JP2016107923A - Charge control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance charge speed of a capacitor.SOLUTION: A charge control circuit is disposed in series, between a DC power source 1 and a capacitor 5. The charge control circuit comprises serial connection of a switch 2 and a parallel resistance part 3. The parallel resistance part 3 comprises a first resistance 31 and a second resistance 32. The second resistance 32 employs a thermistor whose resistance value has positive temperature characteristic. The second resistance 32 employs, for example, a polymer-based thermistor.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a charge control circuit, and is applied to, for example, a technique for charging a sub battery circuit using a capacitor.

  In recent years, hybrid cars and electric cars have been developed to improve fuel efficiency. Gasoline vehicles are also expected to improve fuel efficiency by implementing idling stops.

  However, once the engine is stopped due to idling stop or the like, the battery is not charged by the alternator. For this reason, when the engine is ignited again, a phenomenon called “cranking” occurs in which the battery voltage rapidly decreases.

  If cranking occurs and the battery voltage drops rapidly, there is a risk that the body ECU (electronic control unit) of the automobile will erroneously perform a low voltage reset.

  In order to avoid such a situation, a technology that includes a sub-battery such as a large-capacitance capacitor in addition to the battery and supports cranking is well known.

  For example, the sub-battery is used as an auxiliary power source for releasing the door lock when the battery is lost when the vehicle collides, in addition to measures against cranking.

  Patent Document 1 introduces a technique in which a current from a battery charges a capacitor via a preliminary charging circuit after the ignition key switch is turned on. The precharging circuit is composed of a series connection of a diode and a thermistor as a resistor. It is disclosed that this thermistor has a negative characteristic with respect to a temperature change.

Japanese Utility Model Publication No. 6-27433

  However, thermistors having negative characteristics with respect to temperature changes (hereinafter referred to as “negative characteristic thermistors”) generally have a small current capacity and most products can flow less than 1 A. On the other hand, when a thermistor whose resistance value has a positive temperature characteristic with respect to a temperature change (hereinafter referred to as “positive characteristic thermistor”), in particular, a polymer material is used, the current capacity is up to several tens A. A big one is obtained.

  Therefore, an object of the present invention is to provide a technique for quickly charging a capacitor (for example, a sub-battery) while using a positive temperature coefficient thermistor.

  A first aspect is a charge control circuit that is provided in series between a DC power supply and a capacitor and controls charging of the capacitor, and is connected in parallel to the first resistor and the first resistor, And a second resistor employing a thermistor having a positive temperature characteristic of the resistance value.

  A second aspect is a charge control circuit according to the first aspect, wherein the thermistor is a polymer thermistor.

  A third mode is a charge control circuit according to the first mode or the second mode, wherein the resistance value of the second resistor is lower than the first resistance value of the first resistor, It changes to a second resistance value higher than the resistance value of one resistor.

  A 4th aspect is a charge control circuit concerning a 1st aspect, a 2nd aspect, or a 3rd aspect, Comprising: The said capacitor functions as a backup power supply of the said DC power supply (1).

  The capacitor can be charged quickly while using the positive temperature coefficient thermistor.

1 is a circuit diagram showing a configuration according to an embodiment of the present invention. It is a graph which shows the simulation by which a capacitor is charged (without 2nd resistance). It is a graph which shows the simulation with which the capacitor 5 is charged (the 1st resistance is absent). It is a graph which shows the simulation in which the capacitor 5 is charged in embodiment.

  FIG. 1 is a circuit diagram showing a configuration according to one embodiment of the present invention. The DC power source 1 outputs a DC voltage Vb. The capacitor 5 is charged from the DC power source 1 through the ignition switch 9 and the charge control circuit 6. The charging control circuit 6 is provided in series between the ignition switch 9 and the capacitor 5 and controls charging of the capacitor 5 when the ignition switch 9 is conductive.

  The configuration shown in FIG. 1 is mounted on the vehicle, for example, and the capacitor 5 functions as a standby power source for the DC power source 1.

  The charge control circuit 6 has a series connection of the switch 2 and the parallel resistance unit 3. The switch 2 becomes non-conductive when the voltage Vc of the capacitor 5 reaches a predetermined voltage Vh, and charging of the capacitor 5 stops.

  The voltage Vc is detected by the voltage detector 4. The voltage detection unit 4 includes, for example, resistors 41 and 42 connected in series, and these voltages divide the voltage Vc and apply it to the switch 2. A thermistor may be employed as at least one of the resistors 41 and 42. Since the technique for detecting the voltage in this manner is a known technique, detailed description thereof is omitted here.

  For example, the switch 2 includes a comparator 21, a resistor 23, an NMOS transistor 22, a PMOS transistor 24, and a Zener diode 25. The comparator 21 compares the voltage output from the voltage detector 4 with the comparison voltage Vref. The comparison voltage Vref is a value obtained by dividing the voltage Vh by the voltage dividing ratio of the resistors 41 and 42. Therefore, when the voltage Vc reaches the voltage Vh, the voltage output from the voltage detection unit 4 reaches the comparison voltage Vref.

  In this case, the comparator 21 sets the output potential to “L”, the NMOS transistor 22 is turned off, and the PMOS transistor 24 is turned off. In this way, the switch 2 becomes non-conductive when the voltage Vc reaches the voltage Vh.

  The parallel resistance unit 3 includes a first resistor 31 and a second resistor 32 connected in parallel to the first resistor 31. A positive temperature coefficient thermistor is employed for the second resistor 32.

  Hereinafter, charging from a state where the capacitor 5 is not charged at all (Vc = 0) will be described. When the ignition switch 9 is turned on, since the value obtained by dividing the voltage Vc by the resistors 41 and 42 is smaller than the comparison voltage Vref, the NMOS transistor 22 is turned on and a bias voltage is applied between the gate and source of the PMOS transistor 24. The PMOS transistor 24 is turned on.

  As a result, when conduction of the switch 2 is started, charging of the capacitor 5 is started using the parallel resistance unit 3 as a charging path. The Zener diode 25 has a function of protecting the PMOS transistor 24 from a surge voltage when the ignition switch 9 is turned on.

  The resistance value R2 of the second resistor 32 is low immediately after the start of charging, for example, lower than the resistance value R1 of the first resistor 31. Therefore, the charging current to the capacitor 5 mainly flows through the second resistor 32, and the capacitor 5 is rapidly charged with a large current, specifically, for example, a current of several tens of A.

  When the large current flows, the second resistor 32 generates heat, and its resistance value R2 increases. As a result, the charging current to the capacitor 5 mainly flows through the first resistor 31, so that the period during which the large current flows is transient, and thereafter the capacitor 5 is charged with a relatively small charging current, for example, about 1A. The

  FIG. 2 is a graph showing a simulation in which the capacitor 5 is charged when the second resistor 32 is not provided in this embodiment. Specifically, FIG. 1 shows the time course of charging current and charging voltage (that is, voltage Vc). Hereinafter, the voltage Vb is assumed to be 12V.

  The voltage Vc is expressed by Vb · [1-exp (−t / (C · (R1 + r)))]. However, the capacitance of the capacitor 5 is C, and the elapsed time t from the time when the ignition switch 9 starts to be conducted is introduced. The charging current is represented by (Vb / R1) · exp (−t / (C · (R1 + r))). Here, the case where the resistance value R1 is 10Ω and the capacitance C is 5F is shown. In view of the fact that the configuration shown in FIG. 1 is mounted on the vehicle, the resistance r of the wiring from the DC power source 1 to the parallel resistance unit 3 (this is commonly referred to as “harness” when mounted on the vehicle, for example). It was introduced as 170 mΩ.

  In FIG. 2, the left vertical axis represents the magnitude of the charging current, and the right vertical axis represents the magnitude of the charging voltage. However, since a logarithmic scale is adopted for the charging current, in view of the above formula, it changes linearly with respect to time. The charging voltage increases exponentially with time in view of the above equation. The time required to charge the capacitor 5 to Vc = 8V is about 55 seconds.

  FIG. 3 is a graph showing a simulation in which the capacitor 5 is charged when the first resistor 31 is not provided in this embodiment. The voltage Vc is represented by Vb · [1−exp (−t / (C · (R2 + r)))]. The charging current is represented by (Vb / R1) · exp (−t / (C · (R2 + r))). The resistance value R2 at the beginning of charging is very small, for example, 25 mΩ. Also in FIG. 3, the capacitance C is 5F. In FIG. 3, the left vertical axis indicates the magnitude of the charging current, and the right vertical axis indicates the magnitude of the charging voltage. However, since a normal (linear) scale was adopted for the charging current, in view of the above formula, when the charging time is less than 0.4 seconds, the charging current changes exponentially with respect to time from 60 A to 40 A. Yes.

  In the simulation, it is assumed that the resistance value R2 rapidly increases and the conductance (1 / R2) is 0 after the charging time is 0.4 seconds. As a result, the charging current becomes 0, and the charging voltage does not increase thereafter. Therefore, the voltage Vc remains at 4V and the capacitor 5 cannot be charged up to 8V.

  From the above, it can be seen that 55 seconds is required to charge the capacitor 5 to 8V with only the first resistor 31, and the capacitor 5 cannot be charged to 8V with only the second resistor 32.

  FIG. 4 is a graph showing a simulation in which the capacitor 5 is charged in this embodiment. The voltage Vc is expressed by Vb · [1-exp (−t / (C · (R1 // R2 + r)))]. However, R1 // R2 = 1 / (1 / R1 + 1 / R2), which indicates the combined resistance of the parallel resistance unit 3. The charging current is represented by (Vb / R1) · exp (−t / (C · (R1 // R2 + r))). In FIG. 4, the left vertical axis represents the magnitude of the charging current, and the right vertical axis represents the magnitude of the charging voltage. However, a logarithmic scale was adopted for the charging current as in FIG. Similarly to FIG. 3, the conductance (1 / R2) is assumed to be 0 after the charging time is 0.4 seconds or later. In addition, when the charging time is less than 0.4 seconds, the resistance value R2 is 25 mΩ.

  When the charging time is less than 0.4 seconds, a large charging current flows as in FIG. 3, and after the charging time of 0.4 seconds, the charging voltage rises to 4V. However, unlike FIG. 3, the charging current continues to increase after that, since the charging current flows to the capacitor 5 through the first resistor 31 while decreasing as in FIG. 2. As a result, the voltage Vc reaches 8 V after a charging time of 35 seconds.

  Thus, according to the present embodiment, the time required to charge the capacitor 5 is shorter than when only the first resistor 31 is employed.

  The change in the resistance value of the resistance value R2 depends on the elapsed time from the start of charging and does not depend on the voltage Vc. Therefore, even if the capacitor 5 is charged to some extent and Vc> 0, a large charging current flows in the initial stage of charging. Therefore, the charging time required to charge the capacitor 5 up to the voltage Vh (exemplified here as 8V) is greater than the case where the capacitor 5 is charged only through the first resistor 31. It is shorter to charge through parallel connection.

  As described above, according to the present embodiment, it is possible to quickly charge a capacitor (for example, a sub battery) while using a positive temperature coefficient thermistor.

  It is desirable that the current flow dominantly through the second resistor 32 rather than the first resistor 31 at the beginning of charging, and thereafter the current dominantly flow through the first resistor 31 over the second resistor 32. Therefore, it is desirable that the resistance value R2 of the second resistor 32 changes from the first resistance value lower than the resistance value R1 of the first resistor 31 to the second resistance value higher than the resistance value R1. In other words, the resistance value R1 of the first resistor 31 is desirably set between the first resistance value and the second resistance value.

  For example, the first resistance value is several tens of mΩ, the second resistance value is several tens of kΩ, and the resistance value R1 is set to about several tens of Ω. That is, the ratio of the resistance value R1 to the first resistance value is set to the order of 10 to the third power, and the ratio of the resistance value R1 to the second resistance value is set to the order of the 10th (−3) power. As described above, the resistance value is set such that current flows predominantly from the first resistor 31 to the second resistor 32 at the beginning of charging as described above, and thereafter, the current flows from the second resistor 32 to the first resistor 31. This is desirable from the viewpoint of dominant flow.

  Thus, a positive temperature coefficient thermistor in which the ratio of the second resistance value to the first resistance value changes to about the sixth power is known, and one having a current capacity of several tens of A is also known. Further, the phenomenon that heat is generated by the flow of current and the resistance value increases due to a temperature change due to the heat generation is also commonly referred to as “trip”. Such a positive temperature coefficient thermistor is also known to be realized by, for example, a polymer type thermistor, and is commercially available as, for example, “Polyswitch” (registered trademark).

  As described above, the present invention has been described in detail. However, the above description is illustrative in all aspects, and the present invention is not limited thereto. It is understood that countless variations that are not illustrated can be envisaged without departing from the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 DC power supply 31 1st resistance 32 2nd resistance 5 Capacitor 6 Charge control circuit

Claims (4)

A charge control circuit that is provided in series between a DC power supply and a capacitor and controls charging of the capacitor,
A first resistor;
A charge control circuit comprising: a second resistor connected in parallel to the first resistor and employing a thermistor having a positive temperature characteristic of the resistance value.   The charge control circuit according to claim 1, wherein the thermistor is a polymer thermistor.   It is a charge control circuit as described in any one of Claims 1-2, Comprising: The resistance value of a said 2nd resistance is resistance of a said 1st resistance from the 1st resistance value lower than the resistance value of a said 1st resistance. The charge control circuit which changes to a second resistance value higher than the value.   4. The charge control circuit according to claim 1, wherein the capacitor functions as a standby power source for the DC power source. 5.

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