WO2007071247A2

WO2007071247A2 - Electronic ignition circuit and a method for operating said circuit

Info

Publication number: WO2007071247A2
Application number: PCT/DK2006/000728
Authority: WO
Inventors: Ken Petersen
Original assignee: Danfoss A/S
Priority date: 2005-12-22
Filing date: 2006-12-19
Publication date: 2007-06-28
Also published as: WO2007071247A3; CN101360953A; EP1963747A2; CN101360953B

Abstract

The present invention relates to an electronic ignition circuit comprising a resonator circuit operatively connected to a controllable switch, the ignition circuit further comprising means for controlling the controllable switch in response to a determined level of a current flowing in the resonator circuit. The present invention further relates to a method for operating an electronic ignition circuit comprising a resonator circuit operatively connected to a controllable switch, the method comprising the step of controlling the controllable switch in response to a determined level of a current flowing in the resonator circuit.

Description

ELECTRONIC IGNITION CIRCUIT AND A METHOD FOR OPERATING SAID CIRCUIT

FIELD OF THE INVENTION

The present invention relates to an electronic ignition circuit for oil or gas burners including a circuit for controlling a charging current provided to a resonator circuit. The ignition circuit further comprising means for resetting, by discharging, the resonator circuit.

BACKGROUND OF THE INVENTION

WO 03/052522 discloses an electronic ignition circuit according to the prior art. The electronic ignition circuit suggested in WO 03/052522 comprises a rectifier, a RC-filter, a MOS-FET type transistor and a resonator circuit including a capacitor and an ignition coil.

It is a disadvantage of the ignition circuit of WO 03/052522 that the energy accumulated in the resonator circuit is uncontrollable. Furthermore, the energy accumulated in the resonator circuit is strongly dependent on the load of the resonator circuit - i.e. whether the resonator circuit is operated with open or short-circuited terminals.

Therefore, it is an object of the present invention to provide an electronic ignition circuit that overcomes the above-mentioned problems of prior art ignition circuits by providing an ignition circuit where the energy accumulated in the resonator circuit is controlled in response to a current flowing in the ignition circuit.

It is a further object of the present invention to provide an electronic ignition circuit with increased efficiency compared to the efficiency of prior art ignition circuits. SUMMARY OF THE INVENTION

The above-mentioned objects are complied with by providing, in a first aspect, an electronic ignition circuit comprising a resonator circuit operatively connected to a controllable switch, the ignition circuit further comprising means for controlling the controllable switch in response to a determined level of a current flowing in the resonator circuit.

The relevant current level to be determined may be the current flowing in a primary winding of a transformer. This primary winding forms, in combination with a capacitor, the resonator circuit. By controlling the current in the primary winding of the transformer the energy provided to the resonator circuit may be controlled in a very efficient manner.

The electronic ignition circuit may further comprise means for comparing the determined level of the current flowing in the resonator circuit and a predetermined current level. Such comparison between a determined current level and a predetermined current level may be accomplished using an ASIC.

The controlling means for controlling the controllable switch may comprise current sensing means for determining the level of the current flowing in the resonator circuit, and a control switch adapted to close the controllable switch in response to a result of the comparison of the determined current level and the predetermined current level. The current sensing means may comprise a shunt resistor operative connected to the controllable switch. The control switch may alternatively be replaced by a microprocessor which closes the controllable switch in response to the determined current level. Preferably, the controllable switch is an IGBT-type transistor.

The electronic ignition circuit may further comprise means for discharging the resonator circuit, said discharging means being operatively connected across the controllable switch. Preferably, the discharging means comprises a diode.

The electronic ignition circuit may further comprise means for at least partly rectifying an incoming supply signal and filter means operatively connected to the rectifier means so as to filter the at least partly rectified incoming signal.

In a second aspect, the present invention relates to an electronic ignition circuit comprising means for controlling an amount of energy provided to a resonator circuit, the ignition circuit further comprising means for preventing energy not consumed by a load operatively connected to the resonator circuit from accumulating in the resonator circuit. Thus, according to the second aspect of the present invention no energy is accumulated in the resonator circuit because energy in access of that is consumed in the load is discharged through a discharging arrangement, such as a diode. The amount of energy provided to the resonator circuit may be controlled or regulated by controlling the current provided to the resonator circuit. The combination of controlling the energy provided to the resonator circuit and preventing that energy is accumulated in the resonator circuit ensures that the efficiency of the resonator circuit becomes independent of the load operatively connected to the ignition circuit. Typical efficiencies of the resonator circuit according to the present invention may exceed 80%, 85% or even 90%.

In a third aspect, the present invention relates to a method for operating an electronic ignition circuit comprising a resonator circuit operatively connected to a controllable switch, the method comprising the step of controlling the controllable switch in response to a determined level of a current flowing in the resonator circuit. The step of controlling the controllable switch in response to a determined level of current may involve closing the controllable switch when the current flowing in the resonator circuit exceeds a predetermined level. The current flowing in the resonator circuit may be determined by measuring a voltage drop across a shunt resistor operatively connected to the controllable switch.

In a fourth aspect, the present invention relates to a method for operating an electronic ignition circuit, the method comprising the steps of

- providing current to a capacitor of a resonator circuit by operating a controllable switch in a conducting mode of operation, and

- changing the mode of operation of the controllable switch to a nonconducting mode of operation when the current provided to the capacitor exceeds a predetermined current level.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be explained with reference to the accompanying figures, wherein

Fig. 1 shows a diagram of the electronic ignition circuit according to the present invention,

Fig. 2 shows the charging current of the ignition circuit with short circuited output terminals,

Fig. 3 shows the charging current of the ignition circuit with standard load connected to the output terminals,

Fig. 4 shows the charging current of the ignition circuit with maximum load connected to the output terminals, and Fig. 5 shows the charging current of the ignition circuit with no load connected to the output terminals.

While the invention is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. It should be understood, however, that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

In its most general aspect the present invention relates to an electronic ignition circuit for oil or gas burners. In particular the present invention relates to a high voltage high frequency ignition circuit comprising a power supply, a noise suppression filter, a resonator, a current control circuit, a reset diode and a high frequency transformer wound on a core.

Referring now to Fig. 1 , the noise suppression circuit is constituted by components L1 , R1 , C3, C4 and C5. The power supply consists of the half wave rectifier circuit D1 and C2. This power supply fed the subsequent oscillator with a half wave voltage and current. The electronic ignition circuit further comprises an oscillator circuit being defined by components R2, R3, DZ1 , TR1 , C1 and the transformer T1. The transformer is connected with a feedback winding to the gate of TR1 to provide the feedback needed for the oscillator. The primary winding of the transformer T1 forms a resonator circuit with capacitor C1. The components R2, R3 and DZ1 form a bias circuit for the transistor TR1. Preferably, the transistor TR1 is an IGBT transistor. The electronic ignition circuit further comprises zener diodes DZ2 and DZ3 to protect TR1 against high voltage spikes on the gate. A current control circuit is formed by components X1 , C6, R4, and R5, where R5 is a current measuring shunt resistor.

With the above-mentioned current control circuit the energy charge of the resonator circuit (T1 and C1 ) will always be fixed to the preset value. This preset value is defined by the current measuring shunt R5 and the trigger level of X1. The preset value of the energy charge for the resonator circuit is chosen to the value needed to produce a spark with the correct energy on the output of the ignition circuit. In this way it is easy to change the output power of the ignition circuit just by changing the value of R5.

The efficiency of the electronic ignition circuit according to the present invention is high because the resonator circuit is only charged with the amount of energy necessary to produce the correct spark on the output. By applying this technique an efficiency of around 90% has been reached. Furthermore, the current control circuit in combination with the IGBT transistor also make it possible to produce this high efficient circuit because current control circuit ensures a very short cut-off time for the IGBT transistor.

The electronic ignition circuit further comprises a reset diode, D2, normally inserted as a flyback diode for protection of the transistor. However, in the electronic ignition circuit according to the present invention reset diode, D2, is operated as a reset diode.

For an electronic ignition unit it is a demand that the circuit and transformer can operate under all load conditions - i.e. from short circuit output to no load at all (open output). When the resonator circuit is charged with a fixed energy amount in every cycle of the 50-60 KHz burst, and the load on output doesn't consume that energy, a reset (discharge) of the resonator circuit is necessary. If the reset diode, D2, was absent, and the resonator circuit is not discharged (reset) under every cycle, the trigger level of the current control circuit will never be reached and the charging of the resonator circuit comes out of control. If the charging of the resonator circuit comes out of control everything may in principle happen in the circuit depending on the actual load condition.

The charging current provided to the resonator circuit is depicted in Figs. 2-5 under different load conditions.

When the output of the resonator circuit is short circuited, see Fig. 2, the reset diode will discharge the same amount of energy from the resonator circuit as it was charged with. Fig. 2 shows two curves - curve "1" and curve "C". Curve "C" is a magnification of a section of curve "1 ", which oscillate with a frequency of 50 kHz. Thus, curve "1" is a 50 kHz charging current burst in the positive half-wave (10 ms) of the supply voltage. Referring now to curve "C" charging of the resonator circuit occurs during the positive half period whereas discharging occurs during the negative half period. Since the output terminals are short-circuited charging and discharging of the resonator circuit must be balanced - i.e. energy provided to the resonator circuit is removed again during discharging. In Fig. 2 the area of the positive half period equals the area of the negative half period - i.e. discharging equals charging.

When a normal load is applied to the output, see Fig. 3, the reset diode will only discharge a small amount of energy from the resonator circuit. The remaining energy is consumed by the load. This is clearly seen in Fig. 3 where the area of the positive half period is significantly larger than the area of the negative half period - i.e. the charging of the resonator circuit is higher than the discharging via the reset diode, D2.

In special cases, the reset diode will become inactive. This situation will occur then all the energy from the resonator circuit is consumed by the by load. This example is depicted in Fig. 4 which also shows current spikes in the beginning of each positive half period. These current spikes relate to charging of the capacitor in the resonator circuit

Fig. 5 shows the situation where no load is connected to the output terminals. Since no power can be consumed by the load discharging of the resonator circuit can only occur via the reset diode, D2.

The combination of the current control circuit and the reset diode is unique in that it becomes possible to make a high efficient, very low cost ignition unit, which will comply with all load demands. However, it should be noted that in case the load has well-defined and known properties the reset diode can be omitted in that the charging of the resonator circuit, in the case of a known load, can be balanced to match the discharging of the resonator circuit via the load. Furthermore, the electronic ignition circuit according to the present invention can be used with all high frequency ferrite core high voltage transformers.

The electronic ignition circuit can further comprise a high frequency ferrite core high voltage transformer T1 as mentioned above. This part is not only a part of the resonator circuit and oscillator, but will also transform the relative low voltage on the primary to a high voltage (20 KV) on the output.

The output of this electronic ignition circuit is connected to spark electrodes.

Claims

1. An electronic ignition circuit comprising a resonator circuit operatively connected to a controllable switch, the ignition circuit further comprising means for controlling the controllable switch in response to a determined level of a current flowing in the resonator circuit.

2. An electronic ignition circuit according to claim 1 , further comprising means for comparing the determined level of the current flowing in the resonator circuit and a predetermined current level.

3. An electronic ignition circuit according to claim 2, wherein the controlling means for controlling the controllable switch comprises

- current sensing means for determining the level of the current flowing in the resonator circuit, and

- a control switch adapted to close the controllable switch in response to a result of the comparison of the determined current level and the predetermined current level.

4. An electronic ignition circuit according to claim 3, wherein the current sensing means comprises a shunt resistor operative connected to the controllable switch.

5. An electronic ignition circuit according to any of claims 1-4, further comprising means for discharging the resonator circuit, said discharging means being operatively connected across the controllable switch.

6. An electronic ignition circuit according to claim 5, wherein the discharging means comprises a diode.

7. An electronic ignition circuit according to any of claims 1-6, wherein the controllable switch comprises an IGBT-type transistor.

8. An electronic ignition circuit according to any of the preceding claims, further comprising

- means for at least partly rectifying an incoming supply signal, and

- filter means operatively connected to the rectifier means so as to filter the at least partly rectified incoming signal,

9. A method for operating an electronic ignition circuit comprising a resonator circuit operatively connected to a controllable switch, the method comprising the step of controlling the controllable switch in response to a determined level of a current flowing in the resonator circuit.

10. A method according to claim 9, wherein the controllable switch is closed when the current flowing in the resonator circuit exceeds a predetermined level.

11. A method according to claim 9 or 10, wherein the current flowing in the resonator circuit is determined by measuring a voltage drop across a shunt resistor operatively connected to the controllable switch.

12. An electronic ignition circuit comprising means for controlling an amount of energy provided to a resonator circuit, the ignition circuit further comprising means for preventing energy not consumed by a load operatively connected to the resonator circuit from accumulating in the resonator circuit.