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G8MNY > TECH 14.02.26 19:16l 58 Lines 2450 Bytes #10 (0) @ WW
BID : 52103_GB7CIP
Subj: Thermostatic Iron Repair
Path: JH4XSY<JE7YGF<LU4ECL<LU9DCE<GB7YEW<GB7CIP
Sent: 260214/1003Z @:GB7CIP.#32.GBR.EURO #:52103 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Corrected Jul 22)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
I pickup a "Weller" type iron by "AdcolA" that has electronic temperature
control, using a negative temperature thermistor with the element. This is
rather than "Magnetic Curie Point" temperature switch of Weller system, or a
thermocouple & sensitive op amp system!
In the handle was a 14 pin control chip which was dud & did not trigger the
triac. So I developed this much simpler 1 transistor circuit as a replacement.
24V oﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ
AC 1K ｳ
2A _ｳ_ ｳ
\_/ 12R The thermistor is about 50K cold
ﾃﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ 48W and less than 1K hot. The 3K9 &
ｳ ｳ ｳ + 2K Element 150R set lowest & highest temp
ｳ +ｳ NTC ﾚﾄｴﾃﾄﾄﾄﾂﾄﾄｴ ｳ with my thermistor.
10V_ｳ_=== Therm ｳ47u ｳ/ _ｳ_ ｳ
'/_\ ｳ100u ﾃﾄﾄﾄﾂﾄﾁﾄﾄﾄﾄｴ \_/=LED ｳ
ｳ ｳ Temp ｳ BC337ｳ\e ｳ ___ｳ___
ｳ ｳ ﾚﾄ>pot ｳ ｳ ｳ _\/_/\_
ｳ ｳ ｳ 2K ｳ ｳ ｳ____/ ｳ3A
ｳ ｳ ﾀﾄﾄﾄｴ 3K9 ｳ ｳTriac
ｳ ｳ 150 ｳ ｳ ｳ
0V oﾄﾄﾁﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙ
iron earth
Eﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ
///
The traic is no longer phase fired, as I assume the original IC could do, but a
simple on off including an added status LED (used on some of their irons).
HOW IT WORKS
The 100uF is charged up via 1K & diode to 10V when the zener conducts. The
triac is turned on via the LED & 2K, giving full power to the heater element.
When the thermistor is hot enough (lower resistance) to put 0.6V on the NPN
base with the preset pot load, the NPN conducts, & bypasses the current going
through the LED and gate, keeping the triac off. The 47uF slows the action, so
the triac gets a chance to conduct on both half cycles & even a few on & off,
as shown on the flashing LED.
The circuit needs scoping to check the triac is firing OK on both + & - half
cycles, if not, damage can be done to very small 24V AC transformers!
Also see my Tech Bul on "Soldering Iron Economiser/Boost"
Why Don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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