Figure 3-7.Remote Voltage Programming,
Unity Gain (Constant Current]
3-36 Voltage Programming , Unity Gain (Figure 3-7). In this mode, the output current will vary linearly with changes in the programming voltage. The programming voltage should not exceed 0.6 volts. Voltage in excess of 0.6 volts will result in excessive power dissipation in the instrument and possible damage.
3-37The output current varies at a rate determined by the programming coefficient as follows:
Model | Programming Coefficient |
6259B | 10.0mV/ampere |
6260B | 5.0mV/ampere |
6261B | 10.0mV/ampere |
6268B | 16.7mV/ampere |
6269B | 10.0mV/ampere |
The current required from the voltage source will be less than 20µA. Impedance matching resistor Rx is required to maintain the temperature coefficient and stability specifications of the supply.
3-38 Voltage Programming, Non-Unity Gain (Figure3-8). The power supply output current can be
TM 11-6625-2958-14&P
programmed using an external voltage source with variable gain by utilizing the strapping pattern shown in Figure 3-8. In this mode, the output current is found by multiplying the external voltage source (Es) by [Rp/(RR x Kp)], where Kp is the constant current voltage programming coefficient as given in Paragraph 3-37.The value of reference resistor RR and programming voltage source Es should be such that the value of ES/RR is equal to or greater than 2.5mA.
3-39 External resistors Rp and RR should have sta- ble, low noise, and low temperature coefficient (less than 30ppm per degree Centigrade) characteristics in order to maintain the stability and temperature specifications of the Power supply. Reference resistor RR should not exceed 10K. Note that it is possible to use the front panel current control already in the supply (A5R123) as the gain control (Rp) by simply removing the external Rp and strapping terminals AS and A6 together.
3-40 The output current of the supply may be adjusted to exactly zero when the external programming voltage is zero by either inserting and adjusting R115 as discussed in Paragraph 5-93,or, if the instrument is equipped with Option 021, by adjusting potentiometer R116 as discussed in Paragraph 5-95.
3-41REMOTE SENSING (Figure 3-9)
3-42 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 3-9.The Power supply should be turned off before changing strapping paterns. The leads from the sensing (±S) terminals to the load will carry much less current than the load leads and it is not required that these leads be as heavy as the load leads. However, they must be twisted or shielded to minimize noise pickup.
