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    Abstract: Introduced the monolithic switching power supply chip TOPSwitch structure and the principle of work, have given the ultra width input isolated-type constant voltage switching power supply’s complete application electric circuit example, and to designed some matters needing attention has carried on the explanation with the manufacture process.

    Key word: Isolation; Wide input; Switching power supply

Introduction

The switching power supply (SwitchingPowerSupply) since being published, by its stable, highly effective, the energy conservation and so on fine performance has become voltage-stabilized source’s main product. But because the integrated monolithic switching power supply, is highly its high performance-to-price ratio, the simple peripheral circuit, the small volume and the weight and the non-power frequency transformer isolates superiority and so on way to become in voltage-stabilized source’s outstanding person. Along with each kind of different monolithic switching power supply chip and the electric circuit analysis situs’s application and the promotion, the monolithic switching power supply manifests the huge use value and the magnificent prospect more and more. But, the TOPSwitch usual permission’s input voltage range of variation is 120~370V, this article attempts manufactures the wider input voltage range of variation with it (80~550V) the voltage-stabilized source. The experimental result proof is very successful.

Figure 1

1 chip architecture and constant voltage principle

For the past several years, the American Power source Integration Company (PI), Motorola Corporation (Motorola), the Italian - law semiconductor company (SGS-Thomson), American Onsemi Corporation and so on one after another has promoted TOPSwitch, MC, L4970, NCP1000 and so on different series monolithic switching power supply product. As a result of the TOPSwitch serial products stable property, the price is materially beneficial, therefore this article chose this series one kind of chip to manufacture one kind of input range extremely wide voltage-stabilized source for the core design. This mains input DC voltage scope is 80~550V, output DC voltage 20V, output 20W.

No matter TOPSwitch is three foot seals, DIP8 or the SMB8 seal, its essence is three end components, respectively carries C(Control), source S(Source), drain electrode D(Drain) be the control. The control end’s leading role is, according to its electricity? Ic from moves the adjustment dutyfactor, when Ic change, the dutyfactor based on this changes. Source S and the chip interior power MOS tube source is connected, and as primary circuit public. Drain electrode D and the chip interior power MOS tube’s drain electrode is connected.

TOPSwitch mainly includes the control potential source, the high-pressured current supply, the shutdown/to restart the dynamic electricity road, the parallel adjuster/error amplifier, the band gap datum potential source, the overheated protection and the previous electricity reset circuit, the overflow protection circuit, the oscillator, the PDM keyer, the gate actuation level and the output stage automatically and so on 10 parts. Its internal structure diagram as shown in Figure 1.

Figure 2

    The TOPSwitch fixed turn-on frequency is 100kHz, permission operating region 90~110kHz.

The TOPSwitch constant voltage principle is (i.e. control end electric current) Ic from moves the adjustment dutyfactor through the feedback electric current, thus realizes the constant voltage. For example, when output voltage rise, the feedback electric current along with it rise, the dutyfactor assumes the reverse change to drop, causes the output voltage also along with it drop, thus guarantee output voltage stability. Vice versa.

2 circuit diagrams and principles of work

By TOPSwitch constitution’s monolithic switching power supply as shown in Figure 2, is the typical single end instead stirs up-like the switching power supply.

Figure 2 T is three winding high-frequency transformers, the operating frequency is 100kHz. 3 windings respectively are: Np primary side winding (65 circles); Ns vice-side winding (i.e. output winding, 13 circles); Nf feedback winding (8 circles); The various windings end of the same name has sectioned out in Figure 2. In the transformer the energy transfer process is: When in TOPSwitch power MOSFET breakover, transformer primary side winding cumulative energy; When power MOSFET shutdown, in the primary side winding stores up energy transfer for vice-side winding and feedback winding, after high frequency rectification filter then provides the direct-current output voltage and the feedback voltage.

Figure 3, 4, 5

    DZ1, D1 and R1, C2 have composed the drain electrode clamping circuit and the energy absorption return route, with limits the TOPSwitch drain electrode the peak voltage which possibly produces because of high-frequency transformer’s leakage inductance. DZ1 selects the P6KE200A transient voltage blanker (TVS), its back breakdown voltage is 200V. D1 selects MUR160 ultra-fast to restore the diode, its most greatly reverse pressure resistance value is 600V. Because TOPSwitch leaks - the source smallest breakdown voltage is 700V, but works as when its power MOSFET shutdown, the transformer primary side’s cocurrent input voltage, the primary side winding’s induced tension as well as the peak voltage which produces by transformer’s leakage inductance, three fold puts together, its value possibly surpasses 700V, must therefore increase the clamping circuit and the absorbing circuit in the TOPSwitch drain electrode, with protects power MOSFET not to damage.

C3 is the TOPSwitch control end shunt capacitor, its function is carries on the compensation to the control circuit, and can establish restarts automatically moves the frequency. In the electric circuit will choose the parameter value to restart moves the frequency hypothesis will be 1.2Hz automatically.

D2 and D3 are the high frequency output rectification diodes, D2 is MUR420 ultra-fast restores the diode, its most greatly reverse working voltage is 200V, the fixed commutated current is 4A; D3 is the 1N4148 Bolivia seals the high-speed switch diode, its most greatly reverse working voltage 75V, average commutated current 150mA.

L1 is the filter inductance, its value approximately for 20μH, is made by the crystalless alloy magnetic material puts on the heart inductance, the popular name “magnetism bead”. Its function is filters D2 the switch noise which produces in the reverse recovery procedure.

DZ2 and DZ3 are the stabilovolt, the model are 2CW346. IC2 is the linear optical coupler, the model is PC817A, its internal light emitter diode’s breakover pressure drop approximately is 1V, running current If approximately is 1~5mA, its direct current transmission ratio is 80%~160%.

Figure 6, 7, 8

    The output voltage by in two stabilovolt voltages, PC817A on light emitter diode’s breakover pressure drop as well as resistance R4 the pressure drop three sums determined, therefore changes R4 the size, can change (fine adjustment) the output voltage setting value, simultaneously can also change control circuit’s gain, namely change control circuit’s enlargement factor. Regarding the different output voltage request, only need change the stabilovolt and the limiting resistor R4 size then. As mentioned above, the output voltage Vo constant voltage process is: Vo↑ (↓) →VR4↑ (↓) →If↑ (↓) →Ic↑ (↓) -> dutyfactor ↓ (↑) →Vo↓ (↑).

3 experimental results

This voltage-stabilized source’s experiment profile like chart 3~ shown in Figure 8. When inputs as shown in Figure 3, when is Vi=80V, output voltage vo as shown in Figure 4 (mean value Vo=19.8V), this time TOPSwitch leaks source voltage vDS profile as shown in Figure 5. When input voltage as shown in Figure 6, when Vi=550V, output voltage vo as shown in Figure 7 (mean value Vo=20.3V), this time TOPSwitch leaks source voltage vDS profile as shown in Figure 8. Empirical datum like table 1 arranges in order. In order to explain that limiting resistor R4 to the output the influence, the output voltage row which presently the different R4 value corresponds in table 2.

Table 1 output voltage and input voltage relational table (R4=400Ω, Po=20W)

Table 2 output voltages and resistance R4 relational table (Vi=200V, Po=20W)

May see from table 1, although this voltage-stabilized source the input range is very wide, but its output voltage’s stability is actually quite high, this regarding certain special application situation is very valuable.

When the actual design, uses this power source, must pay attention to the following item:

1), if the input is the exchange, increases the corresponding rectification, the filter link in the transformer input side. If the non-filter link or the filter effect is too bad, will cause the power source to be unable the normal work;

when 2) circles the system high-frequency transformer, should circle the primary side winding in most in the level, the feedback winding comes, the vice-side winding in most outside, various windings should the uniform distribution, simultaneously between the winding be supposed to use the insulating tape to carry on the insulation;

when 3) welds TOPSwitch, should cause its pin as far as possible short;

4) TOPSwitch and MUR420 must add the radiator.

4 conclusions

This article introduced the wide scope input’s voltage-stabilized source, the structure is simple, the perform reliably, the manufacture cost is inexpensive, moreover the product volume is small, the weight is light, therefore, has the very great use value, also has represented the future power source’s development direction.