AN3168

Examples of negative power supplies

Doc ID 17193 Rev 1

12/20

3

Examples of negative power supplies

3.1

Linear power supply

The linear power supply is composed of a step down transformer, a diode bridge, a linear

regulator (U1) and some filtering capacitors (see Figure 14).

Figure 14.

Linear power supply

harmonic content, a 0.5 power factor can usually be assumed. Without consideration of the

transformer, diodes and regulator power losses, the output current is then in Equation 3.

Equation 3

For a typical power factor of 0.5 and a 230 V / 15 V step down transformer, the calculated

given according to the transformer power on Table 2.

The benefits of this solution are:

●

High output current

●

Possibility to easily generate multiple output voltages by using several secondary

windings

The drawbacks of this solution are:

●

High cost

●

High standby losses (due to the transformer magnetizing current)

●

Bulky size of the 50 Hz transformer

Table 2.

Calculated output DC current and measured typical standby power

consumption

Transformer power, S

1.6 VA

3 VA

10 VA

53 mA

100 mA

333 mA

0.08 W

0.5 W

1.1 W

C1

C2

AC mains

T1

V

DD

IN

GND

OUT

V

SS

U1

V

DD

-+

Diode Bridge

DC

DC

V

pf

S

I

×

=