Charger with boost converter. Scheme, description

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Charger with boost converter. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Chargers, batteries, galvanic cells

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IC1 contains a pulsed boost stabilized voltage converter that increases the VIN voltage (nominally 5 V) to a level necessary to maintain the appropriate charge current and load current. The 5V power supply must be equipped with a short circuit protection circuit. IC2 is a positive rail current sensing amplifier that monitors the charge current. The processor can issue CHARGE ON/OFF commands to the device. and FAST/BACK CHARGE.

(click to enlarge)

IC2 generates an output current (OUT pin) equal to 10-4 of the current through the sensor on resistor R9. Transistors Q3 and Q4 are on in fast charge mode, so IC2's output current flows through the parallel connection of resistors R11 and R4 (if Q3's base current is not taken into account). As a result, the feedback signal applied to IC1 (pin 3) keeps the fast charge current flowing through R9 at 500mA. This feedback also allows the regulator to deliver up to 500mA to an additional load on top of a stable charge current of 500mA.

Transistor Q2 limits the battery voltage to 10V (2V per cell). In fast charge mode, an external processor and a multi-channel analog-to-digital converter monitor the voltage at the battery terminals. When the ADC detects a change in the slew rate of the battery, the processor turns off the fast charge mode by driving a high level on the FAST / BUCK CHARGE line.

Transistor Q3 turns off, causing the voltage on the feedback pin (FB) to increase, causing the charge current to decrease to the level of the float charge current (approximately 60 mA). If IC1 turns off, or the total load and charge current exceeds IC1's allowable level, the current direction of resistor R9 is reversed as current begins to flow from the battery. IC2 handles the reversal of current by changing the state of the open-collector output SIGN, which is driven high by R13, turning Q4 off and Q5 on. In this case, the current through the resistor R12 creates a voltage proportional to the battery discharge current (a current of 5 A through R9 causes a voltage of 12 V to appear on the resistor R3). By integrating this voltage over time (measuring it at fixed intervals and multiplying by the duration of the interval), the analog-to-digital processor keeps track of the energy drawn from the battery. Based on the received data and on the measured voltage on the battery, the processor can then re-enable the fast charge mode by pulling low on the FAST/BUCK CHARGE line until the battery is fully exhausted.

The current source based on the high-efficiency pulse converter LT1511 is designed for use in chargers for portable equipment batteries. The charger on the LT1511 has a stable voltage/stable current output characteristic to charge Lithium Ion batteries. It can charge both Nickel-Cadmium and Nickel-Metal Hydride (NiMH) batteries, but using an external end-of-charge circuit. The maximum charge current can be programmed both with resistors and with the help of a DAC. The input current control circuit in the LT1511 allows you to simultaneously use the equipment and recharge the batteries without overloading the AC adapter. In this case, the charge current is automatically reduced to maintain the AC adapter current at the nominal level.

Publication: cxem.net

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