QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 477
LOW NOISE\EMI SWITCHING POWER SUPPLY
1
LT1683
DESCRIPTION
Demonstration circuit 477 shows how the LT1683
switching regulator greatly reduces conducted and radi-
ated EMI by controlling the voltage and current slew
rates of the two output switches. DC477 employs a
push-pull topology which is inherently less noisy than
most other topologies and the high frequency EMI is
reduced by as much as 40dB by slewing the switching
currents and voltages. The design is very well suited for
noise sensitive systems such as medical instruments,
industrial sensing and control, data conversion and wide
band communications.
DC477 can be set up to produce an isolated or non-
isolated +5Vout at 2A from a 36Vin – 72Vin range. The
Board can be modified, by changing the transformer, to
produce multiple output voltages less than or greater
than the input voltage. DC477 uses potentiometers that
set the slew rates of the power switches, allowing the
user to observe the benefit of slew rate control, and to
examine the tradeoff between noise performance and
circuit efficiency.
Design files for this circuit board are available. Call
the LTC factory.
QUICK START PROCEDURE
DC477 is easy to set up to evaluate the performance of
the LT1683. Refer to Figure 1 for proper measurement
equipment setup and follow the procedure below:
1.
Connect the 0 – 2A load between the Vout and Gnd
terminals on the right hand side of the board.
2.
Apply 48V between the Vin and Gnd terminals on the
left hand side of the board.
3.
To measure the output noise connect one end of a
BNC cable to the BNC connector J1. Connect the
other end of the BNC cable to an oscilloscope with a
50 Ohm input impedance … refer to Application Note
AN70 for more precise techniques for measuring the
output noise.
Notes:
1. The temperatures of MOSFETs Q3 and Q4
should be monitored if potentiometers R6 and
R9 are adjusted from their factory settings.
2. The board comes set up for a non-isolated Vout.
The board can also be set up for an isolated
Vout by making the following changes:
Insert R18, R23
Remove R19, R21, R22, C16
R10 = 3.9k
R14 = 510 ohm
C18 = 1uF
Insert C20
