A thermal printhead has a series
of heating elements that will work well under controlled
temperature conditions. If a temperature overload occurs due
to printing without paper or a fault within the driving
circuit or software, one or more of the heating elements may
be damaged or burn out.
To avoid this, never drive
the printhead without printing media loaded (paper, card,
etc.). Care must be taken to ensure the various absolute
maximum ratings detailed in the specification are observed.
In particular, the stated maximum energy level at the
applicable ambient temperature must not be exceeded.
Do not subject the applied
element pulses to any voltage spikes, even those of a short
Take care when designing the
circuits, including the power supply, to allow for switching
large currents. Refer to the detailed specification to
establish the maximum current if all dots are energised.
Also check how many dots may be energised at the same time
as certain wider print width models cannot have all dots
Use the following sequence to
turn on the power voltages for printheads with driver IC’s
mounted on the printhead:-
Apply the driver IC power
source voltage (Vdd)
the control function and clear any data in the printhead
After confirming the control
system operates correctly, apply the power voltage (VH).
For safety purposes, the timing
of large switching current and the timing of the data
transmission (input of data to the printhead) should be set
so that they do not overlap.
Observe the following
precautions to prevent driver IC malfunction which may occur
when large currents are switched:-
the power cable has an adequate current rating.
connecting the VH power source and the Vdd logic
voltage, be careful that no potential difference occurs
safety purposes, it is recommended that a protective
circuit be included in the circuit design to protect the
power cable against excessive voltage.
ESD from external sources
can reach very high levels, particularly under high speed
printing conditions. Such ESD levels can cause damage to the
printing elements and built-in IC’s if precautions are not
taken. The ESD resistant coating applied over the heating
elements on many printhead models will avoid, or help to
avoid, damage but it is recommended that if high ESD is an
expected phenomena, suitable ground/earth path should be
incorporated in the mechanical design.