3DD15 and LA6350 make high-power switching regulated power supply

Some high-end electrical appliances, such as computers, communication equipment, and household audio-visual equipment, have higher power requirements. Ordinary regulated power supplies made with ordinary discrete components or three-terminal voltage stabilizing integrated circuits can no longer meet the requirements of these electrical equipment. The regulated power supply produced by the above method is either bulky, or the power is too small, and the protection function is not perfect. Therefore, the power supply of this type of electrical appliances has begun to transition to switching regulated power supply.

The switching voltage stabilizing circuit introduced in this article is a switching voltage stabilizing power supply designed using the LA6350 monolithic high-power switching voltage stabilizing integrated circuit produced by the American Lambda Company. It is not only simple in circuit, easy to debug, and has complete functions, but also requires The radiator has a small area, high output power, and low production cost. It is an ideal circuit for electronic enthusiasts to make switching regulated power supplies.

LA6350 has the following features:

1) The output voltage is continuously adjustable within 2.5-30V;

2) The output current of a single chip can reach 5A;

3) The switching operating frequency is higher than 22kHz;

4) Conversion efficiency is greater than 90%;

5) Working temperature is -55 degrees ~ +125 degrees

6) It has the functions of soft start, overcurrent quick shutdown and overheating protection.

The circuit is shown in the figure. The circuit uses this chip to produce a practical high-power switching regulated power supply with an output current up to 10A and an output voltage adjustable within 5-12V. Its working principle is: 220V AC power is stepped down by transformer T1, rectified by bridge stack VD1, and filtered by C1 and C2 to obtain DC voltage. Pins ① and ② of the IC are DC voltage input terminals, and their maximum input voltage is +40V. This DC voltage is modulated by the oscillator inside the IC to a high-frequency switching voltage of about 200kHz. The switching frequency of the oscillator is determined by the external oscillation capacitor C4. When the value of C4 is 3300pF, the switching frequency of the power supply is about 200kHz; R3 and C6 are the frequency compensation network of the loop adjustment amplifier, which is input by pin 7. The ④ pin of the IC is the suppression input terminal, and its blocking voltage threshold is 0.7V. The output voltage is fed back to the ④ pin through the sampling resistor R2 and then compared with R1. When the threshold voltage is greater than 0.7V, the output is turned off, causing short-circuit overcurrent. Protective effects. Pin 6 is the output voltage adjustment control terminal. The output voltage is divided by the potentiometer RP1 and the resistor R4 to obtain the adjusted voltage detection value. Adjusting the potentiometer RP1 can control the output voltage. The output voltage value can be calculated by the formula: VO=Vref{ 1＋Rh／(RL＋R4)} for estimation. Among them, Vref is the reference voltage, which is 2.1V. Pin 8 is the output terminal, VT is the current amplifier tube, VD2 is the reverse freewheeling diode, and L is the filter inductor.

The IC is a dedicated switching voltage stabilizing integrated circuit LA6350, and its shell is grounded and connected to the radiator. The power of R5 should be greater than 5W. In the IC peripheral circuit, except for the high-frequency capacitor for the oscillation capacitor C4, the resistors R1 and R2 should be high-precision metal film resistors with an allowable deviation of <1%. The other components have no special requirements. You can select small devices according to the parameters in the figure. Since the output voltage is a high-frequency switching type, the heat sink required for the IC and power transistor VT is only one-third of that of an ordinary regulated power supply, and its performance is much higher than that of an ordinary regulated power supply.