1. Field of Invention
The present invention relates to a current driver for driving a load requiring high current, and more particularly to a dynamically adjusting current driver that prevents overdriving the load by limiting the input current and dynamically detecting the output current.
2. Description of Related Art
Bipolar driver circuits are often used to drive loads having high current requirements. For example, in applications in which the load is a motor, relatively high currents are often required during acceleration and deceleration. This technology is described in U.S. Pat. No. 5,684,427. However, the circuit structure disclosed in this patent does not include a protection circuit to avoid overdriving the load. In other words, the circuit structure disclosed in U.S. Pat. No. 5,684,427 is not able to control the input current supplied to the load. Therefore, an overdrived load due to excess input current often happens.
On the other hand, a relatively large current may flow through the source pin of the load when the driver circuit drives the load. A control signal is used to switch the current flowing through the load. This current switch may cause an electromagnetic induction effect to generate an additional current and voltage noises in the circuit structure. The relationship between the current and the voltage is shown as follows:       i    =                  1        L            ⁢              ∫                  v          ⁢                      ⅆ            t                                    v    =          L      xc3x97                        ⅆ          i                          ⅆ          t                    
L is the inductance of the load. The electromagnetic inductive effect often causes a large current and voltage noises at the output end of the driver circuit because of the inherent large inductance of the load. In other words, the current and voltage value at the output end of the driver circuit is not the authorized value. This noise also causes overdriving load situation.
The lack of a protection circuit may cause the excess input current to overdrive the driver circuit. On the other hand, the inherent large inductance of the load may also generate a large current and voltage noises at the output end of the driver circuit because of the electromagnetic induction effect. Therefore, a new circuit structure is required to avoid the above drawbacks. This driver circuit structure provides a protection function at the input end to avoid the excess input current and provides a dynamic detection function at the output end to avoid exceeding the authorized value for the output current and voltage value.
According to the above descriptions, a large current is often input into the conventional driver circuit. Because there is no protection apparatus in the driver circuit, the large input current may cause an overdrive situation. On the other hand, the huge loading has an inherent inductor that may generate an additional current and voltage at the output end of the driver circuit during discharge and charge phases. Therefore, the present invention provides a circuit design having a protection circuit at the input end and having the function of dynamically adjusting the current at the output end. The circuit structure of the present invention reduces the output current when the output current is over an authorized value in real time. On the other hand, the protection circuit existing in the present invention limits the current input to the circuit to avoid an overdrive situation.
In accordance with the above description, the main purpose of the present invention is to provide a driver circuit apparatus having the function of dynamically adjusting the output current at the output end. This function reduces the output current in real time when the output current is over an authorized value. This function avoids a sudden rise in the output current.
Another purpose of the present invention is to provide a driver circuit apparatus having a protection circuit. The protection circuit may limit the current input into the driver circuit to avoid an overdrive situation.
In accordance with the purpose described in the above paragraphs, the driver circuit of the present invention includes three units, an input current limiting unit located at the input end of the driver circuit, a load driver unit and an output current detection and dynamic adjustment unit located at the output end of the driver circuit. The input current limiting unit limits the current input into the driver circuit within an authorized value. This limiting unit avoids an excess current being input into the load driver unit. The load driver unit receives the current transferred from the input current limiting unit to generate a drive current to drive the load. The output current detection and dynamic adjustment unit is used to detect the drive current of the load driver unit and converts the drive current to a voltage signal, which is compared with a reference voltage. The output current detection and dynamic adjustment unit does not adjust the drive current of the load driver unit if the voltage signal is less than the reference voltage. On the contrary, the output current detection and dynamic adjustment unit reduces the drive current of the load driver unit to avoid the overdrive situation if the voltage signal is larger than the reference voltage.