Keep your (linear) power supply "cool"
Linear regulators have a fix or adjustable voltage at their output, which always is lower than the input voltage. This voltage difference is usually marked as Vdrop (Voltage drop) in the datasheets and means, which voltage is "cut off" from the input voltage that ensures, that the regulator regulates the output voltage in the wished / expected quality. The Vdrop usually depends on the current need - the higher the current, the higher the Vdrop.
The voltage difference between input and output voltage multiplied with the current (that the powered device consumes) results in VA of generated heat, which has to be dissipated by the heatsink into the environment.
Let's assume, that your device consumes 3 ampere, then it's clear, that the bigger the voltage difference between input and output is, the more heat is generated, comparing to a current need of 1A in example.
For DC-powered HPULN-PS's we recommend a guaranteed voltage headroom of 0,6V under full load delivered by your pre-reg, or higher voltage difference for lower current.
As a general rule of thumb we recommend a maximum heat generation of
- 4W in sum for the L-Size HPULN modules
- 2W in sum for the M-Size HPULN modules
- 0,5W in sum for the S-Size HPULN modules
Less heat is better. The recommendation is based on an passive cooled setup with "enough" circumstances, such as openings in the enclosure and mounted far away from other heat producing circuits. To avoid unnecessary heat, MPAudio offers individual transformers matching an individual application's need.
The following blog could help calculating a transformer's secondary voltage: https://www.mpaudio.net/post/which-transformer-voltage-for-my-hpuln