> 3.1 | Linear Regulation

> Power supply with linear regulators is straightforward to design, and the total cost for the components can be quite low. As seen in Section 3.2 the power supply solution must be able to deliver at least 3A. If the module’s desired supply voltage is for example 4V and the regulator input voltage is 12V, the efficiency is (only) 33%. The rest is transformed into heat.
> Figure 3: Linear regulation
> The advantage of this solution is that there is no big requirement on the input power supply and on the input capacitor. Also, big voltage drops can be filtered by the regulator.
> The requirements for the sample circuit are:

> | GSM | GPRS 10
> Input voltage | 12V | 12V
> Average current | 0.5A | 0.9A
> Peak current | 3A | 3A
> Avg. Power dissipation at regulator IC | 4W | 7.2W

> The peak power dissipation of the circuit is 3A x 8V = 24W peak, while the heat power is based on the average power consumption. In this case 3.5Wavg shall dissipate as heat.
> For low dissipations the IC surface alone may be sufficient for cooling. For medium power dissipations the thermal issues can be resolved by having a big copper area on the PCB for cooling purposes. For higher power dissipations extra cooling is necessary. A cooling element as heat sink is often required. The below formula is useful when working with cooling elements.
> PDmax = Maximum power dissipation
> Tjmax = Maximum IC temperature
> TA = Ambient temperature
> JC = Junction/case thermal resistance
> CS = Case/sink thermal resistance
> SA = Sink/ambient thermal resistance
> NOTE: Modules are sensitive to heat. If cooling for the either module or its housing is insufficient, the module will warm up. If the module gets too hot, it will shut down! This may happen during a long call (long warm up period), if the cooling is not sufficient.