JPH0274157A - Switching power supply - Google Patents

Abstract

PURPOSE:To prevent generation of a solder crack due to the low-frequency temperature change of a metal board by placing a thyristor and a surge absorbing circuit on the same metal printed board and by constituting a chip resistance on the metal board by means of combination. CONSTITUTION:A rush current prevention circuit 4, a switching circuit 8, resistances 12, 12', 13 being accessory circuits of said circuits, and a capacitor 7 are placed on the same metal board block 9. A rectifier circuit 3, a control circuit 10, a transformer 11, and a rectifier and smoothing circuit 14 are provided separately from said metal board block 9. Said resistances 12, 12', 13 are constituted by combination of a 3.2X1.6mm chip resistance thereto according to the consumed power of each of said resistances. Thus, a fatigue life for a soldered connection is lengthened.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a switching power supply device used as a power source for various electronic devices.

2. Description of the Related Art A conventional switching regulator in which a thyristor, a surge absorption circuit, a switching element, and their associated circuit components are mounted on the same board on which printed wiring is printed has the configuration shown in FIG. That is, in FIG. 4, 1.2 receives an AC voltage at an input terminal. 3 is a rectifier circuit, and 3' is a smoothing capacitor that rectifies the AC voltage, smoothes the ripple current, and converts it into DC. Reference numeral 4 denotes a rush current prevention circuit, which suppresses the rush current generated to charge the smoothing capacitor 3' when starting circuit operation. 6 is a starting resistor that starts the control circuit 10. The resistor 6 and the capacitor 7 are a surge absorption circuit that absorbs the surge voltage generated between the primary winding Np of the switching transformer 11. The switching circuit 8 is a control circuit 10
converts direct current into high-frequency alternating current using signals from the Reference numeral 9 denotes a metal substrate block in which an inrush current prevention circuit 4, a starting resistor, a resistor 6 of a surge absorption circuit, a capacitor 7, and a switching circuit 8 are mounted as one block on a metal substrate on which printed wiring is printed.

Usually, chip resistors are used as the starting resistor 6 and the resistor 6 of the surge absorption circuit, depending on the power consumption of each.
40v, output 1oow Krasnosinoching power supply,
Starting resistor 6 is O, SW (5, OX 2.5 fl)
chip resistors are used, and the resistor 6 of the surge absorption circuit is 1
Two chip resistors of W(θ, 3×3.16 mg) are used.

Next, the operation of the conventional example will be explained. In FIG. 4, when an alternating current voltage is received at input terminals 1 and 2, the rectifier circuit 3 and smoothing capacitor 3' rectify the alternating voltage, smooth the pulsating current, and convert it into direct current.

At this time, the inrush power supply immediately before starting the circuit operation is limited by the inrush current prevention circuit 4. When the DC voltage generated across the smoothing capacitor 3' exceeds a certain specified value, the control circuit 1o starts operating through the starting resistor 5 and generates a signal for operating the switching circuit 8. When the switching circuit 8 starts operating in response to this signal, the DC voltage is converted into a high frequency AC voltage. The converted high-frequency AC voltage is applied to the rectifying and smoothing circuit 14 on the secondary side via the switching transformer 11 to generate a DC voltage at the output. On the other hand, the parts mounted on the metal substrate, including the switching circuit 8, generate significant heat, and this heat is radiated to the outside through the metal substrate of the metal substrate block 9.

Problems to be Solved by the Invention In the conventional circuits described above, the linear expansion coefficients of the ceramic material of the chip resistor and the metal substrate are different. Repeated stress is applied to the connection parts, causing solder cracks and shortening the lifespan. In addition, in order to ensure longevity, it is necessary to reduce the low frequency temperature change ΔTc of the metal substrate during actual operation.
had to be kept small, leading to larger parts and higher costs.

The present invention has been made in view of these points, and aims to improve the short life caused by solder cracks, and to reduce the size and cost of parts.

Means for Solving the Problems In order to solve the above problems, the present invention mounts a thyristor, a surge absorption circuit, and their attached parts on the same metal substrate on which printed wiring is printed, and a chip resistor on the metal substrate. is 3.2X1.6. A plurality of chip resistors are combined into the same circuit section.

Effects With the above structure, chip resistance against low-frequency temperature changes of the metal substrate and short life due to solder cracks occurring at the solder connection portion of the metal substrate can be improved.

Example Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows an embodiment of the switching power supply device of the present invention. 1 and 2 are input terminals, 3 is a rectifier circuit, 3' is a smoothing capacitor, 4 is an inrush current prevention circuit, 10 is a control circuit, 1
1 is the switching transformer, Np is the primary winding of the switching transformer, 13 is the starting resistor, 12.12', 7 is the resistor and capacitor of the surge absorption circuit, 8 is the switching circuit, 14 is the rectifier smoothing circuit, 9 is the rush current Prevention circuit 4 and starting resistor 13. Resistor 12 and capacitor 7 of surge absorption circuit
This is an aluminum substrate block in which the switching circuit 8 is mounted as one block on an aluminum substrate on which printed wiring is printed.

The starting resistor 13 and the resistors 12 and 12' of the surge absorption circuit are constructed by combining a plurality of chip resistors (V4W) each having a size of 3.2 x 1.6 m depending on the respective power consumptions.

In the example in Figure 1, the starting resistance is 3.2w x 1 for 0.6W.
．． Two 6111+chip resistors and eight resistors 12 of the surge absorption circuit for 2W are constructed.

The circuit operation is the same as that of the conventional example, so a description thereof will be omitted.

A test was conducted on the lifespan of the above circuit due to solder cracks at the solder joint between the aluminum substrate and the chip resistor due to low frequency temperature changes. As shown in Figure 2, the test conditions were to repeatedly turn on the switching power supply for 4 minutes and turn it off for 2 minutes, and to reduce the temperature ΔT on the back side of the aluminum substrate.
This was done by varying c. The test results are shown in Figure 3.

Next, we will discuss the life estimation formula for solder cranks.

Fatigue of minute solder connections occurs repeatedly due to relative displacement between the chip and the board due to temperature changes during use, resulting in high-temperature, low-cycle fatigue accompanied by plastic deformation. Such low cycle fatigue is explained by Coffin-Manso 7, who states that the fatigue life Nf depends on the plastic strain amplitude Δε.
It is known that the empirical formula for (on) holds well.

Fatigue life Nf=K (Δεp)−〇 ・・・・・・
-(1) Here, n is a constant.

Considering the effects of the frequency f and the maximum temperature "m&X" on the crack growth rate, equation (1) becomes the following equation.

N,=Of'(Δεp)exp(E/KT!Ila
-····−(2) Here, C1λ, n is a constant, K is activation energy, and X is Boltzmann's constant. Each constant has been determined for various metal materials. First, regarding the influence of frequency r, nickel (ICckθ1), bone (Go
hn), Kllis and Norris (No.
Based on the results of fatigue tests conducted independently on lead alloys, the constant λ was determined to be approximately equal to λ. The effect of maximum temperature on fatigue failure was determined by the Southern Research Institute (So
uthern Re5earch Institute
), the activation energy E is 0.123
Combining the results obtained for θV of 0 or more, the fatigue life formula for soldered joints is: Nf - Of new Δεp) - "eXp (0,123 (eV)
/KTmax...((9)).

The MIN value in FIG. 3 will be analyzed.

The fatigue life of the above equation (1) is determined by the temperature ΔT of the aluminum substrate.
When written as a function of c, it becomes as follows.

Nf=K(Δtp)−K((α224)−”・
ΔTc−” −−−−−−(41 Also, formula (2) is Nf=Of”((α2α2)l/2)−”・ΔTc−
"eXp""may'... (@) where αtsu is the coefficient of linear expansion of the aluminum substrate, C
2 represents the coefficient of linear expansion of the chip resistor (alumina base), and l represents the length of the chip resistor.

The MIN value in FIG. 3 is calculated by formula (4) since the three plots are almost on a straight line on the logarithmic graph.

(It is clear that the four equations hold true. From its slope, n
You can know 3.6. IC=0.1236V;
Proceed with the analysis based on the starting point.

N = Of” ((a + −(Z!) l/2
)-”ΔTa-”exp(0-123(6V) Z
KTII&! ) ・・・・・・(@(6)
Find C by substituting the conditions and results into the equation.

When ΔTO = 80'C Nf = 10700 cycles When ΔTc = 70'C Nf = 6400 cycles When Δτo = 1oooC Nf = 1685 cycles f = 2.778 x 10-'H1 (period 6 minutes), fIA =0.1406, Tm1L! = 100'
C=373°K, K=1.3806X10-2'
J/'K 115V==1.8 X 10-"J
a = τ 2-4 X 10 / ℃az -0-7X 10
/ 'C, l = 3.2 heads Therefore, to find C at each temperature, ΔTc = eo
At °C C=1.540X10-'ΔTO=70
At ℃ C=1.804X10-7ΔTC=100"
When O, 0 = 1.525 x 10-', G almost matches, and on average C = 1.556 x 10
becomes.

Therefore, it is proven that the hypothesis holds true, and the experimental formula to be obtained is N(=1.558
) l/2 )-36ΔTc-eXp(0,123/K
T,,,) -・-・-(8).

The design standard for ΔTc is determined by the above equation (8) and the application. Table 1 shows the size of the chip resistor and the allowable ΔTc for each application (facsimile, PPO, personal computer) (because the required Nf differs depending on the application).

When using the above cloth 1 and chip resistance of %W (3.2X 1.6cm), the operating temperature range (allowable ΔTc) is 1
Approximately 100% increase in W (6.3 x 3.1 elB).

Approximately 60% increase in IW (sX2.5m).

In addition, Table 2 shows the ratio of lifespan calculated using Formula 81.

Effects of the Invention As described above, according to the present invention, the chip resistance against low frequency temperature changes and the short life caused by solder cracks that occur in the solder connection part of the metal substrate are improved, and the short life caused by solder cracks that occur in the solder connection part of the metal substrate is improved, and the short life is improved in actual operation to ensure the life. It is extremely useful because it can increase the temperature change ΔTc of the frequency, and it can reduce the size and cost of parts.

[Brief explanation of the drawing]

Fig. 1 is a circuit configuration diagram of a metal substrate block of a switching power supply according to an embodiment of the present invention, Fig. 2 is a life test condition diagram, Fig. 3 is a characteristic diagram showing test results, and Fig. 4 is a conventional metal board block diagram. FIG. 2 is a circuit configuration diagram of a switching power supply device including a substrate block. 3... Rectifier circuit, 3'... Smoothing capacitor, 4... Inrush current prevention circuit, 6, 13...
...Starting resistance, 6.12... Resistance of surge absorption circuit, 7... Capacitor of surge absorption circuit, 8... Switching circuit, 9... ...Metal board block, 1o...Control circuit, 11...
... Switching transformer, Np ... Primary winding of switching transformer, ΔTc ... Temperature change of metal substrate. Name of agent: Patent attorney Shigetaka Awano and one other person 1.
2- 3゛- 8-... 7 "- 10=- 11... i Metal stem lock 11 wholesale circuit suite - y + Njitrasoz ATC - gold yen & It bale's two-part change I Tc (dey) 3-゛. Hosho Day 2 Ki t!J Miku (05W, 5.0 w 2.rmm against +1r)
7゛8-・? -・11...! 4゛Np... Surge collection circuit conversion/+ Sojida bribe money lLt rice lock system fIJ circuit switch + link transformer! [EfllL”Fl EI31! Switching Lance’s Primary Encyclopedia

Claims (1)

[Claims] It is composed of a primary side circuit including at least an input rectifying circuit, a control circuit, and a switching circuit, a switching transformer, and a secondary rectifying and smoothing circuit with an AC power input as input, and the primary side circuit including the switching circuit is connected to the positive side of the input rectifying circuit. Connect one end of the inrush current prevention circuit to the terminal, connect the other end of the inrush current prevention circuit and one end of the surge absorption circuit to the connection point of the anode of the smoothing capacitor and one end of the switching transformer primary winding, and The other end of the primary winding, the other end of the surge absorption circuit, and the cathode of the smoothing capacitor are connected to the switching circuit, and the above-mentioned inrush current prevention circuit, surge absorption circuit, switching circuit, and their attached circuit components are connected by printed wiring. It is mounted on the same printed metal substrate, and the chip resistance on the metal substrate is 3.2×1.6.
A switching power supply device that combines multiple mm chip resistors in the same circuit section.