METHOD FOR CURRENT LIMITATION OF A LOAD CURRENT AND CIRCUIT HAVING CURRENT LIMITATION OF A LOAD CURRENT FOR A FLASH MEANS

• US 20130241442A1
• Filed: 09/29/2011
• Published: 09/19/2013
• Est. Priority Date: 09/30/2010
• Status: Active Grant

• Current Assignee: ams AG (Ams-Osram AG)
• Original Assignee: ams AG (Ams-Osram AG)
• Inventors: Trattler, Peter
• Granted Patent: US 9,179,520 B2
• Time in Patent Office: Days
• US Class Current: 315/307
• CPC Class Codes: G03B 15/05 Combinations of cameras with electronic flash apparatus; Electronic flash units
• CPC Class Codes: G03B 2215/05 Combinations of cameras with electronic flash units
• CPC Class Codes: G03B 7/26 Power supplies; Circuitry or arrangement to switch on the power source; Circuitry to check the power source voltage
• CPC Class Codes: H05B 45/00 Circuit arrangements for operating light-emitting diodes [LED]
• CPC Class Codes: H05B 47/10 Controlling the light source

Abstract

The invention relates to a method for the current limitation of a load current, in particular the load current of a flash means. In one step, first a supply voltage (VBAT) is provided. Then a load current (I) is set depending on the supply voltage (VBAT) for supplying the flash means (LED) with power by incrementally reducing the load current (I) until the supply voltage (VBAT) is greater than a threshold value (Vlow). The load current intensity (Imin) of the set load current (I) can be stored in a register (RAM) for the subsequent triggering of the flash means (LED) in a main flash phase (2) with the load current intensity (Imin) stored in the register (RAM). In addition, the invention relates to a circuit having current limitation of a load current of a flash means.

Claims

1. A method for current limitation of the load current for a flash means, the method comprising:

provision of a supply voltage;

(VBAT) and

adjusting a load current for supplying power to the flash means based on the supply voltage, by reducing the load current stepwise until the supply voltage is greater than a threshold value.

2. The method according to claim 1, wherein load current is adjusted in a pre flash phase.

3. The method according to claim 1 or 2, further comprising:

storing the load current intensity of the adjusted load current in a register for subsequent triggering of the flash means in a main flash phase with the load current intensity stored in the register.

4. The method according to claim 2, wherein the load current is increased in a ramp-like manner before the beginning of the pre-flash phase or before the beginning of the main flash phase.

5. The method according to claim 2, wherein the load current increases to a starting current intensity before the beginning of the pre-flash phase, and

wherein the starting current intensity corresponds to a predetermined maximum current intensity, at which the supply voltage is greater than the threshold value, or to a resulting current intensity at which the supply voltage is still greater than the threshold value, and the load current is reduced stepwise in the pre-flash phase starting from the starting current intensity.

6. The method according to claim 2, wherein the flash means is triggered at the beginning of the preflash phase with the starting current intensity.

7. The method according to claim 2, wherein at least one additional load is connected stepwise to the supply voltage in the pre-flash phase, and

wherein the load current is reduced based on the additionally connected load.

8. The method according to claim 3, wherein a parameter selected from a group comprising an exposure time and a gain of a connectible sensor is adjusted based on the load current intensity stored in the register.

9. The method according to claim 1, wherein the stepwise reduction of the load current is interrupted, based on a control signal, in order to operate a priority load for the time period of the control signal.

10. The method according to claim 9, wherein, based on the control signal, the following steps take place:

storage of an interim current intensity, and

resumption of the stepwise reduction of the load current, starting from the stored interim current intensity, after the time period.

11. The method according to claim 3, wherein the load current intensity stored in the register is constant during the main flash phase for triggering the flash means, unless a priority load is operated.

12. A circuit with current limitation of the load current for a flash means, the circuit comprising:

a controllable power supply, to which a supply voltage can be fed and which, based on the supply voltage, provides a load current for supplying the connectible loads;

a comparison means, to which the supply voltage can be fed and which is designed to provide a comparison voltage, which is dependent on a comparison of the supply voltage to a threshold value;

a control unit, which is connected to the comparison means and the controllable power supply, wherein the control unit is designed to reduce the load current by means of the controllable power supply based on the comparison voltage; and

a register, coupled to the control unit, for storing a load current intensity of the load current.

13. The circuit according to claim 12, wherein the comparison means is constructed as a comparator.

14. The circuit according to claim 12 or 13, wherein the controllable power supply has a current source or a current sink.

15. The circuit according to claim 12, wherein a processor can be connected to the control unit, and

wherein the processor is designed to adjust a gain level of a sensor connectible to the processor on the basis of the load current intensity stored in the register.

16. The circuit according to claim 12, wherein the control unit is designed to control the controllable power supply based on a control signal in order to operate a priority load.

17. The circuit according to claim 16, wherein the control unit is designed to store an interim current intensity in the register and to load the interim current intensity from the register.

18. The circuit according to claim 12, further comprising a voltage converter that couples the controllable power supply to the connectible supply voltage and is connected to the comparison means.