4
UVtron DRIVE CIRCUIT
Operating a UVTRON requires a high voltage of about 350 V. Figure 4 shows the basic circuit for the DC-DC con-
verter high-voltage power supply and the operating waveforms for each part. In this case, it is important to lower the
converter oscillation frequency, f, to reduce the capacitance of capacitor C
1
for smoothing the rectified high voltage, and
to raise the power supply output impedance. Here is an explanation of the operation of this circuit. (See Figures 4-1 and
4-2.)
Point (a):
This is the converter oscillation waveform. Pulses with a width of a few microseconds are generated at in-
tervals of a few milliseconds to a few tens of milliseconds.
Point (b):
The height of pulses is raised in proportion to the winding ratio for the step-up transformer.
Point (c)
: High DC voltage Ebb is supplied to the UVTRON's anode by rectifier diode D and smoothing capacitor C
1
.
Point (d):
Discharge starts when ultraviolet light enters the UVTRON. The charge on C
1
begins to flow as discharge
current, i, to generate narrow voltage pulses across R and C
2
.
Point (e):
The charge on C
1
is exhausted, the anode voltage falls below the discharge sustaining voltage Vs, and the
discharge stops. The anode voltage does not recover until the next charge. During that period, the ions in
the UVTRON are quenched.
Point (f):
If no ultraviolet light enters the UVTRON, the anode voltage recovers to Ebb, and there is no discharge un-
til ultraviolet light is received.
The UVTRON repeats this cycle to indicate the presence or absence of ultraviolet light with pulse signal output.
Here, it is important that the converter oscillation interval (l /the oscillation frequency f) be greater than the time re-
quired for the ions generated in the UVTRON tube by the discharge to be quenched, so this interval must be from 5 to l0
milliseconds. This period is called the quenching time. Also, since the capacitance of smoothing capacitor C
1
influences
the discharge current, it is best to reduce the capacitance of C
1
in order to retard the wear on the electrodes and to reduce
the number of ions generated. The optimum capacitance is a few tens of picofarads.
i
+
–
V
1
D
Tr
C
1
C
2
R
UV TRON
A
UV
K
(a)
(c)
(b)
(d)
TPT C0011EA
TPT C0011EA
UVTRON OUTPUT
WAVEFORM
OSCILLATION
WAVEFORM
OSCILLATOR
CIRCUIT
UVtron Drive Circuit
Figure 4-1: UVTRON Drive Circuit
Содержание UVTRON
Страница 1: ...TECHNICAL INFORMATION How to Use UVTRON...
