When doing DIY, many electronics enthusiasts often need a DC regulated power supply that can output large current and excellent performance, and hope that this DC regulated power supply can also conveniently change the output voltage at any time according to their needs. How can we have such a DC regulated power supply?

　　This article introduces a DC-DC regulated power supply made of MP1593. This DC-DC regulated power supply is very small, but it can provide an output current of 2A or even up to 3A, and its performance indicators are very good, which can fully meet the requirements of electronic enthusiasts when DIY. The following is a detailed introduction to some issues such as the principle and actual production.

　　1. Introduction to the structure and working principle of MP1593

　　MP1593 is a step-down DC-DC device developed and produced by the American MPS company (Monolithic Power Systems, Inc). It uses an 8-pin small SOP package with a small size of only 5mm×4mm×1.5mm. The IC allows the input voltage range to be from 4.75~28V, the output current can reach up to 3A, and its maximum working efficiency can reach 95%. The typical data of this IC is: when the input is 12V, the output is 5V, and the current reaches 2.5A, its working efficiency is 90%. Under such a high voltage difference and high current, the IC can work continuously for 24 hours without installing any heat sink, which shows that its power consumption is very small. In addition, the peripheral circuit of this integrated circuit is also very simple and very easy to use.

　　Figure 1 is a typical external application circuit and part of the internal schematic diagram of MP1593

Figure 1 Typical external application circuit and some internal schematics of MP1593

　　The working principle of the integrated circuit is briefly described as follows:

　　The input voltage Vin enters from the pin 2 of the integrated circuit. If a high level (about +5V) is added to the pin 7 (Enable) terminal, the IC is started and enters the working state. During the time Ton (on time), the input voltage is output from the pin 3 of the IC through the turned-on MOS tube V1 and applied to the left end of the inductor L1. The voltage is supplied to the load RL through the filter circuit composed of L1 and capacitor C5, and the electric energy is stored on the inductor L1. During the time Toff (off time), the MOS tube V1 is in the off state. At this time, the self-inductance voltage generated on the energy storage element inductor L1 is negative on the left and positive on the right. Therefore, the voltage applied to the diode D1 is a forward bias voltage, causing the diode to conduct. Therefore, the inductor L1, the diode D1 and the load RL form a discharge loop, and the electric energy stored in the inductor L1 is released to the load RL to provide the electric energy required by the load RL. The waveforms at various points in the circuit are shown in (Figure 2).

Figure 2 Waveform diagram of each point in the circuit

　　The voltage regulation control process of the output voltage Vout is briefly described as follows.

　　The voltage divider circuit composed of resistors R1 and R2 takes out the sampling voltage from the output voltage Vout terminal, and then sends it to the inverting input terminal of the error voltage amplifier Y3 inside the IC through pin 5, and compares it with the reference voltage 1.22V set inside the IC and added to the inverting terminal, so that the output voltage Ua of the error voltage amplifier Y3 changes accordingly. This voltage Ua is sent to the inverting input terminal of the current comparator Y2 inside the IC; on the other hand, the internal resistor R ' of the IC obtains a sampling voltage by sampling the current in the output loop. This voltage is amplified by the current sensing amplifier Y1 to obtain the voltage Ub, which is sent to the inverting input terminal of the current comparator Y2. These two voltages Ua and Ub jointly determine the size of the output voltage Uc of the current comparator Y2, and the voltage Uc is the input control signal of the logic circuit inside the IC. By controlling the logic circuit, the relative length of the on-off time of the MOS tube V1 is changed, that is, the length of the charging and discharging time on the inductor L1 is changed, that is, the relative length of Ton (on time) and Toff (off time), thereby changing the size of the average voltage on the inductor, that is, changing the size of the output voltage Vout, and finally realizing the voltage regulation control of the output voltage Vout. The entire voltage regulation process is essentially a feedback control process. From the voltage regulation control process described above, we can see that as long as the ratio of the external resistors R1 and R2 is changed, the size of the sampling voltage can be changed, thereby changing the size of the output voltage Vout. In fact, this circuit adjusts the size of the output voltage Vout by adjusting the ratio of the resistors R1 and R2.

　　The function definitions of each pin of MP1593 are shown in Table 1.

Table 1 MP1593 pin function description

　　2. MP1593 actual application circuit diagram and some design points

　　The actual application circuit of +5V power supply designed by this IC is shown in Figure 3.

Figure 3: The actual application circuit of +5V power supply designed by this IC

　　There are several points to note about the design of this circuit:

　　1. The resistors, capacitors and other components used here are all SMD components. The advantages of using SMD components are: first, it can make the volume of the entire circuit very small, and second, it can make the components very compact to avoid the connection lines between components being too long, which may lead to external interference and make the circuit unstable.

　　2. Capacitors C4 and C5 cannot use electrolytic capacitors, but must use multilayer ceramic dielectric chip capacitors (i.e. MLCC capacitors). It is best to use X7R or X5R chip capacitors, because this type of capacitor has a better filtering effect and can ensure that the ripple voltage of the output voltage Vout is small.

　　3. C2 must be an X7R chip capacitor and should be as close to MP1593 as possible to minimize the high-frequency interference introduced from the input end. 

        4. D1 must use a Schottky barrier diode with a forward current greater than 3A to ensure that when the MOS tube V1 inside the IC is turned off, the inductor L1 can quickly provide a sufficiently large current to the load.

　　5. R3, R4, and R5 must use chip resistors with an error of 1% to ensure the accuracy of the output voltage Vout. R4 and R5 are used in series to more conveniently adjust Vout so that its accuracy meets the predetermined requirements.

　　6. L1 uses a wound I-shaped chip inductor, and its rated operating current must be above 2A.

　　7. Resistors R1 and R2 form a series voltage divider circuit to divide a voltage of about 5V from the 12V voltage to pin 7 as the start signal of the circuit. The model specifications of all components used in the circuit are shown in Table 2.

Table 2 Electronic components list

　　3. Conclusion

　　When using the integrated circuit MP1593 to design a DC regulated power supply, the following points are worth noting:

　　1. If the output voltage is not +5V but +3.3V, +1.8V or other output voltages, when designing the application circuit of MP1593, the parameters of some components in (Figure 3) need to be adjusted, such as: L1, D1, C6, R3, R4, R5, R6 all need to be re-selected according to the output voltage.

　　How to select parameters? Please refer to the latest version of the MP1593 IC specification sheet released by MPS: MP1593 DatasheetRev 2.0 .pdf.

　　2. When laying out the PCB, attention must be paid to the layout of the ground wire.

　　Generally, the ground wires of the input part and the output part should be gathered at one point and then connected to each other, and the gathering point should be as close to the pin 4 (GND) end of MP1593 as possible.

　　3. When wiring the PCB, L1, D1, and C3 must be connected at one point and the line segment connected to the pin3 end of MP1593 should be as short and thick as possible.

　　4. When PCB wiring is in progress, the area enclosed by components L1, D1, and C4 on the PCB board should be as small as possible. In fact, this requires that these components be arranged as close to each other as possible.

　　The above measures are to make the designed practical application circuit have excellent working stability, so that the output voltage has very good performance indicators in terms of ripple, output voltage accuracy, signal-to-noise ratio, etc. In fact, I have designed three DC voltage regulator circuits of +5V, +3.3V, and +1.8V using MP1593 in portable DVD products. The actual performance indicators of the machine are very good, the ripple on the output voltage is very small, the signal-to-noise ratio of the audio system is measured to be above 90dB, and the brightness signal-to-noise ratio of the video system is measured to be above 60dB, which fully proves that the circuit has good practicality.