The block that analyses electronic circuit allows step-down circuit

April 26, 2018 admin Comments 0 Comment

[introduction] do you want to understand circuit graph what to function there is? What kind of is still the block in circuit graph allows step-down circuit? the block in introducing circuit graph and electronic circuit contains step-down circuit the article.

Circuit graph:

The block that analyses electronic circuit allows step-down circuit

Circuit graph function:

Circuit of block look step-down is a very classical and practical circuit, apply extensively at LED lamp, small home appliance, ammeter, the domain such as intelligent control.

Principle of circuit graph job:

Block look step-down is to use the capacitive reactance of capacitance to restrict electric current, achieve the goal of step-down thereby.

The characteristic that circuit pursues:

1, low cost 2, the design is simple 3, volume is minor

Circuit principle graph analyses:

This exemple is a kind of form with the commonnest circuit of block look step-down: Block allows step-down + half commutate + capacitance filter wave + stabilized voltage.

In circuit, f1 is fuse, had offerred shed protection; R5 is pressure quick resistor, provide surge protection. C2 is to bring compasses electric capacity, to communicate filter wave capacitance. These 3 component matter to the safety of laden circuit and electromagnetism compatibility directly, and this must undertake selling through relevant attestation ability. Capacitance C1 is step-down capacitance, polyester of commonly used CL21 or CBB21 polypropylene capacitance, although the price is high but performance is good.

Alternating current crosses the formula of capacitive reactance computation of capacitance to be Rc=1/(2Π*fC) , here F is mains frequency =50Hz, c is the look value of C1.

Can calculate from this the capacitive reactance that gives electric capacity, reach thereby corresponding electric current. Using actually in the center, the frequency of the voltage of electrified wire netting and electrified wire netting is fluctuant, when be being designed so, the size of capacitance must stay enough surplus will handle worst case, make sure circuit won’t appear unusual with attaint. And in take superabundant amount while, also want to notice the power comsumption of whole circuit, and capacitance capacity also cannot too big.

Resistor R1 is the discharge resistor of C1, place inserting quickly unplug the leftover voltage on capacitance of the C1 when power source outlet or plug contact are undesirable and overlay of voltage of electrified wire netting are formed to follow-up parts of an apparatus high pressure is pounded and prevent to pull out human body of the bring into contact with after power source outlet produces harm to personnel, so constant of this R1C1 time is below good position ≤T (T=1/F, f=50Hz) , but using actually in the center R1 cannot be taken too small, otherwise R1 power comsumption is too big, general we take ≤300mS of RC time constant, notice the compression of this resistor even additionally, compression of our commonly used resistor of 0.25W carbon film is 500V, compression of resistor of 0.5W carbon film is 700V, specific and OK the function manual of referenced resistor manufacturer.

In the limit of of the R2 in circuit, R3 sheds resistor; These two resistor basically are to prevent first electrify and the attaint that inserting the high pressure that unplugs the place when power source outlet or plug contact are undesirable arises to pound pair of rectification diode quickly, capacitance C1 is in first if electrify just is touched be in in wave crest, because C2 assumes short circuit position in electrify instant, right now alternating current source is added on R2, R3 and rectification canal directly, there is 220VAC×1.414=311VDC instant volts d.c. on R2, R3; Capacitance C1 is being inserted quickly unplug when power source outlet or plug contact are undesirable, if capacitance C1 is in place of N+1 wave crest to cut off the power, electrify is in in N+2 wave crest, capacitance C2 arrives in N+1 inside N+2 time dropt ⊿ V (by C2, r1 decides) , there is 220VAC×1.414+ on R2, R3 right now (220VAC×1.414- ⊿ V) volts d.c. of instant of =622VDC- ⊿ V, if consider the wave motion of voltage of electrified wire netting, this voltage will be taller, so R2, r3 should choose to be able to bear or endure voltaic concussion is mixed by force be able to bear or endure high-pressured resistor, choose resistor of high-power oxidation film or golden film resistor commonly, total resistor of R2, R3 cannot too small, also cannot too big, resistance is too little impulse current is big, power comsumption of too big whole circuit increases resistance, the peak value electric current of rectification diode can be compared commonly big, if electric current of 1N400X series peak value is 200A, take R2, R3 commonly so between total resistor =40-50Ω .

The D1 in circuit is rectification diode, but can carry alternating current only as a result of capacitance C1, after passing D1 commutate, capacitance can have flowed only half weeks of one-way electric current, circuit cannot guide continuously, still need the voltaic return that construction enjoys half weeks so, d3 has this effect.

C2, C4 comprises wave of filter of the first class, highest frequency, C1, D2, R4 concerns the compression value that what the attention wants here is capacitance of C2, C4 and highest voltage of electrified wire netting, electrified wire netting, if this product is highest,working voltage is 242VAC, electrified wire netting is highest frequency is 53Hz, criterion C2, ≈(242VAC×1.414)/ of C4 highest compression (1/2ΠFC2) ×R4+5.1≈22.2VDC, so C2, C4 chooses the product of compression ≥25VDC, r4, C3, C5 comprises wave of filter of RC of the 2nd class at the same time stability of D2 general voltage is on 5.1VDC, the size of R4 decided the ripple bulk that the product leaves in low job voltage, r5 is discharge resistor, the action of R5 is above all inserting quickly unplug be in when power source outlet or plug contact are undesirable cut off the power to discharge to filter wave capacitance for an instant, in order to make the impulse current when electrify instant goes from the coupling on capacitance, prevent impulse current to be added to stabilized voltage diode to cause damage of stabilized voltage diode, consider from this bit at the same time, must put stabilized voltage diode at the back of C5 of filter wave capacitance, C6 when handling PCB wiring, the effect of the parasitism inductance that prevents PCB Copper Foil to go up and Copper Foil resistance to filter wave.

Attention:

This exemple is very common and a practical circuit, after understanding its job principle, the key that leave depends on computation namely. Want the voltage value of output according to you, will calculate with how old resistor capacitance. When making this circuit actually, the input is town report, want to notice security.

F1 is fuse