T2130
5 CIRCUIT DESCRIPTION AND SCHEMATIC DIAGRAMS T2130
5.4 POWER SUPPLY I (MODULE 4) PART NO. 625644
This unit contains power supplies for RE2100, AT2110, and T2130. It also contains the audio amplifier
for RE2100.
SWITCH MODE POWER SUPPLY
The power supply is a forward switch mode converter. It converts the 24V DC battery voltage to ±18V DC
and +9V DC. ±18V DC and 9V DC are fed to RE2100.
The output voltage of the +18V DC output is sensed and compared with a reference voltage by an
operational amplifier resulting in an error voltage. The current running in the output transistors is sensed
over a resistor. The error voltage from the operational amplifier is then compared with the current signal
by a comparator.
The oscillator produces a synchronization pulse. This pulse is triggering two flip-flops. One flip-flop is used
to alter between the two output MOS transistors working as a push-pull transformer coupled output stage.
The other flip-flop turns on the selected output transistors. This flip-flop is turned off by the comparator.
So every time the current has reached the level set by the error voltage, the output transistors are turned
off. If the output voltage falls, the output supply current is allowed to raise, the pulse width is enlarged,
and the output voltage is then reestablished. The regulator is then working in a current mode instead of
the usual voltage mode. This is of great advantage for the stability of the control loop, (first order instead
of second order loop).
Current limiting is easily done by limiting the error voltage to a fixed maximum voltage. The current is
limited to approx. 3.5A
The pulse width regulated voltages from the secondaries of the transformer are then rectified and
smoothed by inductors and capacitors.
The sum of the three currents are sensed by a resistor. If this voltage is outside ±0.35V DC approx. (equal
to ±1.5V DC approx.), the converter is stopped and goes into soft start. This is to protect the rectifier diode
against output short-circuit.
All the necessary amplifiers, flip-flops, etc. are contained in the IC U01.
L01, C02-C05 are the input filter.
The 12V DC supply voltage for U01 is made by R01, D02, C06, and C07. If the supply voltage is lower
than approx. 7.5V DC the internal under voltage lock-out is in action.
R02 and C08 determine the oscillator frequency to approx. 50 kHz.
The non-inverting input of the error amplifier is connected to the voltage 12V DC by R03. The inverting
input is connected to the reference voltage by R05.
D23 and OC01 are the feed-back loop of the error amplifier. R48, C46, and R45, C53 are frequency
compensation in the feed-back loop to avoid self oscillations.
R08, R09, and C11 are the feed-back loop of the error amplifier.
The output MOS transistor current is sensed by R16-R20, 5 resistors in parallel to minimize the induction.
The current signal is then led to current sense amplifier input, pin 4. The R14 and C12 make a lowpass
filter to remove noise. The emitter of Q01 follows the ramp voltages on the oscillator capacitor C08. R07
adds some of this ramp signal to the current signal. This is necessary to avoid sub-harmonic oscillations
when the duty-cycle is higher than 50 per cent.
PAGE 5-25
9315
The voltage on pin 1 determines the clamp voltage for the error voltage. This voltage is determined by
R04 and R06. The capacitor C10 is the soft start capacitor, making the duty-cycle and the output voltages
raise slowly.
The two pulse width modulated outputs are led to the two output MOS transistors by R10 and R11. These
two resistors slow down the rise times of the MOS transistors to prevent spurious oscillations. R12 and
R13 secure that the transistors always stay off when the IC U01 is off.
R27, C14, R29, C15, R28, and C16 are snuppers, reducing oscillation due to stray capacitors and stray
inductions in the transformer.
D06 to D11, L02 to L04, and C17 to C22 are the three output rectifiers and filters.
R30 and R31 limit the voltage in case of no load conditions.
The switch mode power supply is followed by regulators for ±15V and ±5V. These voltages are used to
supply the modules in T2130. The +5VA is used to back-up the microprocessor, when switching off. D12
prevents current to flow from C23 to other circuits than U03.
24VA REGULATOR
The regulator is regulating the battery supply so it is limited to 28V. It also protects the AF-amplifier and
the power amplifier from transients on the battery supply.
The output voltage is sensed by the voltage divider R44, R43 and fed back to the shunt regulator D18.
If the output voltage rises above 28V, D18 starts to conduct and the gate of Q06 and Q07 goes lower.
When the gate goes lower the drain to source resistance rises and the output voltage is kept on 28V. If
the output is less than 28V, D18 is not conducting and the gate is high (+50V), thus keeping the drain to
source resistance low (voltage drop D-S = 0.5V).
D17 is protecting D18 from over voltage.
D21 is protecting the gate/source from break-down. The on/off switching is done with RE01 and RE02,
controlled from on/off switch in RE2100.
21V REGULATOR
The 21V regulator is stabilizing the supply for the aerial coupler. The regulator is a low drop regulator. D24
is reference voltage for the regulator. R60 and R61 determine the output voltage.
AF AMPLIFIER
The AF amplifier is built-up around U07.
The amplifier is supplied from the battery via the 28V regulator. In the input there is a transformer to obtain
insulation between -battery and chassis. It also suppresses common mode noise from the multicable to
RE2100.
The input impedance is 600 ohm.
R39 and R38 are setting the voltage gain to 37 dB.
At the output, R40, C36, FP01, FP02, and C37 prevent U07 from oscillating.
When loaded with 8 ohm, output power will be 5 Watt, when loaded with 4 ohm, output power will be 10
Watt
To Next Page
Loading...
Need help?
General
