Circuit Schemes And Functions; Power Supply Circuits; External Power Supply; Primary Power Supply - ELCOM Euro-500 Handy Series Service Manual

Euro-500TX Handy

2 Circuit schemes and functions

2.1 Power supply circuits

2.1.1 External power supply

The switched pulse power supply circuit ONTOP 100-240 V, 50-60 Hz, 24 V/1.5 A, 36 W serves as the
external power supply for the ECR. Its primary function is to produce unidirectional voltage needed for the
proper ECR functionality from the mains voltage.

2.1.2 Primary power supply

The primary power supply serves as the supply of voltage for the +5 V voltage source in the case that the
external power supply is connected. This circuit is built around the MC34063 universal unidirectional vol-
tage changer that guarantees high resistance to the mains interference. Its high efficiency (80 %) secures
effective voltage conversion and low heat emissions (low cooling demands). The output voltage is approx.
8.25 V and is marked as VSS in the scheme.
D1
MBRS340T3
C1
ADP+
4
ADP-
3
1u/35V
2x3,3mH/1,5A

2.1.3 The +5 V power source (VCC) and the NMI signal generator

This power source manufactures the VRAM and VCC voltages. VCC voltage is needed for the circuits that
are at all times powered as the ECR is on. The KA278R05 linear voltage stabiliser is at the heart of this
circuit that fixedly supplies +5 V voltage. Figure 2.2 shows the NMI signal generator as well and this circuit
features NCP301 comparator with threshold level 4.5 V. The main use for the NMI signal is that informs
the microprocessor of the voltage drop and is also used to shut down all the power sources. The D4 diode
produces the VRAM voltage, the R9 resistor ensures the constant charging of the BT1 NiCd accumulator
while the ECR is on, and the JP1 jumper is used for ECR clearing. The figure also shows the PWRSW that
is used to connect the main ECR power switch.
VS S
FMKA140
10
Service manual
EF1
F2
VINf
1
EMI
1.85A
C2
FILTER
2 1u/35V

Fig. 2.1 Primary power supply

C70
D15 100n
VBAT1
NMI
R6
PWRSW
22k
AVA 5400-2P-S
C13
R5
100n
150k

Fig. 2.2 +5 V power supply and the NMI signal generator

U13
8
7
R20
6
0R22
5
MC34063
R22
VIN
5k6
R21
1k
C3
330u/25V
D4
KA278R05 FMKA140
VCC
VRAM
1 2
4
U14
C9
NMI
2200u/25V
U12
NCP301LSN45T1
© Elcom, s. r. o.
D3
FMKA140
L1
1
2
3
120uH
4
C4
470p
VSS
C5
330u/25V
R9
1k0/F
JP1
R30
0R
Batt 3p
BT1
3V6, 60mAh