Voltage Regulators

A common design problem is you have one voltage (say 9 volts from a battery) and you need 5 volts for part of the circuit and 12 volts for a different part of the circuit.

Common circuit voltages are:

3.3 volts

5 volts

+12 volts

-12 volts

Common battery voltages are:

Multiples of 1.5 V: 1.5, 3.0, 4.5, 6.0, 7.5, 9.0 etc.

Voltages from lead acid car batteries are 12-15 volts.

Circuits used to regulate or convert the voltage are called:

Regulators

Converters

Linear Regulators: Output a fixed or adjustable voltage.

Common type is a three-terminal regulator

(Note Input Voltage greater than Output Voltage)

Output

5 volts

Linear Regulator

Input

7-35 volts

For example see LT1083 Spec Sheet. Also see table handed out in class. (Also see figure 6.39 A in handout)

Switching Regulators and DC-DC Converters

Note (Output Voltage can be greater than Input Voltage)

(Dissipates less power than linear regulators)

See Figure 6.39 B in handout.

Also see Fig. 6.44 in handout of dual-polarity switching power supply.

Also refer to the example in class LT1073

Switched Capacitor Voltage Converters

See for example spec sheet for ADM660

Thermal Resistance – Heat Sinks – Spec Sheets

Θ is defined a thermal resistance (Units: ˚C/Watt)

T_J: Junction (device) temperature

T_A: Ambient temperature

P: Power being dissipated

T_J=T_A + Θ P

The thermal resistance is either given as :

1) Θ =Θ_JA : Junction to Ambient thermal resistance

2) Θ =Θ_JC + Θ_CS + Θ_SA

where Θ_JC is the junction to case thermal resistance

Θ_CS is the case to heat sink thermal resistance

Θ_SA is the heat sink to ambient thermal resistance