The voltage peak is the rapid switching action of the output switch and diode and the inductance of the output filter capacitor caused by parasitic and its related wiring. In order to reduce these voltage peak capacitors, it should be designed to switch the application, and the length of the lead must be kept short. Wiring inductances, bandate capacitors, and diamond probes used to evaluate these transients help these peak amplitude. When the switching voltage operator works in a continuous mode, the range of the electrical sensor current waveform is triangular to jagged waveforms (depending on the input voltage). For the given input and output voltage, the peak-peak amplitude of the inductive current waveform remains unchanged. When the load current increases or reduces the hour, the entire sawtooth wave current waveform also decreases. The average value current of the central value is equal to DC load current. If the load current drops to a sufficiently low level, the bottom of the jagged current waveform will reach zero, and the switch switch will be switched from the continuous working mode to the discontinuous operation mode. If the MOST switch is light, the design (no matter how much the inductance value is) will be forced to run non -continuously. This is a completely acceptable way.

In the switching stabilizer design, knowing that the value of peak to peak electrocarchers ripple current (ΔIind) can be used to determine many other circuit parameters. Parameter currents such as peak inductors or peak switches, minimum load currents before the circuit discontinuity, ESR of the output ripple voltage and ESR of the output capacitor can be calculated from the peak ΔIind. When the line diagram of the inductors is displayed in FIG. 22 to FIG. 25 is used to select the value of an inductor, the peak ripple current of the inductor can be determined immediately. The curve shown in FIG. 31 shows different load currents of the expected range of (ΔIind). The curve also shows how the peak inductor ripple current (ΔIind) is from the lower boundary to the upper boundary (for a given load current) with the inductance area (ΔIind). This upper frame indicates a higher input voltage, and the lower frame represents a lower input voltage (see the sensor selection guide). These curves are only applicable to continuous mode operation, and the following examples are selected only when using the inductor selection guide:

VOUT u003d 5V, the maximum load current 800mA

vin u003d 12V,,, VIN u003d 12V, Names, changes between 10V and 14V.

The selection guide in FIG. 23 shows that the vertical line and 12V input voltage of the 0.8A load current intersect in the middle of the upper and lower borders of about 68 μH. 68 μH inductor allows peak to peak electromotor current (ΔIind) to flow, which is the maximum load current. Reference FIG. 31, the peak of the mid -position ripple current (IIP) is roughly entered along the 0.8A line, and the peak value is 300 mAh.

When the input voltage of the inductor is close to 14V, the upper boundary of the inductance increases the ripple current increase. For the curve in Figure 31, it can be seen that for the load current induction of 0.8AThe ripple current (ΔIND) is 300 mAh, 12V in, and the upper limit is 340 mAh at the 14V boundary (225 to 14V). Once a known ΔIIND value is known, the following formula can be used to calculate the relevant switching regulator circuit.

1. Peak inductor or peak switch current

2. The minimum load current before the circuit discontinuity

3. The output ripple voltage u003d the voltage of the ripple u003d the voltage of the ripple u003d the voltage of the ripple u003d (ΔIIND) × (ESR of COUT) u003d 0.30A × 0.16Ω u003d 48mv P-P

Open Core induction

Another increased output ripple voltage voltage Or the possible source of unstable operation is the core of the core. The iron oxygen tube or rod -shaped electromotor has a magnetic line, and the magnetic line flows across the other end of the air from one end of the wire shaft. These magnetic lines generate voltage in the bronze wire of any wire or PC board in the magnetic field of the sensor. The intensity of the magnetic field, the impact of the direction and position PC bronze line on the magnetic field, and the distance between the copper traces and the sensor, determine the voltage generated in the copper traces line. Another method of viewing this induction coupling is to treat the PC copper traces as a turning turn of the transformer (secondary), and the inductor winding is elementary. Many millions can produce an open core electromoter near the copper tracking, which may cause stability problems or high output ripple voltage problems. If it is found that the operation is unstable and the core electromotor is used, the position of the inductor may be a problem about other PC tracking. To determine whether this is the problem, temporarily increase the electric sensor to leave the circuit board a few inches, and then check the working situation of the circuit. If the circuit works normally, and then the magnetic flux from the core electromotor is the root cause of the problem. It may be necessary to correct the problem with a closed -core sensor instead of a trap or electron core, or re -arrange the computer layout. The magnetic flux cutting IC device of the magnetic flux, the positive trajectory of the feedback trajectory or the output capacitor of the IC device should minimize. Sometimes, a trajectory of the positioning of the bearing sensor will provide good results. As long as it happens to be in the center of the inductors (because the induction voltage will automatically offset), it will occur if it deviates from the center 1. If a magnetic flux problem occurs, and even the direction of the sensor is in certain circuits, the winding can work. The discussion of the core electromoter is not to scare users, but to remind users what problems should be carefully used when they use them. The core wire shaft or ""stick"" inductor is a cheap and simple method to create a compact and efficient inductor. They are used by millions of people for many different applications.

Thermal factors

LM2595 have two packaging, one TO-220 (NDH) and a 5-pin surface installation To-263 (KTT). The TO-220 package can be used in the case of the ambient temperature as high as about 50 ° C. There is no need to heat the radiator (depending on the output voltage and load current). Figure 32The curve shows the different input temperature of the LM2595T joint and the output higher than the ambient temperature. The data of these curves at the ambient temperature is 25 ° C (static air). These temperature rise values u200bu200bare similar values, and many factors can affect these temperatures. The higher environmental temperature requires some heat dissipation, or the PC board or a small external radiator

263 The surface installation and packaging label design is designed to welded on the copper on the printing circuit board. This copper and circuit board are the package and other heat components (such as capturing diode and sensors. The area of u200bu200bPC plate copper with welding packaging should be at least 0.4 IN2, and Ideally, there should be 2 square inch or more 2 ounces (0.0028 inches) (0.0028 inches) (0.0028 inches) Copper. The additional copper area increases thermal characteristics, but the area of u200bu200bcopper is greater than about 3 square inch inch, which only achieves heat dissipation. If further heat improvement is needed, double or multi -layer PC boards are recommended to use large -scale copper. Figure 33 in Figure 33 Display curve display LM2595S (to-263 packaging) The knot temperature rises higher than the temperature under 1A load of various input and output voltage of the ambient temperature. These data are collected as a lower-voltage switch staber under the circuit operation. All components are installed on the PC plate to simulate the temperature under actual operating conditions. This curve can be used to quickly check the approximate connection temperature for various conditions, but it should be noted that there are many factors that will affect the knot temperature. In order to obtain the best thermal performance , Extensive copper traces and a large number of printing circuit board copper should be used in the circuit board layout. (One exception is the output (switch) pin. Underwriting) The surrounding air and the flowing air further reduced the thermal resistance. The heat resistance and the value of the packaging temperature of the packaging were approximate values, and there were many factors that affect these numbers. , Location, even the temperature of the board. Other factors are, the width of the trace line, the total copper area of u200bu200bthe printing circuit, the thickness of the copper, the single -sided or double -sided, multi -layer board, and the number of welds on the board. The size, quantity and distance, and whether the surrounding air is still or moved. In addition, some of the components such as capturing the diode will increase the calories to the PC board, and the calories will change with the changes in the input voltage. The type and DC resistance of the material can be taken away from the circuit board as a cooling piece, otherwise it will increase the calories to the circuit board.

]

Delay startup

The circuit in FIG. 34 Use ON/OFF pin to provide a delayed application between the input voltage and display the output voltage time ). When the input voltage increases, the charging of the capacitor C1 will pull the opening/turn -off foot to turn off the regulator. Once the input voltage reaches the final value, the capacitor stops charging, and the resistor R2 will be connected/disconnected. The foot is low, so that the circuit starts the switch. The resistor R1 Includes the maximum voltage application to the open/off -turn (maximum 25V), reduce the power noise sensitivity, and limit capacitors, C1, and discharge current. When the ripple voltage is high, avoid a long delay, because this ripple may be coupled to the on/off pin and causes problems. In the following cases, the lax startup function is very useful. It can be delivered. It allows the input voltage to rise to a higher voltage before the regulator starts. The booster regulator requires less input current at a higher input voltage.

Obscashed lock

Some applications require that the regulator is kept closed until the input voltage reaches the predetermined voltage. The underwriter locking function of the antihypertensive regulator is shown in Figure 35, and Figure 36 and Figure 37 apply the same features to the reversal circuit. The circuit in FIG. 36 has a constant threshold voltage and turn off (ZENER voltage plus about 1 volt). If you need to lag, the circuit in Figure 37 has a turnover voltage different from the closing voltage. The lagging volume is about the value of the output voltage. If the ZENER voltage is greater than 25V, the 47 kΩ resistor needs to be sold from ON/OFF to grounding sales to maintain the maximum limit of the 25V of the opening/level.

Reverse regulator

The circuit in FIG. 38 converts the positive input voltage into a negative output voltage with public grounding. This circuit uses the ground pins of the regulator to the negative output voltage, and then ground to run the feedback pin.

This example uses LM2595-5.0 to generate u0026#8722; 5V output, but by selecting other output voltage is possible other output voltage versions, including adjustable versions. Because the topology of this regulator can generate the output voltage that is greater than or less than input, the maximum output current depends largely on the input and output voltage. The curve is as shown in Figure 39 to provide a guidelines for the voltage conditions of the output load current that may be input and output. The maximum voltage on the regulator is the absolute harmony of the input and output voltage, and this must be limited to the maximum 40V. For example, when the+20V is converted to u0026#8722; 12V, the regulator will see 32V between the input sales and grounding sales. The maximum input voltage specification of LM2595 is 40V. The configuration of this regulator requires an additional diode. The diode D1 is used to isolate input voltage ripples or under light or air load conditions, and the CIN capacitor couples to the output noise. In addition, this diode isolation changed the topology to Closley, similar to the buck configuration, thereby providing good closed loop stability. The Schottky diode is recommended for low input voltage (because its voltage drops are low), but for higher input voltage, you can quickly restore the diode.

In the absence of diode D3, when the input voltage is applied for the first time, the charging current of CIN can be pulled.A few volts in a short period of time.Increasing D3 can prevent the output from voltage greater than the A diode.

Because the operation of the inverter is different, the standard design program is not suitable for selecting the sensor value.In most designs, 68 μH, 1.5A inductor is the best choice.The range of capacitors can also be reduced to several values.The value displayed in FIG. 38 will provide a good result. Most of the reversal designs will be provided.