CN101546914B

CN101546914B - Charger control circuit and charger control method

Info

Publication number: CN101546914B
Application number: CN2008100874306A
Authority: CN
Inventors: 白忠龙; 陈诗蕙
Original assignee: Richtek Technology Corp
Current assignee: Richtek Technology Corp
Priority date: 2008-03-27
Filing date: 2008-03-27
Publication date: 2012-12-26
Anticipated expiration: 2028-03-27
Also published as: CN101546914A

Abstract

The invention provides a charger control circuit and a charger control method matched with a charger. The charger comprises a transformer which comprises a primary side winding and a secondary side winding. The charger control circuit comprises a power switch electrically connected with the primary side winding, a switch control circuit for controlling the operation of the power switch, and a sensing circuit for generating a step-down and time-delay signal according to a voltage of a node between the power switch and the primary side winding, when the power switch is turned off. Then the sensing circuit compares the node voltage with the step-down and time-delay signal to generate a signal and providing the signal to the switch control circuit, so as to control the conduction time of the power switch within an operation cycle.

Description

Charger control circuit and charger control method

Technical field

The present invention relates to a kind of charger control circuit and charger control method.

Background technology

A wherein example of charger is flash of light capacitor charger (photoflash capacitor charger).Its basic structure is positioned at the capacitor C out charging of output end vo ut from input Vin through 10 pairs in transformer shown in Fig. 1 first half, then controlled by the power switch in the charger control circuit 20 21 as for the charging interval; Charger control circuit 20 is generally an integrated circuit.In prior art shown in Figure 1, the switching of the switch of power switch 21 is controlled by ON-OFF control circuit 25, and this ON-OFF control circuit 25 is according to the conducting time point that the current sense result of transformer 10 secondary sides is decided power switch 21.In detail, be voltage through resistance R with the current conversion of secondary side in the circuit, and the voltage after in comparator 23, will changing is compared with reference voltage Vref.When the voltage after this conversion is lower than reference voltage Vref; The electric current of expression secondary side is near zero, and no current is charging to capacitor C out, and this moment, ON-OFF control circuit 25 was a conducting power switch 21; Make and produce induced current on the transformer 10 again, continue capacitor C out is charged.(OFF) time point of closing as for power switch 21 then normally decides (interlock circuit is not shown) according to the current value of primary side, and when the electric current of primary side arrived a certain predetermined value, ON-OFF control circuit 25 was promptly closed power switch 21.

The shortcoming of above-mentioned prior art is: secondary side has the bigger magnitude of current and flows in the charger control circuit 20, is easy to cause noise to cause mistake.In addition, also be easier to take place the surging (spike) of primary side current.

Fig. 2 shows another kind of prior art, in this prior art, from primary side extraction signal, the voltage of first side winding is compared, and is supplied to ON-OFF control circuit 25, the conducting time point of power controlling switch 21 to produce signal.When the voltage of first side winding near zero the time, promptly non-inductive electric current flows on the indication transformer 10, this moment, ON-OFF control circuit 25 was a conducting power switch 21.This prior art can solve a part of shortcoming of Fig. 1 prior art, no matter but be the prior art of Fig. 1 or Fig. 2, the integrated circuit of charger control circuit 20 all needs two pins (P1 and P2 or P1 and P3), just can reach the function of detecting and control.

Because above shortcoming is necessary to propose a kind of charger control circuit, can uses less pin to reach controlled function, and need not introduce signal from secondary side.

Summary of the invention

First purpose of the present invention is the deficiency to above-mentioned prior art, proposes a kind of charger control circuit.

Second purpose of the present invention is to provide a kind of charger control method.

For reaching above-mentioned purpose, from one of them angle, the invention provides a kind of charger control circuit, to cooperate, include transformer in this charger, and transformer comprises first side winding and secondary side winding with a charger; The charger control circuit that is proposed comprises: the power switch that is electrically connected with this first side winding; Control the ON-OFF control circuit of this power switch operation; And circuit for detecting; When this power switch is closed; According to the voltage of one node between this power switch and this first side winding, produce the signal after step-down and time postpone, and the signal after this node voltage and this process step-down and the time delay is compared; Produce signal and be supplied to this ON-OFF control circuit, to control the operation conducting time point of this power switch in one-period.

In the above-mentioned charger control circuit, also can comprise delay circuit, to postpone the conducting time point of this power switch.

In preferred embodiments, the circuit for detecting in the above-mentioned charger control circuit comprises: a RC parallel circuits; And a comparator, one input end receives the voltage signal relevant with this RC parallel circuits, another input reception voltage signal relevant with this node.Said " voltage signal relevant with this node " for example can be this node voltage itself or its dividing potential drop.

For reaching above-mentioned purpose; From another angle; The invention provides a kind of charger control method, in order to control one have a transformer charger, this transformer comprises first side winding and secondary side winding; Said charger control method comprises: a power switch is provided, is electrically connected with this first side winding; When this power switch is closed, detect the voltage of one node between this power switch and this first side winding, obtain first signal relevant with this node voltage; Reduce the amplitude of this first signal and postpone this first signal, to obtain second signal; Detect the crossover point of this first and second signal; And, control the operation conducting time point of this power switch in one-period according to the detecting result.

In preferred embodiments, the step of the detecting node voltage in the said method comprises: obtain first signal relevant with this node voltage; Reduce the amplitude of this first signal and postpone this first signal, to obtain second signal; And the crossover point of detecting this first and second signal.

Below through specific embodiment is explained in detail, when the effect that is easier to understand the object of the invention, technology contents, characteristics and is reached.

Description of drawings

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

Fig. 2 is the schematic circuit diagram of another prior art;

Fig. 3 marks notion of the present invention;

Fig. 4 is a schematic circuit diagram, and an embodiment more specifically of the present invention is shown;

Fig. 5 is primary side current in Fig. 4 circuit, secondary side current, and the oscillogram of AB two node voltages;

Fig. 6 is a schematic circuit diagram, and another embodiment more specifically of the present invention is shown;

Fig. 7 is a schematic circuit diagram, and another embodiment more specifically again of the present invention is shown.

Symbol description among the figure

10 transformers

20 charger control circuits

21 power switchs

23 comparators

25 ON-OFF control circuits

30 charger control circuits

31 power switchs

32 circuit for detecting

33 comparators

35 ON-OFF control circuits

36 delay circuits

The Cin input end capacitor

The Cout output capacitor

A, B node

C1 electric capacity

P1, P2, P3 pin

R, R1, R2 resistance

The Vin input voltage

The Vout output voltage

The Vref reference voltage

The X crossover point

Embodiment

At first please refer to Fig. 3, in charger control circuit 30 of the present invention, only need use a pin P1, can reach the detecting desired and the function of control.Charger control circuit 30 uses circuit for detecting 32 to detect the change in voltage that primary side A is ordered.When secondary side current near zero the time, the voltage that A order is respective change also, the signal that this moment, circuit for detecting 32 promptly export correspondence is to ON-OFF control circuit 35, with the operation of further power controlling switch 31.

More specifically one of embodiment example of the above notion sees also Fig. 4.Circuit for detecting 32 comprises resistance R 1, R2, capacitor C 1 and comparator 33.Comparator 33 is the voltage of A, B two nodes relatively, with the conducting time point of decision power switch 31; As for the time point of closing of power switch 31, then for example can whether arrive default value and decide (interlock circuit is not shown) according to primary side current Ipri.Comparator 33 receives one and enables signal EN, and the operation that only when power switch 31 is closed, just is enabled does not then temporarily act on when power switch 31 conductings.

See also the oscillogram of Fig. 4 and map 5, under power switch 31 closing state, secondary side winding is to output capacitor Cout charging, when the electric current I sec of secondary side near zero the time, the voltage that primary side A is ordered descends rapidly.But resistance R 1 causes pressure drop and resistance R 2 to postpone with the RC parallel circuits generation time that capacitor C 1 is constituted, so the voltage magnitude of Node B is lower and the reaction is slower, produces a crossover point X between the voltage of node A, B.According to this crossover point X, comparator 33 can provide the signal of correspondence to ON-OFF control circuit 35, with the conducting time point of power controlling switch 31.

See also Fig. 6; Generally speaking; Because the A voltage of order descends very rapidly, thus the generation time point of crossover point X be usually secondary side current Isec near or null time point, but if ability conducting power switch 31 will confirm fully that secondary side current Isec is zero the time; Delay circuit 36 can as shown in the figurely be set in charger control circuit 30; Its objective is the conducting time point of delaying power switch 31, make it after crossover point X, postpone just conducting of a period of time, so can guarantee secondary side winding discharge off fully.Delay circuit 36 is not limited to be arranged on the position of icon, also can be arranged on prime or other position of ON-OFF control circuit 35.

As consider voltage that A orders maybe be too high or the magnitude of current maybe be excessive, then comparator 33 might not be its input with the A point voltage directly, and can be as shown in Figure 7, gets the dividing potential drop that A orders and compares judgement, its effect is also identical.

Below to preferred embodiment the present invention being described, is the above, be merely to make those skilled in the art be easy to understand content of the present invention, and be not to be used for limiting interest field of the present invention; To those skilled in the art, when can in spirit of the present invention, thinking immediately and various equivalence variation.For example, the present invention is not limited to and is applied in the flash of light capacitor charger, also can be applicable to any type of charger.And for example, circuit or element that icon is represented with independent calcspar, can be with other circuit integrated or disassemble circuit or element (for example ON-OFF control circuit 35 can be integrated into single circuit with delay circuit 36) for separating.So all equalizations of doing according to notion of the present invention and spirit change or modify, and all should be included in the scope of claims of the present invention.

Claims

1. charger control circuit, this charger is charged to an output through a transformer by an input, and this transformer comprises first side winding and secondary side winding, it is characterized in that, and said charger control circuit comprises:

The power switch that is electrically connected with this first side winding;

Control the ON-OFF control circuit of this power switch operation; And

Circuit for detecting; When this power switch is closed; According to the voltage of one node between this power switch and this first side winding, produce the signal after step-down and time postpone, and the signal after this node voltage and this process step-down and the time delay is compared; Produce signal and be supplied to this ON-OFF control circuit, to control the operation conducting time point of this power switch in one-period.

2. charger control circuit as claimed in claim 1 wherein, also includes a delay circuit, to postpone the conducting time point of this power switch.

3. charger control circuit as claimed in claim 1, wherein, this circuit for detecting comprises:

One RC parallel circuits; And

One comparator, one input end receives the voltage signal relevant with this RC parallel circuits, and another input receives the voltage signal relevant with this node.

4. charger control circuit as claimed in claim 3, wherein, this circuit for detecting also comprises: the bleeder circuit that is electrically connected with said node, and another input of this comparator receives the dividing potential drop that this bleeder circuit produced.

5. charger control circuit as claimed in claim 3, wherein, this comparator receives one and enables signal.

6. charger control circuit as claimed in claim 5, wherein, this enables signal and when this power switch is closed, enables this comparator.

7. charger control method, in order to control one have a transformer charger, this transformer comprises first side winding and secondary side winding, it is characterized in that, said charger control method comprises:

One power switch is provided, is electrically connected with this first side winding;

When this power switch is closed, detect the voltage of one node between this power switch and this first side winding, obtain first signal relevant with this node voltage;

Reduce the amplitude of this first signal and postpone this first signal, to obtain second signal;

Detect the crossover point of this first and second signal; And

According to the detecting result, control the operation conducting time point of this power switch in one-period.

8. charger control method as claimed in claim 7, wherein, the step of this power controlling switching manipulation also comprises: the conducting time point that postpones this power switch.

9. charger control method as claimed in claim 7, wherein, this first signal is the dividing potential drop of this node voltage.

10. charger control method as claimed in claim 7, wherein, the step of this detecting crossover point is only carried out when this power switch is closed.