LM2596 application circuit diagram Daquan (adjustable / regulated / step-down)

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The lm2596 is a step-down power management monolithic integrated circuit switching voltage regulator that can output 3A of drive current with good linearity and load regulation. The fixed output version is 3.3V, 5V, 12V, and the adjustable version can output various voltages less than 37V.

LM2596 performance parameters

Single-row 5-pin package with a maximum input voltage of 40V and an output voltage of 1.2V to 37V. The switching power supply has two types of packages: fixed voltage output and adjustable output. The output current is up to 3A and the operating frequency is up to 150kHz.

Lm2596 application circuit diagram Daquan (adjustable / regulated / step-down)

LM2596 feet function

1 pin (VIN) is the DC voltage input terminal, the highest value can reach 40V, the lowest value is 4.5V;

The 2-pin (OUTPUT) is the open-circuit output of the switch tube emitter, which is the DC voltage output. The maximum output is 37V and the lowest value is 1.2V.

Pin 3 (GND) is the input and output common terminal, that is, the ground terminal;

The 4 pin (FEEDBACK) is the regulated sampling voltage input terminal. This pin is generally connected to the output voltage, and the output voltage is monitored by the partial voltage network in the IC. When the output voltage increases or decreases, the voltage of the pin increases or decreases proportionally. Compared with the internal reference regulation value of 1.23V, the internal amplifier can automatically adjust the output duty cycle of the oscillator to reduce the output voltage. Or increase. Thereby stabilizing the output voltage at the rated value;

The 5 pin (ONOFF) is the enable control terminal, which controls the presence or absence of the output voltage. When the pin is higher than 1.23V, the internal switch is turned off and the output voltage is OV. When the pin is lower than 1.23V, the output is Rated voltage, in actual use, the foot is generally grounded or placed on a voltage lower than 1.23V by an external component.

Lm2596 application Circuit diagram (1): 3.3V, 5V output power supply circuit diagram

To get the +1.8v output voltage, please use the A picture. To obtain a 3.3V, +5V output voltage, please use the B picture.

Lm2596 application circuit diagram (2)

Lm2596 application circuit diagram (3)

The LM2596 supports adjustable output. When inputting 40V, the output can be continuously adjusted to 0~37V. The typical application circuit is as follows:

Lm2596 application circuit diagram (4)

1.1 System overall block diagram

According to the system design requirements, the uninterruptible DC power supply has: uninterrupted power supply to the device when there is no AC power; when the AC power is normal, there are two modes of constant voltage charging and constant current charging; comprehensive design requirements, forming a system block diagram as shown in the figure 1 is shown.

 

1.2 Selection of DC-DC converter scheme

Using the switching voltage regulator LM2596, it can output 3 A of driving current, and has good linearity and load regulation characteristics. It can fix output voltages of 3.3 V, 5 V, and 12 V, and can also achieve 1.2 to 37 V. Adjustable output between.

The device integrates a frequency compensation and fixed frequency generator with a switching frequency of 150 kHz. Compared to low frequency switching regulators, smaller filter components can be used. Since the device requires only four external components, a common standard inductor can be used, which simplifies the use of the LM2596 and greatly simplifies the design of the switching power supply circuit. Under the conditions of specific input voltage and output load, the error of the output voltage can be guaranteed within ±4%, and the oscillation frequency error is within ±15%. External power -down can be achieved with a standby current of only 80 μA; it has a self- protection circuit (a two-stage down-conversion current limit protection and an over-temperature full protection circuit that is powered down in an abnormal situation ).

The DC-DC converter circuit is shown in Figure 2.

1.3 Constant voltage charging circuit design

The constant voltage charging circuit is shown in Figure 3. The circuit consists of an op amp LM324 and a three-terminal regulator W117. The LM324 is connected as a voltage follower with an output voltage U1 = U- = U+ = UX. It can be seen that the output voltage can be changed by adjusting the middle tap of resistor R2. Due to the presence of the op amp, the output voltage is adjusted very smoothly.

1.4 Voltage Control Constant Current Charging Circuit Design

The circuit principle is shown in Figure 4. The constant current source circuit is composed of an operational amplifier LM324, a field effect transistor IRF640, a sampling resistor R3, a load resistor RL, and the like.

The circuit uses a high-power FET IRF640 as an adjustment tube. The tube is an N-channel enhancement MOS transistor. The tube operates up to 100 V, has a saturated drain current of 28 A, and consumes approximately 150 W. When the effect transistor is operating in the saturation region, the drain current Id is approximately the current controlled by the voltage Ugs. That is, when Ud is a constant, it satisfies: Id = f (Ugs), and as long as Ugs is unchanged, Id does not change.

In this circuit, R2 is the sampling resistance of the constantan wire material (the resistance changes little with temperature). OP07 acts as a voltage follower with U+ = U - = Us. Since the gate current is negligible, Id = Is = I2 = Us R2 = U+ R2. Just because Id = U+ R2, the circuit input voltage U+ controls the current Id. That is, Id does not change with the change of RL, thereby achieving voltage-controlled constant current. The parameter charging current in Figure 4 is 200 mA. To change the charging current, simply adjust R2.

Lm2596 application circuit diagram (5): adjustable current limiting regulator composed of LM2596

LM2596 performance characteristics:

Includes fixed frequency oscillator (150KHZ) and reference regulator (1.23v)

Complete protection circuit, current limit, thermal shutdown circuit, etc.

High-efficiency voltage regulator circuit can be constructed with very few peripheral components

Provides multiple voltage levels such as 3.3V, 5V, 12V and adjustable (-ADJ)

The conventional application of M2596 does not have current limiting function. In some electronic design and auxiliary equipment, there is a certain demand for current limiting function. Although the standard application circuit given by the manufacturer cannot complete this function, we can add functions by appropriate. The circuit allows it to implement current limiting. As shown below:

Adjustable current limiting regulator composed of LM2596

 



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read ()  •  Jun 04, 2019  •  Edit


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