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NTE953

Linear Integrated Circuit 4–Terminal Positive Adjustable Voltage Regulator

NTE Electronics 

Design Considerations:

The NTE953 adjustable voltage regulator has an output voltage which varies from VCONTROL to typically

(R1 + R2)

VIN –2V by VOUT = VCONTROL

R2

The nominal reference in the NTE953 is 5.0V. If we allow 1.0mA to flow in the control string to elimi-

nate bias current effects, we can make R2 = 2.2kΩ. The output voltage is then:

VOUT = (R1 + R2)V, where R1 and R2 are in kΩs.

Example: If R2 = 5kΩ and R1 = 10kΩ then

VOUT = 15V nominal

By proper wiring of the feedback resistors, load regulation of the device can be improved significantly.

The NTE953 voltage regulator contains thermal–overload protection from excessive power, internal

short–circuit protection which limits each circuit’s maximum current, and output transistor safe–area

protection for reducing the output current as the voltage across each pass transistor is increased.

Although the internal power dissipation is limited, the junction temperature must be kept below the

maximum specified temperature in order to meet data sheet specifications. To calculate the maxi-

mum junction temperature or heat sink required, the following thermal resistance values should be

used:

Typ

°C/W

Max

°C/W

Typ

°C/W

Max

°C/W

ΘJC

ΘJC

ΘJA

ΘJA

7.5

11

75

80

Solving for TJ:

PD(max) =

TJ(max) – TA or TJ(max) – TA

ΘJC + ΘCA

ΘJA

(Without a heat sink)

ΘCA = ΘCS + ΘSA

TJ = TA + PD (ΘJC + ΘCA) or

TA + PD ΘJA (Without heat sink)

Where:

TJ =

TA =

PD =

ΘJA =

ΘJC =

ΘCA =

ΘCS =

ΘSA =

Junction Temperature

Ambient Temperature

Power Dissipation

Junction to Ambient Thermal Resistance

Junction to Case Thermal Resistance

Case to Ambient Thermal Resistance

Case to Heat Sink Resistance

Heat Sink to Ambient Thermal Resistance

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