Coolmax V-500 Power Supply Review

Secondary Analysis

The Coolmax V-500 has three rectifiers attached to the secondary heatsink.

The maximum theoretical current each line can deliver is given by the formula I / (1 – D) where D is the duty cycle used and I is the maximum current supported by the rectifying diode. Since this unit uses the half-bridge design, the duty cycle is 50 percent.

The +12 V output uses one MUR2020CT rectifier (20 A, 10 A per internal diode at 145° C, 1.15 V maximum voltage drop), giving us a maximum theoretical current of 20 A or 240 W for this output. It is important to understand that this device is not a “Schottky” model, meaning it presents a higher voltage drop and, therefore, lower efficiency.

The +5 V output uses one SB3040ST Schottky rectifier (30 A, 15 A per internal diode), giving us a maximum theoretical current of 30 A or 150 W for this output.

The +3.3 V output uses one SB2045CT Schottky rectifier (20 A, 10 A per internal diode at 135° C, 0.57 V maximum voltage drop), giving us a maximum theoretical current of 20 A or 66 W for this output.

Figure 12: The +12 V, +5 V, and +3.3 V rectifiers

Notice how the +5 V rectifier is “stronger” than the +12 V one. This was a typical scenario 15 years ago. Nowadays, the +12 V output needs to be “stronger” than the other outputs, since the components that pull most of the current/power (the CPU and video cards) are connected to this output.

The PWM controller shown in Figure 11 is also in charge of monitoring the unit’s outputs. It provides over voltage (OVP) and under voltage (UVP) protections.

The electrolytic capacitors available in the secondary are also Chinese, from JEE and Sapcon, and are labeled at 105° C.