Step down current mirror for DC/DC boost converters
View Patent ↗A low voltage current mirror design is used to control a high voltage boost converter. A high amperage reference current emanating from a high voltage inductor based DC-to-DC boost converter is mirrored to a low amperage output current. On-chip CMOS elements are used to measure and manipulate the output current, eliminating the need for a high precision, low resistance, external resistor. The measured and manipulated current is used to control the PWM duty cycle of an inductor based DC-to-DC boost converter, allowing for a lower cost solution in a high voltage, high current situation.
1. An integrated circuit for controlling a boost converter that includes an inductor coupled to a drain of a switching MOSFET, the integrated circuit comprising:
a gate pin to couple to a gate of the switching MOSFET;
a source pin to couple to a source of the switching MOSFET;
a feedback pin;
a first current mirror sub-circuit, the first current mirror sub-circuit configured to produce an output current from a reference current flowing between the source pin and ground, the reference current being larger than the output current; and
a dc-to-dc-control sub-circuit connected to the first current mirror sub-circuit, the dc-to-dc control sub-circuit configured to control a voltage on the gate pin in order to maintain a voltage on the feedback pin.
2. The integrated circuit of claim 1 wherein the dc-to-dc control sub-circuit includes a resistor through which the output current from the first current mirror sub-circuit flows and the connection of the dc-to-dc-control sub-circuit to the current mirror sub-circuit utilizes a voltage across the resistor.
3. The integrated circuit of claim 2 wherein the dc-to-dc control sub-circuit further includes:
an operational amplifier having a first input connected to a reference voltage and a second input connected to the feedback pin; and
a comparator having a first input connected to the output of the operational amplifier and a second input connected to the voltage across the resistor.
4. An integrated circuit for controlling a boost converter, the integrated circuit comprising:
a gate pin;
a source pin;
a feedback pin;
a first current mirror sub-circuit, the first current mirror sub-circuit configured to produce a first output current from a first reference current flowing between the source pin and ground, the first reference current being larger than the first output current;
a dc-to-dc-control sub-circuit connected to the first current mirror sub-circuit, the dc-to-dc control sub-circuit configured to control a voltage on the gate pin in order to maintain a voltage on the feedback pin; and
a second current mirror sub-circuit configured to produce a second output current from a second reference current, the second reference current being the first output current of the first current mirror sub-circuit and the dc-to-dc-control sub-circuit being connected to the second current mirror sub-circuit.
5. The integrated circuit of claim 4 wherein the dc-to-dc control sub-circuit includes a resistor through which the second output current from the second current mirror sub-circuit flows and the connection of the dc-to-dc-control sub-circuit to the second current mirror sub-circuit utilizes the voltage across the resistor.
6. The integrated circuit of claim 5 wherein the dc-to-dc control sub-circuit further includes:
an operational amplifier having a first input connected to a reference voltage and a second input connected to the feedback pin; and
a comparator having a first input connected to an output of the operational amplifier and a second input connected to the voltage across the resistor.
7. The integrated circuit of claim 1 wherein the dc-to-dc control sub-circuit includes an operational transconductance amplifier having a first input connected to a reference voltage and a second input connected to the feedback pin, the operational transconductance amplifier being configured to output a variable current based on a difference between voltages at the first and second inputs, the connection of the dc-to-dc-control sub-circuit to the first current mirror sub-circuit of summing the output current of the first current mirror sub-circuit and the variable current of the operational transconductance amplifier.
8. A circuit configured as a boost converter comprising:
an inductor;
a MOSFET, coupled to the inductor, that switches an inductor current of the inductor from a charging state to a discharging state, and vice versa;
a first current mirror sub-circuit, the first current mirror sub-circuit being fabricated on a different substrate than the MOSFET and configured to produce a first output current from a reference current flowing through the MOSFET while the inductor is charging, the reference current being larger than the first output current, the circuit being configured to utilize the first output current of the first current mirror sub-circuit in the switching of the MOSFET.
9. The circuit of claim 8 further comprising:
a resistor through which the first output current from the first current mirror sub-circuit flows, the resistor being fabricated on the same substrate as the first current mirror sub-circuit, the circuit utilizing the first output current of the first current mirror sub-circuit to develop a voltage across the resistor to control the switching of the MOSFET.
10. The circuit of claim 9 further comprising:
an operational amplifier having an input connected to a reference voltage; and
a comparator having a first input connected to an output of the operational amplifier and a second input connected to the voltage across the resistor.
11. The circuit of claim 8 further comprising:
a second current mirror sub-circuit fabricated on the same substrate as the first current mirror sub-circuit and configured to produce a second output current from the first output current of the first current mirror sub-circuit, the circuit utilizing the first output current of the first current mirror sub-circuit to generate the second output current of the second current mirror sub-circuit to control the switching of the MOSFET.
12. The circuit of claim 11 further comprising:
a resistor through which the second output current from the second current mirror sub-circuit flows, the resistor being fabricated on the same substrate as the second current mirror sub-circuit, the circuit utilizing the second output current of the second current mirror sub-circuit to develop a voltage across the resistor to control the switching of the MOSFET.
13. The circuit of claim 12 further comprising:
an operational amplifier having one input connected to a reference voltage; and
a comparator having a first input connected to an output of the operational amplifier and a second input connected to the voltage across the resistor.
14. The circuit of claim 8 further comprising:
an operational transconductance amplifier having a first input connected to a reference voltage and a second input connected to the feedback pin, the operational transconductance amplifier being configured to output a variable current based on a difference between voltages at the first and second inputs,
the circuit being configured to utilize the first output current of the first current mirror sub-circuit by summing the first output current of the first current mirror sub-circuit and the variable output current of the operational transconductance amplifier.
15. A method of regulating an output voltage of a DC-to-DC boost converter that includes an inductor coupled to a MOSFET, the method comprising:
mirroring, by a first current mirror sub-circuit fabricated on a different substrate than a substrate on which the MOSFET is fabricated, the current flowing through the inductor as the inductor is charging to a smaller output current; and
switching, utilizing the output current of the first current mirror sub-circuit, the MOSFET to alternately charge and discharge the inductor.
16. The method of claim 15 further comprising:
converting the output current of the first current mirror sub-circuit to a voltage using a resistor fabricated on the different substrate.
17. The method of claim 15 further comprising:
converting the output current of the first current mirror sub-circuit to an output current of a second current mirror sub-circuit, the second current mirror sub-circuit being fabricated on the different substrate; and
utilizing the output current of the second current mirror sub-circuit.
18. The method of claim 17 further comprising:
converting the output current of the second current mirror sub-circuit to a voltage using a resistor fabricated on the different substrate.
19. The method of claim 15 further comprising:
summing the output current from the first current mirror sub-circuit with the output current from an operational transconductance amplifier; and
switching, utilizing a summed output current of the first current mirror sub-circuit and the output current from the operation transconductance amplifier, the MOSFET to alternately charge and discharge the inductor.
20. The integrated circuit of claim 1 further comprising a plurality of series connected LEDs coupled between the drain of the switching MOSFET and ground.