Sorensen DCS Series 3kW Supplies
Theory of Operation
RC snubbers across each rectifier (also across the entire secondary of the transformer on some
models) and tape-wound toroids on each transformer secondary lead are used to suppress
transients. The rectifier output is filtered by capacitors C701-711 on the A7 PCB, capacitors
C801-803 on the A8 PCB, and the output inductor to provide the DC output. Energy stored in
the output capacitors and the input bulk capacitor provide the holdup time of the supply.
A blade-type current shunt (R19) attached to the A4 PCB is used to monitor the output current
and provide a feedback signal to the A2 PCB current control circuit. Op amp U2 is a differential
amplifier used to condition and scale the shunt voltage to produce a 0-5V signal.
Output voltage regulation under no load or lightly loaded conditions is made possible by preload
resistor R701 and the down programming circuit (op amp U1, FET Q1 and their related parts)
which draw a small current whenever there is an output voltage. The down programming circuit
also serves to quickly discharge the output capacitors when changes in programming inputs
require a lower output voltage from the supply. The down programming circuit monitors the
control signal from the A2 PCB voltage and current control circuits at pin 6 of U1-B. Whenever
this signal becomes more negative than the reference at pin 5 (approximately -0.125 Vdc), the
output of U1-B goes positive and FET Q1 is turned on by U1-A through resistor R4. Resistor R1
acts as a current shunt for the down programmer to provide feedback to U1-A pin 2 to maintain
a constant current through Q1. Resistor R9 and diode CR4 feedback the current shunt amplifier
output to U1-A to reduce the current drawn through Q1 when the load current provides a
discharge path for the output capacitors.
5.3.5
Auxiliary Supply, OVP, Control, Programming, Monitor Circuit
(A2 PCB)
The A2 Control PCB consists of the following circuits:
1. Auxiliary supply circuit
2. Inrush limit control, input over-voltage shut down, and sync circuits
3. Voltage control, current control, mode indicator, and internal shutdown/soft start circuits
4. Remote/local programming select circuits
5. Remote analog programming input circuits
6. Remote sense line protection circuit
7. Over Voltage Protection (OVP) circuit
8. Remote shutdown circuit and front panel standby switch
9. Output voltage and current readback circuits
10. Fan control and over-temperature shutdown circuit
Auxiliary Supply Circuit
The auxiliary supply circuit is a multiple output, flyback converter used to generate the +28V,
+15V, -15V, +5V, -6.2V, and +5V
REFERENCE
voltages required by the various control circuits.
The main components of the auxiliary supply are oscillator U17, PWM U16, and transformer T1.
Oscillator U17 is a CMOS 555 timer which generates a 60 kHz signal for the PWM and the sync
circuits. PWM U16 produces a 60 kHz variable pulse width output which drives FET Q7. Q7
switches the primary winding of transformer T1. Current and voltage feedback signals to the
Operation Manual
5-7