Basic Instrumentation and Measurement - DC Power Supply

INTRODUCTION

 

The DC power supply is used to generate either a constant voltage (CV) or a constant current (CC). That is, it may be used as either a DC voltage source or a DC current source. We will be using it primarily as a voltage source. Recall that DC is an acronym for direct current. DC means constant with respect to time.

The voltage produced by the power supply is controlled by the knob labeled voltage. The current is limited by adjusting the knob labeled current. As long as the circuit does not attempt to draw more current than the value set by the current knob, the voltage will remain constant.

Current limiting allows the power supply to be set such that it will not generate more current than desired. This can be useful as a safety feature, preventing electrocution due to accidental contact with terminals. In addition, current limiting can prevent damage to equipment and parts which may be unable to handle excessive currents. More details about current limiting will be presented in the experimental procedure. 

Panel Control And Indicator

Front Panel Analog Type

Front Panel Digital Type

FUNCTION DESCRIPTION

FRONT PANEL

1. Power switch : ON/OFF the power input
2. Meter : Indicates the MASTER output voltage (Analog type)

 Indicates the MASTER output voltage or current (Digital type)

3. Meter : Indicates the SLAVE output voltage (Analog type)

 Indicates the SLAVE output voltage or current (Digital type)

4. Meter : Indicates the MASTER output current (Analog type)

A/V selects switch : selects the meter indicates of the slave of the MASTER output voltage or current (Digital type)

5. Meter : Indicates the SLAVE output current (Analog type)

A/V selects switch : selects the meter indicates of the SLAVE output voltage or current (Digital type)

6. Voltage control : for adjustment of the output voltage of the MASTER supply. Also functions as adjustment control for the maximum output voltage of the SLAVE supply when either parallel or series tracking operation.
7. Voltage control : for adjustment of the output voltage of the SLAVE supply when the independent operation.
8. Current control : for adjustment of the output current of the MASTER supply. Also functions as adjustment control for the maximum output voltage of the SLAVE supply when either parallel or series tracking operation.
9. Voltage control : for adjustment of the output current of the SLAVE supply
10. C.V indicator : lights when the MASTER supply is in the constant voltage operation. In either the Series or Parallel  tracking mode, both the MASTER AND SLAVE supplies are in the constant voltage operation.
11. C.V indicator : lights when the SLAVE supply is in the constant voltage operation.
12. C.C indicator : lights when the MASTER supply is in the constant current operation.
13. C.C indicator : lights when the SLAVE supply is in the constant current operation. Also lights when the TRACKING PARALLEL mode is selected.
14. Over load indicator : lights when load on 5 volt supply becomes too large.
15. TRACKING Mode switches: Two push-button switches that select INDEPENDENT mode, series tracking mode, or parallel tracking mode as follows : 

a)      When both switches are disengaged (out), the unit is in the INDEPENDENT mode and the MASTER and SLAVE power supplies are completely independent from one another.

b)      When the left switch is engaged (in) and the right switch is disengaged (out), the unit is in the TRACKING SERIES mode. In this mode, maximum voltage of both supplies is set using the MASTER VOLTAGE controls (voltage at output terminals of the SLAVE supply tracks the voltage at the output terminals of the MASTER supply). Also in this mode of operation the positive terminal (red) of the SLAVE supply is connected to the negative terminal (black) of the MASTER supply. This allows the two supplies to be used as one 0 to double rating voltage supply.

c)      When both switches are engaged (in), the units in the TRACKING PARALLEL mode. In this mode the MASTER and SLAVE supplies are wired together in parallel and both the maximum current and voltage are set using the MATERS controls. The MASTER and SLAVE outputs can be used as two individual (but tracking) power supplies or just the MASTER output can be used as a 0 to rating voltage supply with a 0 to double rating current capability.

16. Same switch as 15
17. “+” output terminal : Positive polarity output terminal for the MASTER supply.
18. “+” output terminal : Positive polarity output terminal for the SLAVE supply.
19.  GND terminal : Earth and chassis ground.
20. GND terminal : Earth and chassis ground.
21. “-“ output terminal : Negative polarity output terminal for the MASTER supply.
22. “-“ output terminal : Negative polarity output terminal for the SLAVE supply.
23. “-“ output terminal : Negative polarity output terminal for 5V supply
24.  “+“ output terminal : Positive polarity output terminal for 5V supply

Rear Panel

25. Fuse holder
26. Power socket
27.  AC select switch : With (28) HI-LO switch selects to permit operation from 100, 120, 220 or 240VAC, 50/60 HZ line voltage.
28.  HI-LO switch : HI position selects high voltage range (120, 240VAC inputs), LO position selects low voltage range (10V, 220VAC inputs)
29. Cooling fan : Ventilates the hot air out, to prevent output stage from thermo shock, and also improves the temperature coefficient.

USAGE DESCRIPTION

 Operation Mode

1. Independent : Two independent outputs and 5V fixed output

Output from 0 to rating volts and 0 to rating amperes.

2. Series : Output from 0 to ± rating volts at rating amperes each.

 Output from 0 to double rating volts at rating amperes.

3. Parallel : Output from 0 to double rating amperes at rating volts.

 Constant Voltage Operation

1. Output current range : 0 – rating voltage continuously adjustable
2. Regulation : Line regulation ≤ 0.01% + 3mV

        Load regulation ≤ 0.01% + 3mV (rating current ≤ 3A)

        Load regulation ≤ 0.02% + 5mV (rating current > 3A)

3. Recovery time : 100µs (50% load change, minimum load 0.5A)
4. Ripple & Noise : ≤ 1mV rms (5Hz-1MHz)
5. Temperature coefficient : ≤ 300 PPM/ºC

 Constant Current Operation

1. Output current range : 0 – rating current continuously adjustable.
2. Regulation : Line regulation ≤ 0.2 % + 3mA

        Load regulation ≤ 0.2% + 3mA

3. Ripple current : ≤ 3mA rms.

 Tracking Operation

1. Parallel Operation

Regulation : Line regulation ≤ 0.01% + 3mV

        Load regulation ≤ 0.01% + 3mV (rating current ≤ 3A)

                                  ≤ 0.02% + 5mV (rating current > 3A)

2. Series operation

Regulation : Line regulation ≤ 0.01% + 5mV

                    Load regulation ≤ 300mV

1. Positive and Negative supply (figure below)

Slave tracking error ≤ 0.5% + 10mV of the master.

B.  Single supply (figure below)

Meter

1. Digital Type
1. Display : 3 – ½ Digits panel meter x 2 (0.5” Red LED display)
2. Accuracy : ± ( 0.5% 0f rdg + 2 digits)
3. Voltmeter : 19.99V of full scale (rating voltage ≤18V), 199.9 of full scale (rating voltage ≥20V)
4. Ammeter : 1.999A of full scale (rating current <>

2. Analog Type
1. Display : Analog Voltmeter and Ammeter each two
2. Class : 2.5
3. Dimension : 50x50 (m/m)

 Insulation

Between chassis and output terminal : 20MΩ or above (DC 500V)

Between chassis and AC cord : 30MΩ or above (DC 500V)

OPERATION INSTRUCTIONS

1. Precaution

i.                    AC input : AC input should be within the range of line voltage ± 10% 50/60 Hz 

ii.                  Installation : Avoid using the supply in a place where ambient temperature exceeds 40ºC. the heat sink located at the rear of the supply must have sufficient air space for radiation.

iii.                Output voltage overshoot : Maybe voltage between output terminals exceeds the present value when the power is turned on or off.

2. Setting Current Limit

i.                    Determine the maximum safe current for the device to be powered.

ii.                  Temporarily short the (+) and (-) terminals of the power supply together with a test lead.

iii.                Rotate the VOLTAGE control away from zero sufficiently for the CC indicator to light.

iv.                Set the meter selection switch to A position to select the current metering mode (Digital type only)

v.                  Adjust the CURRENT control for the desired current limit. Read the current value on the Ammeter.

vi.                The current limit (overload protection) has now been preset. Do not change the CURRENT control setting after this step.

vii.              Remove the short between the (+) and (-) terminal hook up for constant voltage operation.

3. Operation mode

Independent Operation

i.                    Disengage both TRACKING mode switches (both switches out) so that the power supply is in the INDEPENDENT operating mode.

ii.                  Adjust “Voltage” control and “Current” control to the desired output voltage and current.

iii.                Turn off the power supply and the equipment to be powered during hook-up

iv.                Connect the positive polarity of the device being powered to the red (+) terminal of the power supply.

v.                  Connect the negative polarity of the device being powered to the black (-) terminal of the power supply.

vi.                Figure below illustrate the connection procedures.

Series Tracking Operation

i.                    Set the power supplies to the TRACKING SERIES mode by engaging the left TRACKING switch.

ii.                  Set the MASTER A/V switch to the V (voltage metering) position, and the SLAVE A/V switch to the A (current metering) position (digital type only)

(Be careful when connecting power supplies in series to achieve voltages higher than 60V DC total or 60V DC between any connection and earth ground)

iii.                Set the SLAVE CURRENT control to the fully clockwise position. The maximum current is set using the MASTER CURRENT control. Follow the instruction for “Setting Current Limit” (INDEPENDENT USE OF “MASTER” OR “SLAVE” SUPPLY) using the MASTER CURRENT control.

NOTE: Because the supplies are being used in series, either CURRENT control can be used to set maximum current. If desired, the MASTER CURRENT control can be rotated fully clockwise and the SLAVE CURRENT control can be used to adjust the maximum current value. Because current through the two supplies must be equal when they are being used in series, the lowest CURRENT control setting will set the maximum output current.

iv.                Adjust the output voltage to the desired level using the MASTER VOLTAGE controls.

v.                  Turn off the power supply and the equipment to be powered during hook-up

vi.                If “single supply” operation is desired, this allows the power supply to be used as twice the voltage and rating current simply by using the negative (black) terminal of the SLAVE supply and the positive (red) terminal of the MASTER supply. The configuration as shown in figure below

vii.                   If the chassis or  common of the equipment being powered is separate from both the positive and negative polarity power inputs. The output of the SLAVE (negative) supply tracking the output of the MASTER (positive) supply. Configuration as figure below.

Parallel Tracking Operation

i.                    Set the MASTER A/V switch to the V (voltage metering) position, and the SLAVE A/V switch to the A (current metering) position. Output voltage will now be read from the MASTER LED display. Output current is exactly double the value read from the SLAVE LED display (because each supply is providing the same amount of current) (Digital type only)

ii.                  Because both voltage and current of the SLAVE supply track the MASTER supply, the maximum current and voltage are setting using the MASTER controls. Using the MASTER supply output jacks, follow the instructions “Setting Current Limit”. Remember that the actual current output at the MASTER supply output jacks is double the reading on the SLAVE indicator meter.

iii.                Adjust the output voltage to the desired level using the MASTER VOLTAGE controls.

iv.                Turn off the power supply and the equipment to be powered during hook-up.

v.                  Connect the positive polarity of the device being powered to the red (+) terminal of the MASTER power supply.

vi.                Connect the negative polarity of the device being powered to the black (-) terminal of the MASTER power supply. The configuration as below: 

5V Fixed Power Supply Operation

i.                    Turn off the power supply and the equipment to be powered during hook-up.

ii.                  Connect the positive polarity of the device being powered to the red (+) terminal of the 5V supply.

iii.                Connect the negative polarity of the device being powered to the black (-) terminal of the 5V supply.

iv.                If the red OVERLOAD indicator lights, too much load has been placed on the supply. This will cause voltage and current to drop and prevent proper operation of the 5V supply. To correct this situation, the load on the supply must be decreased so that no more than 3 amps of current are required.