Method and apparatus for calculating an average value of an inaccessible current from an accessible current

1. A buck converter having a regulated output current comprising:

a current measuring device measuring an input current to the converter;

a switch coupled to the current measuring device;

a pulse width modulation (PWM) circuit coupled to receive an output voltage from the measuring device;

an analog multiplier coupled to an output of the pulse width modulation (PWM) circuit to receive a signal (D) related to the duty cycle of the regulator and a signal 1−D related to the duty cycle of a rectifier or synchronous switch and to a voltage representative of a predetermined value of output current from the converter.

2. A buck converter having a regulated output current comprising:

a current measuring device measuring an input current to the converter;

a switch coupled to the current measuring device;

a pulse width modulation (PWM) circuit coupled to receive an output voltage from the measuring device;

an analog multiplier coupled to an output of the pulse width modulation (PWM) circuit to receive a signal (D) related to the duty cycle of the regulator and to a voltage representative of a predetermined value of output current from the converter, wherein the analog multiplier comprises:

a first switch coupled between the voltage representative of the predetermined value of output current and a node;

a second switch coupled between the node and a reference voltage;

a low pass filter coupled between the node and input to an error amplifier, wherein the first switch is operated by a signal representative of (D) and the second switch is operated by a signal representative of (1−D).

3. The converter of claim 2 wherein the pulse width modulation (PWM) circuit comprises an error amplifier coupled to the current measuring device by a resistor and capacitor in a feedback loop of the error amplifier, the resistor and capacitor averaging the output voltage from the measuring device to generate a signal related to average input current to the converter.

4. The converter of claim 3 wherein the current measuring device comprises a resistive shunt.

5. The converter of claim 4 wherein a load of the regulator is an LED.

6. The converter of claim 4 wherein a load of the converter is an LED.

7. A boost converter having a regulated average output current comprising:

a switch coupled to receive input current from the converter;

a current measuring device measuring the input current to the converter and generating a voltage representative thereof;

a voltage representing a constant related to a value at the output current is regulated to;

a first analog multiplier coupled to the voltage representing the constant multiplying the constant K by a signal representative of one minus the duty cycle of the converter (1−D) to generate a signal K*(1−D);

a second analog multiplier coupled between the voltage representative of the input current and a first input to a pulse width modulation (PWM) circuit;

a second input the pulse width modulation (PWM) circuit being coupled to receive the signal K*(1−D).

8. The converter of claim 7 wherein the analog multiplier comprises:

a first switch coupled between the voltage representative of the predetermined value of output current and a node;

a second switch coupled between the node and a reference voltage;

a low pass filter coupled between the node and input to an error amplifier, wherein the first switch is operated by a signal representative of (1−D) and the second switch is operated by signal representative of (D).

9. The converter of claim 8 wherein the pulse width modulation (PWM) circuit comprises an error amplifier coupled to the current measuring device by a resistor and a capacitor in a feedback loop of the error amplifier, the resistor and capacitor averaging the output voltage from the current measuring device to generate a signal related to average input current to the converter.

10. The converter of claim 9 wherein the current measuring device comprises a resistive shunt.

11. A buck voltage to current converter comprising:

a source of AC input voltage;

a switch coupled to a load through an inductor;

a current measuring device for measuring current through the switch;

a current source coupled to an analog multiplier for multiplying a current value by a duty cycle of the converter;

a pulse width modulation (PWM) circuit receiving a voltage output from the multiplier at one terminal thereof and for receiving a voltage related to the current

measured by the current measuring device, the pulse width modulation (PWM) circuit generating a signal related to a duty cycle of the converter (D), wherein the switch is operated by the signal to generate a current through the load related to a constant times the input voltage.

12. The buck voltage to current converter of claim 11 wherein the analog multiplier comprises a switch operated by a signal related to 1−D coupled between a node which is an input to the multiplier and a reference voltage and a diode coupled to the node and an output of the amplifier.

13. The buck voltage to current converter of claim 12 further comprising a capacitor and a resistor coupled between an output of the analog multiplier and the reference voltage.

14. The buck voltage to current converter of claim 13 wherein the current measuring device is a resistive shunt.

15. The buck voltage to current converter of claim 11 wherein the source of DC voltage is a rectified dimmed AC voltage.

16. The buck voltage to current converter of claim 15 wherein the load is an LED which may be dimmed by an AC dimmer.