Power Supply Circuitry - Picotest M3500A Service Manual

3.4.1 Power Supply Circuitry

In this section, a basic circuit theory that can help you to troubleshoot the
power supply circuit of M3500A is provided. The power supply circuit
transforms the AC line voltage to required voltage (AC or DC) for various
internal circuits. The block diagram of power supply circuit is shown in
Figure 3-4.
240V
220V
120V
100V
As shown in Figure 3-4, AC power is applied through the line voltage
selector to power transformer. There are four selections of line voltage (240,
220, 120, and 100 Vac) can be applied to M3500A. You must choose a
correct line voltage for your multimeter according to your local power utility
voltage or damage may occur.
The power transformer has a total five secondary windings to produce AC
and DC voltages for M3500A. AC voltage is used to provide the VFD filament
voltage, and each DC supply uses a regulator circuit for various purposes.
Please refer to Figure 3-4 to check the purpose of each supplied voltage.
→
Regulator
37V
Circuit
AC1
⇒
AC2
→
5VD
Regulator
→
3.3VD
Circuit
+18VA
Regulator
⇒
Circuit
-18VA
→
5VA
Regulator
→
3.3VA
Circuit
Figure 3-4
31
For VFD driver Supply Voltage
For VFD Filament Voltage
For Panel MCU and Peripherals
For Main Board DSP and Peripherals
For Analog Front-End Circuit
For Relay Power Supply Voltage
For Slope ADC Digital Circuit
Power Supply Circuit