IRadimed MRidium 3860, Service Manual

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4-8
Power off involves pulling the shutdown line, pin 15 of IR1 low
through R29, and draining the hold on charge from C18 via
D21. The low going off signal is generated with a time delay
on the AB002 processor board using U20 and U21 along with
the charge on C82. This delay requires that the OFF button be
held down approximately 2 seconds to turn the unit off.
4.3.2.3 11V Power Supply
The 11 volt regulated supply, turned on as described above, is
a high frequency switching regulator using an air core 10 uH
inductor and internal 3A switch. R26 and R27 set the supply
to output 11 volts. This supply is used directly by the motor
driver IC U2 and power FETs, Q1-4 to produce the 45kHz
ultrasonic drive power for the US motor. It is also the power
supply for the audio power amp. The 11volts directly feeds
the 5 volt switching regulator of IR2 which in turn powers a
linear 3.3 V regulator, IR3.
4.3.2.4 Logic 3.3V and 5V DC Power Supply Subsystem
IR2 is a LT1767 fixed 5 volt output 1A switching regulator
powered directly from the 11 volts from IR1 once it starts up.
This supply is used by the LCD display, portions of the US
motor driver and directly powers the LT 1767 linear 3.3 volt
logic supply.
4.3.2.5 Battery Charger Subsystem
All battery charger functions are controlled by U1, a BQ24702
Li charger IC suitable for charging up to 4 cells in series. The
battery also contains a gas gauge and charge monitor IC
which limits the charge voltage and currents allowable into
the battery pack. Smart circuits in the battery pack also will
shut off the battery output should any over current event be
sensed. In this case the pack will not delivery power until it is
placed back on proper charge from U1. The MRidium Li
battery pack is a 4S4P design producing 14.8 V with a 6 amp
hour capacity. Output is limited to 3 Amps.
U1 will sense the battery voltage, and if too low, supply only a
small trickle charge limited by R20 until the battery ‘floats’ up
to about 10 volts. There after a 300kHz switching charge
current of 1.5A is delivered via Q9 and TX1, to the battery.
Charge is complete once the pack reaches 16.85 V. This
terminating voltage is set by R89. R19 supplies charge
current feed back to the circuits within U1. R5 is used to
sense the current draw from the AC power adapter. This is
limited to 2A as the charger is rated for 19V at 2A. The
charger chip, U1, will ‘steer’ power to the RAW power buss to
power the pump with priority over the charging current. As
the pump ( and Side Car) may require up to the full 2A
available from the AC adapter, Q9 will be PWM towards off as
current is needed on the RAW power buss. In this way, the
pump can fully operate, delivering any desired IV flow rate,
even if the battery is fully depleted. With U1 ‘steering’ current
to the battery only so long as the pump gets all it requires.