jotron RCH-20, Руководство пользователя

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RCH-20
5-1
5. TECHNICAL DESCRIPTION
Introduction
The Charger consists of 1 printed circuit board.
•
Main board (80011)
Main board (80011)
The charger can be divided into following functional blocks:
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Switch mode regulator
•
Current measurement circuit
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Voltage measurement circuit
•
Temperature measurement circuit
•
Charge control circuits
Switch mode regulator
The supply voltage is supplied trough the bridge rectifier D5, to make the charger independent of
supply polarity.
The microcontroller (IC1) with software controls all functions in the charger, including the switch mode
regulator. The microcontroller operates on 5V, supplied from voltage regulator (IC3).
The switch mode regulator delivers the charging current to the batteries. The switching transistor (Q2
or Q1) is controlled by the PWM (Pulse Width Modulator) output of the microcontroller. The pulse
width is adjusted according to the reading from the current measurement circuit.
Current measurement circuit
The current flowing through the batteries will generate a voltage across the resistors R32 – R36. This
voltage is amplified by IC2A, and fed to one of the A/D inputs of IC1. The reading from this A/D input is
used to correct the duty cycle of the PWM output, and hence adjust the charging current.
Voltage measurement circuit
IC2B and IC2C are used as voltage amplifiers. The offset voltage, supplied from IC2D, is used to give
the amplifiers a 0 – 5V output, which is feed to one of the A/D inputs of the microcontroller, IC1. The
voltage is used by the microcontroller to detect the
∆ V slope which is used for charging termination.
The voltage is measured every 120 second, and compared with the previous reading. A negative or no
change will terminate the charging.
I addition a voltage above approx. 9.7 V will terminate the charging as well.
Temperature measurement circuit
The NiMH batteries contain a 2.2kohm NTC which is used to measure the temperature of the battery.
R15 and R16 act as pull up resistors for the NTC. R30 and 31 is for future use with batteries with
different chemistry and a different NTC value.
The voltage from the NTC is fed to one of the A/D inputs of IC1. The reading from this A/D input is
used to detect a temperature rise in the batteries, which again will make the charger terminate
charging.