Start-up controller for a power converter
Power converters, e.g., AC/DC and DC/DC, typically have unique circuitry for a proper graceful start-up and to develop correct operating voltage biases. Typically this unique circuitry is incorporated in a primary-side controller. This primary-side controller could also be the primary means of control of the power converter once started. However, a secondary-side controller is typically needed for more exact output voltage regulation, duplicating circuitry already present in the primary-side controller. Complication is typically added by linear communication between the two controllers across an isolation barrier. A simplified primary-side start-up controller is envisioned providing minimal circuitry to power up a converter until a secondary-side controller activates and takes control by sending discrete PWM commands across the isolation barrier instead of a linear signal. The start-up controller can provide voltage and current protection if the secondary-side controller fails. The secondary-side controller can be an analog and/or digital design for sophisticated converter control.
1. A power converter, comprising:
a start-up controller, comprising:
a high voltage regulator having an input and an output;
internal bias voltage circuits coupled to the high voltage regulator output;
under and over voltage lockout circuits coupled to the high voltage regulator output;
a current regulator;
logic circuits for generating pulse width modulation (PWM) control signals;
a fixed off time circuit coupled to the logic circuits;
a power driver coupled to the logic circuit and providing the PWM control signals for control of an external power switch;
an external gate command detection circuit coupled to the logic circuits and adapted to receive an external PWM control signal, wherein when the external PWM control signal is detected the external gate command detection circuit causes control of the external power switch to change from the logic circuits to the external PWM control signal; and
first and second voltage comparators having outputs coupled to the internal current regulator and inputs coupled to a current sense input; and
a secondary controller;
wherein the external PWM control signal is configured to be received from the secondary controller.
2. The power converter according to claim 1 , further comprising a blanking circuit coupled between the current sense input and the first and second voltage comparator inputs.
3. The power converter according to claim 1 , wherein the fixed off time circuit time period is determined by a capacitance value of a capacitor.
4. A power converter, comprising:
a start-up controller configured to operate in a first operating mode and a second operating mode, comprising:
a power supply connection configured to be coupled to a first DC voltage;
a current measurement input connection configured to receive a measuring current to the start-up controller;
a pulse width modulation (PWM) input connection;
a power switch control output connection which is controlled by the start-up controller;
wherein the start-up controller is configured to operate in the first operating mode to receive the first DC voltage and to provide a control signal at the power switch control output connection, wherein a fixed off time circuit is adapted to keep the control signal providing an off state for a connected power switch for a certain time period after the start-up controller has turned off the power switch, and wherein the certain time period is set by an external capacitor coupled with the start-up controller, and
wherein the start-up controller is configured to be switched to operate in the second mode, in which:
the start-up controller receives PWM signals through the pulse width modulation input; and
a switch within the start-up controller is controlled to feed said PWM signals to the power switch control output connection; and
a secondary controller;
wherein the PWM signals are configured to be received from the secondary controller.
5. A power converter, comprising:
a start-up controller, comprising:
a high voltage regulator having an input and an output;
internal bias voltage circuits coupled to the high voltage regulator output;
under and over voltage lockout circuits coupled to the high voltage regulator output;
a current regulator;
a supply voltage input connection coupled with a voltage regulator;
logic circuits for generating pulse width modulation (PWM) control signals at a gate control output connection;
a pulse width modulation input connection;
a fixed off time circuit coupled to the logic circuits;
a power driver circuit configured to provide the PWM control signals with a fixed OFF time period; and
a pulse width modulation detection circuit coupled to the logic circuits and to the pulse width modulation input connection and adapted to receive an external PWM control signal through the pulse width modulation input connection, wherein when the external PWM control signal is detected the external gate command detection circuit causes control of signals at the gate control output connection to change from the logic circuits to the external PWM control signal; and
a secondary controller;
wherein the PWM control signal is configured to be received from the secondary controller.
6. The power converter according to claim 5 , wherein the start-up controller further comprises a switch coupling the gate control output connection with either the logic circuits or the pulse width modulation input connection.
7. The power converter according to claim 6 , wherein the start-up controller further comprises a buffer coupled between the switch and the pulse width modulation input connection.
8. The power converter according to claim 5 , wherein the start-up controller further comprises
first and second voltage comparators having outputs coupled to the current regulator and inputs coupled to a current sense input.
9. The power converter according to claim 8 , wherein the start-up controller further comprises
a blanking circuit coupled between the current sense input and the first and second voltage comparator inputs.
10. The power converter according to claim 5 , wherein the power driver circuit is coupled to the logic circuits and further configured to provide the PWM control signals for control of an external power switch.
11. The power converter according to claim 5 , wherein the fixed off time period is determined by a capacitance value of a capacitor.
12. A method of operating a power converter, comprising:
at a secondary controller, generating an external pulse width modulation (PWM) control signal;
at a start-up controller:
receiving a supply voltage at an input connection coupled by a voltage regulator;
generating PWM control signals having a fixed OFF time period at a gate control output connection for control of an external power switch;
receiving the external PWM control signal through a pulse width modulation input connection,
controlling the gate control output connection with the PWM control signals until the external PWM control signal is detected, whereupon the external gate command detection circuit causes control of signals at the gate control output connection to change from the PWM control signals generated by internal logic circuits to the external PWM control signal;
regulate voltage;
regulate current;
operate voltage lockout circuits; and
performing the change by a switch receiving the PWM control signals and the external PWM control signal;
wherein the fixed off time period is determined by a capacitance value of a capacitor.
13. A start-up controller, comprising:
a high voltage regulator having an input and an output;
internal bias voltage circuits coupled to the high voltage regulator output;
under and over voltage lockout circuits coupled to the high voltage regulator output;
a current regulator;
logic circuits for generating pulse width modulation (PWM) control signals;
a fixed off time circuit coupled to the logic circuits;
a power driver coupled to the logic circuits and providing the PWM control signals for control of an external power switch;
an external gate command detection circuit coupled to the logic circuits and adapted to receive an external PWM control signal, wherein when the external PWM control signal is detected the external gate command detection circuit causes control of the external power switch to change from the logic circuits to the external PWM control signal;
first and second voltage comparators having outputs coupled to the internal current regulator and inputs coupled to a current sense input; and
a blanking circuit coupled between the current sense input and the first and second voltage comparator inputs;
wherein:
the fixed off time circuit time period is determined by a capacitance value of a capacitor; and
the external PWM control signal is configured to be received from a PWM input connection and routed inside the startup controller through a buffer and a switch.