TWI234324B - Smart over current protective circuit - Google Patents

Abstract

A smart over current protective circuit using in a charger and discharge protection control integrated circuit is disclosed. By virtue of a dynamic threshold voltage provided by a voltage inverse proportional circuit feeds into the negative terminal of an over current detected circuit, the over current detecting level (OCP point) will be kept nearly at a constant value. Consequently, an undesired over current protection will not happen.

Description

1234324 V. Description of the invention (1) [Technical field to which the invention belongs] The present invention discloses an intelligent overcurrent protection circuit related to charge and discharge protection of a lithium battery, and in particular relates to a voltage inverse circuit intelligently adjusting a threshold voltage, and To achieve the purpose of significantly reducing or unchanged current level changes at the overcurrent detection point. [Previous Technology] One use of portable electronic consumer products is to use AC power with a rectifier carried in the room, and the other most common case is to use the power stored in a random battery to provide its operating voltage. In addition to the use of dry batteries in palm-type electronic products that consume less power, the most common case is the use of rechargeable batteries that can be reused. Depending on the amount of power required, different sizes of rechargeable batteries are provided. Not only save money but also be environmentally friendly. A typical with automatic charging function and contains over-charge or over-discharge " (The protection device of Chase Test 'please refer to Figure 1. The battery is not shown in the figure. The charge-discharge control circuit includes a charge-discharge protection control 1C 30, a typical charge-discharge The protection control IC is a model NT 1 8 5 4 IC from Xinde Technology Co., Ltd. The battery 1 1 can be a lithium battery, a nickel- 氲 battery, or a nickel-cadmium polymer battery. The lithium battery is used as the following. Description: The charge and discharge protection control IC 3 0 is basically composed of six main circuits: over voltage detection and comparison circuit 2 0, over discharge detection and comparison circuit 2 2, over current detection and comparison circuit 2 4. short circuit detection Test circuit 2 5, level shift circuit

1234324 V. Description of invention (2) 2 6 and logic circuit 2 8 The overvoltage detection and comparison circuit 20 is also called overcharge detection circuit. The negative input terminal of the differential amplifier 20a is provided by a reference voltage source 15 at a fixed level. The voltage at the positive input terminal is provided by the power supply terminal V. d Silver resistance Ra, Rb, Rc voltage-dividing circuit composed of Rb and Rc across the voltage, its output end is delayed by the delay device 2 0 b fed to the logic circuit 2 8 judge, and then through the level shift circuit 2 6 Connected to the output terminal (: 01 ^. (: 0111 'is connected to a 1 ^ type metal-oxide-semiconductor half-effect transistor NM0SFET (hereinafter referred to as FET) 32). When overcharged, the FET32 will be turned off. Overdischarge detection comparison circuit 2 2 The negative input of the differential amplifier 2 2 a is also provided by the reference voltage source 15, and the voltage of the positive input is provided by the Rc voltage across the voltage-dividing circuit composed of the power supply terminal VDV resistors Ra, Rb, and Rc. The output terminal is fed into the logic circuit 28 after a delay, and then output to the output terminal DOUT. DOUT is connected to FET 31. When overdischarge, FET 31 will be turned off. When neither overcharge nor overdischarge has occurred, Both FET 32 and FET 31 are in the on state.

The negative input terminal of the differential amplifier 24a of the overcurrent detection and comparison circuit 24 is provided by a fixed threshold start voltage source V τ and the value of V τ 妁 is about 0 · 15 V. The voltage at the positive input terminal is connected to 0 ( Therefore, for the charge control IC 3 0, the '0 C P terminal is an input terminal, which detects the current flowing from the OCP terminal from F E T 3 1 to F E T 3 2 (when charging) or OCP flows from FET 32 to FET 31

1234324 V. Description of the invention (6) / (1? 1 + 1? 2) Input to the gate of transistor 0. When 7_7 is larger, the current of 103 will be larger and the internal resistance RDS (〇n) of transistor Q1 will be smaller. Therefore, the output voltage of transistor Q1 will be smaller via the unit amplifier U1 to the second voltage-dividing resistor circuit. The smaller the voltage at the resistor R5, the smaller the voltage at the node P. According to the method of the present invention, V 佚 is connected to the negative voltage terminal of the overcurrent comparator as VTH. Conversely, the smaller the V BAT is, the larger the V TH is. According to a preferred embodiment of the present invention,

The resistances of R1, R2, R3 and R4 will be adjusted appropriately, so that the relationship between the battery voltage VBAT and V τ is as shown in Figure 5. That is, when V BAT is changed from 3 V to 4 · 2 V, V τ is changed from 0 · 2 V to 0 · 15 V, and the best effect can be obtained. For example, in one implementation, when the lithium battery voltage is 4.2 · ¥, its output current. For 2 · 5A, please also refer to the vG to RDS (on) diagram shown in Figure 2. At 25 ° C, when the drain current is 5A and Vgs is 4.2 scales, (〇η) is 45πΩ, and Vgs is 3W RDs (On) is 55πΩ. In terms of Vth = 015V, at this time. The current protection point of the CP will be (〇15v) / (45mQ) = 3.33α. The output current of this battery is lower than the current protection point of 0CP. The overcurrent protection circuit will not operate. When the battery voltage is 3V, according to the aforementioned energy Conservation, at this time the current from the battery will be (4.2V X 2.5A) / (3.0V) = 3.5A. And according to the circuit of the present invention, VTH = 0.2V and RDS (on) is 55ιηΩ can Calculate the current protection point of this ^ 〇cp will be (0 2〇ν) / (55ιηΩ) = 3.63A. Therefore, the battery wheel output current is lower than the current protection point of 0CP. The overcurrent protection circuit will not operate.

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V. Description of the invention (7) (0.15V) / (55πΩ) =. This is not overcurrent protection. Compared with the traditional V τ which is a fixed value of 0 · 15 V, 2 · 7 2 A will promote the operation of the overcurrent protection circuit. That is, malfunction. Therefore, the 'method according to the present invention' charge-discharge protection control IC combined with the output of the inverse proportional circuit 100 as the critical start of the overcurrent comparator: electricity = will make the voltage at the point where the overcurrent protection circuit works hardly, Text 'unofficial battery voltage. Advantages of the present invention: The present invention only needs to use a ready-made charge and discharge protection and control simple voltage inverse proportional circuit to achieve effective prevention ... a. The purpose of the present invention is to prevent malfunction. According to the present invention, the critical start-up $ current protection circuit is integrated so that The voltage 2 smart adjustment of the current protection circuit's operating point will save the cost of redesign. Almost unchanged. The above description is only a preferred embodiment of the present invention, and determines the scope of patent application of the present invention; for example, the aforementioned Asia-Africa is used to limit the road, it is only an embodiment, and those who are familiar with the relevant art will reverse the proportion of electricity ▲ For example, a negative feedback control circuit may be used instead. Second, it is possible to make appropriate changes from the equivalent modification completed under the spirit disclosed in the present invention. $ Where it has not been removed is included in the scope of patent application described below. Article 3 4 decoration ’s should

1234324 Schematic illustration of the graphic example will be supplemented by the following text / ^ Technical battery charge and discharge protection control 1c and its main 7G parts and their connections to FETs and batteries Figure 2 shows the relationship between VG and RDS (On). Fig. 3 shows the use of the technology in accordance with the present invention to seduce Xi Lei, ★ Gu Congdou's inner neighbors. "V: Electric protection control within 1 ° and 2 °.的 The schematic diagram of the main components and their pins connected to the FET and battery. Please note that v TH6 in the overcurrent protection circuit can be adjusted intelligently. FIG. 4 shows a voltage inverse circuit according to the technology of the present invention. Figure 5 shows the relationship between the battery voltage ¥ _ and the fishing voltage according to the technology of the present invention. 0 Chart number comparison table: 1 5 Reference voltage source 2 0 a Over-voltage comparator 22 a Over-charge voltage comparator 2 6 Level shift circuit 2 5 Short-circuit detection circuit 31, 32, Q1 fet 60 transistor amplifier circuit 1 0 0 voltage inverse circuit COUT overcharge control terminal U1 buffer

11 Battery 2 0 Overvoltage detection and comparison circuit 20b, 22b, 24b Delayer 2 2 Overdischarge detection and comparison circuit 24a Overcurrent comparator 2 4 Overcurrent detection and comparison circuit 3 0 Charge and discharge protection control IC 5 0 First minute Voltage circuit 70 second voltage dividing resistor circuit DOUT over-discharge control terminal OCP over-current control terminal

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Claims (1)

1234324 6. Scope of patent application1. A smart over-current protection circuit for batteries. The smart over-current protection circuit is used in charge and discharge protection control ICs. It is characterized by using a voltage inverse circuit to provide a critical starting voltage to the over-current. At the negative voltage reference terminal of the protection circuit, the critical starting voltage will increase as the battery voltage decreases, and the current level change at the overcurrent detection point will be significantly reduced. 2. The battery intelligent overcurrent protection circuit according to item 1 of the patent application scope, wherein the above-mentioned charge and discharge protection control IC has overcharge detection, overdischarge detection and overcurrent protection functions. 3. For example, the battery intelligent overcurrent protection circuit of the first patent application range, wherein the voltage inverse proportional circuit uses the battery as the first power input terminal, and the charge and discharge protection control IC provides a fixed standard for the overcurrent protection circuit. The bit reference voltage is the second power input terminal, and the voltage output by the voltage inverse proportional circuit is the above-mentioned critical start voltage V TH. 4. For example, the battery intelligent overcurrent protection circuit in the scope of patent application No. 3, wherein the voltage inverse proportional circuit is composed of a first voltage dividing resistor circuit, a FET inverse ratio circuit, a buffer, and a second voltage dividing resistor circuit. One end of the first voltage-dividing resistor circuit is connected to the above battery, and one end is grounded. One of the resistance voltages is connected to a FET gate terminal of the FET inverse circuit. The drain of the FET is connected to the second power input terminal through a resistor. The output end is fed into the buffer, and then the critical starting voltage is output through the cross-voltage of one of the resistors in the second voltage dividing resistor circuit. Page 15 1234324 VI. Application for patent scope 5 · If the patent application scope item 3 of the battery intelligent overcurrent protection circuit, the above voltage inverse proportional circuit makes the battery voltage approximately 4.2 V to 3 V when V τ in Linear change from 0 · 1 5 V to 0 · 2 V. Page 16