JP2006277553A - Electric circuit with constant voltage circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric circuit controlling voltage input to a constant voltage circuit so as not to greatly change and controlling a calorific value in the constant voltage circuit. <P>SOLUTION: A plurality of series-connected diodes 8 and a plurality of NPN transistors 7 are provided between a battery 2 and the constant voltage circuit 4, wherein the number of diodes 8 placed between emitters and collectors of the plurality of NPN transistors 7 is increased one by one from 1 to N. And, the NPN transistor 7 to be turned on is determined depending on how much higher a voltage of the battery 2 is than 20 V. Specifically, 20 V is subtracted from the voltage of the battery 2, and the result divided by a forward voltage drop Vf for a single diode 8 makes the number of diodes 8 to be passed through between the battery 2 and the constant voltage circuit 4. Consequently, the NPN transistor 7 with the number of diodes 8 connected between its emitter and collector is set as the one to be turned on among the plurality of NPN transistors 7. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electric circuit that can be controlled so that an input voltage to a constant voltage circuit does not vary greatly.

In a vehicle, a battery voltage is applied to a constant voltage circuit to form a predetermined constant voltage by the constant voltage circuit, and various loads such as a CPU are driven using the constant voltage. When the battery voltage fluctuates, a constant voltage can be obtained in the constant voltage circuit by causing the Zener diode provided in the constant voltage circuit to generate heat.
Japanese Utility Model Publication No. 5-40914

  When the electric circuit having the constant voltage circuit as described above is employed in, for example, a 24V vehicle, the battery voltage of the 24V vehicle fluctuates as large as 20 to 32V. Must be expected to increase. For this reason, a large heat sink fin is required to dissipate the heat generated in the constant voltage circuit. For example, the mounting area of components required to stably form a constant voltage in the constant voltage circuit There is a problem that an electric circuit having a constant voltage circuit becomes large. As a result, there is a problem that the manufacturing cost of the electric circuit having the constant voltage circuit is increased.

  In view of the above points, an object of the present invention is to provide an electric circuit capable of suppressing the amount of heat generated in a constant voltage circuit.

  In order to achieve the above object, according to the first aspect of the present invention, a constant voltage circuit is provided from the battery (2) so as to be provided between the battery (2) and the constant voltage circuit (4) and connected in series with each other. (4) a plurality of diodes (8) connected in the forward direction and a plurality of diodes (8) bypassed before the voltage of the battery (2) is applied to the constant voltage circuit (4). Until the voltage of the battery (2) is applied to the constant voltage circuit (4) by controlling which of the plurality of switch sections (7) and the plurality of switch sections (7) to turn on By controlling the number of the plurality of diodes (8) to be bypassed and reducing the voltage of the battery (2) by the amount of forward voltage drops of the plurality of diodes (8) to be bypassed, Is input to the constant voltage circuit (4). And Unisuru switch control circuit (6), is characterized in that it comprises a.

  Thus, the switch control circuit (6) controls the number of the plurality of diodes (8) that are bypassed before the voltage of the battery (2) is applied to the constant voltage circuit (4). As a result, the voltage of the battery (2) can be reduced by the amount of forward voltage drop corresponding to the number of bypassed diodes (8), and a predetermined input voltage is input to the constant voltage circuit (4). Can be. Therefore, an electric circuit that can suppress the amount of heat generated in the constant voltage circuit can be provided.

  For example, as shown in claim 2, the plurality of switch sections can be configured by a plurality of NPN transistors (7). In this case, for example, as shown in claim 3, a plurality of diodes (8) and a plurality of NPN transistors (7) are provided, and the emitter-collector of each of the plurality of NPN transistors (7) is provided. The number of the plurality of diodes (8) arranged in each is increased from one to N one by one.

  In the invention according to claim 4, the switch control circuit (6) monitors the voltage of the battery (2) and the input voltage of the constant voltage circuit (4), and based on the voltage of the battery (2), a plurality of It is characterized in that which of the switch units is to be turned on and whether or not to change the turned on switch unit based on the input voltage of the constant voltage circuit (4).

  As described above, even when it is determined which of the plurality of switch units is to be turned on based on the voltage of the battery (2), the switch unit that is turned on based on the input voltage of the constant voltage circuit (4) is selected. By executing feedback control that re-determines whether or not to change to another switch unit, the input voltage of the constant voltage circuit (4) can be made closer to a predetermined value. For example, even if there are temperature characteristics and manufacturing variations of the diode (8), a more suitable switch unit can be turned on.

  In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a circuit configuration diagram of an electric circuit 1 having a constant voltage circuit to which an embodiment of the present invention is applied. This electric circuit is provided in a 24V vehicle, and is driven by using the in-vehicle battery 2 as a power source. Hereinafter, the configuration of the electric circuit 1 of the present embodiment will be described with reference to this drawing.

  As shown in FIG. 1, the electric circuit 1 includes a constant voltage circuit 4 that applies a constant voltage to the load 3 and an applied voltage adjustment circuit 5 that adjusts a voltage applied to the constant voltage circuit 4. It is configured.

  The constant voltage circuit 4 is a well-known circuit, generates a predetermined constant voltage based on an input voltage, and applies the constant voltage to the load 3.

  The applied voltage adjustment circuit 5 includes a switch control circuit 6, a plurality of NPN transistors 7 constituting a plurality of switch units that are driven on and off by the switch control circuit 6, and a plurality of diodes 8. .

  The voltage of the battery 2 is input to the switch control circuit 6 through the input port, and the input voltage to the constant voltage circuit 4 is also input. The plurality of NPN transistors 7 are one of a plurality of diodes 8 connected in series between the positive electrode side of the battery 2 and the constant voltage circuit 4 with the direction from the battery 2 side to the constant voltage circuit 4 side as the forward direction. Corresponding to one, they are connected in parallel.

  Specifically, the collector of each NPN transistor 7 is connected in common to the anode of the diode 8 on the most battery 2 side among the plurality of diodes 8, and the emitter of each NPN transistor 7 is the most connected to the battery 2 among the plurality of diodes 8. It is shifted and connected one by one from the cathode on the side.

  In other words, with respect to the first NPN transistor 7, one diode is connected between the emitter and the collector, and with respect to the second NPN transistor 7, two diodes are connected between the emitter and the collector. The n diodes 8 are connected between the emitter and collector of the nth NPN transistor 7. Then, the base of each NPN transistor 7 is electrically connected to the output port of the switch control circuit 6, and a desired base current flows from the switch control circuit 6, so that each NPN transistor 7 can be driven on and off. ing.

  For this reason, for example, when the NPN transistor 7 in which one diode 8 is connected between the collector and the emitter among the plurality of NPN transistors 7 is turned on, a configuration in which one diode 8 can be bypassed. It becomes. Therefore, when the NPN transistor 7 in which n diodes 8 are connected between the collector and emitter among the plurality of NPN transistors 7 is turned on, n diodes 8 can be bypassed. The configuration is such that the amount of voltage drop from the battery 2 to the constant voltage circuit 4 increases as the NPN transistor 7 having a large number of diodes 8 connected therebetween is turned on.

  The plurality of diodes 8 and the NPN transistor 7 are provided as a set of N sets. When the plurality of diodes 8 are connected to the battery 2 in the forward direction, the plurality of diodes 8 cause a maximum voltage drop of N × Vf based on the forward voltage drop amount Vf at the diode 8. For this reason, if the voltage of the battery 2 is as high as 32V, if the voltage is applied to the constant voltage circuit 4 via the N diodes 8, the input voltage is 32-N. XVf.

  For example, in the case where there are 16 sets of a plurality of diodes 8 and NPN transistors 7, when the temperature characteristics and manufacturing variations of the diodes 8 are not taken into consideration, the forward voltage drop amount of a typical diode 8 is 0.7V. Therefore, by connecting 16 diodes 8 in series, it is possible to generate a voltage drop of 11.2 V at maximum. Therefore, as described above, if the voltage of the battery 2 is 32V and the number of the diodes 8 connected between the battery 2 and the constant voltage circuit 4 is 16, the input voltage of the constant voltage circuit 4 is 32−. 11.2 = 20.8V.

  Next, the operation of the electric circuit 1 having the constant voltage circuit 4 configured as in the present embodiment will be described. First, for example, when an accessory switch (not shown) in the vehicle is turned on, power supply from the battery 2 is started. At this time, first, the voltage of the battery 2 is monitored by the switch control circuit 6. Then, depending on the voltage value of the battery 2 obtained at this time, it is determined which of the plurality of NPN transistors 7 is turned on or none is turned on. When any NPN transistor 7 is turned on, the corresponding NPN transistor 7 is turned on.

  For example, when there are 16 sets of a plurality of diodes 8 and NPN transistors 7, if the voltage of the battery 2 is around 20V, all of the plurality of diodes 8 are connected between the anode and the cathode among the plurality of NPN transistors 7. If the NPN transistor 7 to be turned on is turned on and the voltage of the battery 2 is near 32V, none of the plurality of NPN transistors 7 is turned on.

  Here, which one of the plurality of NPN transistors 7 is turned on depends on how much the voltage of the battery 2 is higher than 20V. Specifically, a value obtained by subtracting 20 V from the voltage of the battery 2 and dividing the result by the forward voltage drop amount Vf of one diode 8 passes between the battery 2 and the constant voltage circuit 4. This is the number of diodes 8 to be made. For this reason, the NPN transistors 7 in which the corresponding number of diodes 8 are connected between the emitter and the collector are set to be turned on among the plurality of NPN transistors 7.

  As a result, basically, the input voltage of the constant voltage circuit 4 becomes approximately 20 V, so that it is possible to suppress the heat generation in the constant voltage circuit 4 sufficiently small.

  However, the forward voltage drop amount Vf in the plurality of diodes 8 varies in the range of 0.5 to 1.0 V due to temperature characteristics and manufacturing variations. For this reason, for example, when there are 16 sets of the plurality of diodes 8 and the NPN transistors 7, when the voltage of the battery 2 is applied to the constant voltage circuit 4 through all 16 diodes 8, A deviation amount × 16 from a typical forward voltage drop amount of 0.7 V is a deviation from a target value of the input voltage of the constant voltage circuit 4. For this reason, when the forward voltage drop amount Vf of all the diodes 8 is 0.5 V, a deviation of the target value − {(0.5−0.7) × 16} = + 3.2 V occurs. There is a possibility, and if it is 1.0 V, there is a possibility that a deviation of the target value-{(1.0-0.7) × 16} =-4.8 V may occur.

  For this reason, the output voltage after passing through the plurality of diodes 8 by the switch control circuit 6, that is, the input voltage of the constant voltage circuit 4, is monitored, and a deviation amount indicating how much the voltage deviates from 20V is obtained. If the amount of deviation is smaller than the forward voltage drop amount Vf of the diode 8, the NPN transistor 7 that is turned on at that time is turned on as it is, and if it is larger, any one of the plurality of NPN transistors 7 is again turned on. Whether it is appropriate to turn on the NPN transistor 7 is required. For example, if the amount of deviation corresponds to the forward voltage drop Vf of one diode 8, the number of diodes 8 connected between the battery 2 and the constant voltage circuit 4 can be increased or decreased by one. Such an NPN transistor 7 is turned on, and the NPN transistor 7 that has been turned on until then is turned off.

  In this way, the input voltage of the constant voltage circuit 4 is monitored, feedback control is performed as to whether or not the currently turned on NPN transistor 7 is suitable, and the diode connected between the battery 2 and the constant voltage circuit 4 By controlling the number of 8, the input voltage of the constant voltage circuit 4 can be made approximately 20V.

  As a result, it is possible to effectively suppress the heat generation in the constant voltage circuit 4, and it is possible to reduce the size of components such as heat radiation fins required to dissipate the heat generated in the constant voltage circuit 4, Cost reduction can be achieved by downsizing the apparatus.

(Other embodiments)
In the above embodiment, the case where a plurality of NPN transistors 7 are used as an example of a switch unit for adjusting the number of diodes 8 connected between the battery 2 and the constant voltage circuit 4 has been described. Not only the transistor but also other switching elements such as IGBTs can be used.

It is a figure which shows the circuit structure of the electric circuit provided with the constant voltage circuit in 1st Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electric circuit, 2 ... Battery, 3 ... Load, 4 ... Constant voltage circuit, 5 ... Applied voltage adjustment circuit,
6 ... switch control circuit, 7 ... NPN transistor, 8 ... diode.

Claims (4)

A predetermined input voltage is applied to the constant voltage circuit (4) based on the voltage of the battery (2), and the load (3) is driven by the constant voltage formed by the constant voltage circuit (4). An electric circuit having a constant voltage circuit,
A plurality of batteries connected between the battery (2) and the constant voltage circuit (4) and connected in a forward direction from the battery (2) to the constant voltage circuit (4) so as to be connected in series with each other. Diodes (8),
A plurality of switch sections (7) for controlling the number of the plurality of diodes (8) bypassed before the voltage of the battery (2) is applied to the constant voltage circuit (4);
The plurality of diodes (by-passing until the voltage of the battery (2) is applied to the constant voltage circuit (4) by controlling which of the plurality of switch sections (7) is turned on. 8), and the voltage of the battery (2) is decreased by the amount of forward voltage drop that is bypassed among the plurality of diodes (8). An electric circuit having a constant voltage circuit, comprising: a switch control circuit (6) configured to be input to the voltage circuit (4). 2. The electric circuit having a constant voltage circuit according to claim 1, wherein the plurality of switch units are configured by a plurality of NPN transistors. The plurality of diodes (8) and the plurality of NPN transistors (7) are provided in units of N,
3. The number of the plurality of diodes (8) disposed between the emitter and collector of each of the plurality of NPN transistors (7) is increased from one to N one by one. An electric circuit having the constant voltage circuit described in 1. The switch control circuit (6) monitors the voltage of the battery (2) and the input voltage of the constant voltage circuit (4), and based on the voltage of the battery (2), the plurality of switch units (7 ) Is turned on, and it is determined whether or not to change the turned-on switch unit (7) based on the input voltage of the constant voltage circuit (4). An electric circuit comprising the constant voltage circuit according to any one of claims 1 to 3.

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