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How to calculate the total dissipation (PT) of the uPC317?

Latest Updated:08/01/2007

Question:

How can I calculate the total dissipation (PT) of the uPC317?
I know that the total dissipation of a 3-terminal regulator is the sum of the dissipation between the input and output and the circuit dissipation. Can I therefore use the following equation to calculate the total dissipation of the uPC317?

PT = (VIN-VO)×IO+VIN×Ibias
    (VIN-VO): Voltage differential between input and output
    IO: Output current
    VIN: Input voltage
    Ibias: Circuit operating current

Answer:

The uPC317 is different from an ordinary 3-terminal regulator in circuit configuration. Specifically, most of the circuit operating current (Ibias<1>) (shown in the block diagram) flows out from the OUTPUT pin as the output current (IO).
The rest of the circuit operating current (Ibias<2>) flows out from the ADJ pin as IADJ. Therefore, total dissipation PT is calculated as follows.

PT = (VIN - VO)•IO + VIN•IADJ, where IO includes Ibias<1>.


However, IADJ can be ignored because it is at the micro ampere (µA) level as described in the electrical specifications, and therefore, the total dissipation (PT) can be calculated by this expression.

PT = (VIN - VO)•IO


Suitable Products
CMOS Operational Amplifiers
Bipolar Operational Amplifiers
3 Terminal Regulators