CN201215897Y

CN201215897Y - Power supply path control circuit

Info

Publication number: CN201215897Y
Application number: CNU2008201125146U
Authority: CN
Inventors: 邱子寰; 朱冠任; 龚能辉
Original assignee: Richtek Technology Corp
Current assignee: Richtek Technology Corp
Priority date: 2008-04-25
Filing date: 2008-04-25
Publication date: 2009-04-01
Anticipated expiration: 2018-04-25

Abstract

The utility model relates to a control circuit of a power supply path, which comprises an external power input node which can receive the power from the exterior, a first power transistor which is electrically connected between the external power input node and a first node, the first power transistor controls the external power input node to supply power to the first node, a second power transistor which is electrically connected between the first node and a battery, and the second power transistor controls the battery to supply power to the first node, and an error amplifier whose output is electrically connected with a grid electrode of the second power transistor, the first input end of the error amplifier is electrically connected with the first node, the second input end is electrically connected with the battery, and an equivalent potential difference exists between the two input ends.

Description

The supply path control circuit

Technical field

The utility model relates to a kind of supply path control circuit.

Background technology

See also Fig. 1, need usually in the portable electronic equipment from outside battery BATT to be charged, electric power for example can receive by power-supply adapter or USB terminal (external power input node).In some application scenario, need system's needs of supply of electric power not have electricity or do not have and directly use external power to operate under the situation of battery at battery, therefore circuit structure design becomes as shown in the figure, and system end can be accepted electric power from power-supply adapter or USB terminal or from battery BATT.The feed lines of external power is controlled by transistor power switch P0, and this switch for example can be controlled by low pressure drop control circuit LDO or ON-OFF control circuit 10; External power can be supplied to system simultaneously, reach when battery BATT power shortage its charging (for the purpose of simplifying drawing, external power, will not illustrate with the irrelevant part of the utility model the control circuit of battery BATT charging).

On the supply path of battery BATT to system, be provided with transistor power switch P1, this switch is controlled by hysteresis comparator 20, when system voltage (voltage at node A place) when being lower than the voltage at Node B place, hysteresis comparator 20 output low level, PMOS transistor P1 conducting is so battery BATT just powers to system.Otherwise when the voltage at node A place was higher than the voltage at Node B place, the expression system obtained electric power from the outside, and hysteresis comparator 20 is exported high levels at this moment, and PMOS transistor P1 closes, so battery BATT does not just power to system.

See also Fig. 2, in above-mentioned prior art, with regard to the operative relationship that system end receives electric power, can be divided into three interval Z1-Z3, in interval Z1, system voltage is fully by power-supply adapter or USB, and its voltage level is higher than the voltage level of battery BATT.In interval Z3, system voltage is far below the voltage of battery BATT, so the complete conducting of PMOS transistor P1.But Z2 between the transition region between these two intervals, because system voltage position standard will cause the situation of hysteresis comparator 20 continuous concussion between switch only a little less than the voltage level of battery BATT.In detail, drop to the voltage that is lower than battery BATT when system voltage, and when just being enough to make hysteresis comparator 20 output low level, PMOS transistor P1 conducting, but after the conducting because battery BATT to the power supply of A node so, system voltage will rise suddenly, AB two internodal pressure reduction change, and hysteresis comparator 20 is transferred to again close, so repeatedly, up to entering interval Z3, hysteresis comparator 20 is stablized till the conducting.

Because therefore above shortcoming is necessary to propose a kind of supply path control circuit, can avoid above-mentioned unsettled situation.

Summary of the invention

The purpose of this utility model is to overcome the deficiencies in the prior art and defective, proposes a kind of supply path control circuit.

For reaching above-mentioned purpose, from one of them angle, the utility model provides a kind of supply path control circuit, comprises: external power input node, and can be from the outside electric power that receives; Be electrically connected on first power transistor between this external power input node and the first node, this first power transistor control external power input node is to the power supply of first node; Be electrically connected on second power transistor between first node and the battery, this second power transistor control battery is to the power supply of first node; And error amplifier, its output is electrically connected with the grid of this second power transistor, and the first input end of this error amplifier is electrically connected with first node, and second input is electrically connected with battery, and has an equivalent potential difference between two inputs.

In the above-mentioned supply path control circuit, the first input end of error amplifier can be electrically connected with first node through a voltage source, and this moment, this voltage source can be resistance or diode.Perhaps, can make between two inputs of this error amplifier and have the input bias voltage.

The utlity model has following useful technique effect: supply path control circuit of the present utility model, can avoid the situation of external power spread of voltage of the prior art.

Below by specific embodiment is illustrated in detail, when the effect that is easier to understand the purpose of this utility model, technology contents, characteristics and is reached.

Description of drawings

Fig. 1 is the schematic circuit diagram of prior art;

Fig. 2 illustrates the problem of the prior art in running;

Fig. 3 marks embodiment of the present utility model;

Fig. 4 illustrates operational scenario of the present utility model.

Symbol description among the figure

10 control circuits

20 comparators

30 error amplifiers

40 voltage sources

A, the B node

The BATT battery

P0, the P1 power transistor

Embodiment

Please refer to Fig. 3, in supply path control circuit of the present utility model, use error amplifier 30 comes power controlling transistor P1.Be provided with equivalent electric potential difference Δ V between 30 liang of inputs of error amplifier, represent with voltage source 40.This voltage source 40 is to illustrate for convenient illustrations, when implementing as for reality, it might not be necessary for the circuit element of an entity, for example, also can between 30 liang of inputs of error amplifier, design suitable input bias voltage (input offset), also can reach identical purpose.As voltage source 40 is the entity circuit element, then for example can be resistance, diode etc.Certainly, also the entity circuit element can both be set, between two inputs, arrange the input bias voltage again.

The effect of above circuit structure sees also Fig. 4, and in interval Z1, system voltage is fully by power-supply adapter or USB, and its voltage level is higher than the voltage level of battery BATT.In interval Z3, system voltage is far below the voltage of battery BATT, so the complete conducting of power transistor P1.But Z2 between the transition region between these two intervals owing to the effect of voltage source 40, keep the potential difference of Δ V between node AB, that is power transistor P1 maintains a stable part conducting state.So, can solve aforementioned prior art problems.

Below at preferred embodiment the utility model is described, just the above for making those skilled in the art be easy to understand content of the present utility model, is not to be used for limiting interest field of the present utility model only; For those skilled in the art, when can in spirit of the present utility model, thinking immediately and various equivalence variation.For example, the PMOS transistor in the utility model also can change with nmos pass transistor and replaces, and circuit only needs the corresponding small size modification of making, and the positive-negative input end of error amplifier 30 is exchanged get final product.So all according to a notion of the present utility model and spirit impartial for it a variation or modification, all should be included in the scope of claims of the present utility model.

Claims

1. a supply path control circuit is characterized in that, comprises:

External power input node can be from the outside electric power that receives;

Be electrically connected on first power transistor between this external power input node and the first node, this first power transistor control external power input node is to the power supply of first node;

Be electrically connected on second power transistor between first node and the battery, this second power transistor control battery is to the power supply of first node; And

Error amplifier, its output is electrically connected with the grid of this second power transistor, and the first input end of this error amplifier is electrically connected with first node, and second input is electrically connected with battery, and has an equivalent potential difference between two inputs.

2. supply path control circuit as claimed in claim 1 is characterized in that, the first input end of this error amplifier is electrically connected with this first node through a voltage source.

3. device as claimed in claim 2 is characterized in that, this voltage source is resistance or diode.

4. supply path control circuit as claimed in claim 1 is characterized in that, has the input bias voltage between two inputs of this error amplifier.

5. device as claimed in claim 1 is characterized in that this first node is electrically connected with circuit system.