A 7 A 6 A 8 A 1 0 + S + G N D - – S

PROGRAMMING

R L

R E S I S T O R

 

Figure 3-4. Remote Resistance Programming

3-21 To maintain the stability and temperature coefficient of the power supply, u se programming resistors that have stable, low noise, and low temperature (less than 30ppm per degree Centi- grade) characteristics. A switch can be used in conjunction with various resistance values in order to obtain discrete output voltages. The switch should have make-before-break contacts to avoid momentarily opening the programming terminals during the switching interval.

3-22 Voltage Programming (Figure 3-5). Employ the strapping pattern shown on Figure 3-5for voltage programming. In this mode, the output voltage will vary in a 1 to 1 ratio with the programming voltage (reference voltage) and the load

on the programming voltage source will not exceed 25 microampere.

A7 A6 A8 A10 +S + GND - -S

REFERENCE

VOLTAGE

Figure 3-5. Remote Voltage Programming

3-23 The impedance (Rx) looking into the external

TM 11-6625-2965-14&P

programming voltage source should be approximately 1000 ohms if the temperature and stability specifications of the power supply are to be maintained . The programming accuracy is 1% of the programmed voltage.

3-24 Methods of voltage programming with gain

are discussed in Application Note 90, Power Supply Handbook; available at no charge from your local

Sales Office.

3-25 REMOTE SENSING (See Figure 3-6)

3-26 Remote sensing is used to maintain good regulation at the load and reduce the degradation of regulation which would occur due to the voltage drop in the leads between the power supply and the load. Remote sensing is accomplished by utilizing the strapping pattern shown in Figure 3-6.The power supply should be turned off before changing strapping patterns. The leads from the +S terminals to the load will carry less than 10 milliamperes of current, and it is not required that these leads be as heavy as the load leads. H o w - ever, they must be twisted or shielded to minimize noise pick-up.

C A U T I O N

Observe polarity when connecting the sensing leads to the load.

A 7 A 6 A 8 A 1 0 + S + A N D – – S

R L

Figure 3-6. Remote Sensing

3-27 For reasonable load lead lengths, remote sensing greatly improves the performance of the supply. However, if the load is located a considerable distance from the supply, added precautions must be observed to obtain satisfactory operation. Notice that the voltage drop in the load leads sub-

3-3