Light-weight welder particularly suited for soft- and silver soldering and the like

Abstract: Light-weight welder particularly suitable for soft and silver soldering and the like using a power varying according to the welding temperature, wherein the sensing member for detect­ ing the welding temperature is the welding tip.

Description: This invention refers to a light-weight solderer or soldering iron particularly suitable for soft and silver soldering and the like, the power of which is variable according to the soldering temperature, wherein the soldering tip is the sensing member for detecting the soldering temperature. Furthermore, the solderer of the invention has an extremely low thermic inertia whereby the power delivered immediately reaches the value of the power required. The solderers available at present to carry out a soldering of this type are essentially of three different types. Trigger-operated rapid or pistol solderers, which are mainly used for soft soldering, have a soldering tip which reaches almost immediately the operating temperature corresponding to the solder melting temperature. The above-mentioned solderers comprise a network voltage transformer having the secondary on the soldering tip. Solderers of the second type are solderers comprising a continously loaded resistor. Solderers of the third type are essentially solderers of the second type provided with a thermostat which controls the power supplied to the resistor, cutting off this power supply whenever the soldering tip reaches an excessive temperature. The above-mentioned solderers have some drawbacks preventing a satisfactory soldering from being carried out thereby. Solderers of the first type or rapid solderers operate at extremely variable soldering temperatures and at constant power. Accordingly, the soldering tip can reach temperatures much higher than the solder melting temperature and thus the soldering tip is "burnt". Furthermore, the solder can also "bind" to the tip, thus preventing any further use thereof. Solderers of the second type, wherein the temperature is controlled by dissipating heat into the environment, have a drawback in that these solderers very easily reach temperatures at which the solder burns, thus causing the solder to "bind" to the soldering tip. In this field document FR-A-2.141.245 discloses a device for controlling the temperature of electric resistances that can be utilized in soldering irons. In this device the resistance member comprises two pieces namely an external hollow member and a resistance member fitted therein. The two pieces are joined and electrically connected in one point only, such that a voltage is generated at said point. The resistance member is alternatively connected, through a timed changeover switch, to the power source and a threshold amplifier, wherein the threshold is adjustable through a potentiometer. When the voltage exceeds the threshold value set by the potentiometer the power supply is cut. This solution has two drawbacks, namely that the temperature gauging and control is not continuous and the resistance member (soldering tip) must consist of two pieces electrically insulated but in a single point, with a consequent complicate and costly stucture that, furthermore, has a high thermic inertia. Welders of the third type have a theorical advantage in that the welding temperature is kept constant by the thermostat, but they have high thermic inertia. Accordingly, the thermostatic control of the tip occurs with a considerable delay and thus the inherent advantages of the above-mentioned structure are almost completely cancelled. Accordingly, the use of the welders available at present is the source of many drawbacks the most serious of which, from an economic point of view, being that the excessively high tip temperature not only causes the solder to burn, but can also damage the costly electronic components to be welded. The above-mentioned welders should thus be used in manufacturing electronic circuits with some precautions which highly increase the manufacturing time. Accordingly, it is an object of the invention to provide a welder completely free from the drawbacks of the welders available on the market. The welder of the invention comprises a tip temperature control circuit automatically controlling the power supplied. Accordingly, the welding temperature is always comprised between the optimal range, thus allowing a "not burnt" welding to be obtained and preventing the electronic components from being damaged when these electronic components must be welded to printed circuits or the like. The solderer of the invention, which is similar to the solderers provided with a thermostat but is free from the drawbacks thereof, is characterized in that the soldering tip is the temperature detecting member which is connected to the temperature control circuit which thus controls the power supplied. Accordingly, the variation of the power supply required for keeping the soldering tip temperature at a constant level occurs practically immediately. The solderer of the present invention will be now described in detail with reference to the annexed drawing, wherein: Figure 1 is a diagram of the whole solderer circuit; and, Figure 1A is a diagram of the protection circuit associated to the diagram of Figure 1. Having an outer structure substantially of the pistol type comprising a lamp for lighting the working area, the solderer of the invention essentially comprises: a network voltage transformer TRF having a primary B and four secondaries BP, B1, B2 and B3; an excitation circuit CQ; a first reaction circuit CR1; a second reaction circuit CR2; a soldering tip PS and a protection circuit CIRP (Fig. 1). Furthermore, the circuit of Figure 1 comprises two diodes D1, D2, a lamp LI for lighting the working area and an input circuit CA connected thereto, a thermistor RQ of the NTC type for protecting the diodes of bridge PR and an operating push button PA. Excitation circuit CQ comprises a resistor RQ1, a resistor RQ2, a capacitor CQ1 and a low vacuum luminous tube TLBV. First reaction circuit CR1 comprises secondary B1 of transformer TRF, a first capacitor CPR1, a second capacitor CCR1,a diode DR1, a rheostat RS1 for controlling the temperature of soldering tip PT and a transistor TR1. Second reaction circuit CR2 comprises secondary B2 of transformer TRF, a first capacitor CPR2, a second capacitor CCR2, a diode DR2 and a transistor TR2. Protection circuit CIRP comprises a diode D3, a diode D4, a thermistor THR and a transistor TR3. As clearly seen in the circuitry, soldering tip PT is connected to secondary BP of transformer TRF, while reaction circuits CR1 and CR2 are connected to secondaries B1 and B2 respectively, and the working area lighting lamp LI is connected to secondary B3 of transformer TRF. The output of bridge PR is connected to capacitor C1, which is preferably of the electrolytic type, and is the solderer input. Diodes D1 and D2 on the network voltage reveal the 100 Hz pulses, namely twice the network frequency, and supply excitation circuit CQ. Capacitor CQ1 is loaded by diodes D1, D2, partially equalizes the pulsing voltage and unloads on the base of transistor TR2 of second reaction circuit CR2. It should be pointed out that the unload pulse of capacitor CQ1 is very strong and the low vacuum luminous tube TLBV de-energizes and turns off at each pulse because the resistance of resistor RQ1 is very high (preferably about 1M ). Reaction circuits CR1 and CR2 comprise combinations of capacitors and resistors causing the phase to rotate from the output of TR1 and TR2 and the reaction on the base thereof, thus obtaining an optimal reaction on the base of TR1. Furthermore, first reaction circuit CR1 comprises a rheostat RS1 in series with the base of TR1, which rheostat RS1 controls the value of the temperature of soldering tip PT. Diode DR1 of circuit CR1 and diode DR2 of circuit CR2 act as peak detectors and load capacitor CC1 and the like with a negative voltage. The bases of transistors TR1, TR2 are normally inhibited but each time that TLBV de-energizes transistor TR2 turns ON whereby primary B of transformer TRF receives power and a reaction signal is developped on secondaries B1 and B2 thereof. This reaction signal supplies a voltage alternatively to the bases of TR1 and TR2 which thus self-oscillate while diodes DR1 and DR2 connected to the bases of transistors TR1, TR2 tend to inhibit these transistors. The new concept of the solderer of the invention is to use the property of conductive metals according to which the ohmic resistance thereof increases according to the increase in temperature. Accordingly, for the purposes of operation of the solderer of the invention the increase in the ohmic resistance of the soldering tip PT due to the increase in the temperature thereof causes a variation of the load on primary B of transformer TRF. Accordingly there is a variation of the inductance of transformer TRF which is connected to capacitor CP, since the circuit is self-oscillating, and a variation of the voltage on the terminals of primary B. This variation of the voltage on primary B and the variation of the voltage on secondaries B1 and B2 together with the variation of the oscillation frequency of transistors TR1 and TR2 affect both the base voltage of these transistors and the reaction signal phase thus causing a rotation of the phase and a modification of the amplitude. Accordingly, as the temperature of tip PT increases the power supplied thereto by transistors TR1 and TR2 decreases and viceversa and thus transistors TR1 and TR2 act as a blocked oscillator at the maximum value of the temperature of tip PT and as a continuous oscillator at the minimum value of such temperature. It should be noted now that low vacuum tube TLBV is intended to trigger reaction circuit CR2 whenever the oscillation thereof is blocked. Figure 1 shows a protection circuit for protecting the solderer against the overheating of transistors TR1 and TR2 or transformer TRF. It is evident that protection circuit CIRCP is connected to the welder circuit at common points a , b , c and d . In use, thermistor THR which operates as a grounded divider and is located close to the dissipator of transistors TR1 and TR2 heats as the temperature of the dissipator increases, thus causing a decrease in the ohmic resistance thereof. Accordingly, the signal from secondary B2 of transformer TRF increases, which signal is revealed by diode D3 and applied to the base of transistor TR3 that turns to ON state short-circuiting the reaction o signal of secondary B2 and blocking the self-oscillation. On the contrary, if transformer TRF overheats, the maximum induction of the core thereof decreases and in the core the power exceeds the value of such maximum induction by high peak values of power on resistor RP. Diode D4 reveals the voltage on resistor RP and causes transistor TR3 to turn ON, thus blocking the oscillation as in the above-mentioned case. The working area lighting lamp LI is supplied by circuit CA which comprises secondary B3 of transformer TRF and rectifier RRR. From the foregoing it is evident that the solderer of the invention completely reaches the objects of the invention.

Claims: A light-weight soldering iron for effecting soft and silver solderings having a soldering tip of a resistive material capable of ohmically producing heat when crossed by an electric current, the ohmic resistance of which increases as the temperature increases; a power supply; a power transferring circuit for transferring current from said power supply to said soldering tip; a control circuit for controlling the power supplied to said tip, in order to control the soldering temperature of said soldering tip, and a temperature detecting member connected to said control circuit, characterized in that said soldering tip is made of one piece and constitutes by itself the detecting member that continuously detects the soldering temperature. The soldering iron of claim 1, substantially comprising in combination: a network voltage transformer (TRF) having a primary (B) and four secondaries (BP, B1, B2 and B3); said soldering tip (TP) being connected to a first (BP) of said four secondaries of transformer (TRF); two power transistors (TR1 and TR2) operatively connected to said primary (B) of transformer (TRF); an excitation circuit (CQ); a first reaction circuit (CR1) including another secondary (B1) of said four secondaries; a second reaction circuit (CR2) including another secondary (B2) of said four secondaries; and a protection circuit (CRP), and wherein said excitation circuit (CQ) is connected to one of said power transistor (TR2) through said second reaction circuit (CR2) and said first reaction circuit (CR1) is connected the other of said two power transistors (TR1) so that said excitation circuit (CQ) is piloting the conducting state of said two power transistors (TR1, TR2) and consequently the passage of power to said soldering tip (TP) through said primary (B) and secondary (BP) of said transformer (TRF). The soldering iron of claim 2, further comprising a rectifying bridge (PR); two diodes (D1, D2) connected to said excitation circuit (CQ) to apply thereto pulses at network frequency which are transformed in very short excitation pulses applied to said first power transistor (TR2) through said first reaction circuit (CR2); a lamp (LI) for lighting the working area; an impedance (CA) for limiting the power applied to said lamp (LI) through another (B3) of said four secondaries of said transformer (TRF); a thermistor (RQ) of the NTC type for protecting the diodes of said rectifying bridge (PR) and an operating push button (PA). The soldering iron of claim 3, wherein said excitation circuit (CQ) substantially comprises a first resistor (RQ1) and a second resistor (RQ2) parallel connected to said diodes (D1, D2) as a load therefor; a low vacuum tube (TLBV); a capacitor (CQ1) forming together with said first resistor (RQ1) a time constant for timing said low vacuum tube (TLBV) on which the load of capacitor (CQ1) discharges and wherein said low vacuum tube (TLBV) triggers said first power transistor (TR2) through said second reaction circuit (CR2). The soldering iron of claim 4, wherein said first reaction circuit (CR1) further comprises a first phasing capacitor (CPR1); a second capacitor (CCR1) connected to a diode (DR1) for generating a DC voltage for inversely polarizing said other power transistor (TR1). The soldering iron of claim 5, said second reaction circuit (CR2) further comprises a first phasing capacitor (CPR2); a second capacitor (CCR2) connected to a diode (DR2) for generating a DC voltage for inversely polarizing said first power transistor (TR2). The soldering iron of claim 2, wherein said protection circuit (CIRP) further comprises a first threshold diode (D3); a second threshold diode (D4); a thermistor (THR) and a third transistor (TR3) and wherein said diodes (D3, D4) are connected to said third transistor to apply thereto warning signals about excessive temperature of said power transistors (TR1, TR2), under the control of said thermistor (THR), and excessive temperature of said transformer (TRF) so that said third transistor (TR3) may shortcircuit the reaction signals from the transformer secondary (B2) included in said second reaction circuit (CR2), thus cutting the power applied to said transformer primary (B).

Inventors: FRANCOLINI ERMANNO, SANTORO GIOVANNI, FRANCOLINI, ERMANNO, SANTORO, GIOVANNI
Applicants: FRANCOLINI ERMANNO, SANTORO GIOVANNI, FRANCOLINI, ERMANNO, SANTORO, GIOVANNI
Application year: 1983
Main classification: B23K3
IPC codes: B23K3