Apex ~ power dissipation with a power amplifier

Is power dissipation a critical design consideration when driving an inkjet print head with a power amplifier?

Yes! Assessment of the power amplifier's internal power dissipation is a critical factor to ensure the drive circuit maintains a proper operating temperature and high reliability.  

 

Today's industrial "drop-on-demand" inkjet print heads use piezoelectric circuitry driven by power amplifiers. The amplifier "sees" the printer head as a very dynamic, capacitive load. The nozzles inside the head are triggered by the amplifier's fire pulse to eject ink drops. A typical amplifier circuit and fire pulse is illustrated below.

Total power dissipation for the power amplifier consists of two components:

1) quiescent power dissipation and

2) output stage power dissipation.

Quiescent power dissipation is caused by the quiescent current draw of the power amplifier which is used internally to bias the various amplifier stages, and it continues to flow even when the amplifier is idling. Power is dissipated in the output stage as a result of the voltage drop across the conducting output stage transistor and the output current that flows through that transistor. The power dissipation causes the amplifier to heat up, necessitating the use of a heatsink to keep transistor junction and amplifier case temperatures below their maximum ratings and ensure reliability.

For further information on assessing these power dissipation requirements, see:

Application Note 57, Apex Ink Jet Print Head Driver Power Dissipation 

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