell, and a temperature compensation voltage output from the first amplifier. And an adder for adding the current compensation voltage of the output of the second amplifier to output a temperature / current compensation voltage, and inputting the temperature / current compensation voltage of the output of the adder and the output voltage of the solar cell. And a comparator that compares a control signal of the output of the differential amplifier with a control signal for stably controlling the output of the switching power supply and outputs a drive signal of a control switch of the switching power supply. And the power output of the solar cell is maximized following changes in temperature and light quantity at the solar cell installation location.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of a solar cell optimum operating point tracking circuit according to the present invention, and shows an example in which a DC-DC converter is used as a switching power supply connected to a solar cell. . In FIG. 1, reference numeral 1 denotes a DC-DC converter, SB denotes a solar cell connected to the input of the DC-DC converter 1, and Rm denotes an output current that changes according to the intensity (light amount) of light applied to the solar cell SB. The current detector to detect, Icon is a constant current feeding circuit, D0-1,
D0-2... D0-n are each constituted by cascade-connecting a plurality of PN junction diodes so as to have substantially the same temperature characteristics as the solar cell SB, or by setting the number of connections to 1 or a small number to be described later. May be adjusted by using VD is a forward drop voltage of each PN junction diode D0, VB is a forward drop voltage when n PN junction diodes D are cascaded, and a circuit for detecting the temperature compensation voltage of the solar cell SB together with the constant current feed circuit Icon. It is.

#A and #B are amplifiers, respectively.
A amplifies the forward drop voltage of one or more cascaded PN junction diodes D to a required temperature compensation voltage V1R. Amplifier #B is the intensity of the emitted light,
That is, the output current of the solar cell SB based on the light amount is detected as a voltage value, and this is amplified to a required current (light amount) compensation voltage V2R. #C is an adder for temperature compensation voltage V1
R and the current compensation voltage V2R are added. #D
Is a differential amplifier, which inputs a temperature / current compensation voltage (reference voltage) VR of the output of the adder #C and an output voltage Vs of the solar cell SB, and outputs a control signal △ VR. R is DC-DC
The load #E connected to the output of the converter 1 is a voltage detector that detects the voltage of the load R and outputs a control signal △ Vo. OSC is a sawtooth (triangular) wave oscillator, #F is a pulse width modulation comparator, and the control switch S of the DC-DC converter 1 is pulsed by the relationship between the control signals △ VR and △ Vo and the sawtooth oscillator OSC. A drive signal for performing width modulation (PWM) control is output. Eo is an output voltage of the DC-DC converter 1, and EB is a storage battery connected as necessary.

Next, FIG. 1 is a circuit diagram of one embodiment of the present invention, and FIG. 2 shows the output current, voltage,
Power characteristic diagram, output current, voltage, and power characteristic diagram of solar cell SB based on temperature change in FIG. 3, relationship between output constant voltage control region of DC-DC converter 1 in FIG. 4 and solar cell optimal operating point tracking operation region The operation of the solar cell optimum operating point tracking circuit according to the present invention will be described based on the current, voltage, and power characteristic diagrams shown in FIG. First, in the solar cell optimum operating point tracking circuit of FIG. 1, n PN junction diodes D having a forward drop voltage VD are connected in cascade, and a constant current is supplied from the constant current feeding circuit Icon to the PN junction diodes D. Direction drop voltage VB (VD
× n) is amplified by a factor of K1 by the amplifier #A, and this is amplified as a temperature compensation voltage V1R (VB × K1) and input to one of the adders #C. Further, the output current Is of the solar cell SB during the operation of the DC-DC converter 1 is detected via the current detector Rm, and is amplified by K2 times by the amplifier #B to obtain the current compensation voltage V
2R (Is × Rm × K2) is input to the other end of the adder #C.

Therefore, the temperature appearing at the output of adder #C
The current compensation voltage VR is

VR = V1R + V2R = VB × K1 + Is × Rm × K2 (1), and a temperature compensation voltage V1R that changes only with temperature.
And a current compensation voltage V2R, which is a linear function of the current that changes in voltage with respect to the current based on the change in the light amount.

Here, the validity of the temperature / current compensation voltage VR in the above equation (1) will be described with reference to FIGS.
FIG. 2 shows a case in which the light intensity changes. Since the solar cell power Ps decreases as the light intensity decreases, the maximum power point moves downward in the solar cell current. Naturally, the solar cell voltage Vs also changes from Vs1 to Vs2. At this time,
The current compensation voltage V2 which is a component of the current compensation voltage VR
Since R is a linear function of the current Is, the optimum operating point tracking operation can be realized.

FIG. 3 shows a case where the operating temperature of the solar cell changes, and as the operating temperature rises, the solar cell voltage Vs
Changes from Vs1 to Vs2, but the maximum power point does not change with respect to the solar cell current. At this time, the temperature compensation voltage V1R, which is a component of the temperature / current compensation voltage VR, is an element that changes its voltage only with respect to the operating temperature, and the temperature / current compensation voltage VR changes from VR-a due to an increase in the operating temperature. VR-b
And the optimum operation point tracking operation can be realized. In this way, by setting the reference voltage for the optimum operating point tracking operation as the temperature / current compensation voltage VR, it is possible to track the voltage that gives the maximum power point of the solar cell following changes in temperature and light amount, A more accurate optimum operating point tracking operation can be performed in response to changes in the external environment.

Although the temperature / current compensating voltage VR is constituted only by the temperature compensating voltage V1R, it operates at almost the maximum power point and can track the optimum operating point, but the current compensating voltage V2R
, It is possible to achieve higher accuracy. Further, the amplification factor K1 of the amplifier #A in the equation (1) may be obtained by setting K1 × VB to Vsmin, which is the minimum value of the solar cell output voltage Vs, when the solar cell output current Is = 0, Further, the amplification factor K2 of the amplifier #B is derived from the maximum value Vsmax and the minimum value Vsmin of the solar cell output voltage Vs, and a derivation formula given by the solar cell output current Is as follows:
It is shown in (3).

[0014]

K1 = Vsmin / VB (2) K2 = (Vsmax-Vsmin) / (Rm × Is) (3)

Next, the temperature / current compensation voltage VR obtained above is inputted to the other side of the amplifier #D, to which the solar cell output voltage Vs is inputted, and the solar cell output voltage Vs is inputted to the temperature / current compensation voltage. VR to operate the amplifier #D
The control signal .DELTA.VR required for this appears at the output of. Then, the control signal ΔVR and the output voltage of the load R connected to the output Eo of the DC-DC converter 1 are used as a voltage detector #
The control signal ΔVo, which is detected by E and controls the DC-DC converter 1 at a constant voltage, is, for example, a pulse width modulation comparator # having the output of a sawtooth (triangular) wave oscillator OSC as one input.
F, each of which is input to the other of the pulse width modulation comparators #F
An output pulse waveform for pulse width modulation is obtained at the output of
The control switch S of the C-DC converter 1 is controlled.
Therefore, the solar cell optimal operating point tracking operation is performed, and the output constant voltage control of the DC-DC converter 1 is performed.

Next, FIG. 4 shows the relationship between the converter output current, the output voltage, and the solar cell voltage during the operation of the DC-DC converter 1, and the output constant voltage control region of the DC-DC converter and the solar cell optimum operating point tracking operation. An example of the region will be described. That is, the output constant voltage control region of the DC-DC converter 1 is a region where the output current is 0.2 A or less, and the output power Po of the DC-DC converter 1 and the supply power P of the solar cell SB.
s has a relationship of [Po <Ps]. Therefore, DC-
The output voltage Eo of the DC converter 1 is stabilized, but the solar cell optimal operating point tracking operation is not performed, so that the solar cell voltage Vs during operation changes. Next, the solar cell optimal operating point tracking operation area is an area where the output current is 0.2 A or more.
In this region, the relationship [Po> Ps] is established, and as is clear from FIG. 4, the solar cell voltage Vs is controlled to a constant voltage by the optimum operating point tracking operation. Is obtained.

In addition, when the output voltage of the DC-DC converter 1 is not stabilized due to a change in the temperature and the amount of light at the installation location of the solar cell SB, that is, when a so-called drooping state occurs,
If the storage battery EB is connected to the output Eo of the DC converter 1, the converter output is stabilized by the constant voltage value of the storage battery EB itself. In this case, when the output power of the solar cell SB changes to an environment that exceeds the load power consumption, the battery can be configured to supply the maximum power of the solar cell SB to the storage battery EB. Further, two input power supplies E as shown in FIG.
1, E2, the corresponding switches S1, S2, the windings N1, N2 of the inductor L and the output winding N, which are magnetically coupled.
In the two-input DC-DC converter constituted by 0, for example, as an input power source, E1 is a solar cell, E2 is a DC power source obtained by rectifying a commercial power source input,
The optimal operation point tracking operation according to the present invention can be applied to the solar cell E1 to supply power from the DC power supply E2 so as to compensate for the shortage of power supply of the solar cell E1.

That is, if the difference between the power supply amount of the entire DC-DC converter and the power supply amount of the solar cell E1 is configured to be supplied from the DC power supply E2, the solar cell E1 always performs the optimum operation point tracking operation. By the action of the DC power supply E2, the output of the DC-DC converter is controlled at a constant voltage without a storage battery, so that the optimum operating point tracking of the solar cell and the output constant voltage control can be realized at the same time, resulting in high efficiency and stability. Further, in the case of a DC-DC converter such as a self-excited flyback type that does not have the pulse width modulation comparator #F, the control signal ΔVo is output to a control circuit that outputs an output constant voltage control signal ΔVo.
This can be realized by inputting VR. In the above-described embodiment, the switching power supply is described as an example using a DC-DC converter.
The present invention can be applied to a case where an AC inverter is used.

Next, in a power supply device using a solar cell, the amount of light in the morning or evening, which is a transition between daytime during which light irradiation is performed reliably and nighttime during which light irradiation is hardly performed, is reduced. The problem in the case of a remarkable change and the remedy will be described. The basic principle of the solar cell optimal operating point tracking circuit of the power supply device described above is that the operating voltage accompanying the change in the external environment (temperature, light amount) of the solar cell is determined by changing the forward voltage of the PN junction diode having substantially the same temperature characteristics as the solar cell. A change in the temperature compensation voltage due to the drop voltage or a change in the output current of the solar cell due to a change in the amount of light is detected as a current compensation voltage, and the amount of change is controlled in relation to the PWM of the control drive switch of the switching power supply. The control amount required for this control is given to the control switch of the switching power supply in the form of a pulse signal.

Therefore, the higher the voltage detected by the solar cell is compared to the temperature compensation voltage or the temperature / current compensation voltage (reference voltage), the wider the pulse width of the control switch becomes, and the closer the reference voltage is, the narrower the pulse width becomes. Further, during a time period such as at night when the voltage detected by the solar cell is lower than the reference voltage, no control pulse is generated to the control switch, and the use of the solar cell is prohibited. At this time, a problem occurs in a time zone, for example, in the morning or evening, when the light irradiation amount (light amount) is extremely reduced. In this time period, the operation in the two time periods of night and day, that is, the operation of the control switch repeats a state of pulse generation and stop at random. And
Due to the random generation of the pulse, an unpleasant operation sound or noise is generated from the power supply, and the power supply repeats unstable operation.

This random operation is caused by the characteristics of the solar cell as shown in FIG. 6, and is an unavoidable characteristic when the solar cell is used as an input source of a power supply device. That is,
When the battery output current Is is zero, the output voltage Vs of the solar cell when there is slight irradiation such as in the morning or evening rises to the open-circuit voltage. Therefore, the use of the solar cell is apparently possible because the voltage is higher than the reference voltage. However, when current supply is started, the voltage drops sharply as compared with the normal operation, so that the voltage becomes lower than the reference voltage and the use of the solar cell is impossible. Therefore, if a solar cell is connected as an input source of a switching power supply in such a situation, the above-described random operation naturally occurs.

Therefore, when the irradiation amount is extremely reduced, the switching power supply is operated for a long period to be set separately.
FIG. 7 shows an embodiment of an operation state detection circuit for providing a solar cell operation state detection circuit that repeats stoppage, and FIG. 8 shows a control time chart, and the circuit operation will be described. FIG. 8 showing a control switch signal of a switching power supply input to CK of flip-flop #I
(A) L edge of PWM output (switch OFF command)
The output bar Q of the flip-flop #I (FIG. 8)
(C)) becomes L, and the timer circuit #M for setting the period, which is composed of the time constants of the resistor R1 and the capacitor C1, is started.
Then, the voltage Vc of the capacitor C1 in FIG. 8B, which gradually rises, is compared with a zero voltage reference voltage Vref0 near zero voltage constituted by, for example, the voltage division of the resistors R2 and R3 by the comparator #K. , Vc> Vref0, the flip-flop #I
Is set to L, the output bar Q of the flip-flop #I
Is fixed to H. This state continues until the timer circuit #M is reset at the set cycle, during which the flip-flop #I does not accept the CK input.

At the same time, the L signal of the output bar Q (FIG. 8C) of the flip-flop #I generated by the L edge (switch OFF command) of the PWM output is input to the CK of the flip-flop #H. Comparator # constituted by two inputs of solar cell voltage Vs and temperature compensation voltage V1R
The output of G shown in FIG. 8D is changed to H as shown on the left side of FIG.
At this time, the use of the solar cell SB is stopped, the output bar Q of the flip-flop #H (FIG. 8E) is set to L, and one input of the AND circuit #L is set to L. A PWM output signal is input to the other input of the AND circuit #L.
When the solar cell is in the unusable state, the signal Psw (FIG. 8 (f)) of the AND circuit #L, which is the control signal of the control switch S synchronized with PWM, is set to L, and the switching power supply is stopped.

Similarly, as shown on the right side of FIG.
When the G output shown in FIG. 8D is L, the flip-flop #H
Output bar Q (FIG. 8 (e)) becomes H, and the AND circuit #
The L output is a control pulse Psw synchronized with the PWM output (FIG. 8
(F)) is applied to the control drive switch S.
Therefore, the operation state detection of the solar cell when the irradiation amount is extremely reduced as described above is performed in synchronization with the operation cycle of the timer #M to be set, and the operation of the switching power supply always has a constant cycle. For example, the operation of the timer #M is 1 s
If it is set to ec, the frequency is 1 Hz, which is not an audible sound, and is a low frequency in terms of noise.
FIG. 9 shows a configuration example of a solar cell optimum operating point tracking circuit of a power supply device incorporating the solar cell state detection function.

[0025]

As described in detail above, the present invention is a solar cell optimum operating point tracking circuit of a power supply device in consideration of temperature compensation and current compensation when a solar cell is used as a DC input power supply of a switching power supply. Therefore, it is possible to always supply the maximum output power from the solar cell with respect to the operating temperature and light intensity of the solar cell due to environmental changes in the installation location of the solar cell. Efficient and highly accurate operation is possible.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram of a power supply device using an embodiment of a solar cell optimum operating point tracking circuit according to the present invention.

FIG. 2 is a characteristic diagram showing a relationship between output current, voltage, and power characteristics due to a change in light amount of a solar cell and an optimum operating point tracking reference voltage.

FIG. 3 is a characteristic diagram showing a relationship between output current, voltage, and power characteristics due to a temperature change of a solar cell and an optimum operating point tracking reference voltage.

FIG. 4 is a characteristic diagram showing an output constant voltage control region and a solar cell optimum operating point tracking operation region of the DC-DC converter according to the present invention.

FIG. 5 is a simplified circuit diagram when the present invention is applied to a two-input converter.

FIG. 6 is a characteristic diagram showing a relationship between output current and output voltage when the amount of light of the solar cell is reduced.

FIG. 7 is a block diagram of an embodiment of a solar cell operation state detecting circuit used in addition to the solar cell optimal operating point tracking circuit of the present invention.

FIG. 8 is a control time chart showing the operation of the operation state detection circuit for a solar cell according to the present invention.

FIG. 9 is an overall block circuit diagram in which an operation state detection circuit is applied to the solar cell optimum operation point tracking circuit of the present invention.

[Explanation of symbols]

Reference Signs List 1 DC-DC converter SB Solar cell Rm Current detector Icon Constant current supply circuit D0-1, D0-2 to D0-n PN junction diode VD Forward drop voltage of PN junction diode D VB PN junction diode n cascade connection #A, #B amplifier #C adder #D differential amplifier #E voltage detector #F pulse width modulation comparator #G, #K comparator #H, #I flip-flop #J Knot circuit #L AND circuit #M Timer V1R Temperature compensation voltage V2R Current compensation voltage VR Temperature / current compensation voltage Is Solar cell output current Vs Solar cell output voltage ΔVR, ΔVo Control signal Eo DC-DC converter output voltage R Load OSC sawtooth Wave oscillator PWM pulse width modulation signal S DC-DC converter control drive switch E1, E2 input power supply D1, D2, 3 diode S1, S2 switch L inductor N1, N2 primary winding N3 output winding Vc capacitor voltage Vref0 zero voltage reference voltage EB battery

Claims (5)

[Claims] 1. A power supply device comprising a switching power supply to which power of a solar cell is input, wherein current is supplied to a PN junction diode provided near the solar cell and having substantially the same temperature characteristics as that of the solar cell. A temperature compensation voltage detection circuit for detecting a forward drop voltage of the PN junction diode; and amplifying a voltage detected by the temperature compensation voltage detection circuit at a required amplification factor to output a temperature compensation voltage of the solar cell. An amplifier, a differential amplifier having the temperature compensation voltage of the output of the amplifier and the output voltage of the solar cell as inputs, and a control signal for the output of the differential amplifier and an output for stably controlling the output of the switching power supply. A comparator that compares the control signal with a control signal and outputs a drive signal of a control switch of the switching power supply. Solar cell optimum operating point tracking circuit in the power supply device using a solar cell, characterized in that it has so as to form a maximum power output of the solar cell. 2. A power supply device comprising a switching power supply to which power of a solar cell is input, wherein current is supplied to a PN junction diode provided near the solar cell and having substantially the same temperature characteristics as the solar cell. A temperature compensation voltage detection circuit for detecting a forward drop voltage of the PN junction diode; and amplifying a voltage detected by the temperature compensation voltage detection circuit at a required amplification factor to output a temperature compensation voltage of the solar cell. A first amplifier; a current detection circuit for detecting an output current of the solar cell; a current detected by the current detection circuit, which is converted into a voltage, amplified at a required amplification factor, and a current compensation voltage of the solar cell is calculated. A second amplifier for outputting the temperature compensation voltage of the output of the first amplifier and the second amplifier.
An adder that adds the current compensation voltage of the output of the amplifier to output a temperature / current compensation voltage, and a differential that receives the temperature / current compensation voltage of the output of the adder and the output voltage of the solar cell as inputs. An amplifier, and a comparator that compares a control signal of an output of the differential amplifier and a control signal for stably controlling the output of the switching power supply and outputs a drive signal of a control switch of the switching power supply. A solar cell optimal operating point tracking circuit in a power supply device using a solar cell, wherein the power output of the solar cell is maximized following changes in temperature and light amount at the solar cell installation location. 3. The operation of the control switch of the switching power supply when the temperature compensation voltage is compared with the output voltage of the solar cell at predetermined time intervals, and when the output voltage of the solar cell falls below the temperature compensation voltage. 2. A solar cell in a power supply device using a solar cell according to claim 1, wherein when the output voltage of the solar cell exceeds the temperature compensation voltage, the control switch of the switching power supply is operated normally. Optimal operating point tracking circuit. 4. A method for controlling the switching power supply, comprising: comparing the temperature / current compensation voltage with an output voltage of the solar cell every predetermined time; and when the output voltage of the solar cell falls below the temperature / current compensation voltage. 3. The use of the solar cell according to claim 2, wherein the operation of the switch is stopped, and when the output voltage of the solar cell exceeds the temperature / current compensation voltage, the control switch of the switching power supply is operated normally. Solar cell optimal operating point tracking circuit in the power supply unit. 5. The solar cell according to claim 1, wherein the plurality of PN junction diodes constituting the temperature compensation voltage detection circuit are cascaded. Battery optimal operating point tracking circuit.