The ripple of switch power source is restrained implement use C normally model, LC, CLC passive filter. πModel 3 rank low because its structure is simple,connect CLC filter, volume is minor, advanced advantage got function apply extensively. According to the formula of switch power source, output ripple and value of output electric capacity become inverse ratio, size of wave motion of the electric current inside inductance and inductance value become inverse ratio. Theoretic use nominal the ripple with be worth large electric capacity, inductance to be able to get better restrains the effect. In applying actually, the type differs in CLC circuit electroanalysis capacitance and different and nominal the capacitance of the value, inductance] to power source ripple restrain the effect to after all what kind of influence still points out without relevant article. Accordingly, be necessary to undertake checking actually study to circuit of CLC filter wave.

 

This literary grace designed the small-power switch power source of 12 V with MAX606, use CLC filter outputs ripple to undertake inhibition to power source. Through using different type to electroanalysis capacitance is reached different and nominal the capacitance of the value, inductance, studied the character of CLC filter, got reducing the simple method of ripple of small-power switch power source.

 

1, circuit design

 

MAX606 is converter of DC/DC of type of step up of a small-sized CMOS, its input limits 3 ～ 5.5 V, output secures 5 V/12 V to may move 12.5 V of ～ of output limits Vin, precision is ±4% . The switch frequency of MAX606 is as high as 1 MHz, the electricity that is as high as 180 MA can be provided when 5 V is outputted, apply extensively in camera of PCMCIA card, memory card, number and hand-held instrument.

 

If the graph is shown 1 times,design circuit, the input when the test carries the lithium battery of use 3.6 V to have power supply, useπModel circuit of the low wave that connect filter is opposite CLC MAX606 output end has ripple filter wave.

 

The graph is circuit of CLC filter wave inside casing of 1 dotted line, through changing the relevant parameter of Cin, Cout, L1, study its characteristic to outputting the inhibition of ripple.

 

 

2, πmodel analysis of sex of CLC filter baud

 

Output impedance considering power source, the equivalent circuit that the picture the place in casing of 1 dotted line shows CLC circuit uses a figure 2 express, to facilitate the analysis joined laden RL, RS outputs impedance for power source.

 

 

Graph 2 in the output end that Ui is switch power source, uo arrives for output laden the voltage of two end.

 

2.1Theory of circuit of CLC filter wave is analysed

 

After power source signal inputs two end of C1, the volts d.c. on laden RL is:

 

 

Type (1) make clear join inductance L to will make UL decrescent, affect the laden regulation of power source. If want to make output voltage stability, should choose the inductance parts of an apparatus with little resistance of equivalent series connection, the resistor of equivalent series connection of inductor circles the dc resistor of line of control and guide to decide by its.

 

To output of switch power source, its communicate signal to be basis of signal of power source ripple namely transfer function of circuit of CLC filter wave:

 

 

From type (2) can see, increase along with frequency, ripple attenuation is bigger; Cin, Cout is bigger, ripple attenuation is bigger, accordingly, πmodel CLC filter has certain inhibition to power source ripple. But, type (2) be all be what reach below good case in L, C, did not consider the material of actual inductance capacitance and their parasitism parameter.

 

2.2 real tests are analysed

 

KH-DD of milivoltmeter of number of TDS2022B (200 MHz of oscillograph of test data You Taike, 2 GS/s) , communication (2 MHz) of 10 Hz ～ measures income, laden use ZX21 dc is worth resistor more.

 

The power source when circuit of 2.2.1 the wave that do not have filter outputs ripple weaveform

 

The graph is shown 3 times it is the MAX606 when carrying for nothing to output voltage ripple weaveform (Uo≈12 V) , namely switch ripple, its frequency is 1.18 KHz, weaveform is stable, vpp=240 MV. The graph is shown 4 times for load 120ΩThe ripple that voltage outputs when is undee, from the graph 4 in can see ripple of the power source after joining load becomes more complex, its are highest Vpp achieves 1.2 V. When be systematic power supply, this ripple will cause serious harm to the system, must undertake inhibition to this ripple.

 

2.2.2πModel different type electroanalysises in circuit of CLC filter wave the ripple below capacitance follows laden change

 

In the graph in the circuit of CLC filter wave of 1, cin, Cout uses 3 kinds of common types respectively electroanalysis capacitance (look value is 220 μF/16 V) , inductance uses annular inductance (inductance is worth 120 μH) , size of ordinal change load, use communication milivoltmeter measures virtual value of its ripple voltage, the graph that if the graph is shown 5 times,gets.

 

 

 

 

From the graph 5 curves can see, along with laden block the value increases gradually, virtual value of power source ripple increases quickly first, reduce gradually after, in 160Ω3 kinds of types electroanalysis when capacitance outputs ripple all very low, satisfy the requirement of power source ripple of average system. From the graph 5 still can see integral level go up, common the straight aluminium that insert type electroanalysises capacitance ripple controls capacity the poorest, stick a Tantalum to electroanalysis take second place, stick an aluminium to electroanalysis filter wave effect is optimal. When laden block the value is less than 500ΩWhen, stick an aluminium to electroanalysis filter wave effect is optimal. When laden block the value is more than 500ΩWhen, tantalum electrolytic filter wave effect is first-rate.

 

The graph is shown 6 times be load is 300ΩDifferent type electroanalysises when the ripple that measures below capacitance is undee, can see be sent on a diplomatic mission use apparently stick an aluminium to electroanalysis ripple is the smallest, use common aluminium to electroanalysis ripple is bigger and ripple has burr, use stick a Tantalum to electroanalysis ripple is reduced somewhat and the improvement that burr also has very old rate.

 

 

The graph is shown 7 times for load 120ΩDifferent type electroanalysises when the place below capacitance measures gotten ripple weaveform. Comparative figure 4 can see, throughπModel after CLC filter wave, ripple already was restrained very little scope. From the graph 7 can see, right now tantalum electroanalysises the ripple of capacitance controls capacity best, extent of the burr in ripple weaveform also decrescent.

 

 

The place on put together is narrated, when considering real work, general circuit place needs electric current to all be tens of milliampere, filter wave circuit is recommended to use on integral level stick an aluminium to electroanalysis capacitance. When load very heavy (laden value is little) when, recommend use Tantalum to electroanalysis capacitor.

 

The ripple below value of 2.2.3 different inductance follows laden change

 

Capacitance is fixed (stick a Tantalum to electroanalysis 220 μF/16 V) , the change pursues 1 in the inductance of circuit of CLC filter wave is worth size, measure the virtual value of the ripple when different load, the graph that if the graph is shown 8 times,gets, among them what inductance uses is arched inductance.

 

 

From the graph 8 in can see, along with inductance the value increases, power source ripple is reduced, remove ripple effect to MH class inductance very apparent. When using 1 MH inductance, ripple voltage virtual value only 3 MV, when using 4.7 MH, ripple voltage virtual value can be reduced to 1.8 MV.

 

The graph is shown 9 times it is for load 300ΩDifferent inductance is worth next ripple weaveform to pursue when, from the graph 9 in can see, along with inductance the value increases, ripple is restrained rate is older, output ripple is smaller. When inductance value increases 1 MH, ripple effect is best, and output basically does not have burr.

 

 

The influence of the load below value of 2.2.4 different capacitance to ripple

 

The graph is shown 10 times to be in different capacitance is worth (stick a Tantalum to electroanalysis) below, change inductance and load and measure the graph that the earnings of virtual value of power source ripple on load exceeds.

 

From the graph 10 in can see, control trend general interest along with inductance, laden change ripple identical, the accretion that can see capacitance is lesser to the inhibition of ripple, and ripple virtual value does not increase along with what capacitance is worth and get inhibition, the accretion that inductance is worth has conclusive effect to the inhibition of power source ripple. But, choice capacitance is worth what is appropriate to the occasion to choose the capacitance of 100 μF above, ability can get better ripple restrains the effect.

 

 

 

 

3, summary

 

πModel circuit of CLC filter wave can remove better ripple to restrain the effect in small-power switch power source, electroanalysis through the change the type of capacitance, adjust capacitance value and the volume that inductance is worth, can rise significantly control ripple function. The characteristic analysis that undertakes to circuit of CLC filter wave can be power source of switch of small-power of design high quality to provide reference.