January 2006, Issue 186

Portable Web Server
Renesas M16C Design Contest 2005 Entry

CONTROL POWER SUPPLY

The power supply for the web site module consists of a 3.3-V regulated DC supply, which is provided via a simple linear regulator. The CompactFlash cards support either 5 or 3.3 V during their configuration phase, but most of the newer cards are designed to run at 3.3 V.

Estimates for the power budget for the module are shown in Table 1. The total amount of power required with a 5-V supply is 425 mW (i.e., 5 V × 85 mA). The regulator power dissipation is 144 mW (i.e., (5 V – 3.3 V) × 85 mA). The rise in the regulator’s temperature is around 9°C (TO-220 without a heatsink). This indicates that the linear regulator can easily manage the heat with a 5-V supply. It also means the web site module should draw less than 0.5 W during operation.

I had some difficulty with the evaluation board I received for the Renesas M16C Design Contest 2005 because it was intended to run at 5 V not 3.3 V. Luckily, the fixes were minor. I rewired the LCD contrast potentiometer and logic supply input so they were supplied directly from the 5-V supply. The M32C/84’s PLL oscillator frequency also needed to slow down from 32 to 24 MHz to remain within Renesas’s specifications.