Smps & Hvps (Also Known As Psu And Power Pack); Summary Of Smps; Summary Of Hvps; Engine Controller - Ricoh B174 Service Documentation

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SMPS & HVPS (ALSO KNOWN AS PSU AND POWER PACK)

6.4 SMPS & HVPS

(ALSO KNOWN AS PSU AND POWER PACK)

The SMPS (Switching Mode Power Supply) and HVPS (High Voltage Power

Supply) are on the same board.

The SMPS unit is a PWM (Pulse Width Modulation) type power supply unit that

supplies DC+5V to the controller and operation panel, and DC+5V, DC+24V and

DC+12V to the engine. It also supplies AC power to the fusing lamp.

It is the high voltage power supply that has DC+24V/DC+5V (used for the image

forming device in digital picture developing method) as the rated inputs. It supplies

electrifying voltage (MHV), supply voltage (SUPPLY), developing voltage (DEV),

blade voltage(BLADE) and transferring voltage (THV).

This circuit controls the fusing lamp temperature. It contains a thermistor, the

LM393 (voltage comparator), and a transistor for switching.

The resistance of the thermistor decreases in proportion when the surface

temperature of the hot roller increases. The voltage is read by pin 60 (AVIN2) of

the CPU. The CPU refers to the parallel combined resistance with the resistor

(R43) connected parallel to it and the voltage distribution from R29. The voltage

that is read changes the 'fuser' signal to high (or low) referring to the set

temperature. Then, when the 'fuseron' signal turns low (high) by Q3 switching, the

S21ME4 inside SMPS (PC3) turns on (off) and this turns the two-way thyristor

(SY1) on (off) to allow (stop) the AC voltage to the fusing lamp.

LM393 is a H/W that protects the system when the fusing lamp control software

does not operate correctly.

When the thermistor temperature goes up to 210°C, the level of pin 1 (LM393) will

turn low to turn the 'fuseron' signal to high (this forcefully shuts off Q3). In other

words, LM393 shuts off the fusing lamp forcefully.

6-5

B174

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