Phone

    00852-6915 1330
  • Contents

Introduction

The LM2576 series of monolithic integrated circuits provide all the active functions for a step-down (buck) switching regulator. LM2576 series are capable of driving a 3A load with excellent line and load regulation. The regulators are simple to use because they require a minimum number of external components and include internal frequency compensation and a fixed-frequency oscillator.

Catalog

Introduction

Catalog

I Voltage Stabilizing Circuit

II Buck Circuit

III Current Boost Circuit

FAQ

Ordering & Quantity

I Voltage Stabilizing Circuit

The basic voltage stabilizing circuit composed of LM2576  only needs four peripheral devices, and its circuit is shown in Figure 1. The selection of inductance L1 depends on the output voltage, maximum input voltage, and maximum load current of LM2576

First, the electric voltage microsecond constant (E·T) can be calculated according to the following formula:

E·T=(Vin - Vout)&TImes;Vout/ Vin&TImes;1000/f (1)

Vin is the maximum input voltage of LM2576; Vout is the output voltage of LM2576; f is the operating oscillation frequency value of LM2576  (52khz).

Figure 1. Voltage Stabilizing Circuit

Generally, the input capacitance  Cin in the circuit should be greater than or equal to 100 μF. when installing, it is required to be close to the input pin of lm2576 as far as possible, and its withstand voltage value should match the maximum input voltage value.

The value of the output capacitor Cout (unit μF) should be calculated according to the following formula:

C≥13300 Vin/ Vout&TImes;L (2)

Vin is the maximum input voltage of LM2576; Vout is the output voltage of LM2576; L (unit μH) is the value of inductance L1. The withstand voltage value of capacitor C should be 1.5 ~ 2 times of rated output voltage. For 5V voltage output, it is recommended to use a capacitor with a voltage withstand value of 16V.

The rated current of diode D1 should be 1.2 times the maximum load current. Considering the state of the short circuit and load, the rated current of the diode should be greater than the maximum current limit of LM2576. The reverse voltage  of the diode should be greater than 1.25 times the maximum input voltage,  The selection of Vin should consider the input voltage  value of LM2576  corresponding to the lowest AC voltage drop (Vac-min) and the minimum input allowable voltage value Vmin of  LM2576,  Therefore, Vin can be calculated according to the following formula:

Vin≥(220Vmin/Vac-min)

If the minimum allowable AC voltage drop is 30% (Vac-min=154V) and the voltage output of the LM2576  is 5V (Vmin=8V), when Vac=220V, the input DC voltage of the LM2576  should be greater than 11.5V, usually 12V.

II Buck Circuit

The buck circuit composed of LM2576 is shown in Figure 2. The output voltage is divided and sampled by R1 and R2, and then sent to the positive input end of the subtractor. The negative terminal is connected to VSET. The VSET signal is the voltage signal given by the microcontroller. The error signal is obtained by the output sample voltage subtracting the D/A conversion voltage. Then add the error signal to the reference voltage (VREF) 1.23V, and send this result to the feedback terminal of LM2576.

Figure 2. Buck Circuit

Compared with traditional direct feedback, the feedback loop in this design is more complicated. This design is mainly due to the following considerations: First, it is easy to control single-chip microcomputer. As long as the output voltage of D/A conversion is changed, the feedback loop works, and the output sampling voltage is automatically approached to the D/A conversion voltage.  Then the voltage adjustment process is complete. Second, it can meet the design requirements of zero voltage output. If simply use the feedback pin of the LM2576.  The minimum output of the reference circuit given in the manual can only reach 1.25V, so you need to "shift" the feedback voltage to a VREF reference voltage level.

The voltage divided by the feedback resistor is also sent to the DAC  of the microcontroller.

III Current Boost Circuit

(a) Fixed output type; (b) adjustable output type

Figure 3. Current Boost Circuit


FAQ

  • Where is LM2576 used?

LM2576 is usually used as a voltage stabilizing device when the input and output voltage difference is large and the output current is also large. Because it is a switching regulator, it has a higher conversion efficiency and low heat generation than a linear regulator.

  • Whats the difference between LM2576T-ADJ and LM2576S-ADJ?

LM2576T-ADJ is the package of TO-220, LM2576S-ADJ is the package of TO-263-5, there is no difference in their functions.

  • What is the difference between LM2940 and LM2576? Which circuit are they applicable to?

LM2940 is a low-dropout linear stabilized integrated circuit. The linear stabilized power supply is characterized by a relatively simple circuit, high precision, and small ripple coefficient. It is suitable for precision power supplies with high voltage requirements. The disadvantage is that the efficiency is very low and the output The current is relatively small (relative to the switching power supply)

LM2576 is a switching power supply integrated circuit. Switching power supply, the circuit is more complicated, but the output current is large, the efficiency is high, the disadvantage is that the accuracy is lower and the ripple coefficient is larger.

  • Why do switching power supply chips LM2576 and LM2596 have diodes, inductors and capacitors behind the output pins?

The function of the diode and the inductance is that the output current can be continuous when the LM25XX is in the off state, and the function of the capacitor is to prevent the output voltage from sudden changes when the LM25XX is turned on and off. In fact, it is filtering.

  • Why the higher the switching frequency of LM2576 and LM2596, the smaller the output inductance and capacitance value?

Quite simply, the capacitive reactance of a capacitor decreases as the frequency increases, and the inductance of an inductor increases as the frequency increases. That is to say, the effect of using an inductance of 33uH in the case of 150Khz is basically the same as the effect of using an inductance of 100uH in the case of 52khz, and the principle of capacitance is the same. LM2596 is an upgraded version of LM2576. But LM2576 also has the advantage of less switching loss and less interference.

Kynix

Kynix was founded in 2008, specializing in the electronic components distribution business. We adhere to honesty and ethics as our business philosophy and have gradually established an excellent reputation and credibility in our international business. With the accurate quotation, excellent credit, reasonable price, reliable quality, fast delivery, and authentic service, we have won the praise of the majority of customers.

Join our mailing list!

Be the first to know about new products, special offers, and more.

Leave a Reply

We'd love to hear from you! Feel free to share your thoughts and comments below. Rest assured, your email address will remain private.

Name *
Email *
Captcha *
Rating:

Kynix

  • How to purchase

  • Order
  • Search & Inquiry
  • Shipping & Tracking
  • Payment Methods
  • Contact Us

  • Tel: 00852-6915 1330
  • Email: info@kynix.com
  • Follow Us

authentication

Kynix

© 2008-2026 kynix.com all rights reserved.