Choosing a Module

The PS-3 DC to DC converters can be supplied in a variety of standard output voltages (3.3V, 5.0V, and 12.0V), or any custom output voltage from 1.2V to 24.0V. These modules are designed to be PCB mounted and feature a three lead connection compatible with the 7805 series of linear regulators.

The PS-3 5.0Vdc (RR-PS3-033) can be used as a drop-in replacement for 7805 regulators, but not requiring the heatsink! These can be very useful for repairs of existing products where the 7805 is overheating.

The useful output voltage range is from 1.2 Volts to the input voltage (Vin) minus 4 Volts. In other words the PS-3 module requires about 4Vdc of overhead to operate at the desired output voltage.

Therefore: Vout <= Vin-4Vdc.

The PS-3 modules are all rated for one Ampere of output current, but the useful output current depends on the current and voltage rating of the input voltage source. The PS-3 DC to DC module will operate at 90% efficiency or better at higher loads.

Step 1:

VAin (to PS-3) equals the power source output voltage times the power source maximum output current.

VAin = Vo * Io

Step 2:

Multiply VAin by 0.90 to get the available output VA (we'll call VAout).

VAout = 0.90 * VAin

Step3:

Therefore: Iout-max = (VAout/Vout) or 1.0 Ampere, whichever is less.

For example, using a 12Vdc 350mA transformer winding (with full-wave rectifiction) as the power source and a PS-3 with 5.0Vdc output:

VAin = 12 * 0.35 = 4.2

VAout = 0.90 * 4.2 = 3.78

Iout-max = 3.78 / 5.0 = 0.756 or 756 mA

Note! In this design originally with a 7805 regulator, the maximum output current would have been 350mA, and at that rating, a substantial heatsink was required.