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3-INPUT portable device power supply design and production

In Electronic Infomation Category: 3 | on April 13,2011

First, the design ideas This paper describes a generic

strong, low-cost design and MC912D60ACFU8 datasheet and manufacture of portable power systems, the system has two power modes, can be an external power supply, can also be built-in lithium battery power supply, the final output voltage of the system are 3V, both exist, give priority to external power supply. Has two external power connector, power adapter and MC912D60ACFU8 price and USB interface, using both, the power adapter has priority. The system can be widely used in various portable devices, there is a strong practical and MC912D60ACFU8 suppliers and good market prospects.

Power module outline package shown in Figure 1.

Figure 1 Power Module

Power system block diagram shown in Figure 2, selected by the input selection circuit external power supply, the power input voltage is 4.5 to 6 volts, there is an external power supply directly through the 3.3V voltage regulator output after If the battery power is low, while lithium batteries by Li-ion battery charging circuit to charge; no external power supply, powered by a lithium battery, the 3.3V low dropout linear regulator after regulator output, power supply selection circuit according to Is there an external power supply, choose from the external power supply or Li-Ion battery.

Figure 2 Block Diagram

Second, the circuit design

1. Input selection circuit

Input selection circuit for the realization of the choice of external power supply, the design used in the current mainstream and power adapter USB power are two ways to adapt to different power supply environment, external power supply voltage between 4.5V ~ 6V need to, when the two co-exist, the adapter has priority, the specific implementation method as shown in Figure 3, consists of the following three conditions:

Figure 3 input selector circuit

only the power adapter, PMOS MOSFET is off, the input voltage step-down by the D1, the post-stage circuit to the power supply, D1 using Schottky diodes, voltage drop of approximately 0.3V;

only USB-powered, PMOS MOSFET is, D1 is used to prevent USB interface, power consumption through a resistor R2;

both exist, PMOS MOSFET is off, power adapter input voltage step-down by D1 after the post-level circuits.

2. Li-ion battery charge management circuit

Lithium rechargeable lithium battery charging circuit chip with CN3052, CN3052 single lithium battery can be constant current or constant voltage charging, requires minimal external components, programmable charge current, constant voltage charging voltage 4.2V. USB bus technology and meet the specifications, is ideal for portable applications areas.

Application circuit in Figure 4, only few external components, output voltage 4.2V, accuracy of up to 1%, CE for the chip enable terminal, active-high.

Green LED indicates the battery is in fault state, is in the red LED to indicate charge status. In this design, TEMP pin to ground, do not use temperature detection. R4 sets the constant charge current is calculated as:

I = 1800V / R4; R4

this design is 10K, charging current is 180mA.

Figure 4 lithium battery charge management circuit

3. The battery output voltage circuit

Not the same for lithium battery, the output voltage can vary between about 3.5 ~ 4.3V, low dropout linear regulator with (LDO) regulator output voltage of the battery, the voltage output constant after 3.3 V voltage regulator chip, the design uses the TPS76333, with a minimum of external components, easy to use, the regulator can output 150mA maximum current of the chip. Schematic in Figure 5.

Figure 5, the battery voltage regulator

4. External power supply voltage regulator

Due to battery power, the LDO voltage regulator circuit, the output current is limited, when there is an external power supply is adopted SPX1117-3.3V voltage regulator for voltage, output current up to 800mA. Circuit shown in Figure 6.

Figure 6, an external power supply voltage regulator

5. Power supply selection and output circuit

Shown in Figure 7, divided into the following three conditions:

Only external power supply, not connected lithium battery, the power input voltage by the SPX1117-3.3V voltage regulator, output 3.3V voltage.

Only lithium batteries, no external power supply, the battery output voltage is regulated by the TPS76333, the output voltage by 3.3V step-down output after D2, D2 for the Schottky diode, the final output voltage is 3V or so.

Both exist, D2 off, by an external power supply, 3.3V output voltage.

power select circuit in Figure 7

6. The system of the whole circuit

Overall system circuit shown in Figure 8.

Figure 8, the whole circuit

Third, in-kind production

Using single-sided wiring, the PCB design is complete wiring diagram, as shown in Figure 9.

Single panel system board to complete performance plans, as shown in Figure 10.

Welding completed circuit board shown in Figure 11.

Figure 9 PCB wiring diagram

Figure 10 System board renderings

Figure 11 physical map

Four components and their parameters

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