430 Ink Jet Printer Service and Maintenance Manual
76
Issue 2
Part No. 306-0430-102
TP34
D9
GF1B
R54
280R
R53
360k
D11
GF1B
Q10
BSP17
C14
100n
24V SUPPLY
TO VALVE
CONTROL
1
1
3
2
4
Figure 29 Pico Valve Control Circuit
The valve is connected between TO VALVE line and the 24 V SUPPLY line.
When the valve is switched on the IO PCB driver pulls the ‘CONTROL’ line low, which pulls the source of the
FET low. The gate is held high by C14, and the FET is turned on, and the drain remains close to the CONTROL
rail, thus the valve has 24 V across it.
As R53 charges C14, after approximately 50 ms the gate/source voltage drops to a point where the FET turns
off, effectively leaving the valve in series with R54. As this is 280 ohms and the valve is 280 ohms, there is a
potential of 12 V across the valve.
When the software turns the valve off, the CONTROL line is made open circuit by the IO PCB driver.
The valves resistance and R54 in series pull the CONTROL line up to 24 V, which discharges C14 via D11.
D9 ensures that the back EMF from the valves inductance does not exceed the FET’s maximum voltage rating.
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